Soil and water conservation

Soil and water conservationC A AnithaSoil Conservation OfficerIWDM-K, ChadayamangalamEngineering measures for arable landsWhich measure to chooseLand slopeAvg annual rfSoil typeMeasure adopted< 2%Soil cover< 6%< 800 mmLoamy/sandy loam with good infiltrationContour bunding< 6%> 800 mmLoamy/sandy loam with good infiltrationGraded bunding< 6%< 800 mmpoor infiltration (clayey)Graded bunding> 6%Bench terracingImportant principles for designIncreasing the time of concentrationIntercepting long slope into several shorter onesProtection against damageReducing the steepness of slope

Types of measuresContour bundingAreas of slope 2-6% and with scanty rfIntercepts runoffConserves moistureIncrease crop yield by 15 20%IT

MAKES

RUNNING WATER

WALKSIT.SLEEP

AND INFILTRATE INTO THE SOIL Critical velocity Infiltration/Percolation Insitu conservation Time of concentration CONTOUR BUNDINGWhen the Land slope increase 4 timesVelocity increases 2 timesEnergy and erosive capacity increases 4 timesi.e. Erosive capacity SlopeThe quantity of Material that can be carriedIncreases 32 timesThe size of the particles that can be transported by the runoffIncreases by 64 times LAY OUT OF CONTOUR BUNDH.IV.IV.IH.IH.IV.IS.LSpacing of contour bundsExpressed by vertical interval ( V.I.) between two consecutive bundsIntercepts water before it attains critical velocity.V.I = 0.3(s/a+b); a=3, b=2 for soils with good infiltrationH.I.= V.I/sx100Length of contour bund/ Ha; L =100 S/ V. I

Graded bundingNot laid in contourLaid along predetermined longitudinal gradeIn slopes upto 10%For safe disposal of excess runoff slowlyShallow channels near to contour at suitable V.I.Purpose is drainage

Specifications of graded bundV.I same as CB.Channel grade varies from 0.05 to 0.4% depending on soil types.Outlets for each terraceDiversion channel for runoff disposalBench terracingPracticed in steep slopesStep like fields along contours by half cutting and half filling Steep slopes converted to level fieldsDegree and length of slope reducedSlopes upto 33%, sometimes upto 50 to 60%Types of bench terracesLevel bench terracesInwardly sloping bench terracesSlopes inward with water disposal channelFor crops susceptible to water stagnation like potato, maize etcIn high rainfall areasOutwardly sloping bench terracesSlopes outward with safe water disposal to the next terraceIn low rainfall areas

Puertorican typeStrip terracesConservation bench terracing(CBT)Consists of natural slope, terrace ridge and channel for runoffIn gentle slopes upto 10%Pastures in sloping areaCrops in terrace

CONSERVATION BENCH TERRACING

Conservation Bench Terrace with Paddy in lavelled and maize in the sloping area, Dehradun (Uttaranchal).Conservation ditchingIn black soils with alternate shrinking and swellingInverted bunds dug in soilStores runoffReduces erosionContour terrace wallIn areas of high rf intensity like KeralaContour bunding with stone pitching on lower side of slopeLand slopes 15-40%Successful in laterite soilsEngineering measures for non arable landsLands not suited for agricultural crops due to natural limitationsLittle economic useContribute to max erosionAbsence of fertile soilBioengineering measures adoptedfunctionsTypes of measures

SLOPE STABILIZATION MEASURES: NON-ARABLE

Diversion drainsContour Trenches Staggered ContinuousCrib structuresGeotextiles (Geojute, Coir Bhovastra etc.)Kutta - crate StructuresRetaining wallsDiversion DrainsThe bed slope (grade) of the drain should be such that it is non-erosive as well as non-silting one.The gradient of diversion drain should preferably be kept within 0.5 per cent.A narrow and deep drain does not get silted up as rapidly as a broad and shallow drain of the same cross-sectional area and is, therefore, self maintaining.Design of a diversion drain is similar to that of a grassed waterway.

Contour TrenchingContinuous contour trenches(CCT)Low rainfall areaLength 10-20 mC/S: 30-30cm or 45-45cmEqualizers width 20-25cmStaggered contour trenches(SCT)Length 2-3m, line spacing 3-5, Depth 40-50 cm; width 50cmHI=A/Q (A=C/S area; Q=expected runoff

Crib StructuresSteep slopes (more than 40%) can be stabilized by constructing log wood crib structures filled with stone/brushwoodCrib can be made with Eucalyptus poles of 2 to 3 m in length and 8 to 12 cm in diameter. These poles are joined together with the help of 20 to 25 cm long nails.

The height of the structure is kept 1.5 to 2 m above the ground depending upon the land slope

Contour wattles provided at 3-5 m interval.Trenches 0.3 wide and 1 m deep dug up on contours and filled with brushwood bundles.Posts of self sprouting spp. planted at 1m interval e.g. Salix, Vitex, Ficus, Erythrina etc.

Wattling and mulching techniques for slopeWattlingGeotextilesNatural geotextiles made of fibres of jute or coir used for stabilisation of degraded slopes in landslides and mine spoil areas and cut slopes along roadsides

Initial establishment of vegetation on highly degraded sloping lands by holding the vegetation in place and conserving moisture and fine soil for its growth.

open mesh size of about 25mm x 25mm found suitable

The cost of geotextile application may vary from Rs. 40 to Rs. 70/sqm for jute and coir geotextile, respectively

Retaining wall

Retaining walls

For stabilizing precipitation bill slopes and river banks.

Thumb rule

Take base width as 2/3rd height of wall.Width reduced in steps to 1 m at top.Kutta-Crate

In certain situations, used cement gunny bags filled with nala bed sand / gravel can be used for construction of barriers for slope stabilisation.

For stabilization of limestone mine spoil slopes, barriers formed by filling mine spoil in used cement bags (Katta crate structures) have been successfully used. Landslide or landslip Erosion

Land slippage occurs on sloping lands that are wet. Soil that is saturated with water slips down the hillside or mountain slope. Land slippage is also known as mud slide or landslide or mass erosion. Banks along highways, streams and ocean fronts are often subject to land slides. Landslide is the downward and outward movement of slope forming material composed of natural rocks, soil, artificial fills or

Mass erosion by landslip Mass erosion by landslides

Slope stabilization

Protection of Slopes by Brushwood Rollers and Gabions

Stream Bank Erosion

Stream bank erosion is the scouring of soil material from the stream bed and cutting of stream bank by the force of flowing water. Stream erosion and gully erosion are distinguishable. Primarily, stream erosion applies to the lower end of head water tributaries and to streams that have a nearly continuous flow and relatively flat gradient, whereas gully erosion occurs generally in intermittent streams near the upper end of head water distributaries.Stream bank gets eroded either by runoff flowing over the stream bank or scouring or undercutting. Stream bank erosion is accelerated by the removal of vegetation, overgrazing, or tillage near the banks. Scouring underneath the bank or on stream bed is affected by the velocity and direction of flow, depth and width of channel and soil texture.

Stream Bank Erosion Control

All rivers and streams while flowing through hilly regions or alluvial plains have a tendency to erode away their banks. This erosion destroys productive crop lands situated on the river margins

CAUSES OF STREAM BANK EROSIONStream bank erosion is mostly caused by the flowing water in rivers and streams. Flood flows cause the major part of the erosion and normal flow after floods also cause considerable amount of erosion

Erosion caused by washing away of the soil material of the bank by flowing current or waves.

2. Sliding of the bank material due to the unstable slope created as a result of erosion caused by the water flow

3. Undermining the toe of the lower bank by currents, waves, swirls etc. followed by the collapse of the over hanging material deprived of support

4. Sloughing or sliding of slope when saturated with water. This usually happens during high floods of long duration when the constant high water level saturates the bank material

5. Sliding of the bank material due to seepage water flowing back into the river after flood water recedes. This seepage saturates the bank material and decreases the internal strength of the material

6. Runoff discharge from the areas adjoining the stream banks into the stream through unprotected land surface. The inflow into the stream creates gullies on the stream bank and accelerates the erosion

Failure of Stream bankSingle row brush dam

Double row brush dam

Gunny Bag Structures(Katta crate structures) For longer durability of the structure, cement and sand / gravel mixture may be used in the ratio of 1:16. The filled gunny bags are laid in a row over one another in three layers to make a height of about 0.6m

Top width:0.5 mSide slopes:0.5 H : 1 VDepth of foundation:0.3 m - 0.5 mHeight above ground level 0.5m -1.0 m Keying into stableportions of banks0.3 m - 0.6 mDry stone masonry check damsLoose Stone Check Dams0.60H0.4HH=0.80.40H1.2HSub structure0.40H0.60H0.4HH=0.50.40H1.2HSub structure0.40H0.60H0.4HH=1.00.40H1.2HSub structure0.40HUpper reachesMiddle reachesLower reachesGabion check damsStone wire crate ( Gabion) as semi-permanent structures are commonly used for drainage line treatmentThe gabion check dams/cross-barriers may be constructed in second and third order (main) gullies/channels for retention of debris and soil accumulation without ponding.Specifications (m)Channel gradient (%)Less than 15 15-25 25-40Base width234Vertical interval (VI)223Horizontal interval (HI)201010

Gabion Design Plan

Dam SpacingSpacing =(HE /K tan cos )K = Constant, value of K = 0.30 for tan < 0.2 and K = 0.50 for tan > 0.2. o = gully gradientHE = Dam height measured from the gully bottom to spillway crest,

Permanent Gully Control StructuresTypesDrop spillway Chute spillwayDrop inlet spillway

Design Criteria Hydrological design Hydraulic design Structural designDrop structure

Drop Inlet Structure

Chute Spillway

Stepped Drop Structures

DROP STRUCTURES ON GULLY

Gabion structures and silt detention barriers

TORRENT CONTROL MEASURES

Spurs: Built out from the bank of a river to deflect the main river current away from eroding bank.

Functions: Protection of adjoining land and property Land reclamation Flow diversionSpurs and Layout

DeflectingRepellingAttracting

Vegetative spurWater harvesting systemsDirect runoff water harvesting systemsFarm ponds/Percolation pondsDug out pondsEmbankment type pondsCheck damsContour trenches/bundsRain water harvesting systemsRoof top WHS

SOLUTIONS FOR A WATER-SHORT WORLD: INTEGRATED WATER RESOURCE MANAGEMENT Harvesting Rainwater

Conserving Precious Natural Resources

Rainwater Harvesting

catch water where it falls

Rainwater harvesting is the process of

Collecting, Concentrating,Improving the productive use, and Reducing unproductive depletion of rainwater 67Components of Rainwater Harvesting

Collection and storage of rainwaterIn situ soil moisture conservationEffective utilization of stored waterStrengthening natural water resources

68Collection and storage of rainwater

a. Watershed approach

b. Water harvesting in farm ponds

c. In situ rainwater harvestingRainwater harvesting.69Rainwater harvesting.1. Collection and storage of rainwater Watershed approach

Water harvesting in relatively big reservoirs on community basis.

Involves full cooperation of Government and Non-Government agencies and local people.

Involvement of several agencies makes the success of the program a bit difficult.

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Water Harvesting on Watershed basis71Rainwater harvesting.1. Collection and storage of rainwater b. Water harvesting in farm ponds

Water harvesting in relatively small (100-200 m3) farm ponds

Does not involve interaction of different agencies

Cost effective and Feasible in hilly terrains with resource poor farmers, having small land holdings

72Rainwater harvesting.277Black polyethylene sheet covered with soil348Silpaulin sheet (UV resistant)419Black polyethylene sheet covered with bricks575Bitumen lining709Cement-concrete liningCost (Rs/m3 water harvested)Lining material

Collection and storage of rainwater

Small dug-out farm ponds

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WATER HARVESTING IN SMALL DAM

ROOF TOP RAINWATER HARVESTINGTo meet the ever increasing demand for waterTo reduce the runoff which chokes storm water drainsTo avoid flooding of roadsTo augment ground water storage (Sustainability)To supplement domestic water requirement during crisis Sustainability)To improve the quality of ground waterTo reduce the soil erosion

NEEDCOMPONENTS OF ROOF TOP RAINWATER HARVESTING SYSTEMThe system usually comprises:A roofA storage tankCollection pitGutter arrangement to transport water from the roof top to the storage tankFirst flush system to divert the dirty water Filter unit to remove debris/silt etc

COMPONENTS OF ROOF TOP RAINWATER HARVESTING SYSTEMMETHODS OF RWH FOR GROUND WATER RECHARGEVarious methods are availablePercolation pitPercolation pit with boreRecharge trenchRecharge trench with boreRecharge well (Shallow)Recharge well (Deep)

RWH RECHARGE THROUGH PITS

RWH - RECHARGE THROUGH TRENCHES

RECHARGE RAINWATER HARVESTING AND RECHARGE THROUGH ABANDONED WELL

WATER HARVESTING SURFACE -STORAGE TANK

RECHARGE THROUGH BOREHOLE IN HARD ROCK AREAS

ROOF TOP RAINWATER HARVESTINGPH Office, IndoreThank you

CGWB