Technical Guideline for Design of Small Scale Reservoir

Japan International Cooperation Agency (JICA)

Oromia Irrigation Development Authority (OIDA)

Technical Guideline for Design of Small Scale Reservoir

May, 2014

The Project for Capacity Building in Irrigation Development (CBID)

Foreword Oromia Irrigation Development Authority (OIDA) is established on June, 2013, as a responsible body for all irrigation development activities in the Region, according to Oromia National Regional Government proclamation No. 180/2005. The major purposes of the establishment are to accelerate irrigation development in the Region, utilize limited resources efficiently, coordinate all irrigation development activities under one institution with more efficiency and effectiveness. To improve irrigation development activities in the Region, the previous Oromia Water Mineral and Energy Bureau entered into an agreement with Japan International Cooperation Agency (JICA) for “The Project for Capacity Building in Irrigation Development (CBID)” since June, 2009 until May, 2014. CBID put much effort to capacitate Irrigation experts in Oromia Region through several activities and finally made fruitful results for irrigation development. Accordingly, irrigation projects are constructed and rehabilitated based on that several Guidelines & Manuals and texts produced which can result in a radical change when implemented properly. Herewith this massage, I emphasize that from Now on, OIDA to make efforts to utilize all outputs of the project for all irrigation activities as a minimum standard, especially for the enhancement of irrigation technical capacity. I believe that all OIDA irrigation experts work very hard with their respective disciplines using CBID outputs to improve the life standard of all people. In addition, I encourage that all other Ethiopian regions to benefit from the outputs. Finally, I would like to thank the Japanese Government, JICA Ethiopia Office, and all Japanese and Ethiopian experts who made great effort to produce these outputs.

Feyisa Asefa Adugna General Manager

Oromia Irrigation Development Authority

Addis Ababa, Ethiopia May, 2014

Introductory Remarks “Growth and Transformation Plan” (GTP) from 2011 to 2015 intensifies use of the country’s water and other natural resources to promote multiple cropping, better adaptation to climate variability and ensure food security. Expansion of small scale irrigation schemes is given a priority, while attention is also given to medium and large scale irrigation.

In Oromia Region, it is estimated that there exists more than 1.7 million ha of land suitable for irrigation development. However, only 800,000 ha is under irrigation through Traditional and Modern irrigation technology. To accelerate speed of Irrigation Development, the Oromia National Regional State requested Japan International Cooperation Agency (JICA) for support on capacity building of Irrigation Experts under Irrigation Sector.

In response to the requests, JICA had conducted "Study on Meki Irrigation and Rural Development" (from September 2000 to January 2002) and Project for Irrigation Farming Improvement (IFI project) (from September 2005 to August 2008). After implementation of them there are needs to improve situation on irrigation sector in Oromia Region.

JICA and the Government of Ethiopia agreed to implement a new project, named “The project for Capacity Building in Irrigation Development” (CBID). The period of CBID is five years since June, 2009 to May, 2014 and main purpose is to enhance capacity of Irrigation Experts in Oromia Region focusing on the following three areas, 1) Water resources planning, 2) Study/Design/Construction management, 3) Scheme management through Training, On the Job Training at site level, Workshops, Field Visit and so on and to produce standard guidelines and manuals for Irrigaiton Development.

These guidelines and manuals (Total: fourteen (14) guidelines and manuals) are one of the most important outputs of CBID. They are produced as standards of Irrigation Development in Oromia Region through collecting different experiences and implementation of activities by CBID together with Oromia Irrigation Experts and Japanese Experts.

These guidelines and manuals are very useful to improve the Capacity of OIDA Experts to work more effectively and efficiently and also can accelerate Irrigation Development specially in Oromia Region and generally in the country.

Finally, I strongly demand all Irrigaiton Experts in the region to follow the guidelines and manuals for all steps of Irrigation Development for sustainable development of irrigation.

Adugna Jabessa Shuba D/General Manager & Head, Study, Design, Contract Administration & Construction Supervision

Oromia Irrigation Development Authority

Addis Ababa, Ethiopia May, 2014

i

Table of Contents

1. Types of small scale reservoirs ......................................................... 1

1.1 Classification based on function ................................................. 1

1.2 Classification based on structural characteristics ..................... 2

1.2.1 Embankment Type (storage tank type) .............................. 2

1.2.2 Excavated type ................................................................... 2

1.2.3 Cut-and-bank type ............................................................. 3

1.2.4 Dam ................................................................................. 3

2. Location setting of the reservoirs ...................................................... 4

2.1 Basic conditions ......................................................................... 4

2.1.1 Irrigation plan .................................................................... 4

2.1.2 Priority to the command area ............................................. 4

2.1.3 Balance between the command area and the

catchment area ................................................................... 5

2.2 Suitable site selection criteria for each reservoir type .................. 5

2.2.1 Embankment Type (storage tank type) .............................. 5

2.2.2 Excavated type ................................................................... 6

2.2.3 Cut-and-bank type ............................................................. 6

2.2.4 Dam .................................................................................. 7

3. Determination of reservoir Capacity and crest level setting ............... 10

3.1 Water demand and the loss ........................................................ 10

3.2 Estimation of available water quantity (Qa) ............................... 10

3.2.1 Specific discharge method .................................................. 10

3.2.2 Run-off coefficient method ................................................. 11

3.3 Ecological/sociological flow quantity of the river ......................... 12

3.4 H～Q curve of the reservoir ......................................................... 12

3.5 Sediment .................................................................................... 13

3.6 Water level rising by flood ........................................................... 15

ii

3.6.1 Formula for estimating the overflow depth .......................... 15

3.6.2 Flood discharge estimation ................................................. 16

3.6.3 Two philosophies to the estimation of water level rising by

flood ................................................................................. 17

3.7 Freeboard and the crest setting of reservoirs ............................... 19

4. Design of reservoirs .......................................................................... 22

4.1 Countermeasures to leakage ....................................................... 22

4.1.1 Embankment Type ............................................................. 22

4.1.2 Excavated type ................................................................... 23

4.1.3 Cut-and-bank type ............................................................. 25

4.1.4 Dam .................................................................................. 25

4.2 Slope protection ......................................................................... 44

4.2.1 Rip-rap works .................................................................... 44

4.2.2 Soil cement works .............................................................. 44

4.3 Slope inclination ......................................................................... 48

4.3.1 Embankment type .............................................................. 48

4.3.2 Excavated type ................................................................... 49

4.3.3 Cut-and-bank type ............................................................. 49

4.3.4 Dam .................................................................................. 49

4.4 Reference of the embankment materials ..................................... 49

4.4.1 Classification of Materials .................................................. 49

4.4.2 Applicable Range of Fill Materials ....................................... 50

4.4.3 General Property of Fill Material ......................................... 57

4.4.4 Random Material ............................................................... 57

4.4.5 Soft Rocks or Gravel ........................................................... 57

4.4.6 Mixing of Materials ............................................................. 58

4.4.7 Removal of Large Material .................................................. 58

4.4.8 Riprap Material .................................................................. 59

5. Hydraulic designs of the spillways .................................................... 60

iii

5.1 Formation of the spill way .......................................................... 60

5.2 Selection of the spillway type ...................................................... 60

5.3 Hydraulic design of spillways ...................................................... 63

5.3.1 Approaching channel ......................................................... 63

5.3.2 Adjustment section ............................................................ 64

5.3.3 Transition section .............................................................. 72

5.3.4 Chute section ..................................................................... 82

5.3.5 Energy dissipater ............................................................... 84

6. Design of intakes ............................................................................. 98

6.1 Formation of the intake .............................................................. 98

6.2 Design of the inclined conduit works .......................................... 100

6.2.1 Position of the intake mouth hole ....................................... 100

6.2.2 Diameter of the hole ........................................................... 100

6.2.3 Inclined conduit works ....................................................... 101

6.2.4 Accessory works ................................................................. 102

6.3 Design of bottom conduit works ................................................. 103

6.3.1 Placement .......................................................................... 104

6.3.2 Structural quality and formation ........................................ 104

6.3.3 Diameter of the conduit ..................................................... 105

6.3.4 In case of the embankment around the conduit being left

until later .......................................................................... 106

6.3.5 Details of the bottom conduit works ................................... 107

7. Preventive measures against sediment ............................................. 111

Annex 1 Calculation Example of Water level in the Reservoir ................ 112

Annex 2 Calculation Example of the Blanket ........................................ 118

References ........................................................................................... 120

List of Authors/Experts/Editors/Coordinators ..................................... 121

1. Types of small scale reservoirs

1.1 Classification based on function

More or less the function of the ponds for irrigation including dams is to

regulate the water quantity, i.e., to store the surplus water and supply it at

the requested time. In case of Aichi Irrigation Canal Construction Project,

there are many regulation ponds along its alignment. The Koshunai

Regulation Pond which was constructed beside the Hokkai Canal Line (L=82

km, Command area=27,000 ha) and the capacity of which was 1,580,000m3

decreased the canal rehabilitation cost to enlarge the canal cross-section by

playing a role of supplying the peak demand of irrigation water.

Photo 1.1 Outline of Aichi Irrigation Project (Phase I)


Japan International Cooperation Agency (JICA) & Oromia Irrigation Development Authority (OIDA) The Project for Capacity Building in Irrigation Development (CBID)

1

Photo 1.2 New Terminal Balancing Reservoir (Mihama Balancing Reservoir)

Photo 1.3 Koshunai Regulation Pond

1.2 Classification based on structural characteristics

1.2.1 Embankment Type (storage tank type)

In this case, the reservoir is formed by an embankment that encloses all around itself. The water is usually poured into the reservoir by pumping from a lake or a river; the irrigation water is supplied into a canal line by gravity. In case of the irrigation to fruit orchards extending on hill slopes, a storage tank is constructed on the hill top.

1.2.2 Excavated type

In this case, the reservoir capacity is made by excavating the ground; it tends to be constructed in a flat plain area. The water is usually supplied into the

Q=100,000m3

Pond No.1 A=203,220m2

Pond No.2 A=157,530m2

Intake

Outlet Spill way


2Japan International Cooperation Agency (JICA) & Oromia Irrigation Development Authority (OIDA)


reservoir from a natural stream directly or through a channel by gravity; and the irrigation water is pumped up from the reservoir on to a canal line.

1.2.3 Cut-and-bank type

In this case, the reservoir capacity is composed of the room caused by excavation in the higher and by banking in the lower; it tends to be constructed on a gentle slope. The water is usually supplied into the reservoir from a natural stream directly or through a channel by gravity; and the irrigation water is sent to a canal by pumping or by gravity depending to the water level in the reservoir.

1.2.4 Dam

In this case, a dam is constructed on a river flow, i.e. the river is blocked by an embankment, and as a result the reservoir is formed in a valley. The water is naturally brought from the river flow. There are two or three types in supplying system of irrigation water, one is sending water on to a canal by gravity or by pumping, and the other is discharging water into the downstream river once and taking it by a headwork or pumping it up on to a canal, that is applied in Egypt.

Table 1.1 Reservoir type and its characteristics

Reservoir type Stored water Irrigation water supply Note

Embankment type By pumping By gravity ditto a storage tank

Excavated type By gravity By pumping In a plain area

Cut-and-bank type By gravity By gravity/pumping On a gentle slope

Dam Brought by river By gravity/pumping valley




2. Location setting of the reservoirs

2.1 Basic conditions

2.1.1 Irrigation plan

There are two kinds of irrigation method/plan in Ethiopia, i.e. the spate irrigation and the conventional irrigation. In the former method, irrigation water is obtained from the river flow that does not exist in the dry season but exists only in the rainy season to mitigate the drought condition caused by the nonuniformity of rain falls in time and place in the rainy season. In the latter method, irrigation water is obtained from the river flow that exists all throughout the year, so that irrigation farming can be done all the year round. At the beginning of irrigation project, an irrigation plan must be built up at first. But it should be recognized that the irrigation farming all the year is more profitable than the irrigation farming limited in the rainy season and there might be a possibility of conducting the full-year irrigation by a suitable reservoir plan even on a seasonal river.

2.1.2 Priority to the command area

The priority should be given to the water demand in the command area. According to this water demand, water supply plan including the facility construction plan shall be studied.




2.1.3 Balance between the command area and the catchment area

The water supply plan shall depend on the balance between the command area and the catchment area considering the priority to the command area. Each supply plan would become as follows.

Table 2.1 Water Supply Plan

water supply capacity in

catchment area (A)

water demand in the command area (B)

Balance between

(A) and (B) Water supply plan

Rainy season only Rainy season only (A) > (B) Spate irrigation

Rainy season only Rainy season only (A) < (B) Spate irrigation + regulation pond

Rainy season only Dry & rainy season (A) < (B) Irrigation canal + dam or pond

Dry season possible Dry season only (A) > (B) Irrigation canal

Dry season possible Dry season only (A) < (B) Irrigation canal + regulation pond

Dry & rainy season Dry & rainy season (A) > (B) Irrigation canal

Dry & rainy season Dry & rainy season (A) < (B) Irrigation canal + dam or pond

＊Fundamentally the irrigation plan shall be decided as shown above. But actually it is often for the irrigation plan to be decided following the policy that priority should be given to answer the farmers’ request at the minimum level under the limited budget conditions.

2.2 Suitable site selection criteria for each reservoir type

2.2.1 Embankment Type (storage tank type)

This type of reservoir is constructed on the top of a hill. The suitability conditions for the site of this type are as follows.

(1) Adequate altitude to the command area and the water resource

(2) Existence of the available water resource such as a natural/artificial lake or a river

Fig. 2.1 Embankment Type Reservoir





This type of reservoir is constructed on a flat plain. The suitability conditions for the site of this type are as follows.

(1) Existence of the available water resource from which water can be led to the reservoir easily by gravity

(2) Adequate altitude to the command area

(3) Suitable geological conditions, i.e. easy excavation and impervious layer if possible

Fig. 2.2 Excavated type Reservoir


This type of reservoir is constructed on a gentle slope of a hill or a mountain foot. The suitability conditions for the site of this type are as follows.

(1) Existence of the available water resource from which water can be led to the reservoir easily by gravity


(3) Availability of excavated materials for the impervious embankment materials

Fig. 2.3 Cut-and-Bank Type Reservoir

Settling basin

Conveyance pipe

Embankment

Excavation




2.2.4 Dam

This type of reservoir is constructed on a valley by blocking the river. The suitable conditions for the site of this type are as follows.

(1) Large enough catchment area that can afford the water quantity of irrigation demand

In case that the catchment area is extremely larger than the command area, the storage capacity is relatively small and the dam height becomes low. Then the reservoir shall be buried soon by sediments. Countermeasures to such situation, following two ways are applied.

1) Sand-trap dam

It is the usual way to construct sand-trap dams on the upstream of the dam.




Photo 2.1 Example of Sand-Trap Dams

2) Changing of catchment basin

The reservoir is planned on a river valley, usually a branch river valley, with a required storage capacity and a relatively small catchment area. The storage water is led from the river on the other large catchment basin by diversion works and a conveyance channel.

Fig. 2.4 Conveyance Channel/Tunnel

(2) Topographical suitability to provide the reservoir with requested storage capacity by constructing a dam with adequate height

The topographical feature with a narrow valley and a wide space in its upstream is often found at a confluence of rivers.

Fig. 2.5 Position of reservoir at confluence of rivers

Conveyance channel (tunnel)





(4) Geological conditions that produce suitable embankment materials around the dam site

(5) Relatively high ground water table in both abutments at the dam site, if possible




3. Determination of reservoir Capacity and crest level setting

3.1 Water demand and the loss

Water demand, in another saying required/effective reservoir capacity (Rc), is decided based on the net water requirement that comes from the irrigation plan, i.e. cropping plan and pattern. But through this process, water conveyance loss and the irrigation efficiency must be considered. Generally the water conveyance loss is estimated to be 10% in pipe line conveyance, and to be 30% in canal conveyance. As for the irrigation efficiency, it is said to be 75% in case of furrow irrigation, and 90% in case of saving irrigation such as drip irrigation. Therefore, the total irrigation efficiency is 52.5% (=0.70×0.75) in case of canal conveyance and furrow irrigation being applied. It is said empirically that in Ethiopia the total irrigation efficiency is about 40%, which would be caused by the high proportion of earthen canal and evaporation during conveyance.

Based on this empirically grasped total irrigation efficiency, the required/effective reservoir capacity is obtained through multiplying the net water requirement by 2.5 times (=1/0.40).

This point should be deeply considered in future because the water resources are limited in Ethiopia so that the water use must be done with losses as little as possible. For example, in case of pipe conveyance and saving irrigation being applied, the total irrigation efficiency becomes 85.5% (=0.90×0.95). Then the required reservoir capacity becomes less than 50% to the case of canal conveyance and furrow irrigation; or if we construct the dam in same scale, the command area becomes more than 2 times.

3.2 Estimation of available water quantity (Qa)

There are many methods to estimate the available water quantity expected from the catchment area. Here, two simple methods are shown that are usually used at the basic design level. Nowadays, especially when the project scale is large, the estimation of available water quantity is done based on data of the river discharge measurement.

3.2.1 Specific discharge method

In case data of the discharge measurement on a river that belongs to the same water system are available, the specific discharge qc (m3/sec/km2) at the measurement point can be calculated. Then we can get the discharge at the




reservoir site concerned through multiplying this qc (m3/sec/km2) by the catchment area A (km2) concerned.

Qa (m3/sec) = qc (m3/sec/km2)×A (km2) ・・・・・・・・・・・・・・ (F. 3.1)

This method gives the estimation on safe side because the discharge measurement is usually done at the main river, the reservoir for small scale project is usually planned on a branch river, and specific discharges tend to decrease along with the catchment area increasing.

3.2.2 Run-off coefficient method

This method is applied in case that the suitable discharge record does not exist. The formula is as follows.

Qa = Rcf×Pr×A ・・・・・・・・・・・・・・・・ (F. 3.2)

Here, Qa; total river discharge in the period under consideration (m3/ month or year)

Rcf; run-off coefficient

Pr; total precipitation in the period under consideration (m/month or year)

A; catchment area (m2)

The methodology for estimating the run-off coefficient is described precisely in Part A, Study Guideline on Hydro Metrology, Ministry of Water Resources.

The following table is shown by SCET International, French institution, as the study result in the region of Byumba and Gittarama, Rwanda. This would be useful as a reference considering the similarity in meteorological and geomorphological conditions between Ethiopia and Rwanda.




Table 3.1 Run-off coefficient in the region of Byumba and Gittarama, Rwanda

3.3 Ecological/sociological flow quantity of the river

Conservation of the river environment is understood generally to keep animals and fishes alive after the development. Therefore the investigation of fishes that make their habitat in the downstream river is done as the one to study about “environment conservation”. And the flow quantity of the river corresponding to the water depth required from the view point of the concerned fish being able to habitat is adopted as the river conservancy discharge (Qeco).

As for the sociological flow quantity of the river, drinking water for cattle/goats would become the main, so that it becomes necessary to survey how many cattle/goats are fed on the concerned river water and estimate the required water quantity (Qsoc).

Net available water quantity (Qa-net) shall be defined as the residual of Qa from which Qeco and Qsoc are deducted; “Qa-net=Qa－(Qeco+Qsoc)”. In case of the accumulated Qa-net becoming less than Rc, i.e. “ΣQa-net＜Rc”, the irrigation plan shall be reviewed. To review means to reduce the command area, to search for an additional water resource, to change the conveyance method, or to change the on-farm irrigation method.

3.4 H～Q curve of the reservoir

It becomes necessary to grasp the relationship between the water level and the reservoir capacity in order to decide the reservoir crest level according to the required reservoir capacity.




Table 3.2 Accumulated volume of Reservoir (Example)

Differential of contour line

(m)

Area on the contour line

(m2)

Mean Area (m2)

Volume b/w contour line

(m3)

Accumulated Volume

(m3)EL. 100.00 10,000.00 0EL. 102.00 2.00 11,000.00 10,500.00 21,000.00 21,000.00 EL. 104.00 2.00 13,000.00 12,000.00 24,000.00 45,000.00 EL. 106.00 2.00 17,000.00 15,000.00 30,000.00 75,000.00 EL. 108.00 2.00 23,000.00 20,000.00 40,000.00 115,000.00 EL. 110.00 2.00 37,000.00 30,000.00 60,000.00 175,000.00

Contour line

98.00

100.00

102.00

104.00

106.00

108.00

110.00

112.00

0.00 40,000.00 80,000.00 120,000.00 160,000.00 200,000.00

(m)

(m3)

Fig. 3.1 H-Q curve of the Reservoir (Example)

3.5 Sediment

The following formula gives the design sediment volume.

Qds=Qs×A×Y ・・・・・・・・・・・・・・・・ (F. 3.3)

Here, Qds; design sediment volume (m3)

Qs; sediment yield (specific sediment rate, specific degradation) in m3/km2 per year

A; catchment area (km2)

Y; durable years of the reservoir

Although the methodology for estimating the quantity of sediment is described precisely in Part A, Study Guideline on Hydro Metrology, Ministry of Water Resources, the actual value that gives an indication at the time of design is not shown but only the following formula obtained by Bureau of Reclamation, USA, is shown.

Qs =1098A－0.24 ・・・・・・・・・・・・・・・ (F. 3.4)




Here, Qs; sediment yield in m3/km2 per year

A; catchment area in km2

Also other formulas have been presented by researchers.

Gottschalk (USA); D = 260 S－0.1 ・・・・・・・・・・・・・・・・ (F. 3.5)

Here, D: Specific degradation (m3/km²/year)

S: Watershed surface area (km²)

Grésillons (France); D = 700 (P/500)－2.2 S－0.1 ・・・・・・・・・・・・・・ (F. 3.6)

Here, D: Specific degradation (m3/km²/year)

P: Annual rainfall (mm)

S: Watershed surface area (km²)

Puech (West Africa); 50 <D <200 m3/km ²/year

As one of estimation methods applied in Japan, Kira-Yoshida formula is presented below.

qs = aFb・Cc・Yd・Pe・P24f・Qmax g・Rf h・・・・・・・・・・・・・・・ (F. 3.7)

Here, qs; specific sedimentation rate

F; catchment area (km2)

C; total reservoir capacity (103m3)

Y; years elapsed after completion of the reservoir (year)

P; mean annual rainfall (mm)

P24; maximum daily rainfall (average of the maximum daily rainfall in a year) (mm/day)

Qmax; maximum flood discharge (m3/sec)

Rf; mean ups-and-downs in the catchment area (m), average differential between max and minimum in the altitude when dividing the catchment area into 4km×4km meshes




Table 3.3 Coefficient for Kira-Yoshida formula

3.6 Water level rising by flood

3.6.1 Formula for estimating the overflow depth

The overflow depth of flood from the spill way weir is calculated by the following formula.

Qf=C・B・Hd3/2 Hd= {Qf /(C・B)}2/3 ・・・・・・・・・・・・・ (F. 3.8)

Here, Qf; flood discharge volume (m3/sec)

C; overflow coefficient of the weir (m1/2/s)

B; length of the weir (m)

Hd; overflow depth (m)

P; Depth of approach channel (m)

In small dams’ case in Japan, the overflow depths adopted range from 0.3m to 1.2m.

Fig. 3.2 Overflow coefficient of the weir

1

n

4;n=1

3;n=0.67

1;n=0 2;n=0.33

Hd

P/Hd

Total reservoir capacity

Coefficient




3.6.2 Flood discharge estimation

Although the methodology for estimating the flood discharge is described precisely in Part A, Study Guideline on Hydro Metrology, Ministry of Water Resources, the actual case is not shown so that the universally popular method called “rational method” would be introduced below.

[Rational method]

For small watersheds, the universally used method is the rational method. This method consists in calculating the peak flow basing on the rainfall intensity, the watershed surface area and Runoff coefficient. It is presented as follows:

6.3/),()( TtiACTQ cp ××= ・・・・・・・・・・・・・ (F. 3.9)

With:

Qp: Flow rate, expressed in terms m3/s,

C: Runoff coefficient,

i: Maximum rain intensity, expressed in terms of mm/h,

A: Watershed area expressed in terms of km²,

The concentration time is determined by the Kirpich formula used for small watersheds. The formula is expressed as follows:

= 38.0

15.1

521

HLtc ・・・・・・・・・・・（F. 3.10）

With:

tc: Concentration time, expressed in terms of min,

L : the distance in meters between the outlet and the farthest point of the basin.

H: The meter descent between the outlet and the farthest point of the basin, expressed in m.

The value of flood Runoff coefficient (C) varies considerably between 0.2 and 0.9, it depends on the slope of the basin, soil and on the land use. In general, the following values are adopted:




Table 3.4 C value of Nature of the plant cover

Nature of the plant cover

C value

Slope Less

than 5%

Slope from 5 to 10%

Slope from 10 to 30%

Slope more than 30%

Platform and road pavement. 0.90 0.90 0.90 0.90

Bare ground, or with non-covering vegetation.

Ground attacked by erosion. 0.80 0.85 0.90 0.90

Small bush. Covering crop, cereals.

0.65 0.70 0.75 0.80

Grassland. Dense bush, savannah.

0.30 0.35 0.45 0.50

Regular forest with tall trees. 0.20 0.25 0.30 0.45

Large primary forest. 0.18 0.20 0.25 0.30

3.6.3 Two philosophies to the estimation of water level rising by flood

There are two philosophies to the estimation of water level rising by flood. One is to consider the design flood to reach the spillway weir at once. The other is to consider the discharge from the spillway weir during the process of water level rising, i.e. considering the storage function of the reservoir to the flood discharge. In the former case, the design scale of spillway becomes large, but the discharge capacity has a margin so that the spillway can stand against almost any kind of unexpected situations. In the latter case, the design scale of spillway becomes small, so that the construction cost can be reduced but the discharge capacity has little margin; and in the most serious case overtopping from the embankment crest might occur. In Japan’s case, considering the storage function of the reservoir is only allowed to the case that the area of full water surface of the reservoir is larger than 1/30 to the catchment area.

The process of considering the storage function of the reservoir is shown as follows.

)()( tQtQdt

dVSe

s −=




With:

Vs: the volume of the reservoir At time t, estimated from H～Q curve

Qe(t): the inflow At time t, estimated from the hydrograph

Qs(t): the outflow At time t, estimated by the formula Qf = C・B・Hd3/2

∫∫∆+

∆

∆+

∆−=

tj

tj se

tj

tj s dttQtQdV)1()1(

))()(((

Therefore, the integration of the continuity equation between two times j t and (j+1) t is:

Yet:

tjQjQdttQ

tjQjQdttQ

VsVsdVs

sstj

tj s

eetj

tj e

jjtj

tj

∆++

=

∆++

=

−=

∫

∫

∫

∆+

∆

∆+

∆

+∆+

∆

2)1()()(

2)1()()(

)1(

)1(

)()1()1(

Assuming that:

The equation becomes:

)1()()()(2)( +++

−∆

= jjjj QeQeQsVst

zf ・・・・・・・・・・・・・ (F. 3.11)

The calculation is done by computer. The calculation procedure is shown on Annex 1.




3.7 Freeboard and the crest setting of reservoirs

Fig. 3.3 Cross-section of Dam and its parameters

H; dam height

B; dam crest width

HWL; high water level (the maximum water level at the time of the design flood overflowing the spillway weir)

FWL; full water level (the maximum water level at the time of daily storage behavior)

H1; water depth at the time of FWL

H2; water depth at the time of HWL

h1; overflow depth at the time of the design flood overflowing the spillway weir

h2; margin height of the reservoir crest to HWL

h2 is given as follows.

In case of R≦1.0m h2=0.05 H2+1.0 ・・・・・・・・・・・ (F. 3.12)

or h2=1.0 ( only to the case of H being lower than 5m, by judging the damage level at the time of failure)

In case of R＞1.0m h2=0.05 H2+R ・・・・・・・・・・・・・ (F. 3.13)

Here, R is the wave height that includes the height of wave swash on the slope, and estimated by the following diagram.

Foundation

Filter

Toe drain




Fig. 3.4 Wave and swash height (R)

Fig. 3.5 How to measure wind current distance (F)

Slope inclination

Smooth slope

Ripraped slope

R ; W

ave

and

swas

h he

ight

(m)

Full line; V=20m/sec Dotted line; V=30m/sec V; average wind velocity

F ; wind current distance on the reservoir (m)

F is adopted, not F’ or F’’

Wind direction




The crest setting is done in the H～Q diagram.

Fig. 3.6 H-Q diagram (Example)

Total reservoir capacity

Design sediment volume Qsd Effective capacity Rc

FWL HWL

Design sediment level

h2 h1

Reservoir crest




4. Design of reservoirs

4.1 Countermeasures to leakage

4.1.1 Embankment Type

In this case leakage occurs through all the surfaces that face the stored water, so that an appropriate treatment or materials in order to give imperviousness to the surfaces must be provided.

The most ideal case is to construct the impervious embankment on the impervious ground. Even in this case, it is better to scrape the ground surface and carry out the re-compaction to the scraped layer together with conducting spraying.

Fig. 4.1 Scrapping & re-compaction on the ground surface

In case of the impervious materials being not enough and the foundation ground being not impervious, the impervious earth blanket would be provided to the surface of the embankment and the ground.

Fig. 4.2 Impervious earth blanket on the surface of the embankment and the ground

In case that the impervious materials do not exist around the project site, construction methods using artificial materials such as the concrete lining, the asphalt lining, the soil cement lining and the rubber sheet lining are applied. In these all cases, more or less the leakage stopper is a thin film, so that it is the problem how to treat the water pressure that functions from behind or from under the sheet at the time of the reservoir becoming empty. It is usual that the drain system is provided under/behind the sheet in the asphalt lining’s case, etc. and air release pipes also in the rubber sheet lining’s case.

Scraping & re-compaction

Impervious earth blanket




Fig. 4.3 Countermeasure example to air and gas

Fig. 4.4 Example of drain works at the slope toe


If the geological and hydrogeological conditions are good and allows constructing the reservoir without any countermeasures against leakage, this type becomes most economical. The following figures are this example which has any countermeasures against leakage even though the reservoir scale is large. Drawing the potential counter lines is significant to grasp the hydrogeological condition of the reservoir.

Drain pipe

Air release pipe (φ25~50)

Sheet

Aggregate for concrete 40~50mm

Filter sheet

VP φ≧75mm

L≧30cm

L≧30cm




Fig. 4.5 Pattern diagram of geological conditions in Koshunai Regulation Pond

Fig. 4.6 Potential counter lines in Koshunai Regulation Pond

But when the geological and hydrogeological conditions are not preferable, it becomes difficult to construct this type of reservoir. It is not able to provide the foundation with a drain system because to be the excavated type makes it

Sand type is also impervious 25m deep below the surface.

25m

ｋ≦1×10－5cm/s ｋ≦1×10－5cm/s

Legend: silt type sand type

2

i=0.06

i=0.12

i=0.02

i=0.10

Flow-in side EL.30

EL.32

EL.34

EL.28

EL.26

EL.27.5

EL.24 EL.24

EL.26 EL.28 EL.30

EL.32

０ｍ 100m

FWL=WL.27.5

Flow-in side

Flow-out side

FWL=WL.27.5




difficult to take out water from the drain system. Therefore, the only applicable method to avoid the leakage is the impervious earth blanket that can stand the back/water pressure by its own weight; other artificial sheet methods are not applicable except the case of the ground water level being deep enough and leakage water never making the ground water level rise up.


This type has no limitation in terms of taking out water from the drain system, so that all the kinds of construction methods as countermeasures against leakage are applicable. It is important to grasp the hydrogeological conditions and design the countermeasure works against leakage adequately in order to save the construction cost.

4.1.4 Dam

(1) Restriction and the blanket works method

There are many countermeasure works to leakage through the foundation. Worldwide the most common countermeasure works, especially in large dams’ cases, are the grouting method by which an impervious curtain is formed in the foundation through the processes of borehole drillings and pumping cement milk into cracks existing in foundation rocks (refer to Fig. 4 .7).

Fig. 4.7 Typical Cross-section of Namioka Dam, Japan

But the grouting method usually requires high construction cost that sometimes reaches 30 % of the total construction cost so that in the micro-dams in Ethiopia the application of this method is not generally considered. Then the blanket works method is the only way left as the countermeasure works against the seepage through foundation. The

Dam crest EL.162.40

Core foundation EL.110.00 Main curtain L=32,000

Assisting curtain L=6,000




Makubetu Dam’s cross-section is shown as Fig. 4.10 as a design example of the blanket works method. Generally the seepage phenomenon through the dam foundation is estimated by the Darcy’s formula,

Q=k・i・A ・・・・・・・・・・・・・ (F. 4.1)

Here, Q; seepage quantity (m3/sec)

k; permeability coefficient (m/sec)

i; hydraulic gradient

A; cross-sectional area of seepage flow passing (m2)

It would be said that the grouting method is the way to decrease Q by making k small, and the blanket works method is the way to decrease Q by giving a long seepage path length and making i small. The design method of blanket works is shown below. The calculation example is shown on Annex 2.

・・・・・ (F. 4.2)

Fig. 4.8 Cross-section of Natural Blanket & Artificial Blanket

Here, qf; seepage quantity through the foundation layer (m3/sec)

h; differential between the reservoir water level and the downstream water level (m)

Artificial Blanket

Pervious foundation (k)

Impervious foundation

Blanket

Natural Blanket

Hydraulic gradient in the foundation

Head loss by the blanket




xr; effective seepage length (m)

xd; bottom length of the dam body (m)

x; required length of the blanket (m)

k; permeability coefficient of the foundation layer (m/sec)

k1; permeability coefficient of the blanket and the dam body (m/sec)

t; thickness of the blanket (m)

d; thickness of the foundation layer (m)

The representative thickness of the blanket is 10 % of the water pressure working on the blanket surface. In most cases, thickness of 1m to 3m is applied; and it is effective to make the blanket thicker together with the position becoming closer to the dam body.

There are two ways to decide the blanket length x. One is to decide the allowable leakage quantity qf at first, then xr, and then decide x. (As the allowable leakage quantity, quantity of 0.05 % of the total reservoir capacity is adopted empirically in Japan.) The other method is to find out a bending point on the qf～x relation curve and adopt this x corresponding to the bending point through trial calculations.

In addition, the abutment slopes also must be covered by blanket works. Fig. 4.11 is this example.

(2) Ground water in the abutment slopes and the seepage phenomena in the foundation

Generally ground water flows down in the abutment slopes toward the river at both banks; and it is usual that spring-out mouths exist around the water surface in the river. If these mouths are pressed and closed by the impervious dam body, what happens? The ground water table in the abutment slopes would rise up, nevertheless the ground water would keep slowing down toward the valley bottom, and the ground water from the both banks collide at the valley bottom. The water that has collided would push up the bottom surface of the dam body and flow toward the open space, i.e. toward the upstream side and the downstream side. The flow potential condition along the bottom of the dam body at this moment would be understood as follows.




Fig. 4.9 Ground water in the abutment slopes and Flow potential condition along the bottom of the dam body




Ph

oto

4.1

Tarb

ela

Dam

Fig.

4.1

0 Ty

pica

l Cro

ss-s

ecti

on o

f Mak

ube

tu D

am, J

apan

(Hom

ogen

eou

s D

am w

ith

Ear

th B

lan

ket)

from

dam

axi

s

Ups

trea

m b

lank

et

Coffe

r da

m

Impe

rvio

us m

at.

Back

fil

Blan

ket

Impe

rvio

us m

at.

Prot

ectio

n

Impe

rvio

us cr

est

Dam

cre

st E

L 81

.40

Low

est E

L.54

.50

Dra

in

The

larg

est

fill t

ype

dam

wit

h t

he

incl

ined

cor

e zo

ne

and

the

hor

izon

tal

eart

h b

lan

ket.

Th

is d

am is

con

stru

cted

on

the

san

d an

d gr

avel

laye

r on

th

e In

das

rive

r; th

e le

ngt

h o

f ear

th b

lan

ket i

s 2

km. T

he

grou

tin

g as

the

fou

nda

tion

tre

atm

ent

is n

ot p

rovi

ded.




In case of this potential arising under the dam body being equal or larger than the seepage potential coming from the stored water, the leakage of stored water does not occur. Therefore, it is able to construct a dam without leakage through its foundation even on a pervious foundation layer if ground water table is high enough; and as the irrigation purpose micro-dam that has no foundation treatment such as grouting works, the dam type must be homogeneous that can press the ground water widely by its impervious dam body. The seepage potential behavior between the ground water and the seepage water from the upstream during the water storing test in Makubetu Dam is shown in Fig. 4.13, 4.14, 4.15. The potential of ground water resists against the seepage potential from the upstream.

Intake

Fig. 4.11 Plain Plan of Makubetu Dam

C L Dam Dam axis

Discharge gate

Spillway

Blanket works

Leakage gauge

Regulation tank Irrigation gate

N Location

0 50m




Fig. 4.12 Potential of Ground water and Seepage potential

Fig. 4.13 Potential condition on the foundation surface（beginning of test・18/3/2003）

④almost no stream

③appearance of dense counter lines

①rising of piezometric head

②extrusion of piezometric head

Seepage potential




Fig. 4.14 Potential condition on the foundation surface （at middle water level ; WL.71.00m・27/5/2003）

⑥small rising of water table

⑤denser the counter line becomes

①water head from the reservoir predominates

65

60

55

70 69

69

②retreat of the extrusion

④appearance of confronting condition

③water head rising




④density of counter lines does not proceed so much

⑤small rising of water table

②head rising

③head rising on foundation

➀small head rising, but confronting condition continues

Fig. 4.15 Potential condition on the foundation surface （at full water level ; WL.76.90m・31/8/2004）




(3) Seepage through the dam body and the residual pore pressure caused by compaction

Once, the pore pressure was recognized to be harmful for the safety of dam body against the sliding failure. This is because the pore pressure reduces the friction resistance by decreasing the effective normal load. This mechanism can be explained by the following formula that defines the safety factor against sliding failure.

・・・・・・・・・・・・・ (F. 4.3)

Here, the friction resistance term is (N－U－Ne) tanφ’, and the portion “(N－U－Ne)” would be called “effective normal load”. Here the pore pressure U functions to reduce this effective normal load by working as a minus factor. In addition, Ne is the normal direction inertia force caused by an earthquake.

And actually in Japan, several sliding failures happened on dam bodies that had had low embankment densities and high moisture content. The horizontal drains inserted in the dam body shown in Fig. 4.7 are to resolve the high pore pressure.

But nowadays when materials are compacted densely under the nearly optimum moisture content condition, such failures have not been happening. In tropical countries, the soils’ moisture contents are usually low so that moisture content adjustment works must be carried out. Therefore, the soils are compacted under the nearly optimum moisture content condition as a result, and such kind of failure caused by high pore pressure also would not happen. On the contrary, the function that the residual pore pressure resists against the seepage flow infiltrating into the dam body begins to attract the attention. In Makubetu Dam’s case (refer to Fig. 4.17), the seepage line reaching the filter zone was not formed during the water storing test. Considering this case and similar phenomena in other dams provided with wide impervious zone, the leakage from dam body would not occur for a considerably long period if the dam body is designed to be a homogeneous type fill dam. In zoned type fill dams provided with a center core, the seepage line reaching the filter zone seems to be formed according to the result of Kyowa Dam’s water storing test (refer to Fig. 4.18, Fig. 4.19).

Also from view point of leakage through the dam body, the dam type of the irrigation purpose micro-dams should be the homogeneous type. But the




embankment must be compacted densely under nearly optimum moisture content conditions. In case of the embankment having low density and the moisture content being too dry, longitudinal cracks on the dam crest might appear. Low density and too dry moisture content condition cause a large settlement together with the saturated region proceeding from the upstream toe to downstream side and upward. And such settlement causes a torque to the dam crest.

Fig. 4.16 Torque to the dam crest

Saturated region

torque




Fig.

4.1

7 R

esid

ual

por

e pr

essu

re p

oten

tial

an

d se

epag

e in

filtr

atio

n Be

ginn

ing

of th

e w

ater

sto

ring

test

(18/

3/20

03)

At m

iddl

e w

ater

leve

l; W

L.71

.00

(27/

5/20

03)

At fu

ll w

ater

leve

l; W

L.76

.90

(31/

8/20

04)

Satu

rate

d re

gion

Appe

aran

ce o

f con

fron

ting

cond

ition

Dee

p in

filtr

atio

n of

EL.

75.0

coun

ter

line

Seep

age

line

alm

ost f

orm

ed

On-

goin

g sa

tura

tion

On-

goin

g pr

oces

s of

Po

re p

ress

ure

diss

ipat

ion

Wat

er h

ead

from

in t

he r

ight

ab

utm

ent s

lope




At m

iddl

e w

ater

leve

l; W

L.71

.00

(27/

5/20

03)

・Po

re p

ress

ure

incr

ease

d ar

ound

P-3

8 du

e to

see

page

. ・

Pore

pre

ssur

e in

the

upst

ream

dam

bod

y do

es n

ot c

hang

e.

・In

the

dow

nstre

am s

ide,

no

chan

ge.

・Po

re p

ress

ure

incr

ease

d ar

ound

P-3

8, P

-40d

ue to

see

page

. ・

Pore

pre

ssur

e in

the

upst

ream

dam

bod

y do

es n

ot c

hang

e

re

mar

kabl

y.

・In

the

dow

nstre

am s

ide,

por

e pr

essu

re d

ecre

ased

by

50 %

.

At fu

ll w

ater

leve

l; W

L.76

.90

(31/

8/20

04)

Pore

pre

ssur

e lin

e 8.

0 t/m

2 be

com

es th

e eq

uilib

rium

line

Fig.

4.1

7’ P

ore

pres

sure

cou

nte

r lin

e at

th

e w

ater

sto

rage

tes

t Be

ginn

ing

of th

e w

ater

sto

ring

test

(18/

3/20

03)




Satu

rate

d re

gion

pr

ocee

d to

do

wns

trea

m s

ide

and

upw

ard

Pote

ntia

l val

ue

Satu

ratio

n is

not

co

mpl

eted

Po

tent

ial c

ount

er

WL=

EL.8

4.50

(20/

10/1

994)

W

L=EL

.91.

48 (2

7/11

/199

4)

WL=

EL.9

7.02

(27/

12/1

994)

Fig.

4.1

8 R

esid

ual

por

e pr

essu

re a

nd s

eepa

ge in

filtr

atio

n d

uri

ng

the

wat

er s

tori

ng

test

in K

yow

a D

am (1

/2)




WL=

EL.9

9.99

(28/

2/19

95)

WL=

EL.1

10.9

6 (2

0/4/

1995

) W

L=EL

.114

.20

(9/5

/199

5)

Fig.

4.1

9 R

esid

ual

por

e pr

essu

re a

nd s

eepa

ge in

filtr

atio

n d

uri

ng

the

wat

er s

tori

ng

test

in K

yow

a D

am (2

/2)




(4) Toe drain

It is necessary to provide the embankment toe to where the seepage slow concentrates with the toe drain. The representative shape of the toe drain is shown as follows.

Fig. 4.20 Design example of Toe drain

Filter materials must satisfy the following conditions.

1) F15/B85＜5, F15/B15＞5

Here, F15; grain size of the filter material corresponding to the percentage passing 15%

B85; grain size of the material protected by filter corresponding to the percentage passing 85%

B15; grain size of the material protected by filter corresponding to the percentage passing 15%

2) Filter materials must not be cohesive.

Fundamentally filter materials must not contain the fine particles, i.e. Silt and clay, more than 5%.

It is desirable that the grain size distribution curves of filter materials are parallel to the ones of the materials protected by filter.

A; Dry masonry

B; Backfill material C; Filter Zone

Base concrete

Filter zone line in case of seepage through foundation concentrating




Fig. 4.21 Suitable range of filter materials

(5) Safety against piping phenomena

In case that the foundation is composed of soil layers, these layers safety against piping phenomena must be considered on deciding the blanket length. This examination shall be done by the critical hydraulic gradient shown by Terzaghi. Water pressure that works to soil particles is pore pressure only in case of the water having no velocity. In case of the water having velocity, soil particles receive the seepage pressure caused by the hydraulic gradient; and when this hydraulic gradient comes over some limit, the pressure overcomes the resisting force among soil particles and soil particles begin to move. The hydraulic gradient at this moment is called “critical hydraulic gradient”. Terzaghi presented the critical hydraulic gradient ic by the following formula in case of soil particles receiving the upward seepage pressure.

・・・・・・・・・ (F. 4.4)

Perc

enta

ge p

assi

ng %

Grain size mm

Material protected by filter

Suitable range

Here,

Unit weight of water (mmN/cm3), or density of water (g/cm3)

Porosity of soil mass

Void ratio of soil mass

Unit weight of soil mass in water (mmN/cm3)

Density of soil particle (g/cm3)




It is said that the critical hydraulic gradient of non-cohesive fine soils ranges from 0.5 to 0.8. In designing of blanket works, safety factor is added. In Japan’s case, safety factor 3~5 is adopted. For reference’s sake, Makubetu Dam was designed on the safety factor 5.

In case that the foundation is composed by sand and gravel layers including cobbles and boulders, the seepage path length shall be considered following the creep length in designing headworks.

Bligh method

S≧C・ΔH・・・・・・・・・・・・・ (F. 4.5)

Here, S; seepage path length along the bottom surface (S=l1+l2+l3 in the figure below)

C; coefficient decided depending on the conditions/kind of the foundation

ΔH; maximum differential in water level between the upstream and the downstream

Lane method

L≧C’・ΔH・・・・・・・・・・・・・ (F. 4.6)

Here, L; weighted creep length (m)

L=Σlv+1/3Σlh (L=l1+1/3l2+l3 in the figure below)

lv; seepage path length in vertical direction

lh; seepage path length in horizontal direction

C’; coefficient decided depending on the conditions/kind of the foundation

ΔH; maximum differential in water level between the upstream and the downstream

ΔH=H1, or H2 ( larger one is applied in the figure below.)




Fig. 4.22 Calculation Parameter of Creep length

Table 4.1 Coefficient of Foundation

Foundation C C’

Very fine sand or silt 18 8.5

Fine sand 15 7.0

Medium sand ― 6.0

Coarse sand 12 5.0

Fine gravel ― 4.0

Medium gravel ― 3.5

Sand & gravel 9 ―

Coarse gravel including cobbles ― 3.0

Boulders including cobbles & gravels ― 2.5

Boulders, and sand-&-gravel 4~6 ―

Soft clay ― 3.0

Medium soft clay ― 2.0

Highly cohesive clay ― 1.8

Hard clay ― 1.6

(6) Treatment to open cracks on the foundation surface

In case of the foundation surface having open cracks, the treatment must be done following the manners below.

• Dig V shaped ditches about 10 cm deep along the cracks.

• Pour mud milk into the cracks.

• Fill the ditches with filter materials, i.e. crusher-run 0~40mm in most cases, and compact them.




4.2 Slope protection

Slope protection works are needed for the all types of reservoirs only except the cut slope collapse of which is not harmful to other facilities or facilities’ functions in the reservoir. There are several kinds of protection works including artificial ones, but in Ethiopia where rock materials are easily obtained rip-rap works are most popular as the slope protection method. In case that the slope requires also the countermeasures against seepage, some other protection works such as concrete facing works, asphalt facing works and soil cement works shall be considered.

4.2.1 Rip-rap works

The range which is provided with rip-rap works shall be decided considering the frequency of the slope portion being exposed to air and rainfall; in Japan’s case, the range shown below is usually adopted.

Fig. 4.23 Rip-rap works

HWL; high water level (the maximum water level at the time of the design flood overflowing the spillway weir)

FWL; full water level (the maximum water level at the time of daily storage behavior)

H1; water depth at the time of FWL

R ; the wave height that includes the height of wave swash on the slope

4.2.2 Soil cement works

The merit of soil cement works is to be able to function as the slope protection and the countermeasure against seepage and more over to be able to resist

HWL+R

Backfill material

Rip-rap works

Base concrete




against back pressure by its own weight. Followings are the introduction of soil cement.

(1) History of soil cement ・In 1951, at Bonny Dam in Colorado, USA ・A trial embankment with soil cement slope protection ・The trial resulted in success. ・Since then, applied to fill type dams’slope protection ・More than 170 projects in USA and Canada from 1961 to 1978 ・Total volume about 7,000,000 m3. [Fundamental usage policy of soil cement for slope protection works] ・Not eternal, consider the loss caused by aging. Bonny Dam’s example;

Here, T: thickness of the slope protection work 0.018cm: Lost thickness of the specimen corresponding to the volume loss 1%

in the dry and wet repetition test 14%, 12 cycles: evaluated volume loss and cycles based on the test 100 cycles: estimated cycles between dry and wet per year 100 years: durable years of the dam

(2) General circumstances around soil cements in Japan

In Japan today, ‘Soil Cement’ is recognized as one of the key elements of the construction methods for cost reduction or environmental effect reduction. The fundamental policy of cost reduction is to utilize the materials obtained there as the construction materials, and the one of environmental effect reduction is not to produce waste materials, i.e. not to transport waste soils out of the construction site. Applications of soil cement to the structures for disaster prevention in mountain areas or the ones for river facilities are the typical examples of the former; and the adoption of soil cement piles in place of cast-in-place concrete piles in the construction works carried out in town is the typical example of the latter.

cmyearsyearcycles

cyclescmT 210100

1100

12%14

%1018.0

=×××=




(3) Information regarding soil cements

1) Guide line of soil cements

‘Guide line of soil cements for erosion control structures’ was published in 2002. Here, the utilization method of sand-and-gravel mixture materials obtained in the construction site is described. The soft copy of this guide line is saved on the CBID guidelines and manuals CD-R.

2) Research and report paper on the slope protection use of soil cement

Slope protection works by soil cement were constructed on the slope surface of the reservoir in Nagara Dam. The research and report paper was published on the journal, Large Dams, in 1987. The soft copy of this paper is saved on the CBID guidelines and manuals CD-R.

3) Research paper on the small scale slope protection by soil cement

The study result on the small scale slope protection by soil cement to the farming road/land was found on the inter-net. The soft copy of this paper is saved on the CBID guidelines and manuals CD-R.

(4) Quality of soil cement

1) Quality criteria

Table 4.2 Quality of soil cement for slope protection use




2) Laboratory test in Bangladesh

Table 4.3 Unconfined compression test

Case Case-1 Case-2 Case-3

Ratio Cement 40kg：soil 1m3 Cement 80kg：soil 1m3 Cement 120kg：soil 1m3

cement 807 g 1,614 g 2,421 g

Soil 22,831 g 22,831 g 22,831 g

Case Case-1 Case-2 Case-3

Compaction type qu=409.8 kN/m2 qu=1024.1 kN/m2 qu=2360.3 kN/m2

Paste type qu=102.3 kN/m2 qu=322.0 kN/m2 qu=498.5 kN/m2

Fig. 4.24 Cement quantity – qu relation

Table 4.4 Water jet spraying test for evaluation of scour-resisting ability

Case Specimen Testing time Specimen’s condition Erosion speed

Case-1 Cement mixing ratio 2%

No.1 30 sec Cut into two pieces

6.5 mm/sec No.2 2 min 20 sec Eroded ditch 4.3cm deep




4.5 mm/sec No.2 15 sec Cut into two pieces



No.1 2 min 30 sec Eroded ditch 7.3cm deep

0.5 mm/sec No.2 2 min 10 sec Eroded ditch 7.0cm deep

No.3 2 min Eroded ditch 5.3cm deep



0.3 mm/sec No.2 2 min Eroded ditch 3.0cm deep


Cement quantity～qu relation

0

500

1000

1500

2000

2500

0 20 40 60 80 100 120 140

cement quantity (kg/m3)

qu (kN

/m2)

compaction type

paste type




Fig. 4.25 Cement ratio – erosion speed

Photo 4.2 Water jet spraying test

4.3 Slope inclination

4.3.1 Embankment type

The slope inclination of the reservoir side shall be decided according to the countermeasure works against seepage, but generally speaking the inclination of 1:2.5 would be standard. To the downstream slope, the inclination of 1:2.0 would be standard. In case of the embankment being higher than 10m, careful examinations would be required.

Cement ratio～erosion speed

0

1

2

3

4

5

6

7

0 2 4 6 8 10 12Cement ratio (%)

Ero

sion s

peed (m

m/sec)





In this case also, the slope inclination of the reservoir side shall be decided according to the countermeasure works against seepage, but generally speaking the inclination of 1:2.0 would be standard. In case of the cut slope being left in uncovered condition, the inclination of 1:1.5 would be standard.


In this case, the slope inclination would follow the above cases.

4.3.4 Dam

In micro-dams’ case, a wide embankment bottom is required from view point of the countermeasure against seepage through the foundation, so that pursuing economical efficiency in terms of the slope inclination is not so significant. Empirically speaking, the inclination of 1:3.0 to the upstream slope and 1:2.5 to the downstream slope would be adequate considering the situation that the wide variety of materials would be used without strict laboratory soil tests.

4.4 Reference of the embankment materials

Embankment and foundation of reservoir shall possess required water tightness and strength, and be sufficiently safe against sliding failure or seepage failure. It should be investigated permeability of foundation in the site, and it is necessary to select an appropriate place for reservoir. About the permeability of foundation, the permeable way of thinking of embankment serves as a reference. The embankment materials are described below.

4.4.1 Classification of Materials

Fill materials shall be classified into soil materials and rock materials, and the latter is further classified into sand and gravel, and rock. Soil is employed as an impervious material, and sand, gravel and rock are utilized as semi-pervious or pervious materials. In view of this general concept, a suitable reservoir type shall be selected in accordance with the type and quantity of the materials.

Fill materials include various grain sizes ranging from fine grain to large rock fragments. From a soil mechanical point of view, these materials are classified by grain sizes into soil materials such as clay, sand and gravel, and rock materials, and also are classified into the three categories of impervious,




pervious and semi-pervious materials at design and construction stages according to the permeability of materials after being compacted.

Impervious shall be defined as those materials where the coefficient of permeability after compaction is less than 1 x 10-5 cm/sec, and pervious as those where soil coefficient is more than 1 x 10-3 cm/sec. Semi-pervious are those materials with a coefficient of permeability between the foregoing two.

4.4.2 Applicable Range of Fill Materials

Fig. 4.26 shows the respective ranges of impervious, semi-pervious and pervious zone for the major dams constructed by the U.S. Bureau of Reclamation, and impervious materials to be used for the Swedish method.

These are common world-wide standards, and therefore are helpful in judging the applicable range of fill materials. The overlapped section indicates that in some cases the materials of same grading can be used for impervious zone, semi-pervious and or pervious zone as the case may be; because the applicable range for each type of material depends on not the absolute value of the coefficient of permeability but the relative value vis a vis other materials used, in other words, combinations of materials.

Fig. 4.26 Appropriate grain size for embankment materials




The explanation of Fig. 4.26 is given as follows;

(1) In the range for impervious material, the most susceptible area to cracking in a dry state after compaction is the 1/3 portion on the fine grain side. According to the results of study for 17 dams carried out by USBR, inorganic clay of low and medium plasticity (Ip<15) is the most dangerous material with regards to cracking as compared with other graded materials.

(2) As an impervious material, the U.S. Corps of Engineers and a French electric company have had successful experience in using coarse grade material which partly deviates from the impervious material range defined by USBR.

Impervious material for which the content of fine grade material of less than 4.76mm is under 40% has been .introduced at more than 10 sites such as Makio dam in Japan, Serre Ponsom dam in France, Hills Greek dam in USA, etc. But attention should be paid to the fact that impermeability is not easily obtainable when the content of fine grade material of less than 0.074mm is under 7%. From this point of view, the USBR standard is judged to be practical.

(3) Out of 65 homogeneous dams in the western part of the USA, 14 dams where slip occurred have been studied to analyze grading of materials. Results indicated that D50 was less than 0.06mm for each dam. Plotted on the grading curve, this corresponds to finer grade than the upper 1/3 of the impervious range defined by the USBR. The upper limit line for the impervious range can thus be considered the boundary for whether or not sliding occurs.

(4) Grain size distribution and quality of fill materials range widely, and grading curves thereof show various patterns. With regard to pervious materials, the type of grain size distribution is closely related to the quality of materials. Grain size distribution is classified into the following three types;

Type I: The maximum grain size is large, with almost no fine particle content. Uniformity coefficient (Uc) is small:




In other words a sharp rise is seen towards the coarse side in Fig. 4.26.

Type II: Various grain sizes are included from large to small, showing good grain size distribution with large uniformity coefficient.

Type III: Good grain size distribution with large uniformity coefficient, but the maximum grain size is small. Large amount of fine particle is included. Grading curve for the material of this type runs parallel to the curve of Type II toward the fine grain side.

Type I is very hard and well-drained with large shearing strength; however, it is characterized by large void ratio and also large compression settlement due to the contact point fracture. Type II is relatively hard material, characterized by large compaction effect and large shearing strength. It is also well drained as the fine particles are contained in proportionately small amount, resulting in small compression settlement. Type III is easily fractured as compared with Type I and II, and characterized by small shearing strength. The drainability for Type III depends on the content of fine particles. If compaction is satisfactorily carried out, compression settlement is limited.




Embankment construction

Embankment

Table 4.5 Characteristics of fill materials and suitability for Embankment construction




Tabl

e 4.

6




(Reference)

Fig. 4.27




Table 4.7 Suitable rock for rock materials

Fig. 4.27




4.4.3 General Property of Fill Material

If reservoir type is designed so as to make good use of quantity and properties of fill material in a reasonable way, almost all kinds of soil, gravel and rock can be used for construction. Therefore, taking into consideration factors of economy and reservoir function, it is desirable to use excavated materials derived from spillway, foundation and diversion tunnel construction, or improved natural materials to the extent possible.

Standard classification of soil, sand and gravel, and properties and adaptability thereof are shown in Table 4.5 and Table 4.6. The suitable rocks for rock materials are given in Table 4.7.

4.4.4 Random Material

Random materials are not precisely defined because properties of constituent materials vary greatly. They collectively refer to materials which are susceptible to alternations of properties due to weathering and other causes.

Random materials should not be used as banking materials of important sections of dam body since the homogeneity of materials is not reliable.

4.4.5 Soft Rocks or Gravel

Most igneous rocks and metamorphic rocks can be used as banking materials for rockfill sections. On the other hand, most sedimentary rocks, including tuff, soft sand stone, shale and mudstone, are vulnerable to weathering and properties such as a weight, hardness, strength and Durability might be altered after the construction of dam body.

Although utilization of these materials should be determined based on detailed material tests, they have been successfully used as random materials for the banking of less important sections of the dam body in recent years. The same holds true for gravel which is considered to have intermediate properties between rock and soil.

Soft rocks could be used as fill materials in the following three occasions, when;

• used as random materials at sections where no changes in air and moisture are expected (such as sections located lower than the low water level at the upstream side),




• used in a similar manner as soil after crushing, and

• Used after mixing with suitable materials gathered at other borrow areas.

In any event, such materials are to be used for banking of less important dam sections. Needless to say, slaking and crushing tests should be carried out. In addition, various tests relating to actual construction works should be conducted, including potential for excavation by ripper blade, results of blasting and degree of crush by roller compaction (including sheep's-foot type roller).

Although laboratory testing of soft rocks is not yet standardized, various tests should be conducted in order to clarify mechanical and chemical properties and to evaluate suitability for fill materials.

Tests usually employed for concrete aggregate test are included such as compressive strength test, water absorption test, impact test, Los Angeles rattler test and slaking test (freezing and thawing test, sodium sulphate method, wetting and drying test). In addition, chemical properties and reactions to mild effects such as direct solar radiation are to be examined.

4.4.6 Mixing of Materials

Improvement of textures of soil materials through mixing is occasionally practiced in order to obtain better fill materials. At a borrow area where materials of different textures are stratified, they can be mixed easily by an excavator. In order to mix materials gathered at different borrow areas, the stockyard method is applicable. In this case, however, a stockyard must be provided and the cost of materials becomes rather expensive.

Nevertheless there are cases where large scale mixing has been conducted using stock yard, mixing plant or harrow method.

4.4.7 Removal of Large Material

In general, maximum allowable diameter of material for fill materials is to be a little less than the thickness after compaction of the subject layer. In case of impervious sections, such diameter is 10 to 15 cm if a sheep's-foot roller is used and a slightly larger if a pneumatic tired roller is employed. In random and pervious sections, maximum diameter of 60 to 100 cm is permissible.




When the number of large gravels is limited, they can be removed by hand or by rake. If the content of large gravels exceeds 20 to 40%, the erection of a screen plant is more advantageous. In case of materials which contain extremely different sizes of components, from silt and sand to large gravel, a comparative study should be made of such cases as utilization of material as impervious materials or random materials without screening, or utilization of the same following screening into pervious materials and impervious materials.

4.4.8 Riprap Material

Riprap works for upstream slope protection are almost always required. The cost of the works sometimes accounts for 5 to 10% or more of the embankment cost. Therefore, due consideration to the works is necessary in design of the dam body. If the thickness of riprap works is increased, various materials available at the site such as muck obtained by the excavation of the diversion tunnel, and boulder and talus materials could be utilized, even if they may not be totally ideal in terms of wave resistivity, size and other properties. Procurement of required volume is to be carefully planned.




5. Hydraulic designs of the spillways

5.1 Formation of the spillway

Fig. 5.1 Formation of spillway

5.2 Selection of the spillway type

When classifying roughly, there are three types in spillways. From these types,

the adequate one shall be chosen considering economical efficiency, safety,

site conditions, etc. The characteristics of these are as shown on Table 5.1.

Overflow weir

Chute channel

Ground slope

Stilling basin

Downstream slope

Dam axis

Damcrest

Reservoir

Approaching channel

Adjustment section

Transitionsection Chute section

Energy dissipater

Subcritical flow

Critical flow Supercritical flow Hydraulic jump

Subcriticalflow




Fig. 5.2 Spillway Type

Table 5.1 characteristics of spillway types

Spillway

type

Flow condition Capacity to floods, etc.

Adjustment

section Transition section

Discharge

capacity to floods

Foundation of

the structure

Channel

flow-in type From the front

Unsteady flow

condition Very small

Ground or

embankment

Front weir

type

From the front

over the weir Flow down in the

channel in the

critical flow

condition

Small to medium Ground or

embankment

Side weir

type

From the side

over the weir Medium to large Ground

Front weir type

Side weir type Channel flow-in type




In terms of the plane view of the overflow weir, many shapes have been being

adopted according to the topographical site conditions as shown below.

Fig. 5.3 Type of Overflow Weir

Approaching channel

Adjustment by gate

Chute section

a. Chute type b. Standard curve type c. Curve type

d. Standard side weir type

e. T shaped side weir type f. Y shaped side weir type

g. On-counter side weir type h. Double side-weirs type i. Bath-tab shaped weir type

Weir crest

Weir crest

Weir crest

Weir crest

Weir crest

Weir crest Weir crest

Weir crest

Intake tower

Tunnel

Bridge

Wall

Channel with side inflow




5.3 Hydraulic design of spillways

5.3.1 Approaching channel

Fig. 5.4 Approaching channel

Flow velocity in the approaching channel (m/sec)

Flow area in the approaching channel (m2)

Water depth in the approaching channel (m)

Design flood discharge (m3/sec)

Width in the approaching channel (m)

Design overflow water head at the weir top including velocity head (m)

Weir height (m)

Gravitational acceleration (=9.8 m/sec2)

・・・・・・・・・・・・・・(F. 5.1)

Approaching channel

The flow velocity in the approaching channel is generally to be less than

4m/sec.

The width of the approaching channel shall be narrowed gently and

decreasingly to avoid turbulence of the flow condition.

The weir height must be at least more than 20% of the overflow water

head (including the velocity head) at the weir top.

The slope around the mouth of approaching channel must be protected

not to be scoured or collapse at the time of flood flowing in.




5.3.2 Adjustment section

The plane shape of the adjustment section should be as linear as possible.

The sectional shape should be as efficient as possible as a discharge

channel.

The minimum overflow depth should be more than 0.4m or so in case of

the reservoir being located in the mountain area and driftwoods or rubbish

being expected to flow in.

The minimum width of the adjustment section should be more than 1.0m;

and this should be more than 2.0m in case of the reservoir being located in

the mountain area and driftwoods or rubbish being expected to flow in.

①� Channel flow-in type

(Rectangular-shaped channel)

Channel width (m); constant width


Flow-in coefficient (bending of side wall is funnel-shaped; C=0.88)

(Bending of side wall is the right angle; C=0.82)

Note) Standard flow-in plane angle is 30°as the funnel-shaped case.

Flow-in angle of the channel bed is the right angle under the condition of Hd/B≦0.6

Funnel-shaped case on plane

; Design water head including velocity head

・・・・・・・・(F. 5.2)

Fig. 5.5 Funnel-shaped case on plane

Fig. 5.6 Channel flow-in type




②� Front weir type and side weir type

Fig. 5.7 Front weir type and side weir type

As overflow weirs, there are several types such as the simple weir type that

consists of “circular weir”, “quarter circular weir”, “sharp-crested weir” and

“broad-crested weir”, and the standard weir type. The simple weir type is easy

to construct but its discharge capacity is low. On the contrary the standard

weir type is not easy to construct but its discharge capacity is high. The

design methods to these weir types are as follows.

(1) Standard weir type

1) Cross-sectional shape of the standard weir type

It is preferable for the cross-sectional shape of the overflow weir to keep a

large coefficient of discharge at the flood event. To fulfill this purpose, the

surface shape of the weir must accord to the lower edge shape of discharged

water flow; and the standard weir type was devised from this point of view.

Effective length of the weir (m)


Coefficient of discharge corresponding to the design flood discharge

(m1/2/sec), also related to the weir shape mentioned later

Design water head including velocity head (m)

・・・・・・・・・・・・・・・・・(F. 5.3)




There are several methods to design the cross-sectional shape of the standard

overflow weir. From among those, we would like to show the design method for

the Harold’s standard overflow weir.

In case of the weir’s upstream surface being vertical and the approaching

velocity being zero, the cross-sectional shape of the weir from its top to the

downstream side is given by the formula F. 5.4.

(a) Cross-sectional shape from its top to downstream side

It is usual for the lower portion to be given the constant inclination 1:(1/0.7)

or so from view point of construction efficiency and the stability of weir body.

The upper point “P” at which the constant inclination begins is given by the

following formula F. 5.5.

(Harold’s curve)・・・・・・・・・・・・・・(F. 5.4)

Vertical distance from the weir top (m)

Horizontal distance from the weir top (m)


・・・・・・・・・・・・・・・・・(F. 5.5)

Downstream side inclination from the point “P” (n=0.7)

x-coordinate value of the point “P”

(b) Cross-sectional shape from its top to upstream side

・・・・・・・・・・・・・・・・・・・(F. 5.6)





2) Discharge coefficient of the standard weir type

The discharge coefficient of the standard weir type is given by the Fig. 5.10

when the drowning phenomena (refer to Fig. 5.9) caused by the influence of

the downstream water level or channel’s bed level do not appear. The

influence of drowning phenomena is negligible when the condition given by

the formula F. 5.7 is satisfied.

Fig. 5.8 Cross-sectional weir shape given by Harold’s curve

Coordinate original point

Fig. 5.9 Influence of the drowning phenomena

・・・・・・・・・・・・(F. 5.7)


and




1n

4; n=1

3; n=0.67

1; n=02; n=0.33

d

P/Hd

In case the weir is high enough so that the value of (Hd/P) becomes less than

0.75 (refer to (Fig. 5.9) and the flow condition at the downstream side of the

weir becomes the supercritical flow, the discharge coefficient of the standard

weir type can be also calculated by the formula F. 5.8 and F. 5.9. These

formulas are called “Iwasaki’s formula”.

・・・・・・・・・・・・(F. 5.8)

・・・・・・・・・・・・(F. 5.9)


Coefficient of discharge corresponding to the design flood discharge (m1/2/sec)

Length of the weir (m)

Design water head (m)

Height of the weir (m)

Fig. 5.10 Coefficient of discharge of the standard weir type corresponding to the design flood discharge

Japan International Cooperation Agency (JICA) & Oromia Irrigation Development Authority (OIDA) The Project for Capacity Building in Irrigation Development (CBID)

68


These formulas were presented by Iwasaki 1957 as the discharge formula for

the two-dimensional standard overflow weir. He examined the coefficient

value based on the theoretical analysis to the two-dimensional potential flow,

and on the experimental tests.

(2) Simple weir type

1) Cross-sectional weir shape and considerations at the designing

Among the several types of simple weirs, prevalent types are “circular weir”,

“quarter circular weir”, and “sharp-crested weir”. The quarter circular weir

and the sharp-crested weir have a relatively high discharge capacity; the

circular weir has disadvantage in the discharge capacity but has advantage of

being constructed as mass-concrete and of the air-supply not being needed.

The cross-sectional shapes of the circular weir and the quarter circular weir

are as follows. The inclination of the downstream surface of the quarter

circular weir is decided considering the weir’s stability and the air-supply to

behind the discharge water flow.

Fig. 5.11 Cross-sectional shape of the circular/quarter circular weir

A thin iron plate is used to the sharp-crested weir type. The thickness of the

iron plate is decided to be less than 0.25Hd (Hd ; design water head)

Overflow water head from the weir top (m)


Height of the weir (m)

Coefficient of discharge

Coefficient of discharge under the condition of H=Hd

a=C under the condition of H=Hd, i.e. the value of a is calculated by

substituting Cd which is calculated by F. 5.8, into F. 5.9.

Flow Flow

Circular weir Quarter circular weir




considering the stiffness as a plate. The lower portion of the iron plate can be

fixed on to the concrete wall surface; in this case, the protruded height is

considered to be the weir height “P” for calculating the discharge coefficient.

In case of the quarter circular weir type and the sharp-crested weir type,

sometimes noise arises due to the vibration of water flow. As the

countermeasure to this phenomenon, there are two ways. One is to attach an

iron plate with a saw-shaped edge to the downstream edge of the weir (refer to

Fig. 5.12); the other is to supply air to behind the discharge water flow by

setting a non-overflow portion to both ends of the weir (refer to Fig. 5.13). In

the latter’s case, contraction arises at both ends of the weir, and the effective

length “B” of the weir given by the formula F. 5.3 becomes shorten. The

effective length “B” corresponding to this case is calculated by the formula F.

5.10. The upstream wall surface of the non-overflow portion is desirable to be

accorded to the weir’s wall surface (refer to Fig. 5.13)

Plane view

Flow

Non-overflow portion

Weir

Non-overflow portion

Side wall

Plane view Flow Weir

Saw-edged plate

Flow Discharge water flow

Fig. 5.12 Countermeasure to noise by an iron plate with a saw-shaped edge

Saw-edged plate




The influence of detachment of the discharge water flow from the weir surface

is considered in the assessment of the discharge coefficient, so that the flow

conditions in the downstream channel are assumed to be same as in the

standard weir type.

2) Discharge coefficient of the simple weir type

The circular weir is adopted under the conditions that satisfy the formula F.

5.11, the quarter circular weir: the formula F. 5.12 and F. 5.13, and the

sharp-crested weir: the formula F. 5.11 and F. 5.12.

Non-overflow

Weir

Fig. 5.13 One example of the weir with non-overflow

・・・・・・・・・・・・(F. 5.10)

Effective length of the weir (m)

Actual length of the weir except the non-overflow portions (m)

Coefficient of contraction at the non- overflow portion (=0.2)


Total width of the channel including the non-overflow portion (m)

Width of the non-overflow portion (m)

and ・・・・・・・(F. 5.11)

・・・・・・・・・・・・・・・・・・・(F. 5.12)

・・・・・・・・・・・・・・・(F. 5.13)




Under the conditions above, the discharge coefficient of each weir type

becomes as follows.

5.3.3 Transition section

The transition section must be designed to be able to transfer the flood

discharge from the adjustment section to the upper end of the chute section

without arising the afflux or the drop-down phenomena in the adjustment

section, or arising extreme turbulences at the upper end of the chute section

that might reduce the energy absorb function of the stilling basin.

There are two types of the transition section. One is the front flow-in (weir)

type, and the other is the side flow-in (weir) type. The latter type is frequently

applied to a relatively large volume of flood discharge.

(1) Front flow-in type

1) Plane shape

The plane shape of the transition section influences discharge capacity of the

spillway. Too much narrowing of the cross-section or too much curvature of

the channel must be avoided. It is desirable for the plane shape of the

transition section to be symmetrical.

In case of the flow condition being gentle, the narrowing manner of the

channel in the transition section can follow the figure below. This is effective

to make the width narrow in the downstream chute section. But if the channel

flow-in type is applied to the adjustment section, the channel width must not

Weir name

Circular weir

Quarter circular weir

Sharp-crested weir

(Standard weir)

corresponding to R1=Hd~0.5Hd

Table 5.2 Discharge coefficient of simple weir types

P; weir height, Hd; design water head, R1; refer to Fig. 5.11




be changed. If narrowed, the flow-in coefficient C in F. 5.2 reduced

significantly.

2) Hydraulic design for deciding the longitudinal shape

The longitudinal shape of the transition section must be designed so as not to

arise the discharge disturbance at the overflow weir and not to reduce the

energy absorb function of the stilling basin. To satisfy the former condition

means not to make the channel’s longitudinal inclination too gentle; and the

latter requires not making it too steep.

There are usually two cases in the flow condition here. One is the condition of

sub-critical flow at the entrance of this section and critical flow at the exit of

this section; the other is in the critical flow condition both at the entrance and

at the exit of this section. If the channel width is decreasingly narrowed in this

section and the supercritical flow appears, impulse waves or wave-overlap

phenomena might arise along the side wall and affect badly to the function of

stilling basin.

In designing of the transition section, it is necessary to consider the width of

the chute section connected to this section because the channel width of the

chute section influences much to the flow-in Froude number and the flow-in

depth in the stilling basin, and then the length of the stilling basin.

(a) Hydraulic design in case of floods flowing down in the sub-critical flow

condition

The following methods shown as ①, ② and ③ below would be applied in

case of the flood discharge being forced to arise the hydraulic jump at the

Fig. 5.14 Plane shape of the transition section

Adjustment Section

TransitionSection Chute section




downstream of the overflow weir and then being transferred to the next chute

section.

Fig. 5.15 Flow condition in the transition section; sub-critical slow

① Calculate h1 and V1 through trial and error by the formula F. 5.14.

② Calculate h2, l1 and V2 by the following formula. li gives the length of the

constant width channel portion.

・・・・(F. 5.14)

Here Weir height (m)


Water depth at just downstream of the weir (depth before hydraulic jump) (m)

Velocity head at just downstream of the weir (before hydraulic jump) (m)

Differential in elevation between upstream and downstream of the weir

(=channel bed elevation downstream of the weir－ditto upstream of the weir)

Velocity at just downstream of the weir (velocity before hydraulic jump) (m/sec)

Gravitational acceleration ( 9.8m/sec2)


Channel width of the adjustment section (m)

Chute sectionApproaching channel

Adjustment section

Transition section




③ Calculate the bed elevation at the end of transition section (C point in Fig.

5.15) by the formula F. 5.16 assuming the one at the beginning of transition

section (B point in Fig. 5.15) as the base elevation.

hm: Friction head loss (m)

Coefficient of gradual shrinkage (θ in Fig. 5.14 =12°30’; K=0.1)

Water depth at the end of transition section, C point in Fig. 5.15 (m)

(Critical depth)

Channel width at the end of transition section, C point in Fig.5.15 (m)

Flow velocity at the end of transition section, C point in Fig. 5.15 (m)

Bed elevation at C point=

Bed elevation at B point ・・(F.5.16)

Froude number at just downstream of the weir before the hydraulic jump

Length of the hydraulic jump (m)

Flow velocity after the hydraulic jump (B point in Fig. 5.15) (m/sec)

Sub-critical flow depth after the hydraulic jump (B point in Fig. 5.15) (m)

・・・・・・・・・(F. 5.15)

(V1＜1 supercritical flow)




(b) Hydraulic design in case of floods flowing down in the critical flow

condition

It is usual to let floods flow down in the critical flow condition through the

transition section in case that the length from the adjustment section to the

chute section is short.

In this case, the longitudinal shape of the transition section can be decided by

the formula F. 5.16. Specifications of B point and C point calculated by F.

5.16 are replaced to the ones corresponding to A point and B point shown in

the following Fig. 5.16.

(＊ The flow conditions are not stable in the critical flow, so that it is not

desirable to let floods flow down through a long distance. But when the length

of the transition section is considerably short, it becomes economical to let

floods flow down in the critical flow condition.)

Fig. 5.16 Flow down in the critical flow condition

Coefficient of roughness

Energy gradient in the vicinity of the transition section (up & downstream)

Hydraulic radius at B point (m)

Hydraulic radius at C point (m)

Approaching channel

Adjustment section

Transition section chute section




(2) Side flow-in type

Spillways of the side flow-in (weir) type must be designed fundamentally not to

let any portion of the weir crest submerged. And the flow condition in the side

flow-in channel should be stable in order to avoid the excessively lopsided flow,

turbulence and wave, which might influence badly to the energy absorb

function of the stilling basin, at the end of the connecting channel (refer to Fig.

5.17) with a gentle longitudinal gradient.

The flow condition in the side flow-in channel is desirable to be the

sub-critical flow in order to let floods flow down stably and safely; and the

Froude number at the end of this connecting channel highly affects the stable

flow condition here, so that the design method introduced below is the one

devised basing on this Froude number. In addition, sometimes the side

flow-in channel itself might become the out-let channel to the river.

1) Cross-sectional and longitudinal design of the side flow-in channel

① It is desirable to give the inclination of 1:0.7 to the slope below P point in

Fig. 5.8 in case of the standard weir type being applied. In other case, this

inclination would be arranged according to each weir type and its shape. The

inclination of the side wall surface opposite to the weir is basically

Connecting channel

Crest Control section

Control section

Fig. 5.17 Illustration of the flow conditioning in the side flow-in channel and the connecting channel




perpendicular; but it is allowed to give a suitable inclination considering the

topographical condition of the ground. Experimentally this inclination of the

side wall surface is mostly to be less than or equal to 1:0.5.

② The longitudinal inclination of the channel bed should be less than or

equal to 1/13 (i1≦1/13).

③ The ratio of the water depth (d) to the bed width (B) is desirable to be 0.5

(d/B=0.5) approximately at the end of the side flow-in channel.

④ the Froude number at the end of the side flow-in channel should be less

than 0.5 (Fr＜0.5). Generally it is desirable to be 0.44 or so.

⑤ The water level (Hc) in the side flow-in channel must not be higher than

1/2.5 of the overflow depth (Hd) in the standard weir type.

Fig. 5.18 Water level (Hc) and Overflow depth (Hd)

In case of the other weir type, the water level in the side flow-in channel must

not be over the weir crest.

⑥ The connecting channel should be gentle enough longitudinally so that the

condition shown in ④ can be satisfied.

⑦ The connecting channel is connected to the chute section through the

intermediary of the weir that is placed at the end of the connecting channel.

The necessity of this weir is judged considering the flood discharge level, the

plane shape of the connecting channel, etc.

Flow velocity (m)

Gravitational acceleration (g=9.8m/sec2) Hydraulic depth (m)

Sectional area (m2)

Width of the water surface (m)

Hire

Hd Hc Hc≦1/2.5Hd




⑧ The side wall of the reservoir side at the connection point from the side

flow-in channel to the connecting channel is allowed to be decreasingly

narrowed or suddenly narrowed.

⑨ The formula is shown below (refer to Fig. 5.17).

In case of the other weir types being applied, the inclination (m) of the weir’s

channel side slope and the unit discharge volume per meter (q) would be

estimated according to each weir type. In case of the side wall surface opposite

to the weir being given an inclination, the following formula is applicable as

the channel’s cross-sectional shape is rectangular at the end of the side

flow-in channel (=at the beginning of the connecting channel).

Fr at the end of the channel;

Then

Now, given: m=0.7 (m; inclination of the side slope of the weir), d/B=0.5

Then

Now, given : Fr=0.44~0.5 in F. 5.18, then

On the other hand, the sectional area (A) at its end (Pe) of the side flow-in

channel is given by

The width of the channel bed (Bx) and the elevation of the channel bed (Zx)

(from the one of its end point (Pe)) at a distance of x from its end point (Pe) are

given by the formula F. 5.21.

・・・・・・・・(F. 5.17)

(m・s dimension expression)・・・・・(F. 5.19)

(m・s dimension expression)・・・・・・・・・(F. 5.18)

・・・・・・・・・・・・・・・・・・・・(F. 5.20)




The length of the connecting channel (l ) is given as follows.

The cross-sectional shape of the connecting channel is designed to be

rectangular and its longitudinal inclination should be the uniform flow; then

this inclination is given by the following formula F. 5.23.

Fig. 5.19 Illustration of the side flow-in channel with an inclined side wall

2) Surface pursuit to the discharge in from the connecting channel to the

side flow-in channel

Plane view Cross-section

Flow

Flow

Unit flow quantity (m3/m)

・・・・・・・・・・・・(F. 5.23)


・・・・・・・・・・・(F. 5.21)

Width of the channel bed at its end (Pe point)

Usually =0.5, B’; bed width at its upstream end

Distance upstream-ward from its end (Pe point)

Total length of the side flow-in channel (=B in F. 5.3)

Longitudinal inclination of the side slow-in channel (≦1/13)

・・・・・・・・・・・・・・・・・・・・(F. 5.22)

Water depth at the end of the side flow-in channel (Pe)




(a) Surface pursuit to the discharge in the connecting channel

The calculation of surface pursuit to the discharge is carried out

upstream-ward from the control section at the channel’s downstream end by

applying the non-uniform flow analysis, the calculation method of which is

the sequential calculation for example, based on the Bernoulli theorem.

This surface pursuit calculation shall be continued until obtaining the Froude

number Fr at the upstream end of the connecting channel (=downstream end

of the side flow-in channel) that satisfies the required condition shown as ④

in the previous section 1).

In case that the length of the connecting channel is short due to the site

topographical conditions, the Froude number at its upstream end becomes

large; and then, it is required to make the longitudinal inclination of the

channel bed (i2) gentler or to place a overflow weir at the downstream end of

this channel in order to satisfy the conditions shown as ⑥ and ⑦ in the

previous section 1).

As for the weir at its downstream end, it must be provided in order to rectify

the spiral flow in case of the length of the connecting channel being

excessively short. On the other hand, when the length of the connecting

channel is long enough, it becomes easy to satisfy the Froude number

condition at its upstream end required as ④ in the previous section 1).

Therefore, to satisfy the condition ⑦ in the previous section 1) is not

necessarily required in case that not to place the weir is more economical than

to place the weir. In case of the weir being not placed, the calculation is

carried out assuming that the control section arises at the downstream end of

the channel.

(b) Surface pursuit to the discharge in the side flow-in channel

The surface pursuit calculation is carried out by the following equation of

motion F. 5.24 (refer to Fig. 5.20)

・・・・・・・・・・(F. 5.24)




Fig. 5.20 Illustration of surface pursuit to discharge in the side flow-in channel

The calculation is performed from downstream to upstream starting at the

downstream end of the side flow-in channel; Δh is obtained by F. 5.24, then

next the ascent of water level at the upstream side by Δx can be calculated.

In this manner, the ascent of water level, i.e. the elevation of water surface can

be calculated to the upstream end of the side flow-in channel; and through

trial and error calculations in terms of B, L, i1, etc., the channel bed elevation

and the longitudinal inclination i1 is decided so as to satisfy the thorough

overflow condition (⑤, 1)).

5.3.4 Chute section

The function of chute section is to let flood discharge flow down smoothly.

The cross-sectional shape of the channel is fundamentally rectangular.

The plane shape is desirable to be linear; in case of its shape being bended

inevitably, the degree of curvature should be as less as possible.

Flow quantity at the downstream cross-section (a1) (m3/sec)

Flow quantity at the upstream cross-section (a2) (m3/sec)

Mean flow velocity at the downstream cross-section (a1) (m/sec)

Here, Ascent of water level through the section

Mean flow velocity at the upstream cross-section (a1) (m/sec)

Flow quantity per unit width (=overflow quantity per unit width (m3・s-1・m-1))

Gravitational acceleration (=9.8 m/s2)




In case of a curvature being inserted in its plane shape, impulse wave shall

arise at the curvature portion. This impulse wave might arise the overtopping

or affect the energy absorb function of the stilling basin, so that even if to inset

a curvature is inevitable due to the topographical or social conditions, its

degree should be as less as possible.

In the chute section, the surface pursuit calculation, which is based on the

formula F. 5.25, is carried out from upstream to downstream starting at the

control section at the upstream end of the channel (refer to Fig. 5.21). The side

wall height is decided basing on this calculation result and considering the

margin to the supercritical flow flowing down.

Fig. 5.21 Illustration of surface pursuit to discharge in the chute section

Transition section Chute section

Energy absorb works

Sectional length

Length of chute section

Here, Water depth at the upstream cross-section (A) (m)

・・・・・・・・・・・・・・・・・(F. 5.25)

Water depth at the downstream cross-section (B) (m)

Flow velocity at the downstream cross-section (B) (m/s)

Differential of channel bed elevation between (A) and (B) (m)

Friction head loss between (A) and (B) (m)

Flow velocity at the upstream cross-section (A) (m/s)




5.3.5 Energy dissipater

The energy dissipater is provided to protect the dam body, the downstream

discharge channel, etc. from being damaged by the supercritical flow that

comes from the chute section with high kinetic energy.

The design flood discharge shall be accorded with the flood discharge of

1/50 probability.

The design flood discharge shall be accorded with the flood discharge of 1/50

probability; but the energy dissipater is to be designed not to damage the dam

body under the flood discharge of 1/100 probability. Therefore, the side wall

height and the margin height are desirable to be estimated to the flood

discharge of 1/100 probability.

It is often that the water depth at the downstream is not enough for absorbing

energy of flood discharge from the chute section. In such case, it is possible to

obtain the necessary water depth by an afflux through narrowing the

downstream channel width gradually or placing the end-sill, or by letting the

bed elevation down through excavating the ground.

The downstream discharge channel is often narrow compared with the width

of the energy dissipater, so that the connecting portion must be protected by

gabions for example.

Coefficient of roughness Hydraulic radius at (A) (m)

Hydraulic radius at (B) (m) Distance between (a) and (B) (m)




(1) Type of energy dissipater

Table 5.3 Type of energy dissipater

Type Method of energy dissipation Applicability/condition

Hydraulic jump

type

dissipate through the hydraulic

jump phenomena

Existence of a water table

at the downstream

Most popular

Collision type dissipate through the collision of

the flood flow to the baffle walls

and the consequent destabilizing

effect

Applicable to especially

high kinetic energy of the

flood discharge

Drop-work type dissipate through letting the flow

drop and the consequent

destabilizing effect

Necessity of dropping due

to topographical

conditions

(2) Energy dissipater of hydraulic jump type

There are many types in this category. We would like to introduce the ones

suitable to small scale reservoirs.

Table 5.4 Energy dissipater of hydraulic jump type

Type Structure and characteristics Applicability/condition

Counter-dam

type

Conjugation depth for hydraulic

jump is artificially kept by the

counter-dam.

Structurally simple.

In case of the flood discharge

becoming larger by1.3 times

than the design discharge, the

absorption function disappears.

USBR Ⅲ type

stilling basin

Hydraulic jump is forced to arise

by chute blocks, baffle piers and

end-sills to reduce the length of

the stilling basin together with

stabilizing the jump.

Discharge quantity per unit

width should be less than 18.5

m3/(m・s)

Flow velocity should be less than

18.0 m/s.

Fr should be more than 4.5.

USBR Ⅳ type

stilling basin

The absorption to the flood is

obtained by placing chute blocks

and end-sills.

Applicable to the condition of Fr

being 2.5 ~ 4.5 where hydraulic

jump tends to be unsteady.




1) Counter-dam type

In this type, the conjugation depth for hydraulic jump to the supercritical flow

depth at the beginning of the apron is kept artificially by the counter-dam.

Usually, the water depth at just upstream of the counter-dam during the

design discharge flowing down shall be accorded with the water depth of

hydraulic jump (refer to Fig. 5.22). The height of counter-dam is given by the

Iwasaki’s formula F. 5.27.

Fig. 5.22 Counter-dam type stilling basin

The distance from the beginning point of the apron to the counter-dam should

be more than 6×d2 in case of the natural hydraulic jump type. If not enough,

it is not able to obtain the steady hydraulic jump even though the

counter-dam is heightened more than the calculation. In this type, the afflux

・・・・・・・・・・・・・・(F. 5.26)

・・・(F. 5.27)

Counter-dam

Flow velocity at the beginning point of hydraulic jump (m/s)

Height of the counter-dam (m)

Discharge coefficient of the counter-dam (C=1.9~2.0)

Gravitational acceleration (=9.8 m/s2)

Here, Water depth at the beginning point of hydraulic jump (m)

Water depth at the end point of hydraulic jump (m)

Fr at the beginning point of hydraulic jump




water level becomes not enough to the discharge more than the design value,

and the hydraulic jump becomes unsteady. In case of the discharge becoming

more by about 1.3 times compared to the design, the water flow becomes

spattered and the basin loses its function.

The disadvantage of this type is that the discharge overflowing the

counter-dam has considerable kinetic energy, so that it is necessary to place a

secondary energy dissipater in the downstream if the conditions in the

downstream river requires. To excavate the ground of the basin and lower the

apron is one way to obtain the conjugation depth for hydraulic jump. In this

case, there is no need to place the counter-dam and the secondary energy

dissipater. Which is suitable is the comparison matter from view point of the

construction cost and the maintenance.

2) USBR Ⅲ type stilling basin

This type is applied to the case of the flood discharge being small and having

low kinetic energy, i.e. the flow conditions of which are that discharge

quantity per unit width should be less than 18.5 m3/(m・s), flow velocity

should be less than 18.0 m/s, and Fr should be more than 4.5.

When the design flood discharge flows down, the conjugation depth for

hydraulic jump d2 given by F. 5.26 must be maintained at the downstream of

the stilling basin.

The dimensions of Chute blocks, baffle piers and the end-sill vary according to

the flow-in depth into the basin d1 and the in-flow Froude number F1; these

are given by Fig. 5.23 and Fig. 5.24. The length of the stilling basin LⅢ is

about three times of d2 (=3×d2).




Fig. 5.24 Height of baffle pier and end-sill applied to Ⅲ, Ⅳ type stilling basin

Baffle pier Baffle pier

End-sill

End-sill

Slope 1:2

Slope 1:1

Chute block End-sill

Baffle pier

Fig. 5.23 Specifications of USBR Ⅲ type stilling basin

The hatched area shows longitudinal shape of the hydraulic jump when the downstream depth equals to the conjugation depth.




3) USBR Ⅳ type stilling basin

This type is applicable for absorbing the supercritical flow of Froude number

(Fr) being 2.5 ~ 4.5 where hydraulic jump tends to be unsteady. In this type, it

is necessary to maintain the downstream water depth deeper than USBR Ⅲ

type’s case by about 1.1 times (1.1×d2). The dimensions of Chute blocks and

the end-sill are given by Fig. 5.24 and Fig. 5.25. The length of the stilling basin

LⅣ is given by Fig. 5.26.

(3) Energy dissipater of collision type

Collision type energy dissipater absorbs/dissipates the kinetic energy of the

supercritical flow from the chute section by collision and disturbance. In case

of the flow-in velocity being small, the dissipating effectiveness by collision

reduces; and the flow might jump out of the basin, so that it is necessary to

give the structural formation, i.e. a tank, according to the hydraulic jump type

energy dissipater. For reference, the collision type energy dissipater for the

discharge use of pipe line is shown as Fig. 5.27. This structure type is effective

to the case of the flow quantity being smaller than 10m3/sec and the flow

velocity being higher than 10 m/sec.

We≒0.5d1

The top surface is inclined by 5° toward downstream.

Fig. 5.25 Specifications of USBR Ⅳ type stilling basin

Wo=2.5W

Fig. 5.26 Lengthof USBR Ⅳ type stilling basin

Length of hydraulic jump




Fig. 5.27 Collision type dissipater for discharge use of pipe line

(4) Energy dissipater of drop-work type

In this category, there are three types according to the difference of energy

dissipation/absorption method, i.e. the forced hydraulic jump type, the

impact block type and the slot-grating type. In the former two types, noises

caused by the water surface vibration might arise at the time of water with low

Φ;Pipe ID

Fillet

(Min. 10cm)

Cross-section

Rip-rap

Min.4×Φ

Base

Plane view

Section A-A

Fig. 5.28 Width of dissipater (W)~Q

W (

m)

Table 5.5 Wall thickness recommended




overflow head flowing into under some environmental or physical conditions.

Supplying air to behind the water mass of discharge, which becomes possible

by providing the side wall just below the discharge out-let with a slit or air

pipe or by making the channel width widened suddenly just at the

downstream of the discharge out-let, is effective to avoid this phenomenon.

In case of Fig. 5.29, the overflow weir is used; but it is also possible to let the

discharge drop down directly from the channel bed.

Fig. 5.29 Illustration of the drop-work type energy dissipater

1) Forced hydraulic jump type

Fig. 5.30 Illustration of forced hydraulic jump type stilling basin

In this type, the free-fell water flow is forced to cause hydraulic jump (refer to

Fig. 5.30). In designing, the length Ld which corresponds to the distance

between the beginning point of free-fall and the beginning point of hydraulic

jump is decided at first. After that, the process and the method is as same as

the case of Ⅲ or Ⅳ type stilling basin. The length Ld is able to be obtained

basing on Fig. 5.31 through the calculation of drop-number (D) shown below,

Baffle pier

End-sill

Downstream water level

Extruded wall at the discharge out-let for air supply

Basin length of Ⅲ, Ⅳ type




differential of water level (hd) between the upstream and the downstream,

overflow depth (He), and free-drop height (Y). In some case, it is necessary to

carry out trial-and-error calculations assuming the water level at the

downstream.

The flow-in depth (d1) at the beginning point of hydraulic jump, the water

depth (d2) at the end point of hydraulic jump and the flow-in Froude number

(F1) are able to be obtained next by next basing on Fig. 5.31 according to the

drop number (D), the free-fall height (Y) and the discharge quantity per unit

width (q).

The form designing to the downstream portion beyond the beginning point of

hydraulic jump shall be carried out in the same manner as in USBRⅢ, Ⅳ

type stilling basin according to d1, d2 and F1. The type of stilling basin is

selected basing on the flow-in Froude number (F1) according to the following

guideline.

① F1＜2.5 ; USBRⅠtype

② F1=2.5~4.5; USBRⅣ type

③ F1≧4.5 ; USBRⅢ type

The USBRⅠtype has a flat apron without additional structures such as piers,

sills, blocks, etc. This apron is extended by the length of 6×d2 (the water

depth at the end point of hydraulic jump) from the beginning point of

hydraulic jump.

・・・・・(F. 5.28)

Here, Discharge quantity per unit width (m3/(s・m)

Gravitational acceleration (=9.8 m/s2) Free-fall height (m)

Critical depth

Flow-in Froude number

Flow-in depth

Flow-in velocity




Extruded wall at the discharge out-let

Impact block type

Extruded wall at the discharge out-let

Forced hydraulic jumblock type

Flo

w-i

n F

rou

de n

um

ber

F1

Len

gth

to

each

kin

d

Drop number D

Flow velocity, water depth, Froude number at the point X

X : the beginning point of hydraulic jump

dc : critical depth

dc : water depth behind the free-drop water flow

Fig. 5.31 Design diagram for energy dissipater of drop-work type

Upper; Impact block type Lower; Forced hydraulic jump type




2) Impact block type

This type’s scheme is to let the free-fall water flow collide against the impact

block, spatter and lose its kinetic energy. The advantage is to maintain the

energy dissipation effectiveness without basing on the downstream water level

relatively.

But the mechanism is the dissipation/absorption by collision and

disturbance, so that the excessively low water level at the downstream might

invite the situation that the spattering becomes too fierce and spattered water

goes over the side wall top. Anyway the impact shock to the pool in the stilling

basin is violent, so that this type should not be applied to the case of the

ground being week mechanically, the drop height being excessively high over

6.1 meter for example, and the required water depth at the downstream being

not maintained. (The required water depth means the one more than 2.5×dc

meter; dc is the critical depth at the time of discharge quantity per unit width

(q) flowing down and is given by the following formula. : dc= (q2/g)1/3) In

addition, “the drop height” here is the larger one when comparing Y with hd,

both shown in Fig. 5.32.

The form and shape of the design is obtained by Fig. 5.32 according to the

critical depth (dc) and the drop distance (Lp). The drop distance (Lp) is obtained

by F. 5.28 according to the drop number (D), differential in water level

between the upstream and the downstream (hd), overflow head (He) , and the

drop height Y (refer to Fig. 5.32). In some case, it is necessary to carry out

trial-and-error calculations assuming the water level at the downstream.

The width of the block and the block interval are 0.4×dc

Fig. 5.32 Illustration of the impact block type energy dissipater

Extruded wall at the discharge out-let for air supply

End-sill

Impact block




3) Slot-grating type energy dissipater

The scheme of this type is the energy dissipation through spreading the

dropping water by the slot-grating. This type is applied to the case of the

dropping height being low, especially effective to the condition of Froude

number (Fr) being less than or equal to 3 (Fr≦3), and applicable to the

condition of Froude number (Fr) being less than or equal to 4.5 (Fr≦4.5). The

advantage of this type is the function of wave-absorption and bring more

smooth water surface even though effectiveness of energy dissipation is as

same as the forced hydraulic jump type. As materials for the grating, wasted

iron bars from railways and logs etc. are used. Designing is carried out basing

on F. 5.29 (refer to Fig. 5.33). The point is to extend the grating toward

downstream enough and let all the dropping water flow down through the

slot.

Length of the stilling basin: about 1.2LG

End-sill: This is placed to obtain the more improved flow conditions.

The shape of the sill is decided according to the one of USBR

Slot-grating

End-sill

Fig. 5.33 Illustration of the slot-grating type energy dissipater

Grating length; ・・・・・・・(F. 5.29)

Discharge volume (m3/sec)

Interval of grating (m)

Slot number (the more the slot number is given, the shorter the grating length becomes.)

Gravitational acceleration (=9.8 m/s2) Overflow head (m)

Width of the grating bar; 1.5W

Here




Ⅳ type. And at this time, the height of the sill becomes about

1.25d1 (d1: water depth at the beginning point of hydraulic

jump to the discharge volume Q). This d1 is obtained by Fig.

5.31 according to the discharge volume per unit width (q)

under the condition of the drop height (Y) and the discharge

volume (Q).

In addition, it is recommendable to give the grating a suitable inclination. This

way is effective to prevent the slots from being plugged up by driftwoods and

let the flood discharge flow down naturally. As a suitable inclination, the

inclination angle more than 3°is recommendable.

4) Margin height and the elevation of the sidewall top

The margin height must assure the safety against the water surface rising

caused by air-water effect and curvature of the channel, or against the

swinging of the water surface caused by wave. The elevation of the sidewall

top at each section/portion is given to be excess the elevation calculated by

adding the margin height to the water surface elevation.

The margin height in the spillway channel is decided as follows.

① Margin height to the sub-critical flow condition

This is given by the following formula (F. 5.30).

② Margin height to the supercritical flow condition


But the margin height should be larger than or equal to 0.6m. (Fb(min)=0.6)

Here, Margin height (m) Flow velocity (m/sec)

Gravitational acceleration (=9.8m/s2)

Water depth (m)

・・・・・・・・・・・・・・・・（F. 5.30）

Here,

・・・・・・・・・・・・・・・・・・・(F. 5.31)

Flow velocity (m/sec)

Margin height (m)

Coefficient (rectangular channel; =0.10, trapezoidal: =0.13)

Water depth (m)




③ Margin height to the energy dissipater’s section


Note; the margin height is estimated on the perpendicular line against the inclination of

the channel bed.

; In case of a bridge for O & M works being installed, clearance more than or equal to

1.0m must be provided.

Fig. 5.34 Clearance between Bridge and HWL

≧1.0m

・・・・・・・・・・・・・・・・・・(F. 5.32)

Here, Flow-in velocity at the beginning point of hydraulic jump (m/sec)

Water depth at the end point of hydraulic jump (m)

Margin height (m)




6. Design of intakes

The intake shall be designed as a facility that is provided with following

functions.

① To discharge irrigation water the maximum quantity of which is the peak

volume required in the irrigation plan.

② To discharge water in emergency case to get down the water level in the

reservoir.

③ To discharge the river water during the construction term.

④ To dissipate/absorb the kinetic energy of the discharged water if

necessary.

6.1 Formation of the intake

The intake facility is composed of the in-let section and the water

transmission section.

The intake section is a structure to take in the reservoir water; as a type of the

structure, the inclined conduit type and the intake tower type are common. To

the in-let section, gates or similar kind of facilities are attached to regulate the

intake quantity. The water transmission section consists of the bottom

conduit or the transmission tunnel and energy dissipating facilities. Selecting

types of each is done basing on the tables below under the consideration of

economical efficiency, simplicity in handling and functions. The combination

of inclined conduit type and bottom conduit type is generally used (refer to Fig.

6.1). In addition, the structure that has the function of intake

tower–cum–spillway as shown in Fig. 6.2 is constructed sometimes; and as

the energy dissipating facilities, the impact box type and a kind of bath-tabs.




Table 6.1 Characteristics of each type of intake facilities

Structure Merit Demerit In

take

sect

ion

Inclined

conduit

Economical

Easily installed without a

stiff ground

Structurally stable and

easy to O & M

On the gentle slope, the facilities’

length becomes long and it is

likely to have a trouble while O &

M works

Intake

tower

Easiness in gate operations

Fewer limitation in

selecting the installation

place

easiness in selecting the

intake depth

High construction and

maintenance cost compared to

the inclined conduit type

O & M becomes troublesome a

little.

Tra

nsm

issi

on s

ecti

on

Intake

tunnel

Safety against seepage flow

Safety against earth

pressure

easiness in O & M

Low applicability to a small intake

quantity from view point of

economy and construction.

Bottom

conduit

Economical Not perfect against seepage flow

Not perfectly Safe against earth

pressure

Almost impossible to conduct O &

M

Table 6.2 Foundation conditions required as a hydraulic structure

Structure Foundation conditions required

Inclined conduit To be a solid ground with no collapse or no descent of bearing

capacity after being saturated by reservoir water.

Intake tower To be sustainable enough against the load and not to descend the

bearing capacity after being saturated by reservoir water.

Intake tunnel To be composed of rocks formation of which is water tight and stable.

To have a reasonable clearance against the reservoir water.

Connecting box To be a stable and solid ground against the settlement or repudiation

caused by vibrations that the intake water flow brings.

Bottom conduit To be a stiff ground.

Do not construct on the embankment except at the core trench

portion.




6.2 Design of the inclined conduit works

6.2.1 Position of the intake mouth hole

The position of the intake mouth holes should be decided considering O & M

works, the water pressure that acts on the gate surface, and the emergent

discharge.

6.2.2 Diameter of the hole

The diameter is decided basing on the following formula.

Pulling up handle

Air release hole Intake mouth hole

(Slide gate)

Sediment flushing gate

Inclined conduit works

Conduit portionBoard stopper

Approaching channel

Flushing portion

Cut-off wall

Bottom conduit section Connecting section

Bottom conduit

Enwrapping concrete

Outlet box

Fig. 6.1 Typical intake works composed of the inclined conduit and the bottom conduit

Fig. 6.2 Intake works composed of the intake tower and the bottom conduit

Slide gate

Inclined core




Q is the maximum intake volume that is calculated by the formula:

Q=(100/α)×Qc: based on the maximum water demand (Qc) in the command

area and the total irrigation efficiency (α).

6.2.3 Inclined conduit works

It is desirable to place the inclined conduit on the stiff ground slope; in case of

the inclined conduit being placed on the embankment, an adequate

structural formation must be given to the joint portion to prevent the

consolidation settlement in the embankment from causing structural

damages.

(1) Inclined conduit

The cross-section area of the conduit is decided considering not affecting the

flow-in condition of the water flow through the intake mouth hole, and the

workability of the intake mouth hole being attached to the conduit. Therefore,

generally the cross-section area of the conduit is adjusted to be about two

times of the hole’s cross-section area; and the following table is given as a

standard.

Here, Cross-section area of the hole (m2)

Intake volume (m3/sec)

Coefficient of discharge (=0.62, usually)

Gravitational acceleration (=9.8m/sec2)

Water depth to the center of the hole (refer to Fig. 6.3) (m)

・・・・・・・・・・・・・・・・(F. 6.1)

Fig. 6.3 Estimation of H




Table 6.3 Standard diameter of Mouth hole and Conduit (unit: mm)

Mouth hole φ100 φ125 φ150 φ200 φ250 φ300

Conduit φ200 φ200 φ250 φ300 φ400 φ500

(2) Dimensions of the cross-section

The conduit must be stable against the water pressure, buoyant force and

other external forces. Cross-sectional dimensions can be decided referring to

the following table and Fig. 6.4.

6.2.4 Accessory works

The conduit must be enwrapped by the reinforced concrete. Steps for O & M

works and the air release pipe shall be attached as accessory works. In case of

the inclined conduit works being long, anchor blocks shall be attached for the

safety’s sake.

(1) Air release pipe

The cross-section area of the air release pipe is calculated basing on the air

volume and the air velocity. 45m/sec is assumed as a standard and should be

Slide gate

Spindle

Conduit

Anchor block

Air pipe (φ=50mm±)

Section x-x

Steps for O & M

Fig. 6.4 Cross-section of the inclined conduit works

Table 6.4 Standard dimensions of the conduit roll concrete (Unit: mm)

Conduit diameter D

Roll height a

Roll width b




less than 90m/sec; and the air volume is assumed to be 15% of the maximum

intake volume. The diameter of the pipe should be more than or equal to

50mm.

Fig. 6.5 Air release pip

(2) Anchor block

Anchor blocks shall be attached to the enwrapping concrete for safety’s sake

against sliding in case of the slope being steep. The interval of the anchor

blocks shall be 9m or so; and the joints’ positions shall be adjusted on the

anchor blocks. The structural formation of these portions shall be designed

referring to Fig. 6.6.

6.3 Design of bottom conduit works

The bottom conduit works must function enough so as to let the maximum

intake volume, emergent discharge volume and the flood discharge during the

construction term flow down to the downstream river, and be placed on a stiff

ground with the bearing capacity that can prevent the settlement of the

bottom conduit works from affecting the dam body’s safety especially in terms

of leakage.

Air release pipe

Here,

Air velocity in the pipe (m/sec)

Maximum intake volume (m3/sec)

Cross-section area of the pipe (m2)

・・・・・・・・・・・・・・・・・・・(F.6.2)

Oily paint

Dowel bar

Joint sealing material

Water stop

Fig. 6.6 Structural formation of the anchor block and the joint




6.3.1 Placement

To be placed on a stiff ground; if not, countermeasures must be provided.

The alignment should be straight; and its axis should be perpendicular to

the dam axis.

6.3.2 Structural quality and formation

The bottom conduit works must stand the inside water pressure and external

forces, and can follow differential settlements, and to be watertight and

sustainable.

As the structural characteristics, there are two types. One is the rigid type

represented by the reinforced concrete structure, and the other is the flexible

type represented by the simple body structure of ductile iron pipe. In case of

the reinforced concrete type with ready-made pipes used as the inner frame,

studies in terms of stress concentration and water tightness must be done.

Fundamentally the bottom conduit works shall be constructed on a stiff

ground. If the bearing capacity is not enough, adequate countermeasures

such as the replacement method or soil improvement method must be

applied.

As examples of the flexible type structure, the ductile iron pipe

S-model/US-model provided with anti-separation system would be cited that

is buried naked in the dam body. The ductile iron pipe S-model and US-model

have excellent retractility and flexibility, and more over have an

anti-separation system against earthquakes. Therefore, this type can adapt

itself wholly to the deformation caused by the land subsidence or earthquakes,

so that it does not receive excessive or concentrated stress. In the design of

this type, the pipe span is decided according to the standard that the relative

deformation between the bottom conduit and the foundation ground must not

exceed the yield deformation of the foundation ground. In addition, the

standard for the void not to arise under the conduit is that the allowable

phase differential between the settlement curve (immediate settlement +

consolidation settlement) of the foundation ground and the conduit line is less

than or equal to 50mm.




6.3.3 Diameter of the conduit

The diameter of the conduit is decided considering the design maximum

intake volume, emergent discharge volume and the flood discharge during the

construction term. The flood discharge is decided based on the probable flood

discharge corresponding to the construction period. And also when deciding

the diameter of the conduit, it is necessary to consider its maintenance. It is

desirable to give the diameter larger than or equal to 800mm.

The capable flow volume of the conduit (Qe) is given by the following formula.

This Qe must be larger than or equal to the design maximum intake volume.

R, A and water depth (h) are expressed as follows based on Fig. 6.8.

The bottom conduit shouldbe placed on the foundationbasically.

Foundation ground

Deposited soil

Filter

Decided considering the channel’selevation in the downstream

Fig. 6.7 Relationship between the foundation ground and the longitudinal inclination

(n=0.13 to centrifugal reinforced concrete pipes, ductile iron pipesand iron pipes)

・・・・・・・・・・・・・・・・・(F. 6.3)

Capable flow volume (m3/sec)


Hydraulic radius (m)

Longitudinal inclination

Cross-section area through which water flows down (m2)

Here,




The flow quantity in the conduit comes to maximum in the condition of

h=0.938D; and the A and R at this moment are shown below.

6.3.4 In case of the embankment around the conduit being left until later

Cross-sectional shape around the conduit is desirable to follow the figure

below.

Fig. 6.8 Flow in the conduit

・・・・・・・・・・・・(F. 6.4)

(Unit: rad)

Table 6.5 Hydraulic specifications at the maximum capable volume flowing down

D (mm)




Fig. 6.9 Cross-sectional shape around the conduit

6.3.5 Details of the bottom conduit works

(1) Enwrapping of the conduit

Followings must be considered in case of the centrifugal reinforced concrete

pipe being used as an inner form and enwrapped by the reinforced concrete.

① The joints must be provided at the interval of 10m to 15m every.

② The joints’ positions of the reinforced concrete should be accorded with the

ones of ready-made conduits for the inner form use (refer to Fig. 6.10). The

ready-made conduit must not be lifted up by the buoyant force that arises in

cast concrete.

③ The joints of the bottom conduit works must be provided with the

structural function that can absorb the longitudinal differential settlement.

Enough care must be taken to the surrounding portion of the bottom conduit

not to let this portion be a water path. That is to say, void must not be left

under the leveling concrete or foundation treatment works, and the

surrounding embankment must be compacted well.

④ The inclination ranging from 1:0.1 to 1:0.3 or so should be given to the side

of the enwrapping concrete for obtaining the enough density in compaction

works and high contact of the soil to the concrete surface.

Fig. 6.11 is one example where the reinforced concrete pipe is used as an

inner form. In this case, the wrapping concrete is designed as a single

reinforcement structure considering the reinforcing bar in the pipe. Double

reinforcement formation is also applicable.




In the flexible type case such as the ductile iron pipe being used as a simple

body structure, it must be provided with an anti-separation system against

the differential settlement caused by the load of embankment, and it is

necessary to confirm water tightness to be secured in design/construction. In

case of the flexible pipe being applied, the pipe with high rigidity should be

selected. The longitudinal deflection degree must be less than or equal to 1%,

Iron bar D13 Joint material

Dowel bar VP pipe

Water stopper

Centrifugal reinforced Concrete pipe

Concrete

Fig. 6.10 Example of the formation of joints’ portions

Reinforced concrete

Leveling concrete

Fig. 6.11 Design example of the bottom conduit cross-section

Table 6.6 Example of dimensions of the bottom conduit cross-section (side inclination=1:0.1)




and the design deflection ratio of the cross-section must be less than or equal

to 3%. When the construction work to its foundation is carried out, it is

necessary to consider securing the water tightness especially around the

conduit bed.

(2) Cut wall

The cut-off wall is provided with to around the conduit to prevent a water path

from arising and soil particles flowing away through the water path. In

designing the cut-off wall, it is necessary to consider selecting suitable

materials or applying suitable construction methods.

There are two types of cut-off walls; one is the concrete type and the other is

the impervious soil type. An example of the concrete type is shown as Fig. 6.14

and the standard quality required as the suitable impervious material for the

soil type cut-off wall is shown below.

Table 6.7 Quality standard of soil materials for cut-off wall

Quality item Standard

Grain distribution Contents of silt and clay ≧ 50%

Maximum grain size 20mm

Moisture content 60%～70%

Plasticity index IP IP ≧ 15%

Ductile iron pipe S-model

Deflection distribution

Fig. 6.12 Design example of the flexible type bottom conduit




The number of cut-off walls is decided according to the hydraulic gradient and

the geological conditions along the bottom conduit works. Fig. 6.13 is shown

to the case of inclined core type; but in homogeneous case also, this manner

shall be followed.

Fig. 6.13 Conditions around the cut-off wall

Waterstop or

sealing material

Waterstop or sealing material

Elastic filler t=20mm

Concrete casting inone time

Concrete casting intwo times

Fig. 6.14 An example of cut-off wall construction

Inclined core

Cover≧1m±

Cover≧1m±

Impervious material




7. Preventive measures against sediment

The sediment precipitating in the reservoir varies according to the topography,

a geological feature, a basin area. It is necessary to anticipate sediment

volume of around 200-1000m3 per annual basin 1km2.

For prevent sediment in the reservoir, it is necessary to note the following

points.

① In the case that water flow into the reservoir from the canal, it should be

constructed the facilities for the purpose of sediment in the inlet of the

reservoir. Please refer to Technical guideline for head-works.

② In the case that water flow into the reservoir from the surface of the earth,

it should be carried out the coating due to the plant to the catchment area,

and the setting of the gutter.

In addition, periodical dredging is necessary because it is difficult to prevent

sediment perfectly even if it is carried out the measures mentioned above.

Photo 7.1 Sediment control Weir at upstream of Eigenji Dam, Japan

Removing sediment by

heavy machineries

Weir to protect entering

soil into the reservoir

River flow




Annex 1

Calculation Example of Water level in the Reservoir The formula to calculate water level in the reservoir with consideration changing water level by inflow and outflow is shown below.

Here, Storage Volume (m3) I: Inflow volume (m3/s), O: Outflow volume (m3/s) Calculation time pitch 1.0h →3600s

Calculation procedure is described below. 1) Calculate I (t + Δt/2) by Hydrograph

2) Calculate O (t + Δt/2) by assuming h (h: Water depth)

3) Calculate V (t + Δt) by Formula (A)

4) Calculate h0 using h-V curve with V (t + Δt) 5) If |h-h0| =< Allowable error (e = 0.0001m), proceed next calculation step.

If |h-h0| > Allowable error, go back 2) and continue calculation until |h-h0|=<e Calculation example is explained below.

………. (A)

hr

First Calculation Assumed water depth (h) after Δt, h =0.02000m




Forth Calculation Assumed water depth (h) after Δt, h =0.0251m

Third Calculation Assumed water depth (h) after Δt, h =0.02478m

Second Calculation

Assumed water depth (h) after Δt, h =0.02618m

∴ h = 0.025m




First Calculation Assumed water depth (h) after Δt, h =0.065m

hr

Second Calculation Assumed water depth (h) after Δt, h =0.06481m

hr

∴ h = 0.065m




First Calculation


Second Calculation Assumed water depth (h) after Δt, h =0.08877m

Third Calculation





Forth Calculation Assumed water depth (h) after Δt, h =0.08784m

Fifth Calculation Assumed water depth (h) after Δt, h =0.08752m

Sixth Calculation Assumed water depth (h) after Δt, h =0.0876m

∴ h = 0.088m




After sequential computation, the result of calculation is shown on the next table.

Result of calculation Maximum water depth is 0.996m. Reference If the storage volume is not considered, the design flood discharge can be decided by Maximum inflow.

Max.

Time Inflow Outflow Water Depth

(m) Remarks

Time Inflow Outflow Water Depth

(m)

Remarks




Annex 2

Calculation Example of the Blanket

An example of Necessary length of artificial blanket is shown below. Setting condition of the calculation is shown on the following figure.

qf; Allowable Seepage quantity thorough the foundation layer

60 ℓ・min-1・(100)-1＝1.0×10-5m3・s-1・m-1

Kf: Permeability coefficient of the foundation layer 2.0×10-3cm/s＝2.0×10-5m/s

Kb: Permiability coefficient of the blanket 1.0×10-5cm/s＝1.0×10-7m/s

Zf: Thickness of the pervious foundation layer 4.0m

h: Differential between the reservoir water level and the downstream water level 5.0m

Zb: Thickness of the blanket 1.5m (Assumed)

X: Necessary length of the blanket (m)

Xd: Bottom length of the dam body 31.5m

Xr: Effective seepage length (m)

Head loss by the blanket Hydraulic gradient in the pervious foundation

Pervious foundation

Inpervious foundation

(1) Calculation of Effective seepage length

( If Xr=< 0, The blanket is not necessary)

(2) Necessary length of the blanket

Here,




In case of Y=<0, Re-calculation is necessary by changing the setting condition.

,




References

1. Pond Design Guideline of Land Improvement Project, The Japanese Society of Irrigaiton, Drainage and Rural Engineering, 2006 2. Dam Design Guideline of Land Improvement Project, The Japanese Society of Irrigaiton, Drainage and Rural Engineering, 1981

3. Headwork Design Guideline and Manual of Land Improvement Project

4. Part A Study Guideline on Hydro Metrology, The Federal Democratic Republic of Ethiopia Ministry of Water Resources, 2002 5. Utilization Guidelines for Sabo Soil Cement, Kajima Institute Publishing Co., LTD, 2002 6. Important Points of Design/Construction and Reservoir Slope Protection Work of Nagara Dam, Journal of the Japanese National Committee on Large Dams volume No. 119, Japan Commission on Large Dams,1987 7. Investigation and Design of the Rural Roads (Soil Cement) [Final Report], JICA, 2010




List of Authors

Name of Guidelines and Manuals Name Field Affiliation

Guideline for Irrigation Master Plan Study Preparation on Surface Water Resources

Mr. Nobuhiko Suzuki Water resources planning

Ministry of Agriculture, Forestry and Fisheries

Mr. Roba Muhyedin Irrigation Engineer OIDA Head Office

Manual for Runoff Analysis Mr. Yasukazu Kobayashi Runoff Analysis LANDTEC JAPAN, Inc.

Manual of GIS for ArcGIS (Basic & Advanced Section) Mr. Ron Nagai GIS Application KOKUSAI KOGYO

CO., LTD.

Manual on Land Use Classification Analysis Using Remote Sensing Mr. Kazutoshi Masuda Remote Sensing KOKUSAI KOGYO

CO., LTD.

Guidance for Oromia Irrigation Development Project Implementation

Mr. Kenjiro Futagami Facility Design/Construction Supervision


Study and Design Technical Guideline for Irrigation Projects (Irrigaiton Engineering Part)

Mr. Naoto Takano Facility Design/ Construction Supervision


(Socio-Economy, Community, Financial and Economic analysis Part)

Mr. Tafesse Andargie Economist OIDA Head Office

(Agronomy and Soil Part) Mr. Abdeta Nate'a Agronomist OIDA Head Office

Technical Guideline for Design of Headworks Mr. Motohisa Wakatsuki Head works design Sanyu Consultants

Inc.

Technical Guideline for Small Scale Reservoir Mr. Haruo Hiki

Project Management/ Planning/Reservoir

Sanyu Consultants Inc.

Technical Guideline for Irrigation Canal and Related Structures Mr. Naoto Takano

Facility Design/ Construction Supervision


Construction Control Manual Mr. Yoshiaki Otsubo Construction Supervision (Bura SSSIP)

Tokura Corporation

Guidance for Preparation of Operation and Maintenance Manual

Mr. Kenjiro Futagami Facility Design/Construction Supervision


Irrigation Water Users Association Formation and Development Manual


Strengthening Irrigation Water Users Association (IWUA) Guideline

Mr. Yasushi Osato Strengthening of WUA Nippon Koei Co.


Small Scale Irrigation Water Management Guideline (Irrigation Water Supply Part)

Mr. Yohannes Geleta Irrigation Engineer OIDA Head Office

(Field Irrigation Water Management Part) Mr. Abdeta Nate'a Agronomist OIDA Head Office

Remarks: Affiliation is shown when he work for CBID project.




List of Experts who contributed to revise guidelines and manuals (1/5)

Office Name Specialty

OIDA Head office Mr. Abdeta Nate'a Agronomist

OIDA Head office Mr. Kibrom Driba Irrigation Engineer

OIDA Head office Mr. Kurabachew Shewawerk Agronomist

OIDA Head office Mr. Lemma Adane Irrigation Engineer

OIDA Head office Mr. Roba Muhyedin Irrigation Engineer

OIDA Head office Mr. Shemeles Tefera Agronomist

OIDA Head office Ms. Sintayehu Getahun Irrigation Engineer

OIDA Head office Mr. Tafesse Andargie Economist

OIDA Head office Mr. Tafesse Tsegaye Irrigation Engineer

OIDA Head office Mr. Tatek Worku Irrigation Engineer

OIDA Head office Mr. Teferi Dhaba Irrigation Engineer

OIDA Head office Mr. Terfasa Fite Irrigation Engineer

OIDA Head office Mr. Tesfaye Deribe Irrigation Engineer

OIDA Head office Mr. Yohannes Dessalegn Economist

OIDA Head office Mr. Yohannes Geleta Irrigation Engineer

OWMEB Mr. Girma Etana Irrigation Engineer

OWMEB Mr. Kedir Lole Irrigation Engineer

Arsi Mr .Dedefi Ediso Agronomist

Arsi Mr. Birhanu Mussie Irrigation Engineer

Arsi Mr. Dinberu Abera Sociologist

Arsi Mr. Hussen Beriso Economist

Arsi Mr. Mulat Teshome Surveyor

Arsi Mr. Segni Bilisa Agronomist

Arsi Mr. Shewngezew Legesse Irrigation Engineer






Arsi Mr. Tamerwold Elias Irrigation Engineer

Arsi Mr. Tesfaye Gudisa Irrigation engineer

Arsi Mr. Teshome Eda'e Irrigation Engineer

Arsi Ms. Worknesh Kine Geologist

Bale Mr. Abboma Terresa Irrigation Engineer

Bale Mr. Abdulreshed Namo Irrigation Engineer

Bale Mr. Beyan Ahmed Economist

Bale Mr. Diriba Beyene Irrigation Engineer

Bale Mr. Firew Demeke Teferi Irrigation engineer

Bale Mr. Gosa Taye Debela Irrigation engineer

Bale Mr. Zeleke Agonafir Agronomist

Borena Mr. Dida Sola Irrigation Engineer

East Harerge Mr. Abdi Abdulkedar Irrigation Engineer

East Harerge Mr. Elias Abdi Irrigation Engineer

East Harerge Mr. Shemsedin kelil Irrigation Engineer

East Harerge Ms. Eskedar Mulatu Economist

East Shewa Mr. Andaregie Senbeta Economist

East Shewa Mr. Bekele Gebre Irrigation Engineer

East Shewa Mr. Dilibi ShekAli Sociologist

East Shewa Mr. Ejara Tola Agronomist

East Shewa Mr. Girma Niguse Irrigation Engineer

East Shewa Mr. Kebebew Legesse Irrigation Engineer

East Shewa Mr. Mulatu Wubishet Agronomist

East Shewa Mr. Tadesse Mekuria Agronomist






East Shewa Ms. Tigist Amare Irrigation Engineer

East Shewa Mr. Zerfu Seifu Irrigation Engineer

East Welega Mr. Benti Abose Economist

East Welega Mr. Birhanu Yadete Agronomist

East Welega Mr. Dasalegn Tesema Economist

East Welega Mr. Gamachis Asefa Irrigation Engineer

East Welega Mr. Getachew Irena Agronomist

East Welega Mr. Kidane Fekadu Irrigation Engineer

East Welega Mr. Milikesa Workeneh Irrigation Engineer

East Welega Ms. Mulunesh Bekele Irrigation Engineer

East Welega Mr. Samson Abdu Irrigation Engineer

East Welega Mr. Tulam Admasu Irrigation Engineer

East Welega Ms. Yeshimebet Bule Economist

Guji Mr. Abadir Sultan Sociology

Guji Mr. Dawud Menza Irrigation Engineer

Guji Mr. Fikadu Mekonin Geologist

Guji Mr. Megersa Ensermu Irrigation Engineer

Guji Mr. Wandesen Bakale Economist

Horoguduru Welega Mr. Seleshi Terfe Economist

Horoguduru Welega Mr. Temesgen Mekonnen Irrigation Engineer

Horoguduru Welega Mr. Tesfaye Chimdessa Economist

Illubabor Mr. Ahmed Sani Irrigation Engineer

Jimma Mr. Lebeta Adera Irrigation Engineer

Kelem Welega Mr. Ayana Fikadu Agronomist






Kelem Welega Mr. Megarsa Kumara Hydrologist

Kelem Welega Mr. Oda Teshome Economist

Northe Shewa Mr. Henok Girma Irrigation Engineer

South West Shewa Mr. Bedasa Tadele Irrigation Engineer

South West Shewa Mr. Gemechu Getachew Irrigation Engineer

West Arsi Mr. Abebe Gela Irrigation Engineer

West Arsi Mr. Demissie Gnorie Irrigation Engineer

West Arsi Mr. Feyisa Guye Irrigation Engineer

West Arsi Mr. Hashim Hussen Economist

West Arsi Mr. Jemal Jeldo Economist

West Arsi Mr. Mekonnen Merga Environmentalist

West Arsi Mr. Mohamedsafi Edris Irrigation Engineer

West Arsi Mr. Molla Lemesa Agronomist

West Arsi Mr. Tamene Kena Sociologist

West Arsi Mr. Tibaho Gobena Irrigation Engineer

West Harerge Mr. Alemayehu Daniel Agronomist

West Harerge Mr. Dereje Kefyalew Irrigation Engineer

West Harerge Mr. Ferid Hussen Irrigation Engineer

West Harerge Mr. Nuredin Adem Irrigation Engineer

West Harerge Mr. Seifu Gizaw Economist

West Shewa Mr. Jergna Dorsisa Irrigation Engineer

West Shewa Mr. Solomon Mengistu Agronomist

West Shewa Mr. Zerhun Abiyu Irrigation Engineer

West Welega Mr. Belaye kebede Irrigation Engineer






West Welega Mr. Busa Degefe Economist

West Welega Mr. Temesgen Runda Irrigation Engineer

Ministry of Agriculture Mr. Amerga Kearsie Irrigation Engineer

Ministry of Agriculture Mr. Zegeye Kassahun Agronomist

Amhara Agriculture Bureau Mr. Assefa Zeleke Economist

OWWDSE Mr. Damtew Adefris Irrigation Engineer

OWWDSE Mr. Demelash Mulu Irrigation Engineer

OWWDSE Mr. Teshoma Wondemu Irrigation Engineer

Latinsa SC. Mr. Aschalew Deme Irrigation Engineer

Latinsa SC. Mr. Daba Feyisa Agronomist

Metaferia Consulting Engineers Mr. Getu Getoraw Irrigation Engineer

Metaferia Consulting Engineers Mr. Hassen Bahru Sociologist

Metaferia Consulting Engineers Ms. Nitsuh Seifu Irrigation Engineer

Remarks: Office Name is shown when he/she works for CBID project.




List of Editors

Name of Guidelines and Manuals Name Field Affiliation

• Guideline for Irrigation Master Plan Study Preparation on Surface Water Resources

Mr. Ermias Alemu Demissie Irrigation Engineer Lecturer in Arba Minch University

Mr. Zerihun Anbesa Hydrologist Lecturer in Arba Minch University

• Technical Guideline for Design of Headworks

• Technical Guideline for Irrigation Canal and Related Structures

Mr. Ermias Alemu Demissie Irrigation Engineer Lecturer in Arba Minch University

Mr. Bereket Bezabih Hydraulic Engineer (Geo technical)

Lecturer in Arba Minch University

• Construction Control Manual Mr. Eiji Takemori Construction Supervision (Hirna SSIP)

LANDTEC JAPAN, Inc.

• Construction Control Manual Dr. Hiroaki Okada

Construction Supervision (Sokido/Saraweba SSIP)

Sanyu Consultants Inc.

• Construction Control Manual Mr. Shinsuke Kubo Construction Supervision (Shaya SSIP)

Independent Consulting Engineer


• Construction Control Manual Mr. Toru Ikeuchi

Chief Advisor/Irrigation Technology

JIID (The Japanese Institute of Irrigation and Drainage)


• Construction Control Manual Mr. Kenjiro Futagami

Facility Design/Construction Supervision


• All Guidelines and Manuals Mr. Hiromu Uno Chief Advisor/Irrigation Technology


• Manual for Runoff Analysis • Manual of GIS for ArcGIS

(Basic & Advanced Section) • Manual on Land Use

Classification Analysis Using Remote Sensing

Mr. Nobuhiko Suzuki Water resources planning


• Guidance for Oromia Irrigation Development Project Implementation

• Study and Design Technical Guideline for Irrigation Projects


• Technical Guideline for Small Scale Reservoir

• Construction Control Manual • Guidance for Preparation of

Operation and Maintenance Manual

• Irrigation Water Users Association Formation and Development Manual

• Strengthening Irrigation Water Users Association (IWUA) Guideline

• Small Scale Irrigation Water Management Guideline

Mr. Naoto Takano Facility Design/ Construction Supervision






List of Coordinators

Name Field Affiliation

Mr. Ryosuke Ito Coordinator/Training Independent

Mr. Tadashi Kikuchi Coordinator/Training Regional Planning International Co.





Contact Person

Mr. Yohannes Geleta (Irrigation Engineer; Environmentalist) (Tel: 0911-981665, E-mail: [email protected])

Mr. Tafesse Andargie (Economist)

(Tel: 0911-718671, E-mail:[email protected]) Mr. Abdeta Nate'a (Agronomist)

(Tel: 0912-230407, E-mail: [email protected])

Oromia Irrigation Development Authority (OIDA) Tel: 011-1262245 C/O JICA Ethiopia Office Mina Building, 6th & 7th Floor, P.O.Box 5384, Addis Ababa, Ethiopia Tel : (251)-11-5504755 Fax: (251)-11-5504465

Documents

Technical Guideline for Design of Small Scale Reservoir