Lecture noteson

Soil conservation Engineeringand

Watershed managementfor

Bsc - 3rd Year Students

Kathmandu Foretry College( KAFCOL)

(For the use of Kathmandu Forestry College Students only)

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Course Tittle : Soil Conservation Engineering and Watershed Management

Unit 1. Lands Degradation Problems in Nepal

1.1 Introduction to land degradation and its consequences1.2 Water Erosion

Erosion is a process of detaching soil particles from the land surface of one place and their transportation and deposition to another place.

Three Processes of Erosion :

1. DetachmentProcess depends upon type of soil, OM, moisture, nature of detaching agents (energy).

2. TransportationProcess depends upon size, density and shape of detached materials and velocity of the transporting agent.

3. DepositionSoil that is eroded from the original location is always deposited somewhere else. This may be close to its place of origin position, it may be the longest distance down to the sea or at any point between the place of origin to the sea.Process depends upon soil particles and velocity of the agent.Example: -- Coarse sand particles in eroded soil move the shortest

distance and deposit first. -- Fine sand and silt deposit next as run-off water slows

down. -- Some very fine silts settle out only in standing water. -- Very fine clay and colloidal humus will not settle out even

in standing water but stay suspended in the water indefinitely

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1.2.1 Types of water erosion Geological (Natural/ normal)

Geological ( Natural/ normal ) erosion are caused by : action of water, geology, wind, temperature, gravity, glaciers, earth quakes.

Examples are : Naturally wearing away of hills and mountains: sculptured hills/ mountains, canyons/gorge , stream channels, deltas etc.

Man-made ( Accelerated ) Man-made ( Accelerated erosion are caused by : human or

anthropogenic activities. Change in land use, destruction of natural cover and soil conditions are main elements responsible for accelerated erosion.

Agents responsible for Soil Erosion are : Water, Wind and Gavity

Types of Erosion by Agents (Water induced ) :

Main types of erosion

1. Rain Drop / Splash Erosion. Rain drops falling into ground cause splash, detach, carry water soil particles with small film of water into air in horizontal/vertical directions. The splash soil particles may move as much as 2 ft. into the air and simultaneously more horizontally as much as 5 ft on level surface. On level surface, the splashed soil particles scatter all over the land surface. The smashed up soil particles disperse and cause surface sealing and reduces infiltration capacity of land surface. Besides, the impact of kinetic energy of raindrops on land surface compacts the soil and further help reduce infiltration capacity of soil. These activities of raindrops increase the runoff, which starts moving down to the slope due to gravitational force causing surface erosion. The bigger the size of rain drops, the greater the kinetic energy and greater will be the rain drop erosion. Direction and strength of wind velocity deflect the rain drops and reduces their kinetic energy and there by reduces rain drop erosion.

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(Figure : Splash of soil particles by raindrop erosion on a level and sloping surface)

2. Sheet Erosion ( Inter-rill erosion). When the rate of rainfall exceeds the rate of infiltration of water into the soil, water starts to flow over sloping surface carrying detached particles in a form of thin sheet or layer. They carry organic matter and fertile top soil. Such a removal of more or less uniform thin layer or sheet of soil from a given area of land surface by the action of rain drop is called sheet erosion or inter-rill erosion. The appearance of light color soil on the land surface, after the removal of thin layer of dark color soil rich in organic matter, is the sign of sheet erosion after rain fall events. The sheet erosion cause loss of organic matter, expose light color sub-soil and eventually cause loss in productivity of surface soil. The sheet erosion occurs in smooth and uniform sloping surface and it removes only the top layer of soil. It is a thin surface flow rather than runoff. Sheet erosion is a function of depth and velocity of run-off for a given size, shape and aggregates of soil particles.Sheet erosion is better termed as "inter-rill" erosion which means detached soil particles by raindrop are moved and transported by thin surface flow of water, the capacity of which to sheet erosion is increased by raindrop impact turbulence.

3. Rill Erosion. As discussed earlier, sheet erosion occurs mainly on the smooth and uniform sloping land. When the land surface is irregular, the irregularity of land surface force the flowing water to flow through a certain well defined direction, which then form small channels called rills. So rill erosion is a removal of soil by water from small but well defined channel. The size of rills vary from minute channels to a size

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that is easily observed. Rills can easily be broken by tilling operations. Detachment and transportation of rill erosion are always greater than sheet erosion. In rill erosion, the detachment of soil particles are from energy of flowing water and not by the raindrop impact as in the case of sheet erosion. Detachment of soil particles by flowing water in rill erosion (D) varies with square of velocity of flowing water ( V2 )and ability of flowing water to transport soil particles (T) varies with fifth power to the velocity of flowing water (V5). If continues, can extend up to sub-soil.

D ∞ V 2 and T ∞V 5

4. Gully Erosion (Channel erosion). Gully erosion is an advanced form of rill erosion. It is a channel erosion that cuts so deeply into the soil that the ground cannot be smoothed out by ordinary operations. It often follows sheet and rill erosion. If rill erosion is unchecked and allow water to move continuously in the channel developed by rill, then gully erosion occurs. Gully erosion can be of V- shaped, if the soil strata at the bottom of gully is strong and gully slopes are weak to erosion and U-shaped gullies are formed, if the soil strata at the slopes of gully are strong and bottom are weak to erosion. Rate and extent of gully erosion is related with amount and velocity of run-off water.

( Figure : gully erosion at a gully head)

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Stages of water erosion:

1st. stage = rain drop erosion

2nd. stage = sheet erosion

3rd. stage = rill erosion

4th. erosion = gully erosion

Dimension of gully erosion :

Rill erosion 1 ft. deep

Small gully > 1 -- .3 ft. deep

Medium gully > 3 – 13 ft. deep

Large gully > 13 -- 30 ft. deep

Ravines > 30 ft. deep

Figure : Different form of erosions

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5. Stream bank Erosion: This is erosion caused by scoring and cutting of river bank due to flooding of river.

Some other types of erosion :

-- Wave erosion

-- Rock erosion

-- Waterfall erosion

-- Tunnel erosion

-- Pothole erosion

-- Snow slide

1.2.2 Agents active in water erosionAgents active in water erosion are : Rainfall intensity and pattern, soil structure and soil erodibility, type and density of vegetation, slope factor, slope length factor, slope gradient factor, cropping management factor and erosion control practice factor

Factors Affecting Water Erosion are :

1. Vegetation : vegetation plays important roles in water erosion. It has great importance in controlling erosion because of the following reasons : i) Vegetation intercepts raindrop reduce its energy and

impact on land surface. Raindrops that could have reached in the soil would be quickly taken by leaf litter. Lands without vegetation will be vulnerable to raindrop, sheet and gully erosions.

ii) Vegetation improves the soil structures by adding organic matter into the soil. High organic matter content soil will be more pores and, which in turn helps increase the infiltration and water holding capacity of soil. Further, the humus layer itself acts as a sponges and absorbs moisture and allows it to enter into the

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soil. Soil having low organic matter and humus layer are susceptible to erosions because of increased runoff.

iii) In the vegetative areas, the root network, the channels of root decay, animal burrows help dissipated runoff water.

iv) The root systems below the soil surface binds and aggregates the soil through the mechanical actions and prevent from erosion and landslide.

v) High surface friction due to leaf litter and increased roughness of the ground in vegetative land tends to spread out the runoff laterally and thus dissipates its energy

2. Soil : Soil particles and their sizes are important factors for soil erosion. The detachability and transportability of soil in the erosion process increase or decrease based on kind and size of soil particles. In fact, detachability of flowing water or runoff decrease with increase of size of soil particles and transportability of flowing water or runoff increases with decreases of soil particle size. For example, the clay particles difficult to detach than sand but easier to transport. Soil with large stable particles such as sand grains or iron cemented soil particles are difficult to detached and transported, which seldom erode.Infiltration capacity of soil play important role in soil erosion. Infiltration which is indirectly affected by permeability of different soil horizon is factor governing runoff and then to erosion. Soil erosion by water occurs when there is runoff or overland flow. When rainfall intensity exceeds the infiltration capacity of soil then runoff or overland flow occurs, which causes erosion. If the infiltration capacity of soil is higher than the intensity of rainfall, then the runoff or overland flow will be lower and less erosion occurs.

3. Climate : In climate, the rainfall and teh temperature play important role in erosion. There is a direct relationship between the amount of rainfall and erosion. Rainfall intensity

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influences both the rate and volume of runoff and then to scale of erosion.Temperature affects climatic type, which governs the types of crop grown and the amount of ground cover that exists. Temperature is important in producing desired level of ground cover to protect soil from erosion. In highlands, maintenance of desired level of ground cover is difficult because of low temperature and short growing season of plants. In such areas, the intense rain can cause severe erosion. Similarly, the soils of the arid regions are low in organic matter because warm temperature have resulted in more rapid decomposition of organic matter. This lower organic matter content in soil makes the soil more susceptible to erosion during intense rains.

4. Physiography : Slope steepness is one of the important factors in soil erosion. Greater the slope more is the erosion. Slope steepness influences erosion in several ways. The increased velocity of runoff water in steep slopes allows more soil to be detached and transported, where surface detention of water is low and breaking of rain drop energy cannot form in steep slopes. Therefore, steep slopes are susceptible to erosion.The slope length is also an important factor affecting soil erosion. If the slope is longer, a large quantity of rain will fall on it and if the rate of rainfall exceeds the rate of infiltration, there will be large accumulation of water at the base. Therefore longer the slope length more is the erosion. There is a relationship between soil loss ( erosion ) and slope length, which states that erosion ( E ) is approximately equal to the square root of the slope length (L1/2 ) . Soil loss varies with square root of slope length.

Slopes facing south gets more sun directly than the slopes of other aspects. Because of high radiation and temperature in southern aspects, soils of southern aspects are lower in organic matter than those facing in northern slopes. Because

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of the low organic matter content in soil and sparse vegetation cover in southern aspects, the southern aspects are more susceptible to erosion than other aspects.

Activities of water, which are responsible for erosion

1. Water-flow2. Lubrication of slope layers3. Saturation of soil4. Weathering and dissolving of minerals

1. Water-flow = Physical force of water-flow (run-off) causes flow-erosion ( sheet erosion, rill erosion, gully erosion ). Flow-erosion is proportional to water depth ( channel ) and slope gradient and inversely proportional to size or strength of the eroded materials. Flow erosion starts when flow energy surpasses slope resistance and increase with increasing run-off. The bigger the water flow, the bigger the flow- erosion.

2.Water- lubrication = It causes slide- erosion on slopes. Water seepage and infiltration reduces friction between soil and rock or between two rocks layers. The bigger the seepage/ infiltration, the more likely the occurrence of slides. Seepage/ infiltration of rail increases more with duration than intensity. Heavy rains of long duration produce more slides than short rain of very high intensity. Yield of underground sources like springs also increases more with high duration of rain than intensity also helps increasing slides. Heavy permeable strata on top almost impermeable ones provide for maximum lubrication ones provide for maximum lubrication of the slide plane and are very susceptible to sliding.

3.Water- saturation = Water- saturation of slopes of deep soil leads to the reduction of angle of repose and liquification of the soil and to slope failure. Highly permeable layers form "pressure tanks" on top of soil layers of little permeability. The soil layers near the surface of little permeability gradually saturates and loose strength while the weight of the pressure tanks increases. When the soil layers near the little permeability strata` becomes

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weak to support the increasing weight of permeable layers slope failure occurs.

4.Weathering = It converts rock into gravel or soil, reduces slope strength and supports erosion of any form. Dissolving of easily soluble minerals leads to the formation of under-ground cavities and later by their breaking in leads to erosion

1.2.3 Water Erosion Prediction Equation (universal soil loss equation, USLE )

The universal soil loss equation ( USLE ) is :

A = R K LS C P where as,

A = Soil loss per unit area, it is an estimate of soil loss from sheet and rill erosion from rain fall events. It does not include the estimation from stream bank erosion, landslides, gully erosion, snowmelt erosion.

R = rainfall factor, K = soil erodibility factor, L = slope length factor, S = slope gradient factor, C = cropping management factor, P = erosion control practice factor.

R (rainfall factor) = This is determined from the product of the kinetic energy of an individual storm (E) times the maximum 30-minute intensity for the storm (I), that is EI. Summation of all storms in a year is the annual value of the R factor. E is calculated according to:

E = 916 + 331 (log I) foot-tons/acre/inch of rain and I in inches/hour, this in metric unit is E = 210.1 + 89( log I) joules/ sq.m/cm of rain and I in cm./hour.

K (Erodibility factor) is determined from a nomograph as illustrated in the figure.

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Erodibility factor is the susceptibility of soil to erosion. So it is a function of soil containing percent of silt, fine sand, organic matter, soil structure, soil permeability.

Figure : Nomograph to determine K factor

Slope Length Factor ( L ) = It refers to overland flow or run-off from where it originates to and where deposition begins. Maximum slope lengths are seldom longer than 600ft. or shorter than 15 to 20 ft. However, it requires judgments and on-site inspection. The Slope Length Factor, L = ( ^ / 72.6 ) m ( feet) L = ( ^ / 22.1 ) m ( meter )

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where as, ^ = field slope length (feet, meter) m = 0.3 for very long slopes gradient less than 0.5 % = 0.6 for very long slopes gradient more than 10 % = 0.5 applicable in most cases ( average value)Slope gradient factor (S) = It is a ratio of soil loss from a given slope steepness to that from a 9% slope under the same condition . It will be evaluated as: ( 0.43 + 0.30 s + 0.043 s 2 ) / soil loss from 9 % slope under the same condition, where as s = slope gradient (%) .

Cropping Management Factor (C) = It is a ratio of soil loss from the condition of interest to that from tilled continuous fallow . This is an integration of several factors that affects erosion, vegetation ( plant canopy), binding effects of plants roots, soil surface, cropping patterns, plant residue, land use/ land management etc. C factor describes the total effects of vegetation, plant residue, soil surface and land management on soil erosion The value of C factor is not constant over the year. Therefore, the value of C factor need to be determined experimentally.

Erosion Control Practice Factor (P) = It is a ratio of the soil loss with the control measures ( Ex : contouring, strip cropping, terracing, etc. ) to that with farming up and down the slope. The value for P are usually based on judgment and experience obtained from non-crop situation.

Modified equation is :

A = R K L S VM, where as,

VM = the vegetation management factor which is the ratio of soil loss from land manage under specified condition to that from the fallow condition on which the K factor is evaluated.

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1.3 Wind Erosion

1.3.1 Factors causing wind erosion

Wind acts on the soil surface the same way as flowing water. Gusty winds are able to dislodge small soil particles, lift them upward and carry them away.

Wind can move larger soil particles by making them jump along the ground. The jumping particles also apply energy to the soil surface each time they hit the ground and dislodge other particles so that they too can be moved by the wind. This process is called saltation.

The largest soil particles that can be moved by wind are about 1 mm. Very fine clay and silt particles ( less than 0.02 mm ) are lifted into the air and carried away as wind blown dust. Sand dunes are severe stage of wind erosion.

The erosive power of wind, as that of water, increases exponentially with velocity, but is not affected by gravity. The erosive power of wind in wet soil condition and vegetation covered soil is slow.

Slope inclination is not a factor in wind erosion, except where slopping terrain may form barriers to wind. However, the length of unobstructed terrain over which the wind flows is important in allowing the wind to gain momentum and increase erosive power. Winds with velocity less than about 12 to 19 km/ hr. at one meter above the ground not quite often dislodge and put into motion sand size particles.Potential average annual soil loss (tons / acre / year) is a function of

I = soil erodibility

K = soil roughness factor

C = Average wind velocity and surface soil moisture

L = field length

V = vegetative cover

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Symbolically, the average annual soil loss due to wind, E =ƒ( I K C L V )tons/acre/yr.

Wind erodibility Soil Group:

Soil Group

Predominate Soil classes Dry soil aggregates ( %)

Erodibility

T/ A/ Year

1 very fine, fine, medium sand/ dune sand

3 220

2 loamy very fine, fine, medium sands 10 134

3 fine, medium, coarse sandy loams 25 86

4 clay, silty clay 25 86

5 loams, sandy clay loams, sandy clays 40 56

6 silt loams, clay loams 45 47

7 silty clay loams, silts 50 38

Responsible factors for wind erosion :

1. Nature of wind ( velocity, direction etc.)2. Types and density of vegetation and ground cover.3. Topographic features ( terrain, flat, undulating, rolling and

continuous )4. Nature of land surface ( plain, degree of roughness, land cover by

plant )5. Characteristics of soil ( physical, chemical, OM, moisture content etc.)6. Biotic factors ( land use, over used, over grazing , plant residue etc.)

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1.3.2 Soil movement due to wind erosion :

Efflation : Very fine particles carried off by wind

Extrusion : Large soil particles carried of by rolling and sliding by wind.

Effluxion : Soil particles of intermediate size carried off by the bouncing action of wind.

Detrusion : Wearing away of rock and land projection by soil particles carried in suspension, this is a result of efflation .

Abrasion : Wearing away of rock and land projection by larger soil particles moving as bouncing, rolling and sliding which is the result of extrusion and effluxsion

1.3.3 Control of Wind Erosion :

1. Avoid removal of vegetation2. Maintain shelterbelts / windbreaks 3. Maintain plant residue / stubble on land4. Plant shrubs / grasses5. Access the spacing of shrubs and trees to reduce wind velocity6. Maintain good balance between grass, shrubs and trees7. Avoid locating LS watering facilities on erodible soils

UNIT 2. Design and Construction of Gully Control structures and Terraces

2.1 Introduction to mechanical control measuresThis is non- vegetative and apply engineering works

Why mechanical control measures ? :

If the condition of eroded area do not permit establishment of vegetation.

If no scope of quick cover of vegetation.

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If establishment of eroded area takes long time by vegetation measures .

Important mechanical measures are :

Rip-rapping : Loose stones are used for the construction of rip-rapping. Stone size should be large enough to resist the force of water. Minimum size of stones be 0.5 m. ( diameter) for bottom / toe of the channel and 0.3m. for the protection of the upper part of the channel

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Retaining wall : These are structures to protect the gully and torrent banks against lateral erosion and undercutting. Concrete ( porous/ non- porous), gabion and loose stones are used for the construction. If loose stones are to be constructed large-sized stones must be used.

Checkdam : Most important device to control torrent and gully erosions is the check dam. This is most common and effective mechanical means of stabilizing active gully erosion.Structures built across stream channels or gullies to stop the lateral and horizontal gully/ channel erosion and to stabilize and stabilizing them by retaining bed load and other debris. Its purpose is to reduce the gradient and break the velocity of flow/ runoff.

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Check dam guide the water flow/ runoff from a higher point to lower point without causing erosion at the gully bed and banks. In general, there are two types of check dam.

1. Non- porous with no weep holes2. Porous dams which release part of the water flow to

reduce hydro-static pressure Concrete (porous/ non-porous), gabion, loose stone, brush wood or wooden check dams are used depending upon site condition, objectives of gully control, availability of construction materials and cost effectiveness.

Mostly used in series to meet the following purposes :

a) to raise the bed level up to a height where safe support is provided for the slopes

b) to reduce the gradient of the channel / increase resistance of the channel bed

c) to reduce the water depth by widening the gully/ channel bed Spur and Embankment: These mechanical measures are used to

control torrent/stream/river bank erosions or bank cutting by diverting flowing water

2.2.1 Check dams

2.1.1.1 Types of check dams

1. Concrete check dam : This is built, where higher structures are required. weep holes are provided to release hydrostatic pressure.

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2. Gabion check dam: This is constructed from gabion boxes with appopriate wire mesh. Usually 10 and 8 gauge GI wire of mesh size 10 by 10 cm. or 15 by 15 cm. size of the stone which is used in gabion should be large enough than size of the mesh. The maximum hieght of the gabion check dam should not be more than 5 m. for mountain gullies and torrents.

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Figure : gabion check dam

3. Loose stone check dam: Big loose stones are used in this type of check dam. The quality, shape, size of the stones used affect the success of the check dam.

4. Brushwood check dam: Logs, branches bamboos are used in this type of check dam. They are piled across the cross-section of gullies. Series of such structures can be installed to plough the gully erosion.

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Figure : Brushwood check dam

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Figure : Plan and layout of check dam

2.1.1.2 Design of check dams Before designing a checkdam, it is necessary to calculate the maximum runoff discharge that should passes through the spillway of the checdam.The runoff discharge Qmax can be calculated from the following formulas :

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a) Formula to calculate Qmax i ) General formula :

Q max = V *A, where asQ max = maximum discharge of the gully catchment at the proposed check dam point (m3/sec or cumecs)A= cross-section area of gully bed (m2)V= velocity of flowing water ( m/sec), which can be obtained from ii) Manning,s formula Manning,s formula = V = ( R 2/3 *S 1/2)/n, where as V = velocity of flowR = Hydraulic radius in meters = Area/wetted perimeter (surface in contact with water)

S = Water surface slope = ratio of vertical drop to the length of the stream

R = roughness coefficient ( obtain from table for major rivers, floodplain, excavated channel at different land condition)

iii ) Rational formula :

Q = CIA/360, where as Q max = maximum discharge from catchments area of gully (m3/sec) C = catchments characteristics constant which varies from 0.4 to 0.95

depending upon types of land I = intensity of rainfall (mm/hr) for the designed return period and for

a duration equal to the time of concentration of the watershed. A = watershed area (ha)

The time of concentration (Tc) is defined as the longest time taken for water to travel by overland flow from any point in the watershed. It is a storm duration that produce max. rate of runoff or the storm duration which will correspond with the max rate of runoff to the outlet. The time of concentration (Tc) can be calculated by Kirpich method, which is :

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Tc = 0.0195 L 0 . 77 × S 0 . .385 , where as

Tc = time of concentration (min)

L = max. length of flow (m)

S = watershed gradient or the difference in elevation between the outlet and the most remote point divided by the length L (m)

After the calculation of Q max , the spillway or notch of the check dam need to be designed, using the following formula :

i. Spillway formula : Q max = CLH 3/2 where as ,

C = constant, L = length of spillway (m) and

H = height of spillway (m)

Here, since the gully width or torrent width is known, the length of spillway need to be assumed. Then substituting the known value in the spillway formula, the height of checkdam can be determined. After calculating the actual spillway height, certain free board usually 5 to 30 cm. need to be added in the actual height of checkdam.

Example : ( Numerical )

Runoff ( Discharge ) calculation by using Rational Formula : The rational formula is : Qmax = CIA/ 360 Given : L = 1.2 Km. ( max. length of flow ) A = 2.1 Km2 (Area of watershed) S = 15 m ( watershed gradient or difference in elevation between the outlet and the most remote point divided by L) C = 0.03 ( catchments characteristics constants )Calculate the time of concentration, intensity of rainfall and Runoff discharge for a return period of 20 years.

Here, Time of Concentration ( T ) = 0.0195 L 0. 7 7 × S 0. 385 = X ( m)

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Intensity of Rainfall for a return period of 20 years,

Therefore, I x = a/( b + T ) = 2850 / (10 + X ) mm/hr = Y mm/hr

0.03 ×Y × 2.1

Q max = _______________ cumecs ( m3/sec )

360

The values of intensity constants "a" and "b" are either given or supplied in a table :

Table : Intensity Constants

_______________________

a b

________________________

1 year 830 5

2 year 1400 7

5 years 2100 9

10 years 2590 10

20 years 2850 10

50 years etc. 3220 11

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2.1.1.2 Design of a Check dams :

After calculating the Qmax, calculate the design of spillway of a check dam as follows :

Qmax = CLH 3/2,

Here, Qmax is calculated from the given example above, C is given, assume L and caculate H. After the calculation of H, place the value in the equation. Manupulate the value of L and H until the Qmax (calculated) comes to equal or more than given Qmax ( discharge) to pass through the spillway.

c) Spacing of check dam :

i ) Spacing :

In most of the gully slopes, the spacing of check dam is arranged in such a way that the top of the lower check dam should be at level with the bottom of the upper check dam. By this spacing method, many check dams are required in steep gully slopes. Therefore, a compensation gradient is required to minimize the number of check dams and then to the cost involved. Compensation gradient is the slope between the top of the lower check dam and the bottom of the upper one. Compensation gradient of about 3 to 5 percent is provided between two check dams.

Spacing of height of check dam (h) * 100

the check dam D = --------------------------------------

% slope of gully (So) - % compensation gradient (Sc)

D = spacing between two successive check dam ( horizontal distance)

h = Height of check dam ( up to notch)

So = slope of the gully or existing slope of bed in %

Sc = Compensation gradient or stabilizing slope of bed in%

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Figure : gully slope, checkdam and compensation gradient

ii) Number of check dam

The number of check dam can be calculated from the following formula (Hiller, 1997) :The number of check dams is calculated as follows :Number of check dams = A ÷ H or A/H. If compensation gradient is used, then the number of check dams = (A-B) ÷ H or ( A-B)/H, where as

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A= the total vertical distance between the first and the last check dam in that particular portion of the gully or torrent.

B = the total vertical distance calculated according to compensation gradient for that particular portion of the gully or torrent.

H = average height of the check dams. d ) Base width of check dam : The base width of the check dam can be calculated by using following formula: i ) Kronfellner - Kraus formula : Here the base width of the check dam is

calculated if the check dam has a height of less than 8m. The base width is :

D1 = 0.35 ( H + U ), where as D1 = base width (m).

H = difference between the crest of the spillway and the base of the check dam (m).

U = depth of the spillway (m).

If the height of the check dam is between 2 to 6m, then the Hoffmann formula may be used to calculate the base width.

ii ) Hoffmann formula :

D1 = 0. 462 H, where as D1 = base width (m).

H = difference between the crest of the spillway and the base of the check dam (m).

e) Top width of the check dam ( Crest thickness) : Following empirical formula can be used to calculate the top width of the check dam or crest thickness, if the height of a check dam is between 6m to 7m.D2 = 1 + H/10, where as D2 = top width or crest thickness of the check dam (m) H = height of the check dam including foundation (difference between the

water level upstream and water level downstream of the check dam (m).

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f) Scouring depth: The depth of foundation of the check dam must be deeper than the bottom of the scouring zone below the check dam. Therefore, it is necessary to find the scouring depth before deciding the foundation of the check dam. To calculate the scouring depth of the check dam, following formula can be used:

Schocklitsch's formula :

4.75 × h 0.2 × q 0..57 S (d 90) = ----------------------- dm

S (d90) = scouring depth ( in meter) below the water level

h = difference between the water level upstream and water level downstream of the check dam (m) or water level difference ( in meter) above and below thw check dam

q = specific runoff, which is the runoff that passes through a section of 1m. of the spillway ( m /sec).

dm = diameter of soil particle in which 90 % soil particles is smaller and 10 % soil particles bigger than 90 mm diameter size.

The modified version to calculate the scouring depth is

h 0. 343

× q

0. 686

S = 0.79 × _______________

d 90 0. .372

where as, h = fall height of a check dam, q = specific runoff d 90 = 90 % soil/ bed material is smaller and 10 % soil/ bed material

bigger than the diameter of 90mm.

2.1.1.3 Stability analysis of check dams

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There are three possibilities of failure of checkdam. They are :

i) Check dam may sliding forwardii) Check dam may overturningiii) Check dam may crushing at the base

i) To check against sliding forward

Check dam has many elements and various forces are acting on it .

P = lateral thrust μ = coefficient of friction ( Table.........)W= weight of check damw = specific weight of soil ( Table.........)H = height of check damY = specific weight of check dam material

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A = top width of spillway sectionB = bottom width of check damØ = angle of internal friction of soil ( Table........)Z = distance of intersection point of resultant of P and WUThe check dam may not slide forward if the lateral pressure (P) is less than the product of weight of check dam and coefficient of friction (W×U) , i.e P < W×U. The lateral thrust ( P ) can be calculated as follows:P = (wH /2 ) * ( 1-sin θ/1+sinθ), W = Y{( A + B)/2 )} H

ii) To check against overturning

The resultant of P and WU should passed within 2/3 of the bottom widthor base of the foundation of checkdam. That is Z < or = 2/3 B, where as Z = distance of intersection point of resultant of P and WU, which can be calculated as:

Z = (A2 + AB + B2) / 3 ( A + B ) + H/3 × P/W

iii ) To check against crushing

In order avoid crushing of a checkdam, the maximum compresive stress at the base of a checkdam should be less than the allowable working stress for acheckdam. In this case the maximum compressive stress Pmax. should be less than the allowable working stress

Pallowable or Pmax < Pallowable

Pmax. can be calculated from the following relationship:Pmax = W/B ( 1 + 6e/B ), where as e = eccentricity of loading.e, the eccentricity of loading can be determined from the table or already given Pallowable for a given checkdam can be determined from the table or already given

Numericals :

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Example 1. Check the stability of a check dam against sliding and bearing pressure based on the following information :

Coff. of friction = 0.60 = uTotal wt. of the check dam per unit length = 2.6 t = WTotal horizontal pressure per unit length = 2.15 t = PSoil bearing capacity = 10 t/m2 = Pallowable

Density of stone masonry = sp. wt. of check dam = 2.15 t/m3 = YDensity of silt = 1.14 t/m3 = eWidth of foundation = 3.5m = B

Is the designed dam section safe ? if not suggest safe alternate design.Solution : a. To check against sliding forward. Formula : P < uW

uW = 0.60 * 2.6 = 1.56 t

Here P > uW, so design is not safe. Increase the value of W by increasing size of the checkdam.

W = Y{( a + B)/2 )} H

b. To check the bearing pressure ( against cruising) : P max < P allowable

Pallowable = 10 t/m2

P max = W/B (1 + 6e/B), where as e = eccentricity of loading.

= 2.6/3.5 (1 + 6e/B) = 0.70 (1 + 6 *0.58/3.5) = 0.70 * 2.9 = 2.069 Here, P max < P allowable

So the design is safe for cruising

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Example 2. calculate the depth of scour to be considered for the check dam having 5mt long spill way with the total discharge of 6.25 m3/sec with 15 mm grain diameter with 2 m. water level difference above and below the check damSolution :

Here, dm = grain diameter = 15mm, h= 2m. = water level difference between the water level upstream and water level

downstream of the check dam q = specific runoff, which is the runoff that passes through a section of 1m. of the spillway

( m /sec).Therefore, q = 6.25/5 = 1.25 m3/sec

Apply Schocklitsch's formula :

4.75 × h 0.2 × q 0..57

S (d 90) = ----------------------- dm

4.75 × 2 0.2 × 1.25 0..57 = ------------------------ 15 = 0.42 mTherefore, the foundation of check dam should be > 0.42. We can add some more for the

further safety ( 20-30%)

Example 3. Find the spacing of check dam provided the height of 1m. on the gully bed having 15 % slope in which 5 % compensation gradient is to be maintained.

Solution : Given h = 1 m slope = 15% compensation gradient = 5 %

height of check dam (h) * 100

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Spacing of the check dam D = --------------------------------------

% slope of gully (So) - % compensation gradient (Sc)

1 * 100 = ----------- = 10 m 15 – 5Example 4. Calculate the number of check dam in a 300 m. long sloping gully having the

vertical distance between the Ist and last check dam is 21 m. and 3% compensation gradient is to be mentioned after construction of 1.5 m height of check damsGiven :Vertical distance between the two check dams = 21mLength of gully = 300mHeight of check dam = 1.5mCompensation graidient to be maintained = 3 %Number of check dams = A ÷ H or A/H. If compensation gradient is used, then the number of check dams = (A-B) ÷ H or (A-B)/H, where asA= the total vertical distance between the first and the last check dam in

that particular portion of the gully or torrent.B = the total vertical distance calculated according to compensation

gradient for that particular portion of the gully or torrent.The compensation gradient has to be maintained as 3 % through out the

300 m long sloping terrace therefore B = 300 * .03 = 9 mH = average height of the checkdams.

Number of check dams = (A-B)/H=(21-9)/1.5=12/1.5 = 8

Other Numericals :

Given : L = 1.2 Km. ( max. length of flow )

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A = 2.1 Km2 (Area of watershed)

S = 15 m ( watershed gradient or difference in elevation between the outlet and the most remote point divided by L)

C = 0.03 ( catchments characteristics constants )

Calculate the time of concentration, intensity of rainfall and Runoff discharge for a return period of 20 years.

Runoff ( Discharge ) calculation by using Rational Formula

The rational formula is : Qmax = CIA/ 360

Here,

Time of Concentration (T) = 0.0195 L0. 7 7× S -0. 385 = X (m)

Intensity of Rainfall for a return period of 20 years, I X =

a / ( b + T )

= 2850 / (10 + X ) mm/hr

= Y mm/hr

0.03 ×Y × 2.1

Q max = _______________ cumecs ( m3/sec )

360

The values of intensity constants "a" and "b" are either given or supplied in a table :

Table : Intensity Constants

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_______________________

a b

________________________

1 year 830 5

2 year 1400 7

5 years 2100 9

10 years 2590 10

20 years 2850 10

50 years etc. 3220 11

2.2.2 Terraces

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Terracing : Terraces are the oldest structural conservation measure applied in sloping lands. They are essentially level or nearly level strips running across the slope. These strips are supported by risers in down hill sides and the whole system looks like a series of steps. Terracing is practiced in many countries for thousand of years.

Objectives :

-- to reduce runoff and velocity of flowing water and thereby minimizing erosion from the land and preventing heavy sedimentation to the streams and low land below.

-- to conserve soil moisture and soil fertility, thus increasing farm production.

-- to facilitate farming practices such as mechanization on steep slopes and there by increasing the arable land.

-- to promote proper land use in hilly regions and to reclaim eroded slopes

2.1.7.1 Types of Terraces :

There are several types of terraces with paticular objectives, functions, climate and crop conditions. Commonly used terraces are :

a ) Level Bench Terraces: This is completely a level terraces i.e all points of the surface is at the same height. The bench is surrounded by a dyke of about 20 cm. height to retain water and a notch can be cut in the dyke to flow water in the next terrace or bench. Terraces to grow paddy belongs to this type and also useful in low rainfall areas and highly permeable.

b) Outward Sloping Terraces : These terraces slope outwards. A drain is usually dug either along the top line or at the toe of the

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riser to collect runoff. This type of terraces are useful in semi-arid areas where rainfall intensity is not high. The amount of earthwork in this type is less than for the level terrace. Here, runoff flows down the filled portion of riser of next terrace so terraces are usually easily eroded.

c ) Conservation Bench Terraces : Level contour benches are built at intervals on the slopes to catch and hold runoff water from the land above. A terrace ridge is built on the lower side of the bench to hold runoff water. This type of terraces are used in arid or semi-arid countries.

d) Reverse Sloped Terraces: Here the terraces are built sloping inwardly towards the toe. The runoff will first be collected at the toe of the bench then gradually drained to a protected waterway. The riser will be kept free from over flowing water and is protected usually by grass cover. This type of terrace is suitable in heavy rainfall regions and on soils with low permeability.

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Benefits of Terraces :

a. protect soil erosionb. minimize sediments and water pollutionc. reduce run-off water and flood damaged. intensify land usee. stimulate improved farming practices and increased

productionf. improve drainage and provide better sites for cultivation

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g. facilitate mechanization of steep slopesh. conserve moisture and maximize irrigation benefitsi. create arable land and enable a wider choice of crops

and cropping patternj. encourage established farming system and reduce

shifting cultivation and forest firesk. create labor intensive programs and create local job

opportunitiesl. beautify landscape and provide a better environment for

farming Limitation for Terraces :

can be built in any slope with deep soil cultivable parts become narrow as slopes become steep slopes need high height riser and risk of failure of riser becomes

high produce limited level land or area for cultivation

2.1.7.2 Design of Terraces:

The design includes : Width, Vertical Interval ( V I ), Lengths and Grades, Riser and Reverse Height, Net Area, Cross-section and Volume of Terraces

In designing the terraces, the Width of Terraces must first be decided.

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Figure : cross-section of terrace

Width :

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The width of terraces are determined by many factors : soil depth, slope, the crop, farming methods, tools to be used and farmers choice and preference. The thumb rule is for manually cultivated terraces, the range of terrace width is about 2mt. to 5mt and for tractor cultivation, the range of terrace width is about 4mt. to 8mt. depending upon soil depth and degree of slope.

Vertical Interval :

This is a elevation difference between two succeeding terraces, which is determined by the slope and desired width of the terraces. VI is important to determine since it gives the approx. height of riser and basic information for calculating cross-section and volume of soil to be cut and moved about.

V I = S x Wb / 100- S x U, where

S = average land slope in %

Wb = width of terrace ( need to be pre-determined )

U = slope of riser ( ratio of horizontal distance to vertical rise)

Example : Terrace of 3mt. width to be built on average land slope of 20 % with riser slope of 1:1. Find the vertical interval

V I = 20 x 3 / 100- 20 x 1 = 0.75 mt.

Terrace Length and Grades :

The length of a terrace is influenced by size, shape and degree of fragmentation of land and permeability and erodibility of soil, the cross-section of terrace and outlets.

The length of terrace should not be very long in one direction as the velocity of flowing water may cause surface erosion. A maximum of 100 mt. in one direction is considered effective.

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The grade of terrace should vary from 0.1 % to 1% that is 1/10 to 1 mt. fall per 100 mt. running length.

Low rainfall and permeable site = grade < 0.5%

High rainfall and impermeable site = grade 1 %

In the case of longer terrace = variable grades should be used e.i 0.25 % for the first part from the top, 0.5% for the second part and 1 % for the last part towards the outlet

Terrace Riser and Reverse Height :

The height of the riser of the reverse type of terrace :

Hr = V I + RH, where as Hr = ht. of the riser

V I = vertical interval

RH = reverse ht ( 1/2 of depth of cut ).

The width of a riser, Wr = Hr x U (riser slope)

Width of terrace, Wt = Wr + Wb ( width of bench )

Linear length of terrace, L = 10,000/ Wt (per ha.)

Net area of terrace, A = L x Wb

Cross-section of Terrace, C = Wb x Hr/ 8

Volume to be cut and filled, V = L x C

2.1.7.4 Construction and layout procedure of protection work :

Lay-out :

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Needs careful field observations of topography, slope, soil depth,texture erosion, presence of rocks, vegetation, landuse, future cropping plan. After the careful observations of above mentioned factors decisions should be taken on the proper type of terraces, their width and tools to be used. The vertical interval, the height and width of riser can be obtained either using above mentioned formula or or prepared specification table (attached ). Before staking out the layout of terrace, it is necessary to decide the site and waterway system. Wind breaks if necessary should also be located. All of these should be integrated into the terracing plan with sketches.

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Figure : Construction consideration and layout of terraces

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Surveying and Staking :

Survey and stakeout the central line of the terraces. This central line stakes should be retained as a guide for the non-cut and and non-fill line during construction. The area above this central line is cut line and down is fill out area.

The second method is to survey and stake both the upper and bottom lines as determined by width of the terrace. Make sure that the space staked out between two lines will give the width of the terrace needed.

General Guidelines :

1) Clear the sites for clear vision to carry-out survey.

2) Surveying and staking should start at the top and proceed downward

3) Stake the graded contour lines

4) Stakes should be placed at every 5 to 10 mt. and at all points where topography changes

5) All the staked lines, waterways, roads etc. should be leveled.

6) Construct when soil is not too dry or too wet.

7) Begin construction from the top of the slope and proceed downwards

8) Begin the cut at the top and fill in the bottom

9) After each 15 cm. fill, the soil should be compacted

10) The edge of the terrace should be little higher than required to take care of settling of soil.

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2.1.7.3 Stability/Protection :

1) New terraces should be protected at its riser, outlets and waterways. Should be carefully protected for at least 2 years.

2) After construction, the riser should be shaped and planted with grasses. Sod forming or rhizome types of grass prefered than tall or bunch types. Although some tall grass like Napier, Setaria can be used but they need frequent cutting. and care. Carpet grass found very useful in protecting riser

3) Terrace outlets (point where the runoff leaves the terrace and goes into the waterways) needs to be protected by sodding, bricks, stones

4) Keep the toe-drain open, and do not permit any accumulation of water in any part of the terrace

5) Allow all runoff to collect in the toe drain for safe disposal of water into protected waterway. Any kind of obstruction in the toe drain should be taken out.

6) Ploughing should be done carefully not to destroy the toe drains and the reverse grades.

7) Do not allow runoff flow over the risers. If necessary dyke along the edge of bench should be built.

8) Keep grasses growing well on the risers. Weeds and vines which kills grasses should be cleared.

9) Any small damage or break of the riser should be repaired immediately.

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Numerical :

1. A 15% hilly land is proposed for construction of bench terrace. Calculate the following parameter of bench terrace using 2.5 m as vertical interval and 1:1 is batter slope. Here calculate the following parameters :a) Total width of the bench ( Wt)b) Length/hac) Earth workd) Area lost

Given : U = Slope of riser = 1:1

S = Average land slope = 15%

VI= Vertical interval =2.5 m

V I = (S x Wb ) / (100- S x U), where

S = average land slope in %

Wb = width of terrace ( need to be pre-determined )

U = slope of riser ( ratio of horizontal distance to vertical rise)

Solution :

a) In a bench terrace,VI = Hr = 2.5 VI = (S x Wb) / (100 – S x U)

or (15 x Wb) / (100 – 15 x 1) = 2.5Wb ( Width of bench) = 14.16Wr ( Width of riser ) = Hr x U = 2.5 x 1 = 2.5 mTotal width of bench Wt = Wr + Wb = 2.5 + 14.16 = 16.66m

i. Length/ha ( terrace length/ha)

L = 10000/Wt = 10000/16.66 = 600 m/ha

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ii. Earthwork (volume) : ( L x Wb x Hr)/8 = ( 600 x 14.16 x 2.5)/8

= 2655 m3

iii. Area lost due to slope = (S + 200) / (200/s + S/100) = (15 + 200) / (200/15 + 15/100) = 15.95 %

2. If the vertical interval of bench terrace is 1.5 m, land slope is 25% and riser slope is 0.50 Compute the width of the terrace

Solution : V.I = (S x Wb) / (100 – S x U)

1.5 = (25 x Wb) /(100 – 25 x 0.50)

Wb = 5.25

3. Calculate V.Iof terrace, if width of terrace =3m; land slope = 20%; riser slope=1:1

Solution : V.I = (S x Wb) / (100 – S x U)

= (20 x 3)/(100 – 20 x 1) = 0 .75m

2.2.3 Waterways

2.1.5.1 Types of waterways/drainage Grass waterways : These are grass waterways in which a parabolic or slightly trapezoidal shaped channel are made and planted with low height rhizome type perennial grass. Grass turfing at the bottom and at the sides of the channel will be more advantageous in vegetative waterways. However, it has some limitations such as it can not be used where the velocity of water flow is more than 2m / sec, it is not safe in steep slopes of more than 10 degree, it needs drop structures if the length is longer than 35m, it is not safe in the area where there is a continuous flow of water, it can't be used until the grasses are well established at the canal course.

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Stone-lined waterways: In this case, flat stones or stones of 15-20 cm diameter are pitched and keyed at the bottom and on sides of the channel. This is used if the slopes are steep and volume of runoff is large. In some cases, wire mesh filled with stones are also used.

Grass waterways with drop structure:

In this case series of drop structures or checkdams, as needed are constructed at the course of channel to break the velocity of running water. These waterways are made in steep slope, which exceeds the prescribed slope limit of grass waterways as mentioned above. The channel course between the drop structures are maintained as in grass waterways. However, the drop structures should not be taller than 1-2m. and the slope between the apron of the upper structure and weir of the structure immediately below should not be more than 3 % for the sake of stability and safety. The drop structure can me made from brushwood, loose stones, mesh wire or concrete.

Concrete waterways: A parabolic or V-shaped waterways can be costructed at the middle of channel with grassed channel slopes in the sites with steep slope, frequent rainfall, seepage sites.

Stepped grass waterways : This is a parabolic grass waterway which is cut by number of steps or drop structures to control the channel flow and to protect the riser and bottom of steps. This is commonly used in steep slopes giving channel slope between 3 - 4 %.

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2.1.5.2 Design of waterways/drainage (hydraulic channels ):

Design of hydraulic channels is applied in selecting a structure which will pass the design flow through the cannels without excessive headwater elevation. In designing the hydraulic channels, It is necessary to determine the peak discharge for the area to be drained. The peak discharge or maximum rate of runoff can be calculated by using Rational Formula i.e

Qmax = CIA/ 360 ( m3 /sec or cumecs ), where as Qmax = maximum discharge or rate of runoff ( cumecs ) C = runoff coefficient A = watershed area from where the runoff accumulates

( ha.) I = intensity of rainfall(mm/hr) for designed frequency for

duration equal to time of concentration. After determination of peak discharge, allowable velocity of flow for vegetative or non-vegetative channels are fixed using the figures given in the table:

Canal Materials

Manning's(n) coefficient

Velocity ( m/s )

Clear Water with

colloidal silts

Waterwith sand gravel/fragment

Fine sand, colloids

0.020 0.45 0.75 0.45

Sandy loam, non-colloids

0.020 0.53 0.75 0.60

Silt loam, 0.020 0.60 0.90 0.60

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non-colloids

Alluvial silts, non-colloids

0.020 0.60 1.05 0.60

Ordinary firm loam

0.020 0.75 1.05 0.68

Stiff clay,very colloidal

0.025 1.13 1.50 0.90

Alluvial silt, colloidal

0.025 1.13 1.50 0.90

Fine gravel 0.025 0.75 1.50 1.13

Coarse gravel, non-colloidals

0.025 1.20 1.80 1.90

Cobbles and shingles

0.035 1.80 1.80 1.50

Table: Maximum allowable velocities for non-vegetative channels having different channel materials After fixing the allowable velocity of flow, then calculate the cross-section area of hydraulic channel to carry out the calculated maximum discharge or runoff by using the formula : Qmax = a × V or a = Qmax / V, where as Qmax = estimated peak discharge or rate of runoff ( cumecs) V = permissible velocity ( m/s ) and a = cross-section area of channel ( m2 )

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After calculating the cross-section area of channel using above mentioned formula, then calculate manually the cross-section area of channel by adjusting dimensions like debth and width of the channel in order to make the manually calculated cross-section area of the channel equals to the cross-section area as calculated from the formula. In other words, Cross-section area from formula (a = Qmax / V) = calculated cross-section area.After determining the cross-section area or height and width of the channel, now calculate the gradient or slope of the channel to be maintained. This can be evaluated by using Manning's Formula, which is : V = ( R 2/3 × S 1/2 ) / n or S = ( nV / R 2/3 ) 1/2, where as S = gradient or slope of the channel n = manning roughness coefficient( figure given in the Table above ) V = allowable velocity of flow ( m/sec) R = hydraulic radius (m), which is cross-section area divided by wetted perimeter i.e a / p and wetted perimeter ( p) is the length of line of inter section of the plane of the cross-section with the wetted surface of the channel. In general, wetted perimeter can be considered as width of the channel. If the hydraulic properties of the channel such as width, depth and slope are known, the Manning's formula can be used to determine Qmax ( cumecs), which is Qmax = 1/ n × a R 2/3 × S 1/2 .

In the case of bank full discharge of channel, the hydraulic properties can be related with channel discharge as :

b ∞ Qmax × b 1/ 2

d ∞ Qmax × b 1/ 3

s ∞ 1/ Qmax × b 1/ 6

,where as b = width, d = depth and s = slope of a channel

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The calculated runoff (Qmax ) should be more than or equal to given runoff ( Qmax ) to accept that the design of waterway or channel is safe.Design of storm water drain:

Storm water drains are waterways, drainage and watercourse in which the runoff occurs and drains during the rainfall or storm . It is important to guide the storm water drain to certain safe point in order protect the land from erosion. The purpose of designing storm water drains are : -- to manage the surface runoff -- to provide safe drainage to excess runoff that may developed during rainfall -- to divert the runoff from entering into gully, erosion or landslide heads -- to divert the runoff and dispose off into safe area or land surface -- to prevent land from the formation of rill and gully erosion and landslide

-- to harvest the runoff for domestic purpose.The storm water drain can be managed by several means. The mostly used techniques are constructing waterways or drainage or diversion ditches. These techniques can be used at places depending upon availability of construction materials, purposes and structures that can be constructed. Before selecting the techniques and designing the structures for the management of storm water drain, it is necessary to know the hydrological elements of storm water such as quantity of peak discharge, velocity of runoff, slope of land, volume of runoff, soil and vegetation conditions and land-use. Waterways are classified into two : Vegetative(Grass) and Non-vegetative or structural waterways.

Shapes and design of waterways :

Based on the site condition, objectives and availability of materials, the shapes of water ways can be chosen. Normally, the shapes are:

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-- Trapezoidal

-- Parabolic and

-- Triangular or V- shaped

Having calculated the Qmax , cross-section area , velocity of flow and surface slope following the steps as described aboveve, the side slope, bottom width and the depth of the channel can be calculated for different shapes of waterways.

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57

Numericals (Examples) :

1. To calculate whether or not the design of channel or waterway is safe.

Always keep in mind that the calculated Qmax > or = Given Qmax

Given :

a) For a Trapezoidal cross-section Given Qmax = 3.5 cumecs

Channel slope, S = 0.3% or 0.003

Coefficient factor, n = 0.045

Side slope, Z = 2

Height of channel/ waterway, d = 1 m.

Base breadth or width of channel/ waterway, b = 2 m.

Now, calculate Qmax = A ×V = Crosection area × Velocity of flow of water

A = b × d + Z d 2 = 2 × 1+ 2 × 1 2 = 4 m2

V = ( R 2/3 × S 1/2 ) / n, R = hydraulic radius and S = channel slope

R = Cross-section area of channel (A ) / wetted perimeter ( P)

P = b + 2 d ( 1+ Z 2 ) 1/2 = 2 + 2 ×1 ( 1 + 2 2 ) 1/2 = 6.47 m 2

Now, R = A / P = 4 / 6.47 = 0.62

V = ( 0.62 2/3 × 0.003 1/ 2 ) / 0.045 = 0.885 m / sec

Qmax ( calculated ) = A × V = 4 × 0.885 = 3.6 cumecs

Here, calculated Qmax > given Qmax , so design is safe and acceptable.

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In this way, we can calculate the safety or acceptance or rejection of channel cross-section of parabolic, triangular or V-shaped channels. If there is rejection,

we can adjust either breadth (b) or height (h) of the channel cross-section and bring it to the acceptable level.

Important : a ) For trapezoidal cross-section: bottom breadth (width), height (depth), side slope, canal gradient are provided

b ) For parabolic cross-section : top breadth ( width ), height ( depth ), channel gradient are provided.

c) For triangular or v-shaped cross-section : top breadth ( width ), height (depth ), side slope, canal gradient are provided.

2.2.4 Bunds

Bunds are structures constructed across the land slope to reduce the length of slope and velocity of runoff in down hill side for agricultural operation. Bunds are generally preferred to construct in the slope between 2 -10 % slope and soil depth ranging from shallow to medium.

Its main purpose are :

To reduce the velocity of runoff To intercept the flowing water or runoff To hold water and maintain moisture in the catchment for a

longer period To allow more water to infiltrate To reduce soil erosion

2.1.6.1 Types of Bunds:

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Contour bunds : This is constructed along the contours, low rainfall areas, soil depth > 20 cm, slope < 7 %, good infiltration capacity, built in series to divide the length of the slope

Graded bunds : This is constructed with some longitudinal slope, this is to be used for partly conservation of moisture and safe disposal of excess water or runoff, suitable for high rainfall areas and soil having less infiltration capacity, poor soil depth, built in series to divide the length of the slope

Peripheral bunds : This is constructed to incircle the boundaries of ares

Marginal bunds : This is constructed in the lowest part of the catchment without any consideration of contour

Side bunds: this is constructed along the slope at the two sides of contour bunds

Lateral bunds : bunds are constructed along the slopes in between two side bunds to reduce the length of contour. This reduces accumulation of runoff along one side

2.1.6.2 Design of bunds .

The design criteria of bunds include following parameters :

Choice of bunds : Choice of bunds depends upon rainfall, soil condition and types of out lets used. Contour bunds are used in low rainfall areas and graded bunds are used in medium rainfall areas with slope percentage between 0.2 – 0.3 %

Spacing : The basic principle that decides the bund spacing are : a) able to intercept the surface runoff before the runoff attains erosive velocity. b) it should meet all requirement for agriculture operation.

Size of bunds Side slopes Alignment Land submergence Moisture conservation /dry period

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Cost Design :

The general relationship between land slope % (S) and the vertical interval between the two consecutive bunds are :

VI = (S /a ) + b, where a and b are constants depend upon soil and rainfall characteristics. Add 25 % extra spacing of bunds if conservation measures are applied and reduce 15 % spacing for unfavorable condition of conservation measures.

Following Formula can also be used for the calculation of spacing between two consecutive bunds :

a) Ramsar’s Formula : For normal to moderate rainfall,

V I = 0.3 ( S/3 + 2) where S = Land slope (%) (

For heavy rainfall area the above equation is modified as :

V I = 30 ( S/3 + 60) and for low rainfall area the equation is V I = 30 ( S/2 + 60)

b) Cox’s Formula :VI = ( X *S + Y) 0.3 where X = Rainfall factor, S= land slope in % and Y = infiltration and crop cover factor. The value of X and Y can be received from the following table :

Rainfall Condition

X values Average rainfall (cm)

Y value

Scanty 0.8 64 1.0

Moderate o.6 64-90 2.0

heavy 0.4 >90 1.5

Size and Height of bunds :

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Bunds height depends on : Depth of water storing, highest flood level, free board, soil infiltration and vertical interval

a ) Cross-section area of Bund=(base width + top width)* Ht/2

B )Bund height = (24 hr. Rainfall storage * VI/50)1/2

Numerical : Calculate the VI of contour bunds on a 4.5 % land slope. The rainfall is moderate with average infiltration and good coverage of land with vegetation

Solution : a) Using Ramsar formula

V I = 0.3 ( S/3 + 2) where S = Land slope (%)

= 0.3 ( 4.5/3 + 2) = 1.05 m

Add 25% extra spacing because the ground cover is good

Therefore, VI = 1.05 + 0.26 = 1.31 m

b) Using Cox’s formula VI = ( X *S + Y) 0.3

= ( 0.6*4.5+2)0.3

= 1.41 m

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Unit 3 Design and Construction of River Training Works

3.1 Spurs :

Spurs are structures/ obstructions constructed in rever banks to divert water away from a specific location (eroding river bank ). Spurs are used to deflect flow into a preferred path.

Spurs are constructed perpendicular to the river bank. Constructed in series of three or more from a varieties of materials and requires toe protection ( apron) at their ends or noses to protect against scouring.

The purpose of these structures are to protect the river banks from the direct impact of the water flow and to train the river by deflecting its flow. These structures are constructed into the river banks with some extension across the river flow.

3.1.1 General Types :

a) Deflector Spursb) Retarder Spurs

a) Deflector Spurs : Impermeable, which function by diverting the flow of water away from the bank.

b) Retarder Spurs : Permeable, which function by retarding flow velocity at the bank and diverting away from the bank.

Specific Types :

a) Bar spurb) T- head spurc) Sloping spurd) Timber / bamboo crib spure) Round nose spurf) Hockey spur

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g) J- head spur

Main functions :

--- deflect flowing water/ channel

--- reduce velocity of flow near the stream bank

--- prevent erosion of bank

--- establish more desirable channel width

--- encourage sediment deposition due to reduced velocity and increased protection of bank

--- halt meander at a bend

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--- channelize wide, poorly defined streams into well defined channel

3.1.2 Criteria for Design:

--- spur length

--- spur orientation

--- spur permeability

--- spur height

--- bed and bank contact

--- spur spacing

Spur Length : Projected length of spur should be perpendicular to the bank or flow direction. Normally, length of spur should be within 20 % of the channel width for both deflector (impermeable) and retarder ( permeable ) spurs. However, field installation have shown that length of 3 to 30 % of channel width have also been successful. Deflector spurs length usually with less than 15% of channel length and retarder spur up to 25 % of channel width are successful.

Spur Spacing : Normally 2 to 3 times the length of spurs. In fact, the spacing of spurs is a function of spur length, spur angle to river bank, permeability and degree of curvature of the bed. The spur angle or flow expansion angle is an angle at which flow expand towards the down stream bank of spur .Spur angle or the flow expansion angle is a function of spur permeability and the ratio of spur length to channel width. As permeability increases, the flow expansion angle or spur angle increases, similarly as length of spur increases the expansion angle or spur angle increases. The expansion angle for impermeable spurs is constant i.e 17 o. Therefore the spacing of spurs can be determined by,

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S = L cot Ø, where as

S = spacing of spurs, L = length of aspur, and Ø = expansion or spur angle.

Spur Orientation: Spurs are normally placed at normal to the bank/ flow of water. Spur angle < 90 degree ( acute angle ) oriented towards upstream and > 90 degree oriented towards downstream. Bank erosion is more severe if the spur is oriented in the downstream. Spur orientation affects spur spacing, degree of flow control, scouring depth at the nose of spur.

Spur Permeability : Deflector spurs can be used on sharp bends to divert water flow away from the bank. It can cause erosion of stream bank at the spur root, if the height of spurs are lower than the height of bank. Under sub-merged condition flow passes over the height of the spurs generally perpendicular to the spurs. Retarder spurs can be used where bends are mild and small reduction in velocity are required.

Spur Height : Height of Deflector spurs should not exceeded the height of river bank. If the flood height is > or = bank height, deflector spur height should be equal to the bank height. If the flood height is lower than the bank height, the height of deflector spurs should be designed not to overtopping occur at bank. For deflectors, the crest profile should slope downward away from the bank line, which will avoid the possibility of stream bank erosion and overtopping of flood water.The crest profile of retarders is generally level.

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Design Parameters of Spurs :

--- Design discharge

--- Flow velocity

--- Scour magnitude

--- Degradation and Aggradations

Design discharge:

Before designing a spur, it is necessary to calculate design discharge of flood. The design discharge can be calculated using the following formula:

Qmax = bA c (cumecs), where as

Qmax = Mean annual flood peak of daily discharge.

b and c are coefficient which can be fixed from the table as given below.

A = Watershed area ( Km.2 ) below elevation of 3000m.

Table : Coefficients for Mean Annual Flood Peak Discharge

___________________________________________________________

Regions Coefficients

b c

_____________________________________________________________

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Karnali ------------------------------------------------1.27 0.864

Gandaki ----------------------------------------------- 2.39 0.826

Kosi ----------------------------------------------- 1.92 0.854

Southern rivers ---------------------------------------- 3.03 0.747

_____________________________________________________________

River discharge can also be calculated from Manning's formula, which is :

AR 2/3

× S

1/ 2

Qmax = ____________ , where as

n

Qmax = Mean annual flood peak of daily discharge (cumecs)

A = Average cross-section area of river ( m2 ), this should be taken corresponding to high water mark. For a multi-channel or braided river, the cross-section should be taken at bank full slope.

R = Hydraulic depth ( m)

S = River slope

n = Manning's roughness coefficient

Hydraulic depth is calculated by dividing average cross-srction area by average width of the river i.e R = A / W, where W is average width of the river. The Manning's roughness coefficient should be fixed as per the width of a river from the table as given below :

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Table : Manning's roughness coefficient ( n )

Major rivers ( width > 50m )

a. Straight, alluvial, sand ------ 0.020 to 0.040

b. Straight, gravel ------ 0.020 to 0.045

c. Irregular section ------ 0.035 to 0.100

Minor streams ( width < 30m )

a. Straight, regular section ------ 0.025 to 0.035

b. Winding, irregular ------ 0.035 to 0.060

Flood plains

a. Pasture, short grass ------- 0.025 to 0.035b. Pasture, high grass ------- 0.030 to 0.050c. Cultivated, no crop ------ 0.020 to 0.040d. Cultivated, field crops ------ 0.030 to 0.050e. Light, scattered brush ----- 0.035 to 0.070 Medium to dense brush ----- 0.070 to 0.160g. Tree land, stumps ---- 0.050 to 0.080h. Heavy stand trees ---- 0.080 to 0.120

Excavated Channel

b. Earth, recently completed ----- 0.016 to 0.020c. Earth with grass ----- 0.018 to 0.033d. Rock, smooth ----- 0.025 to 0.040e. Rock, jagged ----- 0.035 to 0.050Surface Condition

a. Smooth and impervious surface ---------- 0.02b. Smooth and bare surface ---------- 0.10c. Cultivated row crops moderate rough surface --- 0.20d. Pasture or average grassed surface ---------- 0.40e. Forest area with dense cover ---------- 0.80

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Flow Velocity :The flow velocity of a river is calculated from the following formula:

Design Discharge

Average flow velocity ( Va ) = ____________________________________

Average cross-section area of river

If the river is approximately straight and as a thumb rule, the velocity of flow that hits a spur on the river bank can be considered as, V1 = Va, whereas V1 is velocity of flow that hits a spur and Va is average is average flow velocity. If there is a sharp bend, then the velocity of that hits a spur on the river bank can be considered as, V1 = 4/3 Va.

Scouring Magnitude : The scouring depth of a spur can be calculated as,

S = Mean hydraulic depth ( d ) × scour or z factor ( Z ) for bank full condition. Z factor can be assumed from the table as given below.

Mean hydraulic depth = Cross-section area (A) Average width (W) of a river at bank full condition

As a thumb rule, if the angle of flow to the bank of river is 30o, 45o, 90o, the Z value can be taken as 2, 3 and 4 respectively.

Return Period : Return period of a flood does not mean that this flood will only occur once in that return period. It is a probability or chance that the flood can occur within that period. For example, if the return period is 50 years, it does not mean that the similar kind of flood will occur once in 50 years. What it mean is there is probability of having a similar flood 1 in 50 or 2 % risk of occurrence every year. Similarly, if the

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return period is 10 years, there is a probability of having a similar flood 1 in 10 or 10 % risk of occurrence every year.

Relationship between return period, service life and risk of a structure

R = { 1 - ( 1 - 1 / T ) L }100 % where as,

R = Probability or risk that a flood occurs

T = Flood return period (yrs.)

L = Service life of structure

Degradation and Aggradation

Degradation : Bed falling ( Drop in average bed level ). It is also downstream and upstream progressing degradation. It occurs when bed materials load is reduced by a dam, when water discharge increases from a diversion, bed materials size reduces along a river.

Aggradations : Bed rising ( sediment deposition). It occurs due to deposition of bed materials along the central portion of river. Due to aggradations, outside banks are attack and bank erosion occurs. It causes several channels in the river bed and river is braided. It normally occurs in alluvial fans of river.

Guidelines for Spur design and layout :

--- Spacing 2 to 3 times spur length.--- Spur nose ( tips) should be well protected.--- Spurs should be set out in the feild of three or more--- Spurs should be tied in bank and normally be perpendicular to the

bank/flow--- Spurs nose (tips) should be protected by apron.

3.2 Embankments :

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Embankmens are the oldest and most widely used structures to check bank erosion, minimize flooding on the alluvial fans. These structures are constructed on the river banks parallel to the river banks.Embankments are also levees or dykes or revetments. However, these structures should be constructed along the whole eroded length of the river bank with well keyed inthe bank.

These structures are generally made from concreate, gabions filled with stones, earthern and stones, sand bags and logs. Hydraulic properties of river and river characteristics such as:

River Discharge (Qmax)

Bankfull Discharge (Q b)

Width or cross-section of river (b)

Water depth (d )

Slope of river bed ( S ) and

Scouring depth are necessary to calculate for the design of the embankment.

River discharge can be calculated from Manning's formula and other parameters such bankfull discharge, width or cross-section of river, water depth, hydraulic radius, river slope, scouring depth and Manning's roughness coefficient can be calculated as explained earlier.

A free board of about 1mt. should be provided at the top of a embankment to protect against over flow of river and an apron should be provided with 1.5m.horizontal and 1.0 m. vertical and should be larger than the scouring depth. However, the size of apron and free board depends upon the design and type of embankment.

The river characteristics such as width ( b), depth (d), and slope of river (S) are directly related with bankfull discharge. Their relationships are:

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b ∞ Q b 1/2

d ∞ Q b 1/3

S ∞ 1 / Q b 1/6

Figure : Cross-section of embankment or Revetment

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Figure : Construction of Embankment or Revetment

Figure : Different types of Embankment

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3.3 Bolster

Bolsters are tubes of gabion wire or jute net filled with stones are placed along the counter or laid in shallow trenches across the slopes, which act as scour checks and reduce surface movement of debris and prevent the down slope movement of debris while vegetation cover is established. Common type bolsters are :

a) Wire c) Hessian and d) Jute bolsters

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Figure : Construction of Bolster

Functions :

Tubes of 30 cm diameter are made from gabion wire and laid in shallow trenches across the slope. They act to prevent the down slope movement of debris and also prevent the surface scour and gullying. They are constructed and laid down on most long exposed slopes where there is a danger of scour or gullying on the slope

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Materials :

a) Woven gabion panel ( 5*1m or 5*2m), 10 gauge wireb) 12 mm mild steel rod cut into 2m lengthc) Digging and binding toolsd) Skilled and Unskilled labor

Unit 4 : Design and Construction of Water Harvesting Structures

Water Harvesting :

Rainwater harvesting is the accumulating and storing , utilizing of rainwater for reuse, before it reaches the aquifer and loss due to overland flow. It means capturing rain water where it falls or capturing the run off in the houses, village or town The harvested rain can be used for drinking water, irrigation, water for livestock etc. depending upon the level of pollution in the water.

Water harvesting can be undertaken through a variety of ways

Capturing rain from rooftops Capturing runoff from local catchments

Capturing seasonal flood waters from local streams

Conserving water through watershed management

These techniques can serve the following purposes:

Provide drinking water Provide irrigation water

Increase groundwater recharge

Reduce storm water discharges, urban floods and overloading of sewage treatment plants

In general, water harvesting is the activity of direct collection of rainwater. The rainwater collected can be stored for direct use or can be recharged

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into the groundwater. Rain is the first form of water that we know in the hydrological cycle, hence is a primary source of water for us. Rivers, lakes and groundwater are all secondary sources of water. In present times, we depend entirely on such secondary sources of water. In the process, it is forgotten that rain is the ultimate source that feeds all these secondary sources and remain ignorant of its value. Water harvesting means to understand the value of rain, and to make optimum use of the rainwater at the place where it falls. Theoretical assumption (quantity of water that can be harvested) The total amount of water that is received in the form of rainfall over an area is called the rainwater endowment of the area. Out of this, the amount that can be effectively harvested is called the water harvesting potential.

Water harvesting potential = Rainfall (mm) x Collection efficiency

The collection efficiency accounts for the fact that all the rainwater falling over an area cannot be effectively harvested, because of evaporation, spillage loss etc. Factors like runoff coefficient and the first-flush wastage are taken into account when estimated the collection efficiency.

The following is an illustrative theoretical calculation that highlights the enormous potential for water harvesting. The same procedure can be applied to get the potential for any plot of land or rooftop area, using rainfall data for that area..Consider your own building with a flat terrace area of 100 sq m. Assume the average annual rainfall in your area is approximately 600 mm (24 inches). In simple terms, this means that if the terrace floor is assumed to be impermeable, and all the rain that falls on it is retained without evaporation, then, in one year, there will be rainwater on the terrace floor to a height of 600 mm.

1. Area of plot = 100 sq. m. (120 square yards)2. Height of the rainfall = 0.6 m (600 mm or 24 inches)

3. Volume of rainfall over the plot = Area of plot x height of rainfall

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4. Assuming that only 60 per cent of the total rainfall is effectively harvested

5. Volume of water harvested = 36,000 litres (60,000 litres x 0.6)

This volume is about twice the annual drinking water requirement of a 5-member family. The average daily drinking water requirement per person is 10 litres.

Water harvesting can be done through three process :

Roof water harvestingRunoff water harvesting and

Flood water harvesting

a. Rain water harvesting from roof

Figure 1 Rain water harvesting from roof

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Figure 2 Collection process of rain water from roof

Figure 3 Different parts of collection system of rain water harvest from roofCatchment Area : zinc sheet roof or Concrete roof ( size depends on the size of house

Gutter : Size depends. Normally 3”*3”or 4”* 4” size

Water delivery pipes : 4”* 4” size

Water filter tank : size depends

Water collection tank : size depends on water demand, household water consumption/day, rainfall intensity, roof area ( catchment), Dry season period

Water pump : hand pump or electric pump

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b. Harvesting run off water (catchment pond):Water availability for agriculture, home garden can be improved by harvesting runoff water. Small scale catchment pond or impoundments or reservoir are constructed to capture and store rainfall runoff within the catchment area. Amount of runoff generated depends on the catchment characteristics (area and size, type of vegetation, land use, soil, topography, etc.) and rainfall and intensity pattern (amount, duration and intensity)

Small-farm reservoirs sites in elevated or depressed areas (valley) where irrigation is possible are suitable sites. Sites that are commonly owned should be properly managed to ensure sharing among the intended beneficiaries. Places with springs or flowing streams to ensure a year round water supply are good sites for reservoirs. Topography that undulating or rolling with slopes of 2 to 18 % is desirable. The size of catchment pond or impoundments or reservoir depend upon the objectives of water harvesting, financial resources and labor availability

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Design consideration :

Following points should be considered in the design of water harvesting ponds. They are ;

2) Water is the main agent of erosion and landslides in the hills. Storage of water in the pond could threat or cause damage in the certain situation

3) If the water over flow the pond during summer, the overflow water can cause scouring of the side of the pond and gully may form which ultimately can lead to sudden burst of the pond.

4) Therefore, ensure that the feed drains in the pond are well protected against erosion.

Design of water harvesting structure :

Design of ponds :

1 Calculate the desired storage capacity2. Find the depth of water table3. calculate the area of catchment4. calculate amount of runoff at peak rate of rainfall5. Observe the sub soil condition6. Stability of side slope7. Suitability of site8. Safe discharge9. Economics of construction10. Provision of catch drainLayout procedure :The layout procedure of water harvesting pond depends on a) site of the structures to be constructed and b) surveying and pegging of the water harvesting structures

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Consideration in the stability of water harvesting ponds :

1. Pond must be located to gain the maximum amount of water storage for the designed size of the dam

2. The seepage from the pond should be checked or check the soil strata of the bottom so that the seepage will not take place in future

3. The dam and the bottom of the pond with core of clay soil is desirable

4. The top width of the earthen dam should be at least 1m wide and side slope at 1:2. This means 2 m high will be at least 1m wide at the bottom.

5. Never built pond if there is adanger of slope failure or any evidence of slope movement/failure

6. Do not built pond less than 50m upslope from a house7. Core overflow area area should be well protected8. Stone pittiching in the side slope of the pond if the slope is > 50

9. For the embankment to be constructed in the pond, use top width , W = 1.105 H0.5 + 0.91, where W = top width and H = height of dam. In general, up to 5m height of embankment a minimum width of 2.5m is recommended

10. Always built emergency spillway in the pond using weir formula Q = CLH3/2

Types of Ponds :1. If the embankment type of ponds have to be built, consider the

design storage capacity on the basis of requirement and available surface runoff.

2. Earthen embankment in the shape of semi circle can also be built3. Trapezoidal bunds can also be used4. Graded bunds can also be considered between the slope 0.5 -2.0 %

slope5. Catchment storage tank of 100m2 –30,000m2 are also constructed

For long term storage, the most common runoff harvesting tank are :6. Dugout ponds/conservation ponds/farm ponds : These ponds are

constructed by excavating the soil from ground surface. Here ground water or surface runoff are collected

7. Embankment type reservoir; In this kind of pond a dam or embankment around the valley or depression or a creek

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Illustration of runoff harvesting ponds are

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c. Flood water harvesting : Flood water can be diverted from river and store in a pond. Diversion structure, diversion channels are used to divert the river flood. Structure such as spurs and diversion channels are made at the bank of the river to divert the water into the ponds, This water can be used during the water deficiency period.

Advantages of water harvesting:

Excellent alternative source of water in water shortage areas Simple Construction - The construction of rainwater collection

systems is not complicated and most people can easily build their own system with readily available materials.

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Easy to Construct and Maintenance - The installation, operation and maintenance of a household rainwater collection system is controlled by the individual no need to rely on water supply agencies.

Good Water Quality - Rainwater is generally one of the better sources of an alternate water supply when compared with other sources of water that may be available.

Convenience - Rainwater collection provides a convenient source of water at the immediate place where it will be used or consumed.

Systems are Flexible and Adaptable - Rainwater collection systems can be adapted to suit most individual circumstances and to fit most any household’s budget.

Adaptation : Best way to adapt in the scarcity of water imposed by climate change

Improves food production Protects against drought Allows irrigation by gravity (no additional power cost required) Promotes soil and water conservation and ecological balance

Disadvantages of water harvesting : High Initial investment Costs - The main cost of a rainwater

collection system generally occurs during the initial construction phase and no benefit is derived until the system is completed.

Requires large number of labor High seepage and evaporation losses are possible Floating vegetation may infest reservoir Regular Maintenance - Regular maintenance, cleaning and repair

will be required for the operation of a successful rainwater collection system.

Vulnerable Water Quality - The quality of rainwater can be affected by air pollution, insects, and dirt or organic matter. The type and kind of construction materials used can also adversely affect water quality.

Water Supply is Climate Dependent - Droughts or long periods of time with little or no rain can cause serious problems with your supply of water.

Storage Capacity Limits Supply - The supply of water from a rainwater collection system is not only limited by the amount of

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rainfall but also by the size of the collection area and your storage facilities.

Additional power cost require to pump the water

Unit 5 Bio-Enginering Techniques

Definition / Concept :

Various definitions and concepts of bio-engineering are being used. This is besause to suit and specific objective for stabilizing and protecting unstable/degraded slopes, landslides and erosion.

In general, the term bio-engineering is a technique where living vegetation (plant) provides engineering functions to stabilize degraded slope. This can be administered with living vegetation alone or in combination with non-living plant materials or soft engineering to stabilize / protect degraded slopes. In other word, bio-engineering practice can also be administered through the integration of vegetative methods with soft/ normal engineering practices in order to protect/stabilize degraded slopes, land slides and erosion.

Terms like bio-engineering , vegetative engineering or vegetative structures are commonly used by implementers / users.

Why Bio-Engineering ? Bio-Engineering technology emerged based on the following reasons--- engineering practices alone are not always the solution. --- engineering practices are expensive. --- needs high skills and tecnology. --- not always affodable by users due to resource constraints. --- living vegetation has many functions ( hydrological, ecological and

engineering ) where they grow.--- living vegetation provides additional strength to the engineering

structures in integration.

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Functions of Bio-Engineering Practices:

Vegetation/ plants used for bio-engineering work can be woody and non-woody. Both woody and non-woody plants perform engineering, hydrological and ecological functions.

a) Engineering functions :

Catch : Process for holding thin layer of moving soil particles /debris by multi stemmed shrubs and bamboos.

Armour : Process for protecting soil surface and soil particles from movement by providing protective cover.

Reinforce : Mechanism for providing strength to bind the soil particles by densely rooted trees and grass.

Anchor : Process for firmly fixing the soil particles and debris by anchoring action of deep / long and strong roots of trees and shrubs.

Support : Mechanism for providing support to soil mass and rocks from the mechanical action of root system of plants.

Therefore the engineering functions of vegetation are compatible with the functions of engineering structures and are co-existence, because engineering structure protects vegetation and vegetation protects engineering structure. In some cases, vegetation replace engineering structure.

Engineering structures for slope stabilization works are also designed to meet the purposes of catch, armour, reinforce, anchor and support.

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b) Hydrological function :

Interception Leaf drip Stem flow Evaporation Transpiration Infiltration Soil water storage Overland flow Sub-surface flow

c) Ecological functions :

--- Improves harsh environment of degraded slopes into better ecological condition.

--- Improves soil and moisture conditions and generates better micro climate for the establishment and growth of plants

--- Encourage micro-organism and small animals and helps increase the bio-diversity.

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Diagram of Life span / Longevity of Bio-Engineering versus Engineering Structures is given below:

Engineering structure

Time

Bio-engineering

Longevity

Various Forms of Bio-Engineering Techniques : Various techniques can be used based on purpose, site conditions and availability of resources

a) Planting trees, shrubs and grasses : alone or in combination of two or all. Develops dense network of roots in soil and dense canopy of plants helps protect the slope from erosion. Contour line planting at regular interval is general practice in Nepal

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b) Planting Stumps / woody stems : Stumps / woody stems can be planted along the contour lines to trap soil particles and debris falling down the slopes. Sprouting stumps / stems are more preferred.

c) Seeding grass, trees and shrubs : Seeds can broadcasted manually to cover large areas in short time and with low cost. This can be done in a very steep unstable slopes and rocky areas where seedlings and stumps/ woody stem can not be planted directly.

d) Contour Strip planting : Plants are planted in strips along the contour in order to reduce erosion. Strips are left or strips interval are selected in the slope and plants are planted along the contour. Strip intervals depend upon the slope of the field. Cuttings or pot plants are planted. Plant composition may include grass, fruit plants and trees. Only one or two species of plants can be planted if the area is small. This is similar to palisade method

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e) Brush Layering: It is a method of planting branches of sprouting living woody plants making small individual terraces in the slope along the terraces. Small terraces of 15 to 100 cm wide are dug at the toe of the slope with inward inclination of 10 % and the branches are placed crosswise at the terraces and well covered with soil and pressed so that the individual branches are completely embedded and covered by soil thus encouraging root formation. The construction of brush layering should start from bottom of the slope. The distance of individual terrace should be less than 1.5 m to reduce possibilities of slope failure

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f) Turfing/Sodding ; This is a method to turf or sod fresh cutting soil and check erosion. To hold and mat the soil surface by roots, rhizome and stolons of grass and other plants is sodding. Turf and sod consisting of shallow rooting grass slab with soil, rhizome or stolon is placed on the fresh cutting slope and cover by 1-5 cm of soil layer . The size of turf or sod slab of 30 cm square or the size of 30cm * 60 cm are easy to handle. The turf or sod should be kept moist and should be planted when the soil surface is moist. The turfing/sodding should be done on gentle slope less than 350 slope. Watering should be done after plannting. Examples of turf grass are : Cynodon dactylon (dubo) ; Trifolium species (clover)

g) Palisade : Woody cuttings are planted in lines across the slope or along the counters. It forms a strong barrier and trap soil and derbies moving down the slopes. Shrubs and trees suitable are : Adhatoda vasica ; Ipomoea fistula ; Vitex negundo and other fodder trees are also suitable. This can be used up to about 75 % slope in low rainfall where

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conservation of moisture is needed.

h) Fascine : Also called contour wattling. It involves the bundling of branches of sprouting types of live plants and laying them in shallow trenches below the soil surface. After laying them in the trench, they should well cover by soil. After trenching them well inside the trench and cover by soil roots and shoots sprouts after the monsoon. They form a strong line of vegetation and traps the soil and debris moving from the upstream. This technique is suitable for the site having good soil depth and soft cut slopes. This needs live branch cutting of one meter length of sprouting type of species. Bundle of 5 to 6 branches with minimum diameter one cm. are needed. Pegs of living or dead plant should be inserted inside the surface to hold the bundles of branches trenched in the soil. The recommended slope for this technique is about 45 %. Species suitable for this purpose are Vitex negundo ( simali), Pennisetum purpureum ( Napier)

i) Bamboos / Amliso planting : Rooted clum cutting, rhizomes, wild or nursery plants of bamboos or amliso can be planted directly on slopes. These plants perform the slope stabilization effectively once they are established.

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j) Wattling : Bundles of live branches with buds are put in the trench along the contour and covered with thin layer of soil. When the branches put out roots and shoots it forms a strong vegetative barriers for holding soil particles moving down the slope. However, this technique is expensive and suitable for gentle to moderate slopes.

k) Brush wood check dams : Brush wood check dams using bamboos and woods are commonly used to stabilize gullies on slopes. Grass and shrubs are planted down stream of check dam and on slopes os gullies.

l) Vegetated rip- rap : This is a method to strengthen slopes by a combination of dry stone walling and planting vegetation or broadcasting seeds in the gaps between the stones. Side slopes of gullies and gullies bed are some time protected by constructing dry stone walls and grass seeds are sown in gaps between the stones in order to reinforce toe walls and gully beds. Plants to be planted in this technique are either grass or small shrubs with strong root system.

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Broadcasting or sowing seeds of Acaica pennata (Areri) and Butea minor ( Bhujetro) are recommended. Cuttings of Vitex negundo (Simali), Napier and Broom grasses are also recommended. Plants of big trees are not recommended in this method.

m) Loose stone and Gabion check dams : Seedlings of trees, shrubs and grasses are planted either seperately or in combination on gully heads, side slopes, gully bed, in and around the structure to reinforce the structure.

n) Brush wood embankment / spurs : Bamboos and woods are used to construct embankment and spur to protect stream bank erosion. On the back side of the structures, trees, shrubs, grass seedlings and woody cuttings are planted to provide vigor and anchorage to the structures. These techniques have been effective in the torrents and small rivers of Churia and Terai.

o) Jute netting : Jute netting is another way to protect the slopes using woven jute netting and planting grass slips or seedlings. Its main functions are: protection of slopes, by allowing seeds to hold and germinate; improvement of micro-climate on the slope surface by

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holding moisture and increasing infiltration ; act as mulch for the vegetation when the jute net is decay. It is useful on steep and hard slopes where establishment of vegetation is difficult due to harsh environment. Surface of the slope should be cleaned and smoothed, cover the slope with net and peg the net at different points to support the net. Netting should be done just before the rain starts and planting of grass slips or cutting or planting or showing of seeds should be done during rainy season. This method is very useful on steep and hard slopes where establishment of plants is difficult due to steep and harsh environment. Acaica pennata (Areri) and Butea minor ( Bhujetro) are recommended. Cuttings of Vitex negundo (Simali), Napier and Broom grasses are also recommended. Plants of big trees are not recommended in this method. However, this method is expensive, needs skills and cautious mind.

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Application of Bio-Engineering :

Where to apply ? :

Rill erosion, shallow rock failure, shallow mass movement, small gully and small river/ stream bank erosion

Erosion and landslides and Bio-engineering practice

Depth Length Bio-engineering practice

Upto 25cm. upto 30cm vegetative. practice alone

25- 50cm ,, ,, vegetative and Soft engineering

> 50cm ,, ,, soft to hard engineering + veg

Condition of Hazards

(erosion/ landslide) Practice of Bio-engineering

a) very active practice does not work

b) Active practice can be used but high risk of failure

c) dormant (but still active) best condition to apply

d) In active ( dead ) practice not necessary

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Limitations of Bio-engineering

-- cannot apply everywhere and every time.

-- it has some limitations on dimension of slope, nature of landslides and erosion,

--- geo-morphological phenomenon,

--- configuration and degree of physical, climatic and environmental stress

Plants suitable for engineering functions :

Catch : shrubs, bamboo (many stems)

Armour : grass carpets ( dense, fibrous roots )

Reinforce : densely- rooting grasses and trees

Anchor : deeply rooted trees ( long, strong roots )

Support : shrubs, large trees ( deep, dense root systems forming a soil cylinder)

Importance of Different Types of Plants in Bio- engineering

Woody Non-Woody

Trees Shrubs Bamboos Clumpig grasses

Matting grasses

Herbs

Engineerig fonction

Catch * *** *** ** * -

Armour * * - ** *** *

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Reinforce *** *** *** ** * -

Anchor *** ** - * - -

Support *** ** *** ** - -

Hydroligical functions

Intercept ** ** *** *** ** **

Evaporates *** ** *** * * -

Store ** ** *** ** - -

Leaf drip *** ** * - - -

Retard * ** ** ** *** *

Infiltrate *** *** *** *** *** *

Special Functions

Improve * ** - - - ***

Pioner - * - ** * ***

*** Excellent

** Very Good

* Good

- Poor

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Improved plants : Leguminous plants able to extract nitrogen from air and converts into nitrogen compound, which increases the level of nitrates in the soil and helps plant growth

Pioneer Plants : Plants which establish easily in harsh environment . Produce better conditions to establish successive plants

Pioneer/ Colonizing versus Climax Species :

Pioneer/ Colonizing Climex

Plants that first appear naturally and can adopt in harsh environment, they are robust and can withstand in harsh condition. Better to establish newly degraded sites. Need sunlight and are short lived .

Plants permanently appear after series of successions. They need better environment condition to grow and their growth are slow. They appear slowly after crossing series of succesions. Normally appears on already established sites or improved environment.

Special adaptation of pioneer plants :

Condition of Site

Adaptation

Poor soil Plants requiring Low nutrient

Dry soil Drought resistant plants

Moving soil Plants able to recover even after disturbance

Poor germination condition

Plants producing more seeds

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Beneficial and adverse effects of vegetation:

Mechanical Effects Effects

1. Stems and trunks trap materials that are moving down the slope

2. Roots bind soil particles of the ground surface and reduce their susceptibility to erosion.

3. Roots penetrating through the soil cause it to resist deformation

4. Woody roots may open the rock joints due to thickening as they grow

5. Root cylinder of trees holds up the slope above through buttressing and arching

6. Tap root or near vertical roots penetrate into the firmer stratum below and pin down the overlying materials

Good

Good

Good

Bad

Good

Good

Bad

Hydrological Effects Effects

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1. Leaves intercept raindrops before they hit the ground.

2. Water evaporates from the leaf surface

3. Water is stored in the canopy and stems

4. Large or localized water droplets fall from the leaves

5. Surface runn-off is checked by steams and grass leaves

6. Stems and roots increase the roughness of the ground surface and infiltration of soil

7. Roots extract moisture from soil which is then released to the atmosphere through transpiration

Good

Good

Good

Bad

Good

Site dependent

Weather dependent effect

Contributions of Bio-engineering Plants :

Trees: Trees can permanently stabilize the soil horizon up to main rooting zone (2 mt.). Soil srtucture and organic matter content Improves. Provide shelter to the top soil, reduces KE of falling water, reduce peak run-off and surface erosion, riverbed scouring decreases risk of mass wasting.

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Disadvantage : Trees can not prevent natural landslides with deep sliding zones. Trees can not prevent on-going sliding and slipping processes. It takes 5-10 years until a dense rooting system developed Huge and heavy trees increase the risk of sliding due to addiitional weight.

Bushes/ Shrubs : reduce splash erosion, top soil movement. faster react to rill and gully erosions because of dense root system. Stabililize soil within their rooting zone (1mt.). mechanical strees in sliding and steep sloping areas.

Disadvantage : Can not help to stabilize land slides or slopes below the main rooting zone (1mt).

Bamboos: help stabilize slopes / soil horizon within the reach of their main rooting zone of 2m. Under normal condition, can reach up to 2/3 the ht. of culms. Rooting systems extraordinary dense and more or less uniform. Best retaining quality, able to survive in smoothly sliding zones. rooting system extremely resistant to mechanical stress and force in sliding areas. Dense culms prevents all kinds surface erosion however.

Disadvantage: It can not rapidly develop their soil conservation abilities and takes 3 to 6 years to fully expand and grow.

Grasses: can permanently conserve the top soil within the reach their main rooting zone of 25 cm. Protect surface soil, improves the micro-climate at top soil. Establishment of grass layer withen one or maimum two rainy seasons.

Disadvantage : Can not contribute to protect sliding due to shallow root system.

Herbs/ Legumes : contribute by improving soil fertility by adding fixing nitrogen dense rooting species. Extra-ordinary quality as pioneer plants. Provide synergetic effects with other plants.

Disadvantage : Hardly build a dense potential vegetation cover alone.

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Engineering Structures : to stabilize gully erosion, stream bank erosion, land slides, stabilize steep slopes. These structures require high cost and repair, no guarantee for permanent cure.

Biological or Vegetative measures : need time to establish, low cost , less maintenance, use of local materials, once establish it guarantees for permanent cure provided there is no natural havocs and abuse by people.

Biological or Vegetative Measures :

1. Agronomic Conservation Measures

2. Vegetative Conservation Measures

Agronomic Practices:

--- Crop Rotation ( maintain soil structure, less erodable than poorly structured soil )

---- Cover Cropping ( used to prevent erosion, use permanent crops such as orchard, horticulture crops, helps add OM through roots, residues/ remnant of plants, when legumes are used adds nitrogen, improves soil physical condition )

---- Mulching ( covers soil, prevent from splash erosion, affords infiltration, regulate soil temperature, improves moisture and reduced evaporation

---- Contour Farming ( practice of ploughing, planting and cultivating land across the slope, acts as small terraces, holds water and minimize erosion)

---- Minimum Tillage ( tilling only on seed bed instead of conventional practices, minimizes erosion and tilling costs, manages soil for water intake and reduces water and wind erosion)

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---- Green Manuring ( practice of ploughing in a growing crop, improves the condition of soil by humas formation and OM, if legumes are used nitrogen adds to soil, also adds P, K and lime to the top soil through decay of deep roots containing P, K and lime, newly constructed terraces more advantages by adding fertility to soil )

---- Composting/ Farm Manuring ( resuses from animals on the farm, consists of solid and liquid in a ratio of 3:1, contains N, P, K

---- Conservation Plantation : Harsh environment : sandy, steep slopes, dry, eroded, rocky, water logged, flood plain, low moisture, poor soil , poor productivity and other harsh conditions. Planting materials : trees, shrubs, grasses, seeds that can stand in harsh environment .

Plantation : with or without soft structural works ( soil works) e.g

--- contour terracing

--- contour trenching

--- contour bunding

--- contour wattling

Forest and grazing land :

Forests : helps controlling erosion. Protects soil from water and wind erosion. The vegetation on forest acts as shield against splash/ raindrop impacts. The root system binds the soil and decreases the erosive power of running water. The OM content of forest soil helps soil infiltration capacity and reduces overland flow / runoff.

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Forests helps control erosion in different ways.

Tree canopy intercepts the rainfall, which would have direct impact on soil causing splash erosion. Tree increases the evapo-transpiration. Under growth or ground vegetation acts as blanket to soil surface, intercepts rain drops and protects soil from direct impact of rainfall. Under growth or ground vegetation helps infiltration capacity of soil and breaks water velocity. The root system binds the soil particles and protects against running with water.

Lack of vegetation intensifies erosion through the structural weakness and absence of armouring of the soil surface. Therefore, forests need to be managed not only for productive point of view but also for protective purposes. The forests of steep slopes, fragile lands, near river bank/ stream should strickly be managed under protection.

In Nepal, erosion in forest lands are mainly due to: heavy felling of trees, over grazing of forests floor, forests fire, excessive removal of leaf litters/ fodder /undergrowth, shifting cultivation and encroachment. These factors cause degradation of forest and degraded forests are vulnerable to erosion.

Control Measures : Structural, vegetative and both

Structural measures (Curative): Check dams, runoff diversion channel, wattlings, fascines, conservation pond, retaining wall, terracing, bunding, trenching, foot trail improvement.

Vegetative measures : conservation plantation ( trees, shrubs, grasses, seedings ), forest management

Preventive measures : prevent over grazing and over felling of trees, practice stall feeding, reduce unproductive cattle, prevent forest fire, shifting cultivation and forest encroachment, avoid unsustainable use of forests resources.

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Grazing land : Grazing land problems responsible to erosion :

--- over stocking of animals

--- grazing beyond the carrying capacity of land

--- excessive trampling

--- year round grazing

--- lack of ground cover

Control measures : Structural measures (Curative): Check dams, runoff diversion channel, wattlings, conservation pond, retaining wall, terracing, bunding, trenching, foot trail improvement.Vegetative measures : palatable grass and shrub planting, seeding improved varieties of grass, control undesirable/ unpalatable invader plants.Preventive measures : avoid overgrazing and over stocking, adopt rotational/ diferred grazing, control fire, adopt stall feeding, fencing. Criteria for vegetative measures :--- Choice of species based on disturbed sites --- Site characteristics (affects the choice of species): soil, slope, degree of disturbances, moisture condition , existing vegetation etc.( Species selection and planted should grow satisfactorily in a given site condition)--- Pioneering / colonizing species ( in badly degraded sites)--- Mixture of grasses and legumes

--- Use of natural vegetation

--- Perinnial / multipurpose species

--- Plant rooting habit

--- Wide range of vegetation ( mixture of grass/ shrubs/ trees )

--- Grass followed by shrubs and tree seedlings and Heterogeneity of species

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General criteria for selection of plants :

--- ability to grow on poor site condition (exposed, water logged degraded, dry, harsh environment)

--- fast growing/ high rate of biomass production--- nitrogen fixing--- coppicing ability--- preferred by the local communities

For Gullies plugging :

--- Intensive plantation around gully heads / sides--- Use vegetative gully plugging by planting agave and other plants in

dense lines across the gully bed.--- Construct live checkdams--- Where vegetation alone is not adequate, construct brush wood

checkdams or check dams using sand bags by intensive plantation.--- In active and deep gullies use gabion/ loose stone check dams with

platation.--- Plant grasses/ shrubs/ trees on the gully slopes depending on site

conditions For Degraded slopes :

--- improve pits soil by adding compost/farm yard manure/humus rich forest soil

--- established vegetation along the contours ( if slopes are too steep use contour trenching, bunding, terracing, wattling etc.)

--- encourage natural regeneration.

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Unit 6 Conservation Techniques Soil Conservation techniques used by DSCWM)

6.1 Gully and Landslide TreatmentsGully treatments are generally done to prevent further degradation of the gully and its watershed through controlling runoff and erosion. Gully control can be done either from vegetative or structural measures or combination of both in the gully and its catchment. The activities in the gully treatment includes :

Gully head diversion ditches/drainage Gully head plugging by building structures like check dam Gully bank and its catchment revegetation, counter wattling and

turfing Gully bank slope correction Conservation ponds to store and divert excess runoff Appropriate landuse practice in the gully catchments Fencing the gully periphery and its catchment to prevent from

cattle grazing

Landslide treatment :

Landslide treatment refers to the vegetative and structural measures applied in the landslide area and its catchment. These activities are generally done to reduce soil erosion and mass movement from landslide and reduce devastating effects on the downstream and surroundings, where landslide occurs threatening the life and property. The activities under the landslide treatment are:

Construction of diversion channels around the landslide area to drain water or to stop water to enter into the landslide

Structural erosion control measures such as construction of retaining wall/breast wall and check dam

Landslide stabilization through bio-engineering practices Conservation ponds to store and divert excess runoff Appropriate land use practice in the gully catchments

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Fencing the gully periphery and its catchment to prevent from cattle grazing

6.2 Slope stabilization

Slope stabilization refers to the vegetative and structural measures applied to stabilize degraded slope and reduce erosion. This activity include :

Tree and grass planting with necessary conservation measures using bioengineering techniques

Erosion control measures such as micro-gully plugging, contour wattling and structures such as check dam, retaining wall etc.

Improvement of drainage system Silvi-pasture management Fencing the slope to check livestock grazing

6.3 Sream/River bank Erosion ControlStream/River bank erosion control measures refers to prevent stream / river bank erosion or bank cuttings through vegetative and structural measures. Its main aim is to prevent bank erosion and protect the land from stream/river cutting. The activities under the Stream/River bank erosion control include :

Construction of embankment/revetment Construction of spurs Construction of water flow retarding structures Channelization efforts to manage discharge Flood plain stabilization through bio-engineering measures Vegetative measures Silvi-pastoral management in the catchment

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6.4 Road Slope Erosion ControlThe road slope erosion control measure refers to vegetative and structural measures applied in the road slope to reduce erosion and protect the road from erosion and landslides and to improve the road for general traffic. It is similar to slope stabilization to maintain stability of the slope. The activities under this programme are :

Trees and grass planting with necessary conservation measures such as contour terracing, cotour trenching, contour bunding

Retaining/breast walls with planting bio-engineering plants Erosion control measures such as micro gully plugging,

contour wattling, and structure like check dam Improvement of roadside drainage system Fencing road slopes for livestock control

6.5 Cultivated, Forests Lands and Pasture Lands Cultivated : Erosion from cultivated lands are due to :

Improper land use: cultivation of steep slopes not suitable for cultivation

Improper cultivation practices: ploughing up and down hill slopes etc.; continuous use of land for the same crop without fallow or rotation

Inadequate use of farm manure Compaction of soil through the excessive use

Erosion from cultivated land can be control through adapting :

Agronomic practice : it includes mulching and crop management. Crop management includes : high density planting, multiple cropping and cover cropping

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Mulching : It is a method of spreading mulches above the ground to keep the soil cool during warm and warm during cold and moist. It also conserve moisture in the soil and root zone of the plant. Mulching enhance the rate of growth of plant by providing moisture to the plant. Mulching materials are leaves, straw, sawdust and other organic materials. Mulch reduce the rain drop erosion, surface flow and increases infiltration. Mulching should be done during dry season to conserve moisture and reduce evaporation loss.

High density planting : To cover the ground as quickly and as densely possible

Multiple cropping : it includes crop rotation and strip cropping

Soil management : includes conservation tillage such as contour farming and minimum or no tillage. Contour farming refers to all the field operations such as ploughing, seeding, planting and other cultural practices along the contour. Contour farming reduce the velocity of runoff/overland flow, controls soil erosion and conserve moisture

Mechanical method : Mechanical method includes tillage. The effect of tillage on the soil erosion is function of aggregation, surface sealing, infiltration and resistant to erosion. For soil conservation, the conservation tillage should be adopted in which tillage should not be more than necessary, till only when the soil moisture is in favorable limit. Adopt minimum/no tillage practices which is the preparation of seed bed with minimum disturbances of soil

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Forests land : Forests vegetation has played various roles in controlling erosion. Causes of erosion in forest area :

Heavy felling Heavy grazing Shifting cultivation Lack of mixed vegetation Roles of forest in soil conservation:

Three roles of forests

Canopy level : intercepts rainfall and increase evapo-transpiration Ground level : intercept the rain, increase evapo-transpiration, litters

at ground acts as sponge for water retention and reduce run-off Root level : Root system of vegetation helps to bind the soil and

increase the infiltration rate

Pasture lands :

Problems of erosion :

Overgrazing Premature grazing Continuous grazing Trampling

Soil conservation measures :

Reduction of number of livestock Pasture land improvement Stall feeding Fodder plant and grass planting in community land Fodder and grazing management in community forests

Unit 7 Conservation Farming Techniques ( adopted by DSCWM)

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7.1 Shelter Belts/Green Belts :

This is a belt of trees, shrubs and grass maintained to protect soil from wind erosion and conserve moisture to increase productivity of cultivated land. It generally includes planting of trees, shrubs and grass in rows mostly across general wind direction. Its main objective is to reduce the wind velocity and thereby reduce the wind erosion and conserve soil and moisture foe better production of agricultural land. Tall wind resistant crops and normal crops are planted alternatively in narrow strips perpendicular to the direction of prevailing winds.

This programme includes the following activities :

Surveying and preparation of location/orientation of strips Planting of trees, shrubs, hedge and grass in combination as

a shelter belt in apredesigned pattern of spacing and height Protection of vegetation by fencing Seedling production Water erosion control measures in case of erosion prone

area7.2 Hedgerows:

These are simple erosion control practices on sloping land. In these practices nitrogen fixing trees, shrubs, grass, fruit trees and other crops are planted as hedge in a rows along the contour. Various trees and crop species are established in the hedgerows to enhance farm income and diversity. Trees, shrubs horticulture plants, grasses are planted in the outer edges of strip. Food crops are planted in the strip between the rows . These practices help slow down the passage of rain water and trap soil to gradually form natural terraces. These practices also improve soil fertility and crop production. Contour hedgerows are indigenous practices, which are adopted in many developing countries. These activities Include :

Planting of fruit, grass, trees, grass in the strip of rows along the contour

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Plantation of food crops between the rows Advantages :

Reduces soil erosion Improves soil fertility and soil moisture Provides biomass for green leaf manure Provides shading for young plants Serves as a source of fodder, fuelwood and light construction

materials Improves soil structure and water infiltration Provides a source of mulch

Limitations :

Loss of land for cultivation due to establishment of contour hedgerow

Hedge rows compete with food crops planted between the rows Hedgerow plants may be host to pests Retention of excess water may result in soil slippage on steep slopes

7.3 Minimum tillage/Zero tillage :

This is a technique to adopt minimum tilling practice in the farm land. In this practice heavy equipments and full tilling operations will not be carried out. Full tilling practices disturb and dislodge the soil particles and structures and cause erosion. Simple farm equipments such as hoes and digging sticks are used to prepare land and plant food crops. This practice is common and effective in controlling soil erosion particularly in highly erodible and sandy soil.

Advantages :

Lessens the direct impacts of raindrops on bare soil, thus minimizing soil erosion

Minimizes degradation of soil structure Slows down the rate of mineralization, leading to more

sustained use of nutrient in the organic matter Requires less labor than full tillage

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Can be practiced on marginal soil/land that might not otherwise be fisible to cultivate

Limitations :

Inadequate seed bed preparation may lead to poor establishment and low yield of crops

Rooting volume may be restricted in soils.

7.8 Cover cropping

Cover crops are close growing crops planted mainly for protecting soil between regular crops. The types of cover crops can be annual or perennial legume crops (beans, cow peas, peas, rahar) and grasses depending on actual needs of the farmers.

Cover cropping is a practice to protect soil from erosion and to improve the condition of soil through green manuring. In cover cropping usually short term crops (less than 2 years) planted in the fields or under the trees during fallow period. Cover crops are also inter-planted with grains crops such as maize or planted once in a cropping cycle. Cover cropping is also practiced to suppress weeds under the tree crop and supply as a forage to livestock. The practice of cover cropping can also be used in fallow systems to improve soil fertility and shorten the fallow period. Most of the cover crops belong to the legume family such as : kudzu, pigeon peas, mung bean, arahar, cow pea etc.

Cover crops

Cover crops protect the soil from wind and water erosion by covering it and, because they form a mulch, they greatly reduce annual weeds in the next growing season. They are frequently used to cover the soil over winter either alive or as a dead, dense mat. They can also be used in summer, especially when a crop fails because of adverse weather. Examples include red and sweet clover, hay or pasture seedings, hairy vetch, winter cereals and buckwheat. A volunteer crop seeded from harvest losses, can also be a

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cover crop. On the Prairies, organic farmers use annual legumes as cover crops for at least part of the season rather than leaving summer fallow bare. Indian Head lentils and Sirius peas have been developed for this purpose.

Advantages :

Improves soil fertility, physical and chemical properties of soil

Reduces soil erosion and water loss Suppress weeds Reduces need for fertilizer and herbicides Provides human food and animal forage Increases soil organic matter Helps retain moisture in the soil and prevent soil from

drying

Limitations :

May compete for soil moisture and nutrients with the perennial plants

Involves additional farm labor and inputs May result in weed problems May be alternate host for pest Some cover crop species may contain chemicals which

inhibit subsequent crop growth7.9 Mulching

Mulching is a soil and water conservation practice in which a covering of cut grass, crop residues or other organic matters is spread over the ground between rows of crops or around the plants. This practice helps to retain soil moisture, prevents weed growth and enhances the soil structure. It is commonly used in areas subject to drought and weed infestation. The choice of mulch depends on locally available materials. The optimum density of soil cover ranges between 30% to 70%

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Advantages :

Intercepts the direct impacts of rain drop on bare soil and reduces runoff and soil loss

Suppresses weeds and reduces labor costs of weeding Increases soil organic matter Improves soil chemical and physical properties Increases the moisture holding capacity of soil Helps to regulate soil temperature

Limitations :

Possible habitats for pests and diseases Not applicable in wet condition Difficult to spread evenly on steep land Lack of available materials suitable for mulching Some grass species used as mulch can root and become a weed

problem

7.11 Compost manure

Compost is a type of organic fertilizer derived from the decomposition of plant and animal waste. It is an excellent source of plant nutrients. Composting is common in home gardens. There are many ways to prepare compost manure depending upon socioeconomic and biophysical factors. The use of compost is a traditional soil fertility management practice through out the developing countries. Composting involves the decomposition of plant animal waste. The decomposition process involves bacteria, beetles and earthworm. Moisture content, adequate supply of air and temperature control are important parameters for quality compost production.

Advantages :

Generates nutrients for crop

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Generates heat and maintain temperature Maintains soil structure and increases soil infiltration Minimize soil pollution

Limitations :

Compost making requires a large quantity of plant materials or biomass

Limited use in low land where severe weed infestation is a problem

Difficult to practiced on steep slopes High labor requirement to harvest, haul and distribute

7.10 Green manure

Green manure are plants that are shown specifically to improve soil fertility. They are not harvested for food and not allow to flower.

A green manure cover crop, or plowdown crop, is any crop that is turned into the soil to add organic matter, nitrogen or other nutrients. It is a Plowing-under of a green crop or other fresh organic materialsTraditionally, green manure crops are sown and allowed to grow, either until the land is needed again or until the plants have reached a certain growth stage. At this point, they are cut down, dug in to the soil and are left to decompose, releasing vital plant nutrients back into the soil which are then used by the next crop.

But if it is not dig, then green manure crops can also be composted or used as a mulching material instead.

There are many varieties of plants which are suitable for use as a green manure crop and some of these are listed in the table below.

However, if there is not enough land left, to devote entirely to growing a green manure crop, it is also possible to sow some green manure crops (e.g white clover) on paths between beds. And crops, such as field beans, can even be sown in between rows of vegetables in your raised bed system if

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you are short of space. Mixtures of green manure plants can also be used. For example: fieldbeans/mustard; or vetch/clover/rye.

When selecting the crops that you are going to grow, you should bear in mind the following points:

Choose either a quick or a slow-growing crop - to fit in with the time that the land will be left vacant.

The season of the year. (Not all varieties will survive the winter.)

Whether you want your crop to fix nitrogen or not.

Your soil type and how much drainage it offers.

When is the Green Manure Crop Ready for Use?

On the whole it is better not to leave your green manure crop in the ground for too long, as land occupied in this way can not be used for growing other crops. Also, if green manure plants get too old, then they can become tough and will take longer to decompose and be incorporated into the soil by soil organisms. For most green manure crops, it is usually recommended that they are cut and used before they flower.

How to Use Green Manure Crops

Usually, green manure crops are cut down and dug into the top 15-20 cm of soil with a spade. But, veganic gardeners, or anyone else who wishes to avoid digging the soil, can simply hoe off young plants (or chop down older ones) and leave them on the soil surface as a mulch. If plants are chopped down, then to prevent any regrowth of the stubble, cover the ground with a light-excluding mulch (e.g. black polythene/newspaper) until you are sure that the green manure crop is dead. If you are in a hurry to start replanting the ground, then you can of course simply plant through the mulch. In any case, you will need to allow several weeks before planting the next crop in the mulched area, in order to give the mulch some time to decompose and release its nutrients back into the soil. Alternatively, if you do not wish to use your crop as a mulch, then you can compost it instead. Composting is in fact a very good way of using up any crops which have been allowed to get too old and tough!

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The best time to cultivate the green manures is after most of the plants have started to bloom or are close to heading, but before they go to seed. Waiting too long allows the plants to become woody and will be slower to decompose. Harvesting earlier is fine but the plants will not have reached their maximum amount of stored nutrients and potential organic matter. Use a spade, mower, or string trimmer to chop up the green manures, then either mix them in with the top few inches of soil or rake them up and compost them. If they are removed to be composted, remember that you are removing soil nutrients temporarily and compost will need to be added before planting. If the green manure is turned into the soil, wait until they have decomposed before planting the next crop. This is usually one to three weeks depending on the crop, the soil and the weather.

Suitable Green manure crops :

NAME LATIN NAME

WINTER HARDY

SOWING TIME

WILDLIFE VALUE

GROWING TIME

Alfalfa Medicago sativa Yes Apr-July Bee 1-2 mths or a

few yrs*Winter Field Beans

Vicia faba Yes Sept-Nov Bee plant overwinter

Buckwheat Fagopyrum esculentum No March-

AugHoverfly nectar up to 2-3 mths

*Clover, Alsike

Trifolium hybridum Yes Apr-Aug Bee plant 1-2 mths or a

few yrs*Clover, crimson

Trifolium incarnatum Possibly March-

Aug Bee plant 2-3 mths

*Clover, Essex red

Trifolium pratense Yes Apr-Aug Bee plant 1-2 mths or a

few yrs

FenugreekTrigonella foenum graecum

Possibly March-Aug

Butterfly nectar 2-3 mths

*Lupin, bitter

Lupinus angustifolius Possibly March-

June Bee plant 2-3 mths

Mustard Sinapis alba Possibly March-Sept None 2-8 wks

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Phacelia Phacelia tanacetifolia Yes March-

Sept Bee plant

2 mths(summer), 5-6 mths (winter)

Rye, grazing

Secale cereale Yes Aug-Nov Bee/caterpillar

food autumn-spring

*Trefoil Medicago lupulina Yes March-

AugBee/butterfly nectar up to a few yrs

*Tares, winter Vicia sativa Yes March-

SeptBee/butterfly nectar

2-3 mths or overwinter

Advantages of Green Manure

1. They're cheap and easy to grow. 2. A packet of green manure seeds is easy to carry home - unlike a

large sack of animal manure!

3. They can increase soil fertility.

4. They improve soil structure and help prevent soil erosion.

5. They encourage efficient use of land. So why not grow a green manure crop on your unused land this winter?

6. Most green manure crops are very attractive to wildlife.

7. Bare soil encourages weed growth, so green manure bare ground to keep weeds in check.

8. By taking up nutrients from the soil, green manure crops prevent them from being washed away when it rains.

9. Some green manure plants (legumes) are nitrogen fixers.

10.Green manuring increases the humus content of the soil.

Limitations :

• Seed cost and availability vary considerably.

• Seeding, maintenance and incorporation requires extra time, labor and fuel.

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• Green manures may harbor pests and plant disease so a good rotation should be followed.

• Some cover crops are difficult to turn under and may require repeated tillage which will accelerate organic decomposition and soil erosion.

• While the green manure residue decomposes, there may be a short period when nitrogen will be unavailable to the following crop.

• Residue of any sort can become allelopathic (exude toxic chemicals) to the following crop and may interfere with seed germination.

• Living or winter-killed green manure can retard spring soil-warming by acting as a mulch. This, in turn, can delay or retard growth of temperature-sensitive crops such as corn.

• Some green manure crops, such as oilradish and buckwheat will become a weed in the succeeding crop if they are allowed to set seed.

7.11 Strip cropping

It is a conservation practice mainly to grow crops in systematic strips or bands, which serve as barriers to water and wind erosion.

Contour strip-two or more crops are grown along the contours in alternative strips.

Field strip cropping- The alternative strips are uniform widths across the field and not necessarily curved to conform to the contour.

Wind strip cropping- Tall wind resistant crops and normal crops are planted alternatively in narrow strips perpendicular to the direction of prevailing winds.

7.5 Relay cropping

Growing of another crop before harvesting the main crop. There is no need of tillage operation. Example: Paddy-lentil

7.6 Multiple cropping

Growing of more than one crop on the same land in a year.

7.7 Mixed cropping

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Growing of two or more crops together at the same time in same land. Example: wheat + mustard, wheat + peas etc.

Unit 8. Erosion Process and Monitoring

8.1 Erodibility of SoilErodibility of soil is defined as the resistance of soil to erosion. In other terms, it is termed as resistance of soil to both detachment and transport against the detachment and transporting agents. In erodibility of soil, the properties of soil are most determinant and important factors. Erodibility of soil varies with soil texture, aggregate stability, shear strength, infiltration capacity and organic and chemical content of soil. Erodibility of soil also depends in part on topography, slope steepness, and level of disturbances imposed on soil by human activities.

In the case of soil texture, soil having large particles are resistant to detach and transport, since it requires greater raindrop kinetic energy and greater force for transport. Similarly, fine particles of soil also resistance to detachment because of their cohesiveness. The least resistant particles are silts and fine sands. Thus soil with a high silt and sand content are more erodible. By experiment, it was observed that soils with 40-6-% silt content are most erodible and soils with 9-30% clay content are also found most susceptibility to erosion. However, the range of different soil textures susceptible to erodibility are found different in different studies.

In terms of aggregate of soil, for example, clay particles combine with organic matter to form soil aggregate or clods is more stable to erosion. Erodibility of soil also depends on types of clay materials content on soil aggregates. Soil with high content of base minerals are more stable to erosion as they contribute to chemical bonding of the aggregates. The greater the proportion of soil aggregates, the more resistant to erosion

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In shear strength of soil, which is a measure of its cohisiveness and resistance to shearing forces, the more shear strength of soil, the less is erodibility, but it can cause mass movement of land.

The infiltration capacity is influenced by soil pore space or size, pore stability and form of soil profile. Soil with stable aggregates maintain their pore space better and is less erodible than the soils with swelling clays and minerals because of having low infiltration capacity.

The organic and chemical contents of soil are important because of their influences on aggregatee stability. It has been found that that soils with 0-4% organic matter content can be considered erodible.

In the case of wind erosion, the erodibility of soil depends upon wet and dry aggregate stability and moisture content of soil. Wet soil is less erodible to wind than dry soil with low aggregates. Other elements of erodibility of soil by wind erosion are same as the elements discussed above in water erosion.

Soil Erodibility Factor ( K) : The soil erodibility factor (K) reflects the susceptability of soil to erosion. The soil erodibility factor ( K) is a function of soil's percent silt and very fine sand, percent sand, percent organic matter, index of soil structure, index of soil permeability. K value can be obtained if grain size distribution, organic content, soil structures and permeability are known.

Parameters for Consideration of Soil Erodibility :

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The parameters for the consideration of soil erodibility are :

Particle Size : Soil particle size is a major determinate of soil erodibility, which is defined as the products of % silt and and very fine sand % sand

Organic Matter : This is combination of organic matter contents in top soil and subsoil. OM in the range of 0 - 4% is inversely related to erodibility or succeptable to erosion

Soil Structures : Soil structures such as type of soil and size particles of are important in determining erodibility. Structures are:

i. Very fine grannular and very fine crumb ( <1mm)ii. Fine grannular and fine crumb (1-2mm)

iii. Medium grannular, medium crumb (2-5mm)iv. Platy prismatic, columber, blocky and very coarse

grannular Soil Permeability : (Surface and sub-surface)

1. Rapid to very rapid2. Moderately rapid3. Moderate4. Moderately slow5. Slow6. Very slow

Nomograph need to be referred for determining the Soil Erodibility Factor ( K)

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Some Factors Responsible for Soil Erodibility :

1) Slope Length and Gradient factor :

Erodibility also depends on slope steepness, slope length, velocity and volume of surface runoff. As these factors increases, the erodibility of soil increases. The relationship between erosion , slope steepness and slope can be expressed by an equation :

Q ∞ tan m A x Ln , where as Q = erodibility per unit area, A = gradient angle, L = slope length, m and n are factors, which values depends upon interaction of other factors in the erosion - slope relationship. These factors are : grain size of materials, rainfall, slope and its shape, surface runoff, type of vegetation cover, processes of erosion.

Slope length also affects erodibilty. Longer the slope, more will be the erosion. As slope increases, the land surface catch large amount of rain. If the infiltration capacity of land surface is slower than the intensity of rainfall then overland flow occurs. As slope gradient increases, the

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detention of water on land surface becomes less, the velocity of flowing water will be high, which in turn, will detached and transport more soil causing erosion.

2 ) Vegetation :

The major role of vegetation is to intercept raindrops so that their kinetic energy is dissipated by the plants. The effectiveness of vegetation cover in reducing erosion depends upon the height and continuity of canopy, the density of plant cover and the root density. Ground cover by vegetation not only intercepts the rain but also dissipitates the energy of flowing water and wind, imparts roughness to the flow and thereby reduces the velocity Erosion rates varies cube or fifth power of velocity, V 3 or V 5. The effect of root network of the vegetation is in openning up the soil, thereby enabling water to penetrate and increasing infiltration capacity. Generally, forests are the most effective in reducing erosion because of their canopy. A dense growth of grass may be also efficient as forests. It has been noted that for adequate protection of erosion 70 % of the ground surface must be covered by vegetation. Mechanical binding of soil particles by the net work of root. Vegetation improves the soil structures by adding organic matter. Humas layer acts as sponges and absorbs enough water and moisture which helps water to enter into the soil. Vegetation obstruct the velocity of flowing water and helps dissipitate energy of running water and sometime hold the soil particles flowing through the running water. However, the rain drops interceptd and collected by the canopy may form larger drop which when drops on the ground are more erosive

8.2 Erosivity of Rainfall :

Soil loss is closely related to rainfall partly through the raindrops and contribution of rain to runoff. Effect of intensity of rainfall is cosidered to

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be the most important factor. It has been found that average soil loss per rain event increasaes with the intensity of the storm.

It also appears that erosion is related to two types of rain events, the short intense rain where the infiltration capacity of the soil is exceeded and the prolonged rain of low intensity which saturate the soil.

The most suitable expression of the erosivity of rainfall is an index based on the kinetic energy (KE) of the rain. Thus the erosivity of a rain is a functions of its intensity, duration and the mass, diameter and the velocity of the rain drops. To compute erosivity requires an analysis of the rain drop size and distribution of rain. Rain drop size characteristics vary with the intensity of the rain, the medium drop diameter increases with the increase in rainfall intensity. However, the medium drop size decreases with increasing intensity presumably because greater turbulence makes larger drop size unstable. Some studies have shown that drop size and rainfall intensity is not always constant and both vary for rain of same intensity but different origin.

Wischmier and Smith relationship is : KE = 13.32 + 9.78 log I, where I = rainfall intensity (mm/hr) and KE = kinetic energy of strom ( J/m2/mm )

Hudson Equation is : KE = 29.8 - 127.5 / I

To compute the KE of the storm, a trace of the rainfall from automatically recorded rain gauge is analyzed and the storm divided into small time increments of uniform intensity. For each time period, knowing the intensity of the rain, the KE of rain at that intensity is estimated from one of the above equations and this multiplied by the amount rain received gives the KE for that time period. The sum of the KE values for all time periods gives the total KE of the storm.

Calculation of erosivity :

Time from Rainfall Intensity KE Total KE

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start (min) (mm) ( mm/hr) ( J/m2/mm) ( col. 2 × col. 4 )

0-14 1.52 6.08 8.83 13.42

15-29 14.22 56.88 27.56 391.90

30-44 26.16 104.64 28.58 747.65

45-59 31.50 126.00 28.79 906.89

60-74 8.38 33.52 26.00 217.88

75-89 0.25 1.00 ------ -------

8.4 Erosion Monitoring : (Justification/ Importance)

Erosion monitoring is a continuous process for studying the level of erosion and runoff from a paticular land-use, where the maximum sustained productivity is threatened by excessive soil loss or erosion. Such study should aim at collecting information on erosion and runoff by allocating an area into different plots having different land use.

Nepal has serious erosion problems in almost all ecological regions. It has caused serious on and off site environmental, economic and social impacts. The main causes of soil erosion in Nepal are due to fragile geology of mountains, high erosivity of vaused by monsoon rain and unsustainable

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human activities. Land degradation, gully formation, landslides, riverbank erosion, floods are prevelant. Therefore, studies on soil erosion are of great importance to understand such problems. In addition, the runoff and soil loss behaviors are different in different land use type, condition and treatments. Therefore the basic information on the runoff and soil loss patterns under different land use types is needed for better watershed management. Erosion monitoring entails how effectively the government resources and efforts are being utilized to minimize erosion. Information received from erosion monitoring can be taken as a basis for future planning of sustainable soil conservation interventions. In other word, erosion monitoring gives insight for better land use recommendations and justify the implications of conservation activities.

8.4.1 Run-off Plot monitoringErosion monitoring is a technique to enclose a part of land and monitoring the surface erosion and runoff from the enclosed area by collecting the overland flow in tanks placed at the bottom of the enclosure. This technique is known as runoff plot or erosion plot (EP) monitoring, which has been used extensively all over the world to measure runoff and soil erosion from small areas.

A number of such run-off plot monitoring works has been carried out in the different parts of middle mountain physiographic zone of Nepal by different organizations at different times. Such organizations are Department of Soil Conservation and watershed Management (DSCWM), National Agricultural Research Council ( NARC ) and International Centre for Integrated Mountain Development (ICIMOD).

Objectives of EP or Run-off plots: Main objectives of erosion or runoff plots are :

1. To estimate the run-off and soil loss under different land-use practices

2. To study the effects of conservation measures

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Methodology : Run-off or erosion plot (EP) monitoring consists of studying surface runoff and soil erosion with corresponding rainfalls for the land type where the EP is located. Through the size of EP varied from 48-100m2 , the lay-outs of the EPs were almost the same that is it could be rectangular and elongated towards the land slope. In most of the cases, EPs size were 100m2 in size, 20m along the slope and 5m across. EPs were bordened on all sides with metal sheets buried in the ground and a gutter was set up at the bottom to direct the runoff and its contents to the collection tank system. The parameters studied in the EPs technique are related with rainfall pattern, a meteorological station was installed near the EP to record rainfall data.

For each rainfall day or event, runoff volume was measured from the water collected in the tanks/drums. Sediment samples were collected from the tanks containing runoff volume by agtating the water in the tanks. A sample bottle of known volume, usually 500 or 1000ml. was used for this purpose. After the sample was filtered, oven-dry and weighed, the amount of sediment in the sample bottle was determined. Based on this figure, the actual sediment in the tank and drum was calculated, and by summing the quantities of sediments from all the tanks or drums, the total soil loss from the particular event or day was determined.

Following information need to be collected before setting EP plots at site :

-- Altitude of the site

-- Land use

-- Soil type

-- Soil Texture

-- Slope/ gradient of EP

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-- Crop rotation / Cropping patterns

-- Treatments to be administered ( Each EP should have one treatment )

-- Rainfall data by erecting rain gauge

Treatments : Treatments need to be pre-determined based on the objectives of study. Example of treatments are :

In Kulekhani Burrow Pit ( 1985 - 1989), the treatments were :

3. Outward sloping terraces4. Inward sloping terraces5. Outward sloping terrace with cotour ridges6. Hillside ditching ( hillside ditch at 8m. intervals)

In Tistung EP (1996-2000), the treatments were :

1. Farmers' practice without hedgerows2. Farmers' practice with hedgerows of most prefered

species Alnus nepalensis3. As treatment II but without nutrient inputs4. Farmers' practice with hedge of second most preferred

species ( Indigofera sp.) 5. Farmers practice with hedgerows ( Alnus nepalensis )

and inclusion of fruit trees, vegetables and cash crops for higher economic gain

The Tistung site represented outward sloping rainfed agricultural terraces. The major crops grown in the treatments were potato, maize and mustard

Examples :

Kulekhani Burrow-pits ( 1985-1989)

Site location and characteristics :

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The EPs were located at an altitude of 1650m in Markhu village of Kulekhani watershed, Markhu district. The plots were laid on the former grazing land with very shallow and stony soil. The soil texture was clay to clay loam with very low humus content. The original gradient of the plot ranged from 14% to 22%. The major cropping pattern was maize followed by mustard. The following four treatments were applied in the EPs :

I. Outward sloping terrace

II. Inward sloping terrace

III. Outward sloping terrace with countour ridges

IV. Hillside ditching ( hillside ditch at 8m. intervals )

The rainfall, runoff percent and soil loss in the above treatments from 1985 to 1990 are presented in Tables 1 and 2. These figures and information on EP have been obtained from Kulekhani Erosion Plot Annual Reports of DSCWM.

Table : Rainfall and runoff percent for different treatments, 1985-1990, Kulekhani.

Year Rainfall (mm) Runoff %

Treatment I Treatment II TreatmentIII TreatmentIV

1985 1662 18.1 23.0 19.4 25.2

1986 1559 23.7 27.1 27.9 31.0

1987 1295 24.4 24.1 22.9 30.3

1988 1470 11.9 10.8 12.7 16.4

1989 1338 14.4 12.4 15.3 18.2

1990 1185 20.7 16.1 22.5 22.7

Average 1418 18.8 18.9 20.1 24.0

Table : Soil loss for different treatments, 1985- 1990, Kulekhani

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Year Soil loss ( t / ha )

Treatment I Treatment II Treatment III Treatment IV

1985 1.22 1.27 2.66 1.58

1986 2.58 2.37 3.98 3.68

1987 1.07 0.85 1.27 1.35

1988 1.58 1.15 1.45 2.01

1989 1.17 1.27 2.18 1.88

1990 1.49 1.18 1.91 1.94

Average 1.52 1.35 2.24 2.07

Applying the same procedures, techniques and principles as explained above but with different treaments, various EP sites at Tistung (Makwanpur district), Subbakuna (Surkhet district), Jhikukhola (Kavrepalanchowk), Yarshakhola (Dolakha district), were established in collaboration of DSCWM and ICIMOD.

Design consideration : It includes :

1. Plot design : Size of EPs varies, however DSCWM used 16m by 5m ( 80m2 ) EP. EP are bordered with metal sheet extending 40-50cm. above surface and 25 cm. buried in the ground.

2. Runoff Tank design : For collection of runoff and sediments that produced by rainfall event, two metal tanks ( A and B ) are installed for each EP. The maximum capacities of A tank was 3m3 and that of B tank was 1.5m3. Tank A consists a divisor that allows about 1/4 of the overflow into tank B. The effective capacity of two tanks per treatment with two replications is 9m3 However, the size of tanks should be designed in such a that they can accommodate maximum 24 hr. rainfall of that area.

3. Replication design : EP plots can be divided into blocks. Selection of replications for each treatment is determined by random selection from each block. Although three replication for each treatments is desirable, there were only two replications in each treatment.

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Measurement Procedures : It includes :

1. Field measurement : The average water depth in the tank is computed by taking water depth at four corners of the tank and averaged them. The volume of the runoff water in the tank is directly determined by taking reading from the Calibrating Chart. The water depth is measured every morning at 9 AM. The amount of rainfall is recorded by both a standard rain gauge and an automatic rain gauge. Both the rain gauge should be placed near the EP. Intensities of rainfall are calculated on the basis of the recorded marking on the chart. Water samples for sediment analysis are to collected in plastic bottles and be taken in the laboratory for analysis.

2. Laboratory Procedures : About 500mm of water sample need to be taken for filtration. Filter the water carefully and oven dry the sediments to calculate its amount by the use of physical balance.

3. Calculation Procedures :

Total Runoff in litres = Volume of water tank A (litres) + Volume of water outflow from tank A

Volume of water outflow from tank A (litres) = Reciprocal or ratio water inflow from tank A to Tank B × volume ofwaterin TankB ( litres).

Sediment weight ( gm) / litre = Volume of water in Tank A (litres) × Average sediment weight (gm)/ litre for tank A + Volume of water outflow from Tank A ( litres) × average sediment weight (gm)/litre from tank B.

Precautions and Error ( Drawbacks) :

1. EP only provide information on surface soil loss.

2. Generalization of erosion and runoff of a paticular land use system using the information produced from such a small scale plot level studies can produce insignificant and meaningless results.

3. Extreme variation of biophysical conditions for a given land use type often poses problems in interpreting the EP data.

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4. Plot level studies of soil loss and runoff is limited within the enclose or plot but not associated with upland runoff outside the boundary, which have implications on soil loss and runoff on paticular land use or treatment. Therefore, soil loss and runoff obtained from EPs might be very low than from the whole landscape

5. Sediment sampling is taken by stirring water contents in the collection tank in order to make all the contents in the tank homogenous. This is only true if the sediment consists of clay, silt and very fine sand. The coarser and heavy particles will be found on or near the bottom of the tank. Sediment sampling may not content the samples of all kinds of soil particles that brings by runoff.

6. EPs are located to represent the surrounding land, the soil of which tend to be less disturbed as compared to the surrounding areas. So, soil loss figures may be less compared to the actual situation in the given land use.

7. Displacement of plot borders, occasional leakage from gutter, overland flow from the tanks during extreme events of rainfall and keakage from sediment collection bottles during transportation to laboratory could also lead to some errors

8.4.2. Paired Catchment Studies :

Another way of erosion monitoring is paired catchment studies. In run-off or erosion plot study, only a small area or plot are used to monitor erosion of that particular land, which does not represent the erosion problems in real field practices. Therefore, to reflect the erosion status or problem to some extent to field reality, paired catchment studies are being carried out. In this case, paired catchments are taken, in which one is treated and another is controlled. These pairs are studies with and without treatments or one is left in natural system and another receive some treatments.

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Paired catchments studies aims at monitoring the erosion in the aspects of land-use, hydrology, micro-catchment, soil and water conditions, socio-economic, agriculture and livestock.

Paired catchment study needs ( Components) : Paired catchments ( treated and natural ), hydrological and meteorological stations, Stream gauging station.

Such paired catchments are located in Kulekhani and Phewa Tal with differently treated and control environment. In the paired catchment studies, the information such as areas, soil, gradient, aspects, land-use, vegetation types and covered, runoff, rainfall are taken. Based on these factors sediment and runoff are calculated.

8.4.3. Sedimentation Survey :

Sedimentation survey is another way erosion monitoring. Sedimentation survey of Phewa Lake, Kulekhani Reservoir, Begnas Lake and Rupa Lake are carried out. These sedimentation surveys involved measurements of water and sediments in the lakes using boat and echo-sounding instruments , which is a micro-processor-controlled depth recorder. This is based on the fact that decrease in water depth indicates deposition or sedimentation in the lakes and increase in water depth indicates erosion in the lake bottom. In Nepal, two methods are generally being used in sedimentary survey. In Method I, sediment deposition and erosion at lake bottom are calculated by multiplying the mean of the average water depths of two cross-sections by the area of the lake surface between these two cross-sections. In this method, benchmarks and survey lines are fixed between the bench marks. The measurements are taken in the fixed survey lines repeatedly. The survey lines are marked at several places with known and fixed intervals and these positions are recorded in the chart at the time of echo sounding survey. The distance and water depth are recorded manually from the sounding profile and processed to

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estimate the average water depth using Microsoft Excel Spread Sheet Software. If sounding profile is not clear, the water depth can be measured manually using boat and rope tied with stone and incorporated with the echo sounding graph for the analysis. In Method II, A bathymatic map is prepared, water depths of two contour lines are taken and averaged. This averaged water depth is multiplied by the area of the lake surface between these two contours using the bathymatic map for the calculations of sediment deposition and erosion at lake bottom

The End

Additional informations

Water Climate

Water Climate : Water climate is a sum or integration of all weather conditions including solar radiation, precipitation ( rainfall and snow ), cloud, temperature, relative humidity and wind pressure over a given period of time.

Solar energy : Of the above mentioned elements of water climate solar rediation plays principle role in water climate, since sunshine decides the solar energy that reach to the ground through which the hydrological regime is affected.

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Cloud cover : cloud cover is second important element of water climate, since it entails the quantity and intensity of solar radiation that reaches in the ground and reflects back to space. This also has some implication in hydrological regime or cycle.

Temperature: This is impatacted and influenced by radiation, cloud cover and humidity.

Wind and its pressure : wind represents the air movement where as pressure represents weight of air in the atmosphere.

Humidity : This is the amount of water vapor in the atmosphere

Precipitation : This is amount of rainfall and snow that fall in the ground.

All the above mentioned elements constitute water climate. However, the amount and quantities of the elements that reaches in the ground depends on latitude, longitude aspects wind direction and barriers. Understanding water climate is important, since all its elements affect the hydrological cycle and regime.

Climatic Zones of Nepal : ( MPFS, 1982)

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Because of wide and varied topography of Nepal, a wide range of climates have been identified. The followings are broad climatic zones of Nepal :

Sub-Tropical Zone -- This is a hot monsoon zone below 2000m., in which summer is hot and wet and winter mild and dry. The Terai, Bhabar, Siwaliks and Inner Terai zones have this type of climate

Warm temperate Zone -- The lower middle mountains up to an elevation of 2100m have this type of climate. The summer is warm and wet and winter cool and dry.

Cool temperate Zone -- This type of climate prevails in the higher middle mountains up to an elevation of 3300 m. The summer is mild and wet and the winter is cool and dry.

Alpine Zone-- In the high mountains, up to an elevation of 4800 m, the summer is cool and the winter is extremely frosty

Arctic or Tundra Zone-- This type of " arctic or tundra" climate prevails in the high himal above the snow-line where there is perpetual frost, snow and low precipitation.

Agro-Climatic Zones of Nepal :

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2) Growing season of agricultural crop is based on temperature and rainfall. Plants grow slow and growing season of crop are short in areas having low temperature. Areas having high temperature and low rainfall also affects the agricultural crops. However, temperature plays vital role in the growth of agricultural crops. Based on temperature, seven mean monthly air temperature zones are recognized through which agro-climatic zones are classified.

-- temperature > 22 c

-- "" 20- 22 c

-- "" 16- 20 c

-- "" 10-16c

-- "" 4- 10c

-- "" < 0 c

There is a strong relationship between mean annual air temperature and elevation. As elevation increases, mean annual air temperature decreases. A regression model showing the relationship between mean annual air temperature (T) and elevation (E) has been developed. This relationship is:

T = 25.3822 - 0.0054 E

3) Agriculture needs various forms of energy, to produce food, fodder, fiber and other agricultural crops. Out of which, solar

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energy is a major part of energy inputs among all . These energy needs are :

m. Solar energy : radiation and temperaturen. Human energy: irrigation fertilizers, mechanization

facilities,o. Mineral sources : soil, water and air p. Animal energy : OM, compost, animal waste, ploughing

Natural inputs such as : solar radiation, temperature, rainfall, snow, relative humidity are equally important and play vital role in agriculture production.

Physiographic Inputs : topography, aspects and slopes are equally important.

Agro-climatic classification are generally based on the number of rainfall months, mean monthly temperature and annual rainfall. Based on these factors, agro-climatic zones are classified as follows :

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Agro-climatic Zones :

1. Lower Sub-Tropical Monsoon Zone: the altitude is < 800m., mean annual temp. is > 21c and rainfall is >1000mm

2. Upper Sub-tropical monsoon Zone : altitude varies from 800-1200m, mean annual temp. is 19-21c and rainfall >1000mm

3. Warm temperate Monsoon Zone : altitude varies from 1200-1900m, mean annual temp.is 15-19c and rainfall > 1000mm

4. Cool temperate Monsoon Zone : altitude varies from1900-2800m, mean annual temp. is 10-15c and rainfall < or >500 mm.

5. Subalpine Monsoon Zone : altitude varies from 2800-4100 m. mean annual temp.is 3-10c and rainfall < or >500 mm.

6. Alpine monsoon Zone : altitude varies from 4100 - 4700 m. mean annual temp. is 0-3c and rainfall scattered

7. Aractic Zone : altitude > 4700 m. Mean annual temp. < 0c, rainfall is scattered and snowfall.

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Factors affecting micro-climate patterns

Micro-Climate :

This is a local climatic condition of a given pocket or specific area, which is based on great variations of land use, land form and physiography. In Nepal, there is a great variety in microclimate because of vast changes in land-use, land form and physiography. It has been said that at each 100 m. elevation differences in mountain and hills in Nepal, there is a change in micro-climate. Variation of florestic composition at altitudinal change reflects the variation in micro climate. There are several factors affecting micro climatic condition of a given area.

Factors affecting micro-climate patterns :

The most influential factors for creating variation of micro climate are light / radiation ( temperature), humidity, wind and frost. Where as the factors that create the micro climate are : air drainage, aspect, slope, vegetation, soil etc.

Light/ Radiation : Southern aspect receive more light and radiation than northern aspect. Reaching light and radiation also vary in east west faces and ridges

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Slope : Steeper the slope, more pronounce are the variation of light and radiation, evapo-transpiration, soil moisture content and so on.

Air/wind : In deep valleys and shallow basins , the drainage of air/wind is limited or poor and fluctuates . These areas are usually foggy and temperature also tend to fall than the normal mountain slope. Local wind in mountain region varies, which affects temperature in the areas and there by affects the suitability of crops.

Vegetation : Vegetation patterns changes as micro climate changes and vice-versa. Areas having vegetation and water source are generally cool and humid than the area where vegetation and water source are absent. Temperature, humidity also differs and makes the area different from other.

Soil : Stand of vegetation and types differs according to the condition of soil. As vegetation patterns changes, there will be change in micro climate.

Frost/ hailstone : Occurrence and frequency of frost and hailstone is different and random in different physiographic zones, districts, valleys and bottoms which also affects micro climate.

NATURAL DISASTER.

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Flood and Landslide

Flood :

By definition, a flood is " an overflow of lands used by man and not normally covered by water ". What causes the overflow obviously is more water than than the river's channel can carry. However, nature of river channel itself is responsible for over-flow of river channel. The main source of the excess water is rainfall. In the case of snow-fed rivers, excessive snow-melt could swell up the streams. Obviously, flood is basically the result of rainfall runoff, which is too great to be supported by the existing river channels. This uncontrolled high runoff overtops the natural or artificial banks and starts spreading over the flood plain causing damage and threatening the property in the vicinity of the flood plain.

Flood can't be controlled but one can prevent damage likely to be caused by the flood, by manipulation of the components of land resources from where the flood originates.

Causes of flood : Man's interferences with the natural ecosystem has crucially modified the existing hydrological regime and the water balance. Interferences like uncontrolled and destructive harvesting of timber and fuel wood, clearing forests to give ways to shifting cultivation / settlement and over grazing have greatly decreased the water holding capacity of the land, the consequences of which is increased runoff. During

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heavy rains, the runoff so produced is often not retained by the land. It just moves down through many steep, barren, eroded slopes and reaches down into small narrow streams and rivers. These streams and rivers in the hills carrying sand, silt, water surges, which erode their own banks, have a tendency to deposit the sediments they carry on the main rivers beds increasing the bed load and resulting in the spread and surge of water over the flood plains. Virtually, it is a flat land where peak runoff turns into floods, which suffers the greatest damage. Flooding of the main rivers of Nepal are the clear examples of having an immense volume of runoff and the bed load being transported from its tributaries.

Effects of Floods :

Floods affect and damage property mainly through the process of inundation in low-lying areas, backed by up-stream destruction, river bank erosion and the shifting of river channels. The surrounding areas of flood plains and valleys may suffer heavily from floods, since the flood plains and valleys created a long time ago by the rivers, have become the centers of economic growth and are heavily populated and exploited for agriculture.

However, the effect and the problem of flooding in developing countries has largely been aggravated by the socio- economic problems and environmental factors. Increased population has left no alternatives except for people to occupy and migrate to

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highly fragile lands. In developing countries, 50 to 80 % of the population occupy fragile lands, and 10% of the world's population live in the steep and fragile lands of the earth. Cultural practices on these lands have destroyed and inhibited the natural protective means, which would have prevented flood erosion.

Loss and siltation of prime agricultural land, siltation and destruction of lakes, reservoir and irrigation structures, water pollution, and the destruction of settlements and communications are the principal damage brought by floods.

The meandering and shifting problems of rivers may create legal problems. Meandering and shifting of rivers causes damages on one bank leaving the fertile alluvial land on the opposite bank having different land rights. This problem may cause serious disputes in the community, where the availability of flat land is scarce.

Preventing Flood :

Flood is largely a result of abuse of land, natural resources and hydrological function. To prevent primary damage of flood to some extent, a three phase action program has to be carried out simultaneously :

a ) Treatment of watershed ( land use management )

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b) Treatment of upstream or torrents, and

c) Treatment of main rivers

a) Treatment of watershed :

It includes vegetative, simple mechanical measures adjustments in existing land-use. Purposes of these measures is to increase the rate of infiltration, decrease runoff volume and velocity, conserve soil and water. Watershed treatment is one of the most effective and widely used measures in the control of runoff and sedimentation, which cause floods in lower reaches. The treatments include afforestation, contour farming, vegetative waterways, management of forest, grass land, agriculture, water resources and so on.

b) Up-stream treatment : This treatment is mainly concentrated on the up-stream torrents, gullies and water ways. Objectives of this treatment is to retard the runoff and to stabilize the source of sediments that reaches in the down stream. Structures used for retarding flood water ( runoff ) and minimizing sedimentation are check-dams, sediment detention basins, catchment ponds, channel improvement structures are commonly used.

c) Treatment of main rivers : This is treatments in which big structures are usually built in the main rivers in order to prevent the flood hazards. In this treatment emphasis is given in to river training by stabilizing the river channel. The objectives of this measures are:

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--- to prevent the tendency of channel shift or changing the river course.

--- to maintain the river channel capacity for the transportation of sediment load and excess runoff.

--- to protect the bank cutting.

--- to protect the flood plain from flooding.

For channel stabilization, following river training works are usually warrented :

--- river training work to prevent the river from mentaring and causing bank erosion

--- river training work to to provide sufficient cross-section area fro easy flow of sediments.

--- river training work to keep sufficient depth of water for navigation.

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Following are engineering structures widely used for channel stabilization or river training works:

--- Embankments ( Refer Unit 2. of lecture note)

--- Spurs ( Refer Unit.2. of lecture note)

--- Guide banks ( are structures usually constructed to confine the river flow in a certain direction in order to protect other structures, like bridge or a weir from damage. this structure are built in banks in parallel to flow ).

--- Pitching on bank slopes ( this is done on the banks of the river, parrellel to the river flow. Its purpose is to check the erosion on banks due to direct impact by the river, and to check the sliding of banks due to the scouring action of the water. bank slopes can be pitched by laying loose boulders, concreate blocks or even grass turfing ).

--- Cut-offs ( An artificial cutoff can be made in order to make river flow straight from its mendering position and reclaim the land. this is a very simple and temporary measure of channel stabilization work and shortening of the river channel ).

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In addition to above mentioned measures, flood prevention measures also includes the integration of following practices :

e) Flood Prevention : This is simply a watching, guarding and alerting from excessive rain. If excessive rain is occuring since long duration, preventive measures need to be applied in order make safe from flood damage.

f) Flood Prediction : With the data and information of past discharge and rainfall record and rise and fall of river level up stream gauges, chances of occurring flood can be predicted, or flood warning can be predicted. Flood prediction can help us to take timely action for minimizing the flood damage. This is a flood warning system, if there is such warning, quick communication to the community should be done to make them alert from the likely damage that can happen from the flood.

c) Flood Plane Zoning : Zoning of flood plane should be made in order to minimize the risk from flood. Basically this is categorized into three zones. They are :

Critical Zone : This is a zone of river channel, which gets flooding in every monsoon. In such a zone, no human settlement and any infrastructure should be planned.

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Restrictive Zone : This zone is very close or adjoining area to critical zone. This area may get flooding when there is a big flood. Construction of infrastucture should be avoided except some agriculture practices.

Warning Zone : This zone falls adjoining to restrictive Zone. This zone will have a chance of flooding if there is largest and unprecedented flood. Construction of infrastructures need necessary precaution.

d) Physical interventions : Refer Preventing Flood as mentioned above.

Flash flood :

Flash floods are events with very little time lapsing between the start of the flood and peak discharge. They are often associated with short intervals between storm incidence and arrival of the flood wave, but this is not always the case. Floods of this type are particularly dangerous because of the suddenness and speed with which they occur. Flash floods are more common with isolated and localized intense rain fall originating from thunderstorms.

Landslides :

The term landslide is used to denote the downward and outward movements of slope forming materials along surface of separation. They

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are mass movements of land caused by various factors such as heavy rain, earthquake, or geological factors. Landslides are rather quick mass wasting processes. Mass wasting or movement are generally : debris slides, rock slides, debris flows and deep seated rotational slides. Plane rock slides occur on steep slopes where bed rock is close to the surface. Debris and soil slides occur on steep slopes that are deeply weather residual soils. Landslide causes damage to cultivated land, settlements, roads and other infrastructures.

Landslides can be classified in terms of two criteria:

-- Types of movement

-- Types of material

Types of movement : Rock falls, topples, slides ( debris, rock slides ) and flows

Types of materials : Bedrocks, soils

Rock falls : They are movement of masses of geologic materials detached from slopes or cliffs. they occur by free fall, bouncing and rolling. Depending upon the type of materials, they are referred as rock falls, soil fall, debris fall earth fall etc.

Topples : Block of rock that falls, tilt or rotate forward on a pivot or hinge point and then separates from the main mass and falling and rolling down to the slopes.

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Slides : Movement of soils or rocks along a distinct surface of rupture which seperates the slide materials from more stable underlying materials. Two major types are : rotational and translational slides.

Rotational : In this type, the surface of rupture is curved concavely upwards and the slide movement is more or less rotational in an axis that is parallel to the contour of the slope.

Translational : In this case, the mass moves out or down and outwards and slides out on top of the original ground surface. Such a slide may progress over great area. Slide material may range from loose unconsolidated soils extensive slabs of rock.

Flows: Flows are many kinds such as : Creep, Debris, Debris avalanche, Earth flow, Mud flow, Lahar.

Creep flow : This is steady downward movement of slope forming materials. Creep is indicated by curved tree trunk, bent fences or retaining wall, tilled poles or fences and small soil ripples.

Debris flow : This is a rapid mass movement in which loose soils, rocks and organic matter combine with air and water to form a slurry that then flows down slope. Debris flow areas are usually associated with steep gullies and drainage basin.

Debris avalanche : This is a varieties of very rapid to extremely rapid debris flow.

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Earth flow : In this case, a bowl depression forms at the head of land slope. The central area is narrow and usually becomes wider as it reaches the valley floor. This type of flow generally ocurs in fine- grained materials or clay- bearing rocks on moderate slopes and with saturated conditions.

Mud flow : This is an earth flow that contains of materials that is wet enough to flow rapidly and that contains at least 50 % sand, silt and clay-sized particles.

Lahar : A lahar is a mud flow or debris that originates on the slope of volcano. Lahar are usually by heavy rainfall eroding volcanic deposits, sudden melting of snow and ice due to heat from volcanic events or by the breakout of water from glaciers, crater lakes dammed by volcanic eruptions.

Causes of Landslides :

Several factors like geology, geomorphology, hydrology, climate and vegetation, which interact each other in a complex ways are responsible for landslide or slope stability.

Geology : The composition, texture, physical and chemical content of rock and soil as well as the shear strength of particles, permeability, structures, weathering and other characteristics of rock and soil play important roles in landslide. The solid constituents, mineral content and their distribution in rocks and soil such as grain, size, distribution, shape, area, surface

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characteristics, amount of cement, mechanical strength of particles, clay minerals, inter particle bonds, presence of water and chemicals, nature of bedding planes, joints, faults, folds, fractures and their orientation etc. are important factors, which play vital role in landslides or slope stability.

Geomorphology : Steepness of slope, strength of slope forming materials, relationship between slope and stability, presence or absence of former landslides also is a basis to analyze scope of landslide.

Hydrology : Hydrology of a particular area is another factor in landslide and slope stability. Amount and source of water, water movement, ground water flow and pressure of water are equally important factors to be considered in landslides and slope stability.

Climate : Climate such as temperature and precipitation are important factors to be considered in landslides and slope stability. These two elements vary from region to region, which in turn, makes variation in the scale and the severity of landslides that may occur in different regions. In temperate regions, with moderate rainfall and change in ground water flow and water pressure may activate landslides. Similarly, in semi-arid regions with heavy rainfall and in temperate and tropical regions, where monsoons or cyclonic storm occurs may have debris landslide.

Vegetation : The mechanical action of root network for holding the rock mass as well as its role for controlling direct water movement or permeability and ground water movement in the land mass are imperative in landslide.

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Factors Supporting Landslide ( Triggering factors ) :

In addition to the factors responsible for landslides or slope stability as mentioned earlier, there are some more factors, which backup landslide or slope failure. If there is a abrupt or gradual variation or change in shearing stress and strength of materials and water content in the geological mass, landslide may occur. The elements that alters the shearing stress and strength of materials are : vibration, absence of lateral support, weight, water pressure and friction, weathering ( physical and chemical actions).

Vibration : Vibration from earthquake, blasting, traffic, thunder storm weaken the shearing stress and strength of materials of geological mass and may cause landslides.

Absence of lateral support : The removal of lateral support by erosions, quarries, previous slope failure, constructions etc. also affect shearing stress and strength of geological mass and help causing landslide.

Weight : Weight of rain, snow, hailstone, accumulation of debris, loose rock materials, volcanic materials, waste piles, weight of physical infra-structures etc. may enhance the landslide.

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Water pressure and friction : Water pressure in the rock pores and frictional changes in the rock fractures due to water help change and affect the shearing stress and strength of geological mass and may cause landslides.

Weathering : The weathering of rock mass due to physical and chemical actions also affect the shearing stress and strength of rock mass and help enhance landslides.

Mitigation Measures :

Since landslide falls under one of the natural hazards, its mitigation measures needs combination or integration of several interventions. Curative/ rehabilitative, preventive measures and public awareness programs need to be incorporated.

Curative/ Rehabilitative measures : These are measures, where immediate actions are administered in landslide that are already occurred in order to safe-guard the property and people from the further effect of landslide. These measures need high level of investment and technology. Retaining walls, breast walls, gully control ( check-dams), water diversion structures, river training works and re-vegetation are some of the important curative measures to control landslides.

Preventive measures : Preventive measures are those interventions that need to be administered in an area where landslides are likely to occur or there are high possibility to occur landslide in future. This measures are applied before landslides occur. Preventive measures help people to be

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alert from the effect of landslide damage that may occur in future. Drainage improvement, terrace improvement, gully control, plantation of trees and grasses, catchment ponds, trail improvement, slope stabilization, water source protection, forest protection, grazing management, fodder management, fruit tree plantation, agro-forestry, improved agriculture practice are some of the preventive measures.

In both the programs, involvement or participation of local community is imperative in order to internalize and develop a sense of felling in local people that the programs are for their benefits. Once the people realize about the benefits of the programs, they will be ready to participate and share the cost of construction and maintenance of the program and sustainability programs can be existed.

Public awareness programs: Local people may not be aware of landslide, how they occur, how to recognize the landslide prone areas, what will be their impacts in daily life, what precaution measures need to be taken for prevention and rehabilitation, technical know-how, social and economic implications. Therefore, it is very urgent to carry out awareness program in the local community. Interactions programs in academic institutions, open discussion and interactions in public gathering, field demonstration, observation tours, newsletter, film strips, documentary, slide show, slogans, early warning process and system, extension works, motivation etc. are some of the effective public awareness programs. Public awareness program also help mobilize and generate public participation.

Other disasters ( fire, earthquake, volcanic eruption )

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Fire : Fire as a natural disaster, has affected a substantial portion of forests of the world. Although it is a disaster, fire has been a powerful natural factor affecting forests, wildlife and rangeland. Lowlands such as swamps, maeshes, prairies and semitropical forests of high humidity also have been burned and their vegetation markedly affected.

Fire plays several major roles in fire dependent ecosystem around the world. Fire has always been a natural and extremely important environmental factor since it has influence on species traits and life history as well as ecosystem characteristics and processes such as carbon, nutrient, water cycling, productivity succession and diversity.

Fire is irregular in frequency, intensity and burning pattern. These characteristics are primarily controlled by climate, fuel accumulation and flammability, soil site condition and topography. Fire frequency is greatest in grasslands, grasslands usually burn every 2 to 3 years.

Influences of Fire : Fire influences,

q. Physical and chemical properties of siter. Dry matter accumulations. Genetic adoptions of plant speciest. Species establishment, development, composition and

diversityu. Wildlife habitat and wildlife populationv. Presence and abundance of forest insects, parasites and

fungi

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Causes of Fires :

w. Lightningx. Meteoritesy. Volcanic eruptionz. Sparks from falling quartzite rocksaa.Human activities

Kinds of Fires : Three kinds of fires are recognized according to the level at which they burn. They are : Ground fires, Surface fires and Crown fires

Ground fires : Fires sweeping the forests floor may generate or called ground fires. In ground fires, the thick accumulations of organic matter burns, which overlies mineral soil. This is flameless and may kill most plants with roots growing in organic matter. Ground fires burn slowly and usually generate very high temperatures. Ground fires tend to serve as ignition sources for surface fires.

Surface fires : This is a most common type of fire. It burns over the forests floor and range consuming litter, humus and killing herbaceous plants, shrubs and fauna. The greater the fuel accumulated on the surface, the greater the mortality of plants and fauna. The amount of mortality depends on the species, the age and rooting habits. For example, the young pines succumb to a surface fire, where as older individual of the same species survive due to thicker bark protecting the cambium layer from heat damage. A shallow rooting plant will be more susceptibility to fire injury compared to that of deep rooting plants. However, surface fires tend to kill young trees of all species and most of the trees of less fire resistant species of all sizes (often just the above ground portion ). The pole-size to mature trees of fire -resistant species survive light surface fires. Killing of plants by

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surface fires are due to damage of cambium, root injury and scorching of the crowns by hot gases rising above the flame.

Crown Fires : Surface fires fueled by accumulations of organic matter and whipped by winds may scorch and ignite crowns of trees, thus generating a crown fires. Crown fires travels from one crown to another and kills most trees in its path. Conifers are most susceptible to crown fires because of the high flammability of their foliage and occurrence in pure stand than broad leafed species.

Fire is one of the management tools of vegetation and wildlife, however wildfires are always harmful and detrimental to the environment than controlled fire or burning.

Control of fires : The following techniques are used to control wildfires :

bb. Fireline : a narrow line of 2 to 10 ft. wide, from which all vegetation is removed down to mineral soil by sterilization of the soil, by yearly maintenance or by clearing just ahead of firing out from the line.

cc. Firebreak : a fireline wider than 10 ft., frequently 20 to 30 ft. wide prepared each year ahead of the time it may be needed for use in controlling a fire.

dd. Fuelbreak : a strategically located block or strip on which a cover of dense, heavy, or inflammable vegetations has been changed to new vegetation of lower fuel volume or inflammable are maintained to control fires.

ee.Fuel modification : fire control practices including cleanup of fuel hazards, permanent fuel reduction on limited areas or periodic fuel reduction on large areas.

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Indigenous Technology and Knowledge

Please refer report on "Salient Indegenous Technology Practices for Watershed Management in Nepal " by D. D. Kandel and M.P. Wagley. (Copy available in Library)

Desertification

Please refer Policy and Programme Responses for Combating Desetification by M.P. Wagley in " Combating Desertification - A national report of the National Seminar on Desertification and Land Improvement ". (Copy available in Library)

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