Guidelines for Preparation of

Estimates & DPR

for Minor Irrigation Projects

Guidelines for Preparation of Estimates & DPR for Minor Irrigation Projects

Index Chapter

No. Description

I General

II Hydrology

III Data required for Design of Minor Irrigation Project

IV Soil properties and their influence on design of dams

V Fixation of Principal Levels

VI Design of earth dams

VII Design of spillway

VIII Design of canal

IX Preparation of cost estimates

X Important instructions & Preparation &Submission of DPR

Appendix

No. List of Appendixes

1 Chapter II Survey & Investigation of Book of specifications

2 Technical Circular No - 53.-Preliminary Check Statement for General

Feasibility of Projects

3 E-in-C letter no 3332745/2011 dt 29/03/11 “estimation of Land width

proposed to be acquired for canal for Sadhyata”

4 Form-141 “Proposal for Sanction of Survey & Investigation

5 “Sample sanction order of “Sadhyata” of govt

6 Design Series TC-1- Check List for data required for design of Earth Dam

7 Design Series TC-2 - Check List for data required for design of Gravity Dam

8 Design of Spillway -lecture note of Director CWC

9 Design of Energy Dissipators -lecture note of Director CWC

10 Prescribed form of collection of Agriculture statistics - Page 353 of volume II

of book of technical Circulars

11 Information of officers related with proposal form-133

12 Form-141 A “Parameters for minor storage Irrigation Projects”

13 Form-142 “Basic Information for Minor Irrigation Schemes”.

14 Proforma of T.C.70

15 Proforma to accompany AA – T.C.70

16 Check list of according AA to Irrigation Schemes.

General

1. Scope: These guidelines are applicable for minor irrigation projects in Madhya

Pradesh having culturable command area upto 2000 ha.

2 Terminology: Minor Irrigation Project: It is a project having culturable command

area of 2000 hectares or less.

3. Feasibility Report1: (refer foot note) Executive Engineer shall prepare a

feasibility 1report on the basis of Toposheets, information available on internet &

site inspection in the format given in page 2-16 in chapter II Survey &

Investigation of Book of specifications volume I under the heading

“Reconnaissance Survey Report of Minor Irrigation Projects”. This should be

completed on the basis of Technical Circular No – 53 “Preliminary Check

Statement for General Feasibility of Projects”. (Relevant portion of chapter II is

enclosed as Appendix 1 & T.C.No -53 as Appendix –2)1.

Executive Engineer shall inspect schemes proposed for irrigating up to 200

Hectares & Superintending Engineer for schemes proposed for irrigating more

than 200 Hect. Land width proposed to be acquired for canal should be estimated

on the basis of E-in-C 3332745/2011 dt 29/03/11 (enclosed as Appendix -3). After

vetting of hydrology by the Chief Engineer, the culturable command area of the

project may be estimated @ 170 Hectares per million cubic metres for submission

of feasibility report.

The feasibility report as prepared above should be forwarded to Government along

with Form-141 “Proposal for Sanction of Survey & Investigation” with

recommendation of higher officers. (Appendix –4)

4. Estimate for survey work: After getting clearance of “Sadhyata” the Executive

Engineer of concerned Irrigation Division will prepare the estimate for survey

1 Presently as per Govt orders proposals of “Sadhyata” are directly submitted online by Executive Engineers in

prescribed form 141. But in this submission various technical details & points of technical suitability are missing hence above proposal has been made for decision at appropriate level.

work of the project. The estimate for survey work will be submitted to the

competent authority for sanction.

5. Survey work of the project: After sanction of estimate, survey of the project

should be got done as per chapter II Survey & Investigation of volume I of Book

of specifications (enclosed as Appendix1). Details of Topographical surveys,

extent, scale, contour interval etc are also given in this chapter.

Fixing alignment of dam embankment: As far as possible the alignment should

run on high grounds or ridges; and large depressions must be avoided. Alignment

should be as straight as far as possible. Alignment should be away from river

bends & meanders. Alignment should be along firm soil. Valuable culturable

land, wells, villages should be avoided as far as possible. Temples, mosques,

graveyards, cremation grounds, etc. should be avoided.

Survey should also include Collection of village maps & khasra of villages in the

CCA & other datas mentioned in Chapter III “Data Required for Design of Minor

Irrigation Projects”

All instructions given in Sanction order of “Sadhyata” of Govt should also be

complied. (Sample sanction order of govt is enclosed as Appendix -5).

6. Preparation of the project report: After completion of survey work of the

project, the plotting of the survey work should be done. Thereafter the

preparation of the project report should be started. Preparation of Detailed project

report & estimate may be done as per following steps.

Hydrology: Hydrology of the project containing flood and yield should be

prepared as per Chapter II. The yield from the catchment should be estimated so

that storage of the project can be decided. Similarly the peak design flood for

design of spillway should be estimated. The yield and peak flood of nearby two

irrigation projects should be studied. This should be got compared with the

estimated yield and peak flood obtained from the procedure as given at Chapter II.

Soil investigation: These should be done and evaluated as per Chapter IV.

Hydraulic and structural design:

It should be done On the basis of Techno economic feasibility.

Hydraulic parameters: FTL, MWL, LSL etc. at water availability of 75%

dependability should be decided as per Chapter–V “Fixation of Principal

Levels”

Design of dam: This shall be done as per Chapter - VI and relevant TC/IS

codes.

Type of spillway: Flush bar/waste weir/spillway. This shall be decided as per

Chapter -VII,

Design of Spillway: Flush bar /waste weir/spillway: This shall also be done as

per Chapter -VII.

Design of canal and its structures: This shall be done as per Chapter VIII and

concerning IS Codes.

The project estimate should be prepared as per Annexure – IX “Preparation of

cost estimates”.

10. Preparation & Submission of Project Report: - After preparation of DPR it

must be submitted to E-in-C along with all enclosures as given in Chapter X.

Other important instructions & circulars issued by department from time to

time & important points to be kept in view while preparation & submission of

DPR are also given in this Chapter.

Chapter II

Hydrology

Basic Data/ Information Required for Hydrological Design

General: Brief History of the Project giving salient features related to the Dam

& spillway.

Data Required

Maps & Plans: Catchment Area Plans Scale 1:50,000 or 1:25,000 showing

contour lines

a. River course & tributaries to be shown with their names

b. Location of all gauge & discharge sites

c. Location of water storage structures intercepting the catchment

d. Location of ordinary & SRRG raingauge stations in & around the

vicinity of the catchment of dam site / G.D. site

e. Location of nearby minor medium and major dams

I-Flood Studies

Following basic data are required for flood computation studies.

Critical Flood Events: Rain fall & corresponding run off data for three

or four flood events with date & time experienced in the catchment.

1. Hourly gauge /discharge data at the nearest G & D station preferably

on the same side of ridge

2. Corresponding hourly rainfall data of rain gauge station including data

& charts of SRRG located in the catchment or in the close vicinity of it

3. If observed short duration data are not available, then

a. For catchment area less than 25 Sq.Km. and 100 year flood category,

flood estimation should be done on the basis of sub-zone wise formula as

given below. The area of sub zones (As per CWC sub zonal reports)

covering whole Madhya Pradesh is shown in the map enclosed.

Sl.No. Sub-zone no.

Name of sub-zone Formula Remarks

1 1(b) Chambal Sub-zone Q= 19. A 0.84 Q= Discharge in Cumecs & A=Area in Sq.km

2 1(c) Betwa Sub-zone Q= 25. A 0.75 -do-

3 1(d) Sone Sub-zone Q= 25. A 0.75 -do-

4 3(a) Mahi Sub-zone Q= 21. A 0.80 -do-

5 3(b) Lower Narmada and Tapti Sub-zone

Q= 23. A 0.75 -do-

6 3(c) Upper Narmada and Tapti Sub-zone

Q= 21. A 0.84 -do-

7 3(f) Lower Godawari Sub-zone Q= 19. A 0.84 -do- (Note: For more details TC-52 may be referred given in end of this chapter).

b. For other conditions, synthetic unit hydrograph approach should be

adopted and respective sub zone reports published by CWC is to be

referred & used.

4. Generalized P.M.P. (Probable Maximum Precipitation) Atlas for those

river basins for which CWC have prepared & published.

5. For 100 year storm isopluvial maps published by IMD may be referred.

6. Type of strata of bed and sides of Nalla /River

7. Other Miscellaneous data like silt load etc.

Criteria for classification of dam according to size and inflow design flood:

This criteria has been given in IS 11223: 1985 "Guidelines for fixing spillway

capacity". The dams may be classified according to size by using the static head at

FRL (from FRL to minimum tail water level) and the gross storage behind the dam as

given below. The overall size classification for the dam would be greater of the

following two parameters.

Classification Gross Storage Static Head at FRL

Small Between 0.5 and 10 million

m3

Between 7.5 m and 12

m

Intermediate Between 10 and 60 million

m3

Between 12 m and 30

m

Large Greater than 60 million m3 Greater than 30 m

Inflow design flood criteria:

Size as determined

above Inflow design flood for safety of Dam

Small 100 year flood

Intermediate Standard project flood (SPF)

Large

Probable maximum flood (PMF)

Drawings:

o L - Section of longest stream in the catchment for computing

equivalent slope

o The suitable cross sections upstream and downstream of proposed dam

axis including L- section with observed HFL marked with time & date

II-Yield Studies

Following basic data are required for Yield Studies

Rainfall Data:

Monthly rainfall data for all the rain gauge stations in and

around the catchment for minimum 40 years.

Run-off Data:

a. Monthly Runoff Data at the location nearest gauge & discharge

sites for minimum 15 years

b. Monthly average data of all the water storage structures

intercepting the catchment

c. Monthly volumes of out flows from spillways of intercepting

storage structures

d. Monthly data of storage/spillway in nearby two tanks for

comparison of data

Steps for Computation of Yield

(A) Based on Observed Discharge Data at G&D Site -By annual R-R

relationship :

a. Mark the location of proposed Dam site on Toposheet.

b. Mark the Catchment Area on Toposheet& measure it by Planimeter or

by any other method.

c. Mark rain gauge stations in and around the catchment & construct

"Thiessen's polygon" by drawing perpendicular bisectors to the lines

joining rain gauge stations.

d. Measure effective catchment area of each rain gauge

e. Calculate influence factor for each rain gauge station.

Effective Catchment Area

Influence Factor = ----------------------------

Total Catchment Area

f. Collect annual rainfall data of the considered rain gauge stations for 40

years

g. Compute weighted rainfall by multiplying rainfall with Influence Factor

h. Select nearby G&D site where discharge data for minimum 15 years

are available.

i. Collect annual runoff data (Rg) at G&D site.

j. Compute linear relation between weighted rainfall (Wg) & Runoff

(Rg) at G&D Site by using "Linear regression analysis"

Rg= AWg+B

Here a and B are coefficients, which are given by

N((∑Wg.Rg)- (∑Wg)(∑Rg))

A = -------------------------------------

N((∑Wg2)-(∑Wg)

2

(∑Rg)-A(∑Wg)

B = --------------------

N

Where N – number of observation sets between Rg and Pg. then

correlation coefficient „r‟ is calculated as

N(∑Wg.Rg)- (∑Wg)(∑Rg)

r = -------------------------------------------------------

√[N(∑Wg2)-(∑Wg)

2]x[N(∑Rg

2)-(∑Rg)

2]

„r‟ lies between 0 to +1 as Rg can have only positive correlation

withWg. It indicates good correlation if 0.7<R<1.0.

k. Compute standard error between weighted rainfall (Wg) & Runoff

(Rg) at G&D Site. Standard error should be minimum and limited

upto 5%.

SE = ∑( Rg-R’g)]2 - [∑(Wg-W’g)(Rg-R’g)]

2

∑(Wg-W’g) 2

(N-2)

l. Compute runoff at dam site (Rd) using total rainfall at dam site

(Wd) and correlation computed step f.

Rd= A Wd + B

m. Convert runoff (Rd) to volume in cubic unit

Yield(Y) = Rd * Catchment area

n. Arrange yield (Y) in descending order

o. Compute probability of every year from (N+1) years, where N is

number of years for which runoff data are available.

p. Considering yield at 75% dependability, the yield is calculated

using formula. {M/(N+1).}x 100

(Note :The yield of nearby two irrigation projects be studied. This

should be compared with the estimated yield as above)

B. Based on Binnie‟s Table :- In the absence of observed runoff data, yield

may be estimated using Binnie‟s Table given below.

REFERENCES: (Indian Standards must be of latest version.)

1. IS 11223 : 1985 Guidelines for fixing spillway capacity

2. TC-52

DESIGN SERIES TECHNICAL CIRCULAR NO.52 (Issued vide memo

No.65/BODHI/TC/R&C/2006 DATED 13-1-2006.) TECHNICAL

CIRCULAR FOR ESTIMATION OF DESIGN FLOOD FOR SMALL

DAMS

3. IS 4987 : 1994 Recommendation for establishing network of Rainguage stations.

BINNIES TABLE CONVERTED IN MKS

Annual Rainfall in mm

Yield/Sq.Km of CA in TCM

Annual Rainfall in mm

Yield/Sq.Km of CA in TCM

Annual Rainfall in mm

Yield/Sq.Km of CA in TCM

Annual Rainfall in mm

Yield/Sq.Km of CA in TCM

500 83 510 87 520 91 530 95

540 99 550 103 560 107 570 111

580 115 590 119 600 124 610 128

620 133 630 137 640 142 650 147

660 152 670 157 680 162 690 167

700 172 710 177 720 183 730 188

740 193 750 199 760 205 770 210

780 216 790 222 800 229 810 234

820 240 830 253 840 247 850 259

860 265 870 272 880 279 890 285

900 292 910 299 920 306 930 313

940 320 950 327 960 334 970 341

980 349 990 356 1000 364 1010 371

1020 379 1030 386 1040 393 1050 401

1060 400 1070 415 1080 422 1090 430

1100 437 1110 445 1120 452 1130 459

1140 466 1150 474 1160 481 1170 488

1180 496 1190 503 1200 511 1210 518

1220 526 1230 533 1240 541 1250 548

1260 556 1270 564 1280 571 1290 579

1300 586 1310 594 1320 602 1330 609

1340 617 1350 625 1360 633 1370 640

1380 648 1390 655 1400 663 1410 671

1420 679 1430 687 1440 695 1450 703

1460 711 1470 719 1480 727 1490 735

1500 743 1510 751 1520 759 1530 767

1540 775 1550 783 1560 791 1570 799

1580 807 1590 815 1600 824 1610 832

1620 840 1630 849 1640 857 1650 866

1660 874 1670 883 1680 891 1690 900

1700 909 1710 917 1720 926 1730 935

1740 944 1750 953

Chapter III

Data Required for Design of Minor Irrigation Projects

Whenever a problem of design of Minor Irrigation Project is to be dealt, following

information should be collected.

For Data required for design of Earth dam and Gravity dam: - Design Series TC-1 and TC-2

should be referred. (enclosed as Appendix 6 & 7).

1. Geological Data: Geological investigation may be done for the suitability of

foundation, water tightness of the reservoir and depth of cut off trench.

2. Hydrological Data: The data should be collected as per Chapter 2.

3. Miscellaneous Data/Calculations:

a. Proposed full tank level and maximum Water Level

b. Maximum wind velocity for determination of wave height

c. Minimum draw down level/canal sill level

d. Calculations for tail water rating curve

e. Requirements for roadways

f. Capacity and elevations of sluice

g. Chemical analysis of river water and ground water

h. Length of dam, non-overflow and over flow

i. Type of dam: earthen, masonry etc. to be provided

j. Details of saddle dam, if any etc.

4. Soil Test for Borrow Area and Foundation soils

Adequate number of soil samples should be got tested in Irrigation Research Laboratory

Hathaikheda Bhopal or other Material Testing Laboratory of department or Government

Engineering College situated in the vicinity.

Samples from each borrow pit at every 0.30 m depth should be collected. For foundation,

the soil samples be collected along proposed dam line for every one-metre depth at least

upto 3m depth or till the suitable strata is reached. On each side of nalla / river, samples

from foundation soil should be taken at locations of maximum, middle and minimum

height of dam embankment.

Collection of soil samples for investigations for establishing suitability of construction

materials should be done as per (Appendix VI of) Chapter II Survey & Investigation of

Book of specifications enclosed as Appendix I & Appendix 6.02 of W. D Manual VOL-II

PART-II.

Soil tests to be conducted for soil samples are as below:

a. Mechanical analysis

b. Liquid limit, plastic limit and shrinkage limit

c. Proctor's Maximum Dry Density and Optimum Moisture Content

d. Free swell index

e. Specific gravity

f. Permeability

g. Triaxial shear test (C and f)

h. Total soluble salts, Sulphate, Carbonate, Organic matter

i. Dispersibility

5. List of Drawings:

An index plan, scale 1:50,000 or 1:25,000, showing location of the scheme,

main and subsidiary nalla/drains, catchment Area, command area, locations of

rain gauge or river gauging stations, railway stations, adjacent scheme existing

or contemplated. This map should include all sites and locations, which may

find/mention in the report. It would be preferable if main sites and locations are

underlined. Always give latitudes and longitudes on the plan.

Other drawings which should be prepared are :-

A Lead Chart

B Basin plan & grid (Site plan showing arrangement of works with

contours)

C L-section of dam embankment showing soil /rock strata of foundation

and cut of trench

D Elevation Area storage (capacity) curve

E L- section & Grid plan of canals with a few typical X- sections

F Maximum Cross sections of dam,

G L-section of spill channel with plan

H Command Area map showing canals, chak, position of outlets,

Drainage‟s tracks etc.

I Drawing of important & typical structures of Dam & canal.

J Submergence area plan at contour interval not more than 0.5 m on a

scale preferably 1:4000 and should cover elevation of at least 3 m

above the proposed M.W.L. at dam site

K. Block level plan of dam site

L Tail water rating curve (Elevation discharge curve) along with

high flood level

M. L-section & Cross section of river in upstream and downstream

of proposed dam site covering sufficient length & upto 3 m above

H.F.L. on both sides and indicating highest flood levels during floods

received so far

N. Borrow area plan showing location and description of characteristics

of proposed material to be used in the construction of the dam

including, soil, sand, gravel etc.

O. Borrow area plan indicating

Depth and size of borrow pits/ are

Quantity of earth available in each borrow pit/area

Log of exploration of borrow pit/area indicating type of soils

available at different depth

Soil test results of soil of each borrow area

Chapter IV

Soil Properties and their Influence on Design of Dams

SYNOPSIS:

Many dams fail due to improper assessment of effect of soil properties of borrow area and

foundation soils on the stability of dams and appurtenant works. Here an effort has been

made to high light the different soil properties such as dispersivity and swelling pressure and

their effect on dam design. This will help in safe design of dams and will reduce the

number of dam failures. Five Annexes have been enclosed explaining soil classification

including description, average properties for different type of soils, suitability of soils for

construction of dams, degree of expansion of fine-grained soils and general guidelines

for embankment sections.

Generally the following soil tests are conducted before designing an earthen embankment.

These tests should be conducted on soils in the borrow area, foundation and existing

embankment (if any).

1. Particle size distribution

2. Atterberg limits

3. In situ moisture content and density test

4. Proctor maximum dry density and optimum moisture content

5. Total soluble solids with EC, pH, carbonates, bicarbonates, and

sulphates

6. Specific gravity

7. Permeability of disturbed samples and field permeability

8. Triaxial shear test for cohesion and angle of internal friction

9. Dispersivity by

(a) Pin hole test

(b) Crumb test

10. Free swell index

11. Swelling pressure

12. Compressibility

13. Ionic concentration of river water

14. Organic matter

1. Particle size Distribution:

Particle size distribution by sieve analysis (for particle size greater than 0.075

mm) and by hydrometer analysis (for particle size smaller than 0.075 mm) is

carried out in order to determine percentage of components (Table 1) present

in the soil.

Table 1. Grain size classification of soils:

S. No. Soil Type Particle size

1 Clay Less than 0.002 mm

2 Silt 0.002 to 0.075 mm

3 Fine sand 0.075 to 0.425 mm

4 Medium sand 0.425 to 2.000 mm

5 Coarse sand 2.000 to 4.750 mm

6 Fine gravel 4.750 to 20.00 mm

7 Coarse gravel 20.00 to 80.00 mm

Grain shape varies with particle size and mineralogy. Soil grains are classified

in three categories.

a. Bulky Grains: If the dimensions of the soil particles are about the

same, as in sand and gravel, the soil grains are described as being of a

bulky shape. Coarse-grained soils are bulky (except for mica).

b. Flaky or scale like grains: These resemble a piece of paper and are

extremely thin compared to their length and breadth.

c. Needle like grain shape:

Fine grained soils: These are soils more than 50% of which

pass through 75 micron IS Sieve.

Coarse grained soils: These are soils 50% or less of which pass

through 75 micron IS Sieve.

Clay (Particle size less than 0.002 mm)

Clays are plastic fines. They have low resistance to deformation when wet, but

when dry they are hard, cohesive masses. Clays are virtually impervious,

difficult to compact when wet and impossible to drain by ordinary means.

Large expansion and contraction with changes in water content are

characteristics of clays. The small size, flat shape and type of mineral

composition of clay particles combine to produce a material that is both

compressible and plastic. The clays having higher liquid limit are more

compressible. At the same liquid limit, the higher the plasticity index, the

more cohesive is the clay.

Small amount of organic matter in colloidal form in clay will result in

appreciable increase in liquid limit without increasing plasticity index. Clays

with high organic matter create voids through decay.

Silts (Particle size 0.002 to 0.075)

Silts are the non-plastic fines. They are inherently unstable in the presence of

water and have a tendency to become quick when saturated. Quick silts are

often called bull's liver by construction people. Silts are fairly impervious,

difficult to compact and are highly susceptible to frost heaving. Silt masses

undergo change of volume when distorted or strained in shear (the property of

dilatancy). The dilatancy property together with the "quick" reaction to

vibration affords a means of identifying typical silt in the loose, wet state.

When dry, silt can be pulverised easily under finger pressure (i.e. very slight

drystrength)

Silts differ among themselves in size and shape of grains, which are reflected

mainly in the ability to compress. Higher the liquid limit of a silt, more

compressible it is. The liquid limit of a typical bulky- grained, inorganic silt is

about 30 percent, while highly micaceous or diatomaceous silts (so called

elastic silts) consisting mainly of flaky grains may have liquid limit as high as

100 percent.

Soils containing large quantities of silt and clay are the most troublesome to

the engineer. These materials exhibit marked changes in physical properties

with change of water content. Dry clay is hard and suitable as a foundation for

heavy loads, but may turn into a soft, highly compressive material when wet.

Many of the fine soils shrink and crack on drying and expand on wetting,

which may adversely affect structures founded upon them or constructed of

them.

Coarse Grained Soils ( Gravel& Sand)

Gravel and sand have essentially the same engineering properties, differing

mainly in degree. Well-graded compacted gravel or sands are stable materials.

The coarse grained soils, when devoid of fines are pervious, easy to compact,

little affected by moisture and not subjected to frost action. Gravels are

generally more pervious, more stable and less affected by water or frost than

are sands, for the same amount of fines.

As sand becomes finer and more uniform, it approaches the characteristics of

silt with a corresponding decrease in permeability and reduction in stability in

the presence of water.

The soil classification based on particle size distribution and Atterberg limits

have been given in Annex 1.

2. Atterberg Limits:

The behaviour of all soils with fines and particularly clays varies considerably

with water content. Clay may be almost like a liquid or it may be very stiff

depending upon its water content.

If a fine-grained soil is mixed with a large quantity of water, it is in a liquid

state.

If the water content is gradually reduced, then the following apply:

a. Liquid limit: The limit of water content, at which soil water suspension passes

from zero strength to an infinitesimal strength, is the true liquid limit.

b. Plastic limit: The moisture content at which the soil has a small plasticity, as

determined by a standard test, is called the plastic limit.

c. Shrinkage limit: The moisture content, at which its further reduction will not

cause a further reduction in the volume of soil, is called shrinkage limit. At

shrinkage limit, voids in soil are completely filled with water.

In between plastic and shrinkage limits, the soil displays the property of semi

solid. Between the plastic and liquid limits, the soil exhibits plastic behaviour.

Table 2. Moisture content variation and Atterberg limits:

STATE LIMIT SATURATION VOLUME COLOUR

Liquid state Liquid

limit

Plastic

limit

Shrinkage

limit

100% Decreases Dark Plastic state

Semi solid state

Solid state Decreases Constant Light

d. The liquid limit is indicative of the compressibility of the soil. Soils having a

liquid limit above 45 are compressible in nature. Small amount of organic

matter in colloidal form in clay will result in an appreciable increase in liquid

limit without increasing the plasticity index. Liquid limit of bulky grained

inorganic silt is about 30%, which may be increase to 100% for elastic silts

consisting mainly of flaky grains.

If the shrinkage limit is less than 15, it is likely to develop cracks in the

embankment. If it is less than 10, the soil should not be used in embankments,

as the section is likely to develop extensive cracks. Soils having shrinkage

limit more than 25 are also not suitable for dam construction.

The shrinkage limit should be higher than the optimum moisture

content (OMC), otherwise dam section will develop cracks on moisture

reduction (drying).

If the shrinkage limit of the soil is lower than the OMC, then the soil

should be used for the inner core only. Outer shell should consist of

soils having a shrinkage limit higher than OMC.

e. Plasticity index: It is the difference between the liquid and plastic limits. For

non-plastic soils, the plasticity index is zero. For clayey soils, the plasticity

index is higher. It indicates the moisture contents over which the soil is in

plastic condition. The plasticity index depends upon the clay present in the

soil. The information regarding the type of clay in the soil may be obtained by

considering the plasticity index in relation to the liquid limit.

f. Shrinkage index: The numerical difference in between plastic limit and

shrinkage limit, is called shrinkage index.

In Annex 2 the suitability of soils for construction of dams based on soil

classification is available for general guidance.

3. In Situ Moisture Content and Density:

These values indicate whether the natural/embankment soil is dense or not,

and if the natural moisture content is near the OMC or not.

Various criteria for quality control have been proposed. Table 3 lists suggested

limits of density and moisture control.

Table 3. Criteria for control of compacted dam embankments

Type of

material

% of

4.75mm

& above

by dry

weight

of total

material

retained

Percentages based on 4.75 mm fraction

15 m or less in height Greater than 15 m height

Minimum

acceptable

density

Desirable

average

density

Moisture

limits

Wo-Wt

Minimum

acceptable

density

Desirable

average

density

Moisture

limits

Wo-Wt

Cohesive

soils

controlled

by the

Proctor test

0-25 95% of

MDD

98% of

MDD

-2% to

+2%

98% of

MDD

100% of

MDD

2% to

0%

(note 2)

26-50 92.5% of

MDD

95% of

MDD

95% of

MDD

98% of

MDD

more

than 50

(note 1)

90% of

MDD

93% of

MDD

93% of

MDD

95% of

MDD

Cohesionless

soils

controlled

by the

relative

density test

Fine

sands

with 0-

25

Dd=75 Dd=90

Soils

should

be very

wet

Dd=75 Dd=90

Soils

should

be very

wet

Medium

sands

with 0-

25

Dd=70 Dd=85 Dd=70 Dd=85

Coarse

sands

and

gravels

with 0-

100

Dd=65 Dd=80 Dd=65 Dd=80

Wo -Wt is the difference between optimum water content and fill water

content in percent of dry weight of soil MDD is the Proctor's maximum dry

density.

Dd is relative density

(note 1) Cohesive soils containing more than 50 percent gravel sizes should be

tested for permeability of the total material if used as a water barrier

( note 2) For high earth dams special instructions on placement moisture limits

will ordinarily be prepared.

Above table has been also given in page 4-69 in volume I of book of

specifications.

4. Proctor Maximum Dry Density and Optimum Moisture Content

Soil compaction refers to the process of obtaining increased density of soil in a

fill by reduction of its pore space by the expulsion of air. The bearing capacity

of any soil usually increases with increasing dry density and decreasing

moisture content. High density assures high shear strength and greater

imperviousness. When a soil is submerged, its effective density is reduced and

with this it's bearing capacity.

The moisture content of a soil is defined as the ratio of the weight of water

present in the soil to the dry weight of solid soil particles. The moisture

content at which the weight of soil grains obtained in a unit volume of the

compacted soil mass is maximum is called the "optimum moisture content"

and the dry density so obtained is called "Maximum Dry Density" (MDD). As

coarse-grained soils do not absorb the water and are not appreciably amenable

to lubrication, they do not display distinct Optimum moisture content. For

coarse and fine-grained soils, average values are 8 to 15 and 17 to 36

respectively as given in Annex 3. At OMC, the soil is broadly 90% saturated

depending upon type of soil, meaning that about 10% of the void space is

occupied by air.

Warning: The OMC should always be less than the shrinkage limit. Otherwise

on exposure to sun, cracks will develop in such soil. If such soil has to be used

in embankments, then it should be covered with good suitable soil, so that

moisture reduction in such soils is avoided.

5. Total Soluble Salts, E.C., pH, Carbonates, Bicarbonates and Sulphates

Total Soluble Salts: These consist of sodium, calcium, magnesium, and

potassium. The suitability of soil depends upon the percentage of sodium in

comparison to other cations. In dispersive soils, the increased salt

concentration (without an increase in sodium salt) reduces the dispersivity of

the soil. A very high percentage of total soluble salts may cause failure of an

embankment by formation of cavities caused by removal of salts with seeping

water.

Electrical Conductivity: This measures the ability of the solution to conduct

electricity and is expressed in millimhos/cm or micromhos/cm. E.C. value in

millimhos/cm at 250 c can be converted to salt concentration in parts per

million or milligram per litre with reasonable accuracy by multiplying by 640.

Table 4. Electical Conductivity showing severety of salt content

E.C. in miili-mhos/cm Severity

Less than 1 Normal

Between 1 and 2 Fairly good

Between 2 and 3 High

Between 3 and 4 Very High

1 miili-mhos/cm=1000 micro-mhos/cm

pH value: The pH value represents the concentration of hydrogen ions (H) in

water. It is the logarithm of the reciprocal of the hydrogen ion concentration.

A value of pH less than 7 indicates acidic character while pH value more than

7 is indicative of alkaline character, while 7 is neutral. Alkaline soils (pH > 7)

are more prone to dispersivity.

Carbonates: of calcium and magnesium are not soluble in water. Only

carbonates of alkali metals like sodium and potassium are soluble in water.

Bicarbonates: Bicarbonates are generally soluble in water. High concentration

of bicarbonates may result in precipitation of calcium and magnesium

bicarbonates from soil, increasing the relative proportions of sodium ions,

which is harmful for stability of embankments.

Sulphates: The sulphates (principally soluble sulphates) present in soil or

ground water in contact with concrete/masonry works attack the cement paste

causing deterioration and disintegration. The free lime of cement acts with

sulphates finally forming calcium sulphate aluminate. This compound

crystallises on drying causing expansion and ultimate disintegration of

concrete. As such, soils having sulphates in appreciable quantity should not be

used adjoining concrete/masonry structures. If it is essential to use soils

containing sulphates then suitable admixtures should be added to

concrete/mortar to save them from the ill effects of sulphates.

Salt concentration is expressed in parts per million (PPM) or milligram per

litre (mg/l) both units being equal.

6. Specific Gravity:

This is the ratio of weight in air of a given volume of soil solids to the weight

of an equal volume of distilled water, at a given temperature.

The specific gravity of engineering soils usually varies between 2.6 to 2.8. If it

is less than 2.6, it may indicate possible presence of organic matter.

7. Permeability:

The rate of movement of gravitational water through soil pores is termed the

permeability of soil.

Permeability of disturbed/undisturbed soil samples should be measured in the

laboratory. Permeability of foundation and embankment soils should also be

measured in situ. The soils are categorised as permeable, semi permeable or

impermeable as per the following limits.

Impermeable : with permeability less than 1 x 10-6 cm/sec

Semi permeable: with permeability 1x 10-6 to 1x 10-4 cm/sec.

Permeable : With permeability more than 1x 10-4 cm/sec.

The dam embankments should be impermeable. The permeability of the

downstream section of embankment should not be less than that upstream.

8. Triaxial Shear Test

This is a test in which a cylindrical specimen of soil encased in an impervious

membrane is subjected to a confining pressure and then loaded axially to

failure.

a. Unconsolidated Undrained Test (Q test)

This is a soil test in which the water content of the soil sample remains

unchanged during the application of the confining pressure and the

additional axial (or shearing) force. No drainage and hence no

dissipation of pore pressure is permitted during the application of the

confining pressure and then the axial load.

This test is usually performed on partly saturated soil and is used

mostly for analysis of the stability of the earth dam under the "end of

construction" condition.

b. Consolidated Undrained Test (R test)

Drainage is permitted after application of confining pressure so that the

sample is fully consolidated under this stress. No drainage is permitted

under the application of the axial load. This test is carried out with pore

water pressure measurement, for obtaining effective stress values of

cohesion and angle of internal friction.

The values of C and ɸ obtained from this test, are used to check

stability of the upstream slope under the sudden draw down condition,

after the soils are fully saturated.

c. Consolidated drained Test (S test)

Drainage is permitted after application of the confining pressure and

during the axial loading. The values of shear parameters so obtained

are almost the same as the effective stress values obtained from

undrained tests with pore pressure measurement.

The values of C and f obtained from this test are used to check stability

of the downstream slope when the reservoir is in operation.

Generally, the 25th percentile strength values are used in the stability

analysis of slopes (i.e. 75% of the samples exhibit strength values).

9.Dispersivity:

Dispersive soils are clay soils, which are highly susceptible to concentrated

leak by a process of colloidal erosion. These clays have a predominance of

dissolved sodium cations in the pore water, whereas ordinary erosion resistant

clay has calcium and magnesium as the dominating dissolved cations. These

are eroded by a process in which the, individual colloidal clay particles go into

suspension in practically stilled water. All colloidal particles carry a like

electric charge, which prevents the particles from attracting each other.

Dispersivity of clayey soils is determined by two tests namely:

a. Sherard's pin hole test

b. Crumb test

These two tests should be carried out on a given sample and if the soil is found

dispersive by any of the two tests, it should be categorised as dispersive.

Higher values of pH and sodium concentration and lower values of total dissolved salts

promote soil dispersivity

Soils containing the clay mineral montmorillonite, are prone to dispersion. Generally,

dispersive clays have been red, brown, grey (some nearly white), yellow and all

transitions among them. No black colour soils with obviously high organic contents

have tested dispersive. All tested fine grained soils, known to be derived from in situ

weathering of igneous and metamorphic rocks, have been found non dispersive as well

as soils derived from lime- stone.

Salt, hydrated lime, gypsum, alum and fly ash may be used to treat dispersive soils

after observing their effect on the soil in laboratory

.

Dispersive soil can be used as fill material by keeping placement moisture content on

the wetside (about 1%) of optimum moisture content. Such soil should be compacted

in thinner layers using pneumatic tampers to obtain a high degree of density, and

permeability less than 1x10-6 cm/sec and good bond with the structure/ foundation

rock. As far as possible non- dispersive soils should be used near structures and at rock

interface.

With dispersive soils the frequency of density and moisture control tests should be

increased.

One should closely observe the compacted soil surface for cracks and take measures

for prevention/correction of moisture by appropriate methods.

Effectively seal surface cracks in the foundation rock by slush grouting.

10. Free Swelling Index:

This indicates swelling potential of fine-grained soils when water is added to

them. If the free swell index of a soil is more than 100, then such behaviour

may require special attention. The degree of expansion of fine-grained soils

based on their properties is available at Annex 4.

11. Swelling Pressure:

The characteristics of swelling and the swelling pressure of black cotton soils

are attributed to the presence of montmorillonite or a combination of

montmorillonite and illite clay minerals. Clay minerals are made of colloidal

particles having diameters less than one micron. The presence of specific clay

minerals is determined by an x-ray diffraction test.

Degree of expansion: The fine-grained soils exhibit low to very high degree of

expansion depending upon the presence of clay minerals. Based upon the

Atterberg limits and free swell of a soil the degree of expansion and degree of

severity is indicated in at Annex 4.

As per IS 6186 : 1986, Bentonite, a characteristic type of fine- grained clay, is

an alteration product of volcanic ash containing not less than 85 percent of the

clay mineral montmorillonite.

Black cotton soils have a predominance of the montmorillonite clay mineral.

The grain size distribution and index properties of expansive soils expressed in

percentages are in the following ranges.

Gradation:

Clay (less than 2 micron) 50 to 70%

Silt (0.075 mm to 0.002 mm) 20 to 35%

Fine and medium sand (2 mm to 0.075 mm) 30 to 50%

Coarse sand and Gravel (greater than 2 mm) Less than 10%

Index Properties:

Liquid Limit 60 to 100%

Plastic Limit 30 to 50%

Plasticity

Index 30 to 40%

Shrinkage

Limit 8 to 12%

If a high liquid limit (greater than 55 %) is accompanied by a low shrinkage

limit (lower than 10) swelling pressure and free swell tests should be

conducted.

The swelling pressure is determined by conducting a one dimensional swelling

pressure test using either fixed or floating rings on both undisturbed and

remoulded soils in the partially saturated condition. Two methods are used to

determine swelling pressure.

Consolidometer method in which the volume change of the soil is

permitted and the corresponding pressure required to bring back the

soil to its original volume is measured.

Constant volume method in which the volume change is prevented and

the consequent pressure is measured. The details of the two methods

are available in IS 2720 (Part XLI): 1977.

If the swelling pressure is more than 50 kPa, treatment is necessary. In canals,

treatment is provided by a cover of cohesive non-swelling soils over swelling soils

as per IS 9451: 1994

12. Compressibility:

The decrease in volume per unit increase of pressure is defined as the

compressibility of soils. It is measured only for undisturbed samples.

Compressibility is a property of a soil pertaining to its susceptibility to

decrease in volume when subjected to load. The phenomenon of

compressibility is associated with a change in volume of the voids and, to a

very limited extent with changes in the soil particles.

Soils having only air voids will be compressed immediately upon application

of load. In saturated soils, the pore pressure will increase significantly with an

increase in the soil's compressibility. In general a very compressible cohesive

soil will develop high pore pressure when loaded, unless there is an

appreciable amount of air present. Compressibility of sand and silt varies with

density. Compressibility of clay varies directly with water content and

inversely with shear strength.

13. Ionic concentration in river water:

Ionic concentration in river water below 1.2 meq/litre is considered low. River

water passes through embankment. As such it may dissolve salts present in the

embankment and foundation. Small quantities of calcium and magnesium salts

in soil may increase dispersivity of soils and thus such reservoir water may

aggravate a piping problem.

14. Organic matter:

Even a small amount of organic matter in colloidal form in clay, will result, in

an appreciable increase in liquid limit of the material, without increase in

plasticity index. The tendency for soils high in organic content is to develop

voids by decay while this makes them undesirable for engineering use. Soils

containing even moderate amounts of organic matter are significantly more

compressible and less stable than inorganic soils.

In Annex 5, general guidance for embankment slope inclination based on soil

classification and height of embankment has been provided for guidance.

CONCLUSIONS:

The inference of soil test result help in designing the earthen embankments/ dams

with proper safety measures and economy.

Following inferences need special attention.

1. S.L.(shrinkage limit) of soil should be higher than its optimum

moisture content (OMC), otherwise cracks will develop upon moisture

reduction below O.M.C.

2. Soils having S.L. less than 10 should not be used in dam embankment,

as the dam section is likely to develop extensive cracks.

3. If S.L. is in between 10 to 15, than it is likely to develop cracks in the

embankment.

4. Specific gravity of most inorganic soils is in between 2.60 to 2.80.

Values less than 2.60 indicate possible presence of organic matter in

appreciable quantity.

5. Permeability of the downstream portion of an embankment should be

higher than the upstream portion; otherwise dam may fail on this

account only.

6. The soils containing appreciable quantities of colloidal particles (less

than 0.001 mm in diameter), sodium, the clay mineral Montmorillonite

& illite, are prone to dispersion. Higher values of percent sodium in

soil make it dispersive.

7. The dispersive soil may be used safely in dam embankment except

near masonry/concrete works and near foundation rock, if the permeability

of the embankment may be ensured to be 1x10-6 cm/sec or less.

8. Soils of high swelling potential are not suitable as embankment

material.

9. The soils containing appreciable quantities of sulphates should not be

used adjoining the concrete/masonry works. If it is essential to use, then a

suitable admixture should be added to the concrete/mortar to make safe.

REFERENCES:

1. 'Earth Manual' Publication of United States Bureau of Reclamation

2.

I.S. 1498:

1970.

Classification and identification of soils for general

engineering purposes"

3 I.S.12169:

1987. "Criterion for design of small embankment dams"

4 ASTM

Special Technical Publication No. 623(1977).

"Dispersive clays, Related Piping, and Erosion in

Geotechnical Projects"

5 I.S.

6186:1986 Specification for bentonite

6 I.S. 3873:

1993

Laying cement concrete/stone slab lining on canals

Code of practice

7 I.S.

9451:1994 Guidelines for lining of canals in expansive soils

8

I.S.

2720(Part

XLI:1977)

Methods of test for soils-Part XLI Measurement of

swelling pressure of soils.

ANNEXURE-I

Soil Classification including Description

a. Coarse grained soils: These contain more than half materials larger than 75

micron IS sieve size, the smallest particle visible to the naked eye.

(i) Gravels - More than half of coarse fraction is larger than 4.75 mm IS Sieve

size.

Clean gravels (Little or no fines) GW Well graded gravel, gravel sand mixture,

little or no fines

-- do -- GP Poorly graded gravel or gravel sand

mixture, little or no fines

Gravel with fines(Appreciable

amount of fines) GM

Silty gravel, poorly graded gravel - sand -

silt mixture

-- do -- GC Clayey gravel, poorly graded gravel - sand

- clay mixtures

(ii) Sands - More than half of fraction is smaller than 4.75 mm IS sieve size.

Clean sands ( Little or no fines) SW Well graded sands, gravelly sands,

little or no fines

-- do -- SP Poorly graded sands or gravelly sands,

little or no fines

Sands with fines (Appreciable amount of

fines) SM

Silty sands, poorly graded sand - silt

mixtures

-- do -- SC Clayey sands, poorly graded sand clay

mixtures

b. Fine grained soils: These contain more than half of materials smaller than 75 micron

IS sieve size. The 75 micron IS sieve size is smallest particle size visible to the naked

eye.

Silts and clays with low

compressibility and liquid limit

less than 35

ML

Inorganic silts and very fine sands rock

flour, silty or clayey fine sand or clayey

silts with none to low plasticity

-- do -- CL

Inorganic clays, gravelly clays, sandy

clays, silty clays, lean clays of low

plasticity

-- do -- OL Organic silts and organic silty clays of low

plasticity

Silts and clays with medium

compressibility and liquid limit

greater than 35 and less than 50

MI Inorganic silts, silty or clayey fine sands or

clayey silts of medium plasticity

-- do -- CI

Inorganic clays, gravelly clays, sandy

clays, silty clays, lean clays of medium

plasticity

-- do -- OI Organic silts and organic silty clays of

medium plasticity

Silts and clays with high

compressibility and liquid limit

greater than 50

MH

Inorganic silts of high compressibility,

micaceous or diatomaceous fine sandy or

silty soils, elastic soils

-- do -- CH Inorganic clays of high plasticity, fat clays

-- do -- OH Organic clays of medium to high plasticity

c. Highly organic soils:

Pt Peat and other high organic soils with very high compressibility

ANNEXURE-II

Suitability of soils for construction of dams

Relative

Suitability

Homogeneous

Dykes

Zoned Dam Impervious Blanket

Impervious Core Pervious Shell

Very Suitable GC GC SW, GW GC

Suitable CL, CI CL, CI GM CL, CI

Fairly Suitable SP, SM, CH GM, GC, SM,

SC, CH SP, GP CH, SM, SC, GC

Poor -- ML, MI, MH -- --

Not Suitable -- OL, OI, OH, Pt -- --

(Extract from Appendix A of I.S. 12169-1987)

ANNEXURE-III

Average properties for different types of soils

S.

No. Soil Group

Maximum Dry

Density

(Kg/cum)

Optimum

Moisture Content

(Percent)

Cohesion Kg/sqm Degrees

1 GC >1840 <15 NA >31

2 GM >1830 <15 NA >34

3 SM 1830+16 15+0.4 500+500 30+4

4 SC 1840+16 15+0.4 1100+600 31+4

5 ML 1650+16 19+0.7 900+NA 32+2

6 CL 1730+16 17+0.03 1200+200 28+2

7 CH 1510+32 25+1.2 1300+600 19+5

8 MH 1310+64 36+3.2 2000+900 25+3

(Extract from Table 2 of I.S. 12169-1987)

ANNEXURE-IV

Degree of Expansion of fine grain soils

Liquid

Limit

Plasticity

Index

Shrinkage

Index

Free Swell

(Percent)

Degree of

Expansion

Degree of

Severity

20-35 <12 <15 <50 Low Non Critical

35-50 12-23 15-30 50-100 Medium Marginal

50-70 23-32 30-60 100-200 High Critical

70-90 >32 >60 >200 Very High Severe

(Extract from Table 8 of I.S. 1498-1970)

ANNEXURE-V

General guidelines for embankment sections

S.

No. Description Height upto 5 m. Height above 5 m.

Height above 10 m.

and upto 15 m.

1 Type of Section

Homogeneous/

Modified

homogeneous section

Zoned/ Modified

homogeneous/

Homogeneous

section

Zoned/ Modified

homogeneous/

Homogeneous section

2(a) Side slopes for

coarse grained soils U/S D/S

(i) GW, GP, SW, SP Not Suitable Not Suitable

Not suitable for core,

suitable for casing

zone

(ii) GC, GM, SC, SM 2:1 2:1 2:1 2:1

Section to be decided

based upon the

stability analysis

(b) Fine Grained Soil

(i) CL, ML, CI, MI 2:1 2:1 2.5:1 2.25:1 --do--

(ii) CH, MH 2:1 2:1 3.75:1 2.5:1 --do--

3 Hearting zone Not required May be provided Necessary

(a) Top Width -- 3 m. 3 m.

(b) Top level -- 0.5 m above MWL 0.5 m above MWL

4 Rock Toe Height

Not necessary upto 3

m height.

Above 3 m height,

1m height of rock toe

may be provided.

Necessary.

H/5, where H is

height of

embankment.

Necessary.

H/5, where H is

height of

embankment.

5 Berms Not necessary Not necessary

The berm may be

provided as per

design. The minimum

berm width shall be

3m.

(Extract from Table 1 of I.S. 12169-1987)

Chapter V

Fixation of Principal levels

General :-

(1) Water planning is most important feature of any project. You must try

to utilise as much water as available at any particular site. To make it clear

we should try to use at least 90% of 75% dependable yield at any particular

site. The principal levels of dam must be fixed accordingly.

Minor projects may have dam category “large dam or small dams”, hence all

the specification / consideration i.e. finalisation of principal levels etc. shall

be done as per the category “large dam or small dam”.

Small Earth Dam

An earth dam may be termed as a small earth dam if it fulfils all the following criteria;

Its height is less than 15m above the deepest riverbed level

The volume of earthwork involved in dam construction is less than 0.75 million

meter cube

Storage created by the embankment is less than one million meter cube; and

The maximum flood discharge from the intercepted catchment area is less than

2000 cumecs

A sample calculation for fixation of Principal Levels of Small Dams is given below.

For fixation of Principal Levels of Large Dams following IS Codes should be

referred.

IS code no Subject

5477 Pt I Methods for fixing the capacities of reservoirs:

General requirements

5477 Pt II Methods for fixing the capacities of reservoirs: Dead storage

5477 Pt III Methods for fixing the capacities of reservoirs: Live storage

5477 Pt IV Methods for fixing the capacities of reservoirs: Flood storage

10635 Free board Computations.

Note :- I S codes must be of latest version

Sample calculations for fixation of Principal Levels of Small Dams

JALANDHAR TANK PROJECT

FIXATION OF PRINCIPAL LEVELS

(A)Yield Calculations:- Yield should be calculated on the basis of Rainfall & Run–

off datas as discussed in detail above in chapter II “Hydrology”. However in the

absence of observed runoff data, yield may be estimated using Binnie‟s table as given

below.

(1) Total catchment area 3.28 Sq mile or 8.46 sqkms

(2) 75% dependable rainfall 38.35 inch or 974.09 mm

rain gauge station since year

1963-64 to 2008-09

(2) 75% dependable yield for C.A 3.28x 31.485 x 0.90 = 92.94 Mcft

= 2.632Mcum

(3) Live storage of the tank considering =2.632 Mcum

net yield. 2 (Refer foot note)

(4) Limited to 0.3 x C.A = 0.3 x 8.46 =2.538 Mcum

Live storage - 2.538 Mcum

(B) Fixation of LSL (Dead Storage)

(1) Dead Storage considering silting 0.50 x 3.28 x 100 x 43560

@ 0.50 acreftPer year per sq mile 1000000

of catchment area for 100 years. =7.14Mcft or 0.202Mcum

(2) Corresponding R L - RL 506.80

having capacity - 0.209 Mcum

(3) So LSL is fixed at -506.80 M

Provide LSL RL 506.80M with Dead storage - 0.209 Mcum

2 Currently 80% of the net yield is considered in Minor schemes , but Dam directorate has recommended to

utilize 100% hence decision is needed.

(C)Fixation of full tank level (FTL)

(1) Kharif requirement of Sept/2 + Oct = 0

(Refer monthly water requirement)

(2) Evaporation losses of Kharif season = 0.329 Mcum

(Calculations should be enclosed)

(3) Rabi requirement = 1.678 Mcum

(Refer monthly water requirement)

(4) Evaporation losses of Rabi season = 0.452 Mcum

(Calculations should be enclosed)

(5) Dead storage = 0.209 Mcum

Gross capacity of tank = (1) + (2) + (3) + (4) + (5)

= 0 + 0.329 + 1.678 + 0.452 + 0.209

= 2.668Mcum

This capacity is available at RL. 510.60 M . Hence F.T.L is fixed at R.L

510.60 M

Check by Formula

Live Storage = Gross Storage – Dead Storage

= 2.700 – 0.209 = 2.491 Mcum

Designed Irrigation 415 Ha

Live Storage Mcum = K/200 + R/170 + P/131

= 0 + 415/170 + 0 = 2.44Mcum

Which is almost the Live capacity fixed.

(E) Fixation of M.W.L–

By taking 0.90 M flood lift

M.W.L is fixed at (510.60 M +0.90 M) = R.L 511.50 M

However for fixation of M W L alternate studies for technoeconomical

feasibility should be done & following factors should also be considered

while fixing flood lift & MWL.

(1) Availability of site for surplussing arrangements.

(2) Topographical features & levels available.

(3) Quantum of flood & routed flood.

(4) Capacity of D/S channel.

(5) Affected population & property due to MWL.

(F) Fixation of TBL– As per Technical Circular No 22 for this size of

project free board of 2.00 M is required;

Therefore TBL is fixed at (511.50 + 2.0 M) = R.L 513.50M

Chapter VI

Design of Earth Dams

For design of small Earth Dams guideline as given below should be followed. For

large Earth Dams relevant TCs mentioned in different paras of this guideline & IS

code no 8826 “Design of Earth & Rockfill Dam should be followed.”

Guidelines for Design of Small Earth Dams

(Design Series Technical Circular No.-42)

1.0 GENERAL

A large number of small embankment dams are being designed by the local design

office and built in the state. In designing a small embankment dam, use of IS: 8826-

(Guidelines for design of large earth and Rock-fill dams) is made. This sometimes,

results in uneconomical and unwarranted provisions in design. It is, therefore, felt

necessary that a separate Technical Circular should be available for guiding the design

of a small embankment dam in the state.

1.1 Small Earth Dam

An earth dam may be termed as a small earth dam if it fulfils all the following criteria;

Its height is less than 15m above the deepest riverbed level

The volume of earthwork involved in dam construction is less than 0.75 million

meter cube

Storage created by the embankment is less than one million meter cube; and

The maximum flood discharge from the intercepted catchment area is less than

2000 cumec

2.0 SCOPE

This technical circular provides guidelines to design a small earth dam.

3.0 TERMINOLOGY

For the purpose of this circular, following definitions shall apply:-

3.1 Casing or Shell: - All zones other than core in a zonal earth dam are called Casing.

3.2 Core: - A zone of impervious earth within a zoned earth dam.

3.3 Cut-off:- A barrier of impervious material provided in foundation of a dam, to reduce

seepage of water through foundation and abutments.

3.4 Edging: - A short protection on the downstream edge of the top width of dam.

3.5 Embankment Dam: - A dam composed of any type of soil including rock.

3.6 Free board: - The vertical distance between the top bund level of an embankment

and the maximum reservoir water level.

3.7 Full Reservoir Level (FRL):- It is the highest level of the reservoir at which water is

intended to be held for various uses including part or total of the flood storage without

allowing any passage of water through spillway.

3.8 Homogeneous Earth Dam: - An embankment dam composed of single type of

material.

3.9 Horizontal Filter: - A layer of uniform or graded pervious material placed within

body of the dam horizontally.

3.10 Impervious Blanket or Clay Blanket: - An upstream impervious soil layer of

specified thickness laid over a relatively pervious stratum and connected to the core.

3.11 Impervious Strata: - The strata have range of permeability similar to core material.

3.12 Inclined/Vertical Filter or Chimney Filter: - A layer of uniform or graded pervious

material placed inclined/vertical in the body of the dam.

3.13 Inner Cross Drain: - A trench filled with filter material to collect seepage from inner

longitudinal drain and carry it to toe drain.

3.14 Inner Longitudinal Drain: - A trench filled with filter material and laid along the

downstream toe of the core of dam to collect seepage from core of the dam.

3.15 Lowest Water Level (LWL) or Minimum Draw Down Level (MDDL):- The

lowest level to which a reservoir may be lowered keeping in view the requirements

for hydropower generation or irrigation and other needs.

3.16 Maximum Water Level (MWL):- It is the highest level to which the reservoir water

will rise while passing the design flood with the spillway facilities in full operation.

3.17 Pore Pressure:-The pressure developed in the air-water fluid within the voids of the

soil mass under external force when drainage is prevented.

3.18 Relief Well: - Vertical wells or bore holes, downstream of or in downstream shoulder

of an earth dam, to collect and control seepage through or under the dam so as to

reduce water pressure.

3.19 Rip-Rap: - It is a protection to an embankment material against erosion due to wave

action, velocity of flow, rain wash, and wind action etc., provided by placing a

protection layer of rock fragments or manufactured material.

3.20 Rock-Toe / Boulder Toe:-A zone of free draining material comprising of rock

fragments/boulders/cobbles etc. provided at the toe of the dam.

3.21 Sudden Draw-Down:-The rate of lowering of reservoir water level which does not

allow full dissipation of pore pressure simultaneously with the lowering of the

reservoir water level.

3.22 Toe Drain: - A trench filled with filter material or without it along the downstream

toe of an earth dam to collect seepage from horizontal filter and lead it to natural

drain.

3.23 Turfing: - It is a cover of grass grown over downstream slope of an embankment to

prevent erosion of soil particles by rain-wash and wind action.

3.24 Zoned or Zonal Earth Dam: - An earth dam composed of zones of different types of

soils.

4.0 CLASSIFICATION

Based on materials used in construction an earth dam can be classified as hereunder:-

4.1 Homogeneous Dam:-As defined in para 3.8 above.

4.2 Zoned or Zonal Earth Dam:- As defined in para 3.24 above.

5.0 FUNCTIONS AND DESIGN REQUIREMENTS OF DIFFERENT

COMPONENTS OF THE DAM

5.1 Components

Different components of an earth dam may be listed as below:-

i) Core or hearting

ii) Casing or shell

iii) Internal drainage arrangement

iv) Slope protections

v) Edging

vi) Impervious or clay blanket

vii) Cut-off (puddle trench)

viii) Relief wells

ix) Downstream drainage arrangements

5.2 Core or Hearting

Core is a zone of impervious earth and provides an impermeable barrier within the

body of the dam.

5.2.1 Location of Core

For small dams core should be centrally located.

5.2.2 Dimensions of Core

Following considerations govern the core thickness:-

i) Availability of suitable impervious material for core

ii) Resistance to piping

iii) Permissible seepage through dam

iv) Availability of other material for casing, filter etc.

In general slopes of central core are to be provided as 1:1on the both upstream and

downstream. However, depending upon availability of core material, slopes may be

provided steep up to ½ (H): 1(V) after satisfying the property requirement of core

material and recording reasons for the same.

5.2.2.1 Top width of Core

It should be provided as 3m minimum.

5.2.2.2 Top Level of Core

For small earth dams, the top level of the core be provided at a level equal to MWL +

0.5m.

5.2.2.3 Suitable Core Material

To determine suitability of soil as core material, its testing is necessary. Soil groups

generally suitable for core construction are indicated in Annexure-I. Specifically soils

having permeability less than 10-5

cm/second, Plasticity Index (P.I.) > 15, clay content

> 30% and liquid limit between 30 to 50% are suitable for core construction. To avoid

swelling tendencies the P.I. shall not exceed 30. Soils having PI less than 10 may have

dispersive qualities and should be used with utmost care.

The design series technical circular (T.C.) No. 11 “Core in earth dams” should be

referred for the purpose.

5.3 Casing or Shell

On outer side of core, a cover of relatively pervious soil is provided. This protects the

core from external damages such as erosion from the rainwater, weathering and also

under conditions of sudden draw sown and steady seepage. Shell helps core to retain

its moisture content and thus prevents cracks in it.

5.3.1 Casing Material

The relatively pervious soils are suitable for casing. These are not subject to cracking

on direct exposure to atmosphere and are relatively free draining. Soil groups suitable

for casing are shown in Annexure-I. Soils with coefficient of permeability greater

than 10-2

cm/second develop no pore pressure and are free draining. Moorum is a

casing soil.

5.3.2 Top Width

Top width for small earth dam should be kept minimum as 4.5m uniformly

throughout the length of the dam. Surface drainage of crest should be provided by

sloping the crest in a grade of 1 in 50 to drain towards upstream.

The design series technical circular (T.C.) No. 10 “Crest Width of Earth/Rock fill

Dams” should be referred for the purpose.

5.3.3 Slope and Section

The slopes of casing depend upon soil properties. General guidelines for embankment

section are recommended in Annexure-II.

For more than 10 M heights of dams, slopes are to be decided on the basis of stability

analysis

The design series technical circular (T.C.) No. 40 “Stability analysis of earth dam”

should be referred for the purpose.

5.3.4 Free Board

The objective of free-board is to provide assurance for safety of the dam against

overtopping due to inflows into the reservoir, wind set up, wave run up, mind slides,

seismic activities, and extreme settlement of the embankment and/or its foundation.

For computation of free board, design series technical circular No. 22 issued by

BODHI may be referred to. Minimum free board to be adopted is 2m.

5.3.5 Shrinkage and Settlement Allowance

Shrinkage and settlement allowance shall be provided:-

i) For dams founded on rock: - The allowance shall be provided at a rate of 1%

of the height of the dam.

ii) For dams founded on soil or compressible foundation:- The allowance shall be

considered as 2% of the height of the dam.

The shrinkage allowance is to be computed on above guidelines for various heights

i.e. wherever there is a berm or change of slope and also for top bund level of the

dam. These points should be raised vertically by the magnitude of shrinkage

allowance to be provided. The points so obtained shall be joined starting from original

base width.

5.4 Internal Drainage Arrangement

An internal drainage arrangement helps in safe passage of seeping water. This

arrangement as far as, possible shall be provided with locally available sand and

gravel.

The design series technical circular (T.C.) No. 49 “Control of seepage through body

of earth Dams” should be referred for the purpose. The arrangement comprises as

here under:-

5.4.1 Horizontal Filter

This filter is provided in the downstream portion of the dam. It collects seepage from

chimney filter, body of the dam and also from its foundation and leads seepage, thus

collected, to the downstream toe drain.

5.4.1.1 Thickness

Horizontal filter of graded pervious material satisfying filter design criteria as

described in IS: 9429-1999- Code of practice for drainage system for earth and rock-

fill dams shall be provided. The thickness of sand filter layer shall be kept as 1m. if

suitable gravel is available at dam site in plenty, this may be used in filter. In this

case, gravel layer of about 0.3m thickness each over and beneath the gravel layer. The

bottom layer of sand may be omitted if the dam foundation is rock. The slope of these

layers shall be 1 in 100 towards rock toe.

5.4.1.2 Extent

The horizontal filter may be extended in to the body of the dam up to the downstream

edge of the cote. In case of a homogenous dam where core is not provided, the filter

may be extended up to a point where imaginary hearting line with 1:1 slope touches

the stripped ground level.

5.4.2 Chimney Filter

Chimney filter collects seepage from core and allows it to flow to horizontal filter.

Chimney/vertical filter being a pervious barrier intercepts all potential transverse

cracks through body of the dam and prevents piping. This is useful in case of

homogeneous section where the dam is made of dispersive silty and clayey soil.

Chimney filter is a costly preposition and requires strict quality control and layout

standard during construction. Hence before a provision is made in the dam section its

necessity should be utmost established.

5.4.2.1 Location

In a zonal section, the chimney filter shall be located flushed with downstream slope

of the core and connected with downstream horizontal filter layer. Whereas in case of

a homogenous dam chimney filter should be provided vertically with its downstream

edge flushed with downstream edge of the top width of dam and properly connected

with downstream horizontal extended filter.

5.4.2.2 Top Level

The top level of chimney filter in case of a zonal section shall be kept equal to top

core level. For homogeneous section, it should be kept equal to FRL + 0.6m provided

it is covered by at least 1.2m earth cover all around.

5.4.2.3 Thickness

Depending upon availability of filter material, thickness of chimney filter should be

kept between 2 to 2.5m looking to intermixing of adjacent zones compaction

consideration earthquake effects etc. Thickness less than this may not be effective on

practical consideration. The filter may be constructed using available sand. However,

filter design criteria should be ensured. In case the available sand does not satisfy the

filter design criteria, liberal provisions in the width of filter can be made, consulting

design organisation.

5.5 Downstream Inclined Filter

This filter is provided flushed with inclined upstream surface of rock-toe. It drains

seeping water from the downstream portion of the dam and prevents migration of dam

earth through boulder toe. This filter is connected with horizontal base filter.

Thickness of each layer of gravel and sand constituting the filter should be kept as

0.3m.

5.6 Rock-toe

It is a zone of free draining material consisting of cobble size material provided at t he

downstream toe of an earth dam. The principal function of a rock-toe is to facilitate

drainage of water and protect the lower part of the downstream slope from tall water

erosion. It also reduces the possibility of sloughing due to saturation of downstream

toe area, in case, where dam seat soil strata are of impervious nature.

5.6.1 Height

The height of the rock-toe or boulder-toe depends upon availability of material, head

of water, downstream tail water level and provision of other drainage features of

seepage control. For small dams, it is recommended upto 20% of the head of water

with maximum and minimum limit of 4m to 1m respectively. The inner slope of rock-

toe which flushes with the downstream inclined filter shall be kept as 1:1. The rock

toe need not be provided beyond the ground level exceeding the FRL.

5.7 Toe-Drain

It collects water seeping through body of the dam and leads it to natural drainage

system. Longitudinal and cross drains beyond the tow drains are sometimes provided

when out-fall conditions are poor. Toe drain is usually provided as a part of rock-toe

i.e. hidden below rock-toe.

5.7.1 Section

The section of the toe drain should be able to carry total anticipated seepage from the

dam and its foundation. The minimum depth of toe drain shall be kept as 0.6m and

increased gradually towards nalla portion.

The bottom width of the drain shall be kept as 1m with side slopes as 1:1. The drain

id filled up with filter material and the filter should satisfy filter design criteria.

5.8 Out Fall Drain

Out fall drain shall also be provided away from dam toe depending up-on the general

ground levels to safely drain the seepage water collected in the toe drain through

cross drains at regular interval. In addition, the out fall drain also acts as rain water

drainage to the s\downstream area near the toe of the dam.

5.9 Slope Protection

5.9.1 Upstream Slope Protection

For small dams, upstream slope shall be protected by providing 22 cm dry stone hand

placed rip-rap (Pitching) using picked up boulders, over 15 cm. picked up spalls. In

case picked up boulders and/or spalls are not available at or near dam site, quarried

stones and/or spalls be used for hand placed riprap.

5.9.1.1 Extent

The protection shall be provided from an elevation (MDDL – 0.6m) to TBL.

However, at sites where there is a possibility of flows parallel to the embankment

below the MDDL (or lowest water level), and exigencies below MDDL, riprap may

be extended further below the MDDL as required.

i) The riprap shall, as far as possible, be terminated at lower end in a berm

provided in the embankment.

ii) Where berm is not provided due to any specific reason, the riprap shall be

terminated duly keyed to a toe support (toe wall).

For details design series T.C. No. 8 (First Revision) issued by BODHI shall be

referred-to.

5.9.2 Downstream Slope Protections

To protect downstream slope, turf shall be provided on its entire length. The slope

shall also be properly drained.

For details of drainage arrangement, design series T.C. No. 9 issued by BODHI

should be referred-to.

5.10 Under-Seepage Control Measures

Suitable under-seepage control measures for a small earth dam, depending upon site

condition, geology, importance of dam and economic value of water stored in the dam

may be determined on the basis of design series T.C. No. 27 issued by BODHI.

6.0 BASIC AND SPECIAL DESIGN REQUIREMENT

6.1 The basic and special design requirements for the design of embankment dams are to

ensure-

a) Safety against over-topping

b) Stability of slopes

c) Safety against internal erosion

d) Control of cracking

6.1.1 Over-Topping

Sufficient spillway capacity and free board should be provided to prevent over-

tapping of embankment during and after construction. For this, proper hydrological

studies may be carried out; the free board should be sufficient to prevent over-topping

by waves and should take into account the settlement of embankment and its

foundation. Freeboard shall be provided as per T.C. No. 22- Freeboard requirement in

embankment dams issued by BODHI.

6.1.2 Stability Analysis

6.1.2.1 Necessity

Stability analysis may not be necessary for small dam‟s upto 10m height provided a

good foundation is available at dam site. Stable slopes can be decided on the basis of

experience.

For small dams up to 10m-height, section may be decided as per general guidelines

for the section and the recommended slopes as given in Annexure-II. Embankment

where height is above 10m and upto 15m, stability analysis may be carried out in

accordance with the IS: 7894-1975 (Revision-1) Code of practice for stability analysis

of earth dams.

Cracking

Cracking of impervious zone may be one of the root causes of failure of embankment

dam; leading to erosion, piping, breaching etc. Cracks are mostly due to differential

settlement in embankment earthwork on account of abrupt changes in foundation

grade. The other causes of crack could be poor quality control during construction,

use of faulty construction materials and earthquakes etc.

6.1.2.2 Preventive Measures

The following measures if adopted during construction will help to check the

occurrence of cracks in embankment:

i) For the hearting or core, soils having values of P.I.>15 should be used. Soil

should be compact at OMC or slightly more than OMC.

ii) Well graded filter should be provided in the downstream side of the core

(chimney filter) so that even if cracking occurs, harmful effects will be

prevented.

iii) Low density deposits in foundation may be removed, if it is economically

viable or other alternative site/design be followed.

iv) Any vertical steps or ledge rock in the abutment should be avoided. Steep

slope of abutment should be dressed to about 1(H): 2(V).

v) The size of hearting core should be increased to reduce the possibility of

transverse or horizontal cracks extending through it.

6.1.3 Stability At Junctions

Junctions of embankment dam with foundation abutments, masonry structure like

over-flow and non-overflow dams and outlets need special attention with reference to

following criteria

a) Good bond between embankment dam and foundation

b) Adequate creep length at junction

c) Protection of embankment dam slope against scouring action

d) Easy movement of traffic

6.1.3.1 Junction With Foundation

Embankment dam may be founded on soil over burden or rock. For foundation on

soils or non-rocky strata, vegetation like bushes, grass roots, trees etc., should be

completely removed. After removal of these materials, the foundation surface should

be moistened to the required extent and adequately rolled before placing embankment

material. For rocky foundation surface should be cleaned off all loose fragments

including semi-detached and over hanging surface blocks of rocks. Proper bond

should be established between the embankment and the rock surface of the

foundation. For achieving this, a 10cm. thick layer of cohesive soil in muddy form be

pasted on the clean rocky foundation and rolled. This treatment after drying leaves a

base for earth work. Due to rolling, the mud also fills up the cracks and joints of

foundation up to some extent.

6.1.3.2 Junction With Abutment

In order to get good contact between the impervious core of the embankment and the

rock overhanging, the rocky abutment should be suitably shaped and prepared.

Vertical surface should be excavated to form slopes, not steeper than 0.25(H) to 1(V).

a wider impervious zone and thicker transition should be provided, at the abutment

contact to increase the length of path of seepage and to protect against erosion. In

addition to para 6.1.4.1, sufficient creep length should be provided between

impervious section of the dam and the abutment so as to provide safety against piping.

The creep length should be not less than four times the hydraulic head.

6.1.3.3 Junction With Non-Overflow Dam

Junction of non-overflow masonry or concrete dam with embankment dam is

provided by a batter not steeper than 1(H) to 2(V) to the end face of the non-overflow

section block coming in contact with the impervious core. A wider impervious zone, a

thicker transition shall be provided at the abutment contacts to increase the length of

path of seepage and to protect against erosion. Sometimes, the junction of earth dam

with non-overflow dam is provided with earth retaining walls perpendicular or skew

at the junction of non-overflow dam.

7.0 This circular supersedes T.C. No. 40/W (M) 63 Dated 18-05-1963 – Type profile

of earth dam.

ANNEXURE-I

Suitability of soils for construction of dams

Relative

Suitability

Homogeneous

Dykes

Zoned Dam Impervious Blanket

Impervious Core Pervious Shell

Very Suitable GC GC SW, GW GC

Suitable CL, CI CL, CI GM CL, CI

Fairly Suitable SP, SM, CH GM, GC, SM,

SC, CH SP, GP CH, SM, SC, GC

Poor -- ML, MI, MH -- --

Not Suitable -- OL, OI, OH, Pt -- --

(Extract from Appendix A of I.S. 12169-1987)

ANNEXURE-II

General guidelines for embankment sections

S.

No. Description

Height upto 10m.

.

Height above 10 m.

and upto 15 m.

1 Type of Section Zoned section Homogeneous

section

Zoned/ Homogeneous

section

2 Side slopes U/S D/S U/S D/S

(a) GW, GP, SW, SP 2:1 2:1 Not Suitable

Not suitable for core,

suitable for casing

zone

(b) GC, GM, SC, SM 2:1 2:1 2:1 2:1

To be decided based

upon the stability

analysis

(c) CL, ML, CI, MI -- -- 2.5:1 2.25:1 --do--

(d) CH, MH -- -- 3.75:1 2.5:1 --do--

3 Hearting zone May be provided Necessary

(a) Top Width 3 m. 3 m.

(b) Top level 0.5 m above MWL 0.5 m above MWL

4 Rock Toe Height NecessaryH/5, where H is the water head.

Necessary H/5,

where H is the water

head

5 Berms

Not necessary

The berm may be

provided as per

design. The minimum

berm width shall be

3m.

ANNEXURE-III

Average properties for different types of soils

S.

No. Soil Group

Maximum Dry

Density

(Kg/cum)

Optimum

Moisture Content

(Percent)

Cohesion Kg/sqm Degrees

1 GC >1840 <15 NA >31

2 GM >1830 <15 NA >34

3 SM 1830+16 15+0.4 500+500 30+4

4 SC 1840+16 15+0.4 1100+600 31+4

5 ML 1650+16 19+0.7 900+NA 32+2

6 CL 1730+16 17+0.03 1200+200 28+2

7 CH 1510+32 25+1.2 1300+600 19+5

8 MH 1310+64 36+3.2 2000+900 25+3

(Extract from Table 2 of I.S. 12169-1987)

ANNEXURE-IV

Degree of Expansion of fine grain soils

Liquid

Limit

Plasticity

Index

Shrinkage

Index

Free Swell

(Percent)

Degree of

Expansion

Degree of

Severity

20-35 <12 <15 <50 Low Non Critical

35-50 12-23 15-30 50-100 Medium MArginal

50-70 23-32 30-60 100-200 High Critical

70-90 >32 >60 >200 Very High Severe

(Extract from Table 8 of I.S. 1498-1970)

REFERENCES:

List of Technical Circulars

S.

No.

TC No Subjects

1 1 CHECK LIST OF DATA REQUIRED FOR DESIGNS OF EARTH DAMS

2 2 CHECK LIST OF DATA REQUIRED FOR DESIGNS OF MASONRY DAMS

3 8 PROTECTION OF UPSTREAM SLOPES FOR RESERVOIR EMBANKMENT

4 9

REVISED DOWNSTREAM SLOPE PROTECTION OF RESERVOIRS

EMBANKMENT

5 10 CREST WIDTH OF EARTH/ROCKFILL DAMS

6 11

CORE IN EARTH DAMS

7 12 PROVISION OF BERMS

8 13 SHRINKAGE/SETTLEMENT ALLOWANCE IN EARTH/ROCKFILL DAM

9 22 FREE BOARD REQUIREMENT IN EMBANKMENTS DAMS

10 27 UNDER SEEPAGE CONTROL MEASURES FOR EARTH AND ROCKFILL

DAM/CORRECTION

11 32 DESIGN CRITERIA FOR MINOTR IRRIGATION SCHEMES

12 40 STABILITY ANALYSIS OF EARTH DAMS

13 41 DESIGN OF NON OVERFLOW GRAVITY DAM SECTION

14 42 GUIDELINES FOR DESIGN OF SMALL EARTH DAMS

15 43 GUIDELINES FOR DESIGN FOR RIGIDDIAPHRAGM WALL FOR SEEPAGE

CONTROL

16 49 CONTROL OF SEEPAGE THROUGH BODY OF EARTH DAM

17 51 ESTIMATION OF DEAD STORAGE OF SMALL DAMS UP TO 5 MCM UP TO

500 Ha CCA

LIST OF I S CODES/References

S. No.

IS Code Subjects

1 12169 Criteria for design of small embankment dams

2 8826 Guide lines for design of large earth and rock-fill dams

3 7894 Code of practice for stability analysis of earth dams

4 8237-1985 Code of practice for protection of slope for reservoir embankment

5 8414

Guidelines for design of under-seepage control measures for earth and rock-

fill dams

6 9429-1999 Code of practice for drainage system for earth and rock-fill dams

7 10635-1993 Free board requirement in embankment dams-guidelines

8 1498 Classification and identification of soils for general engineering purposes

9

"Design of small dams" by United States Bureau of Reclamation

10 Theory & design of irrigation structures, Volume II by R S Vashney,

S.C. Gupta & R.L. Gupta

11 IS 7894 Stability analysis of Earth Dams

12. IS 11223 : 1985 Guidelines for fixing spillway capacity

13. IS 12720 : 1993 Criteria for structural design of spillway training walls and divide walls

14. IS 11155 : 1994 Construction of spillways and similar overflow structures - Code of practice

15 IS 4997 : Criteria for design of hydraulic jump type stilling basins with

horizontal and sloping apron

16. IS 12804 : 1989 Criteria for estimation of aeration demand for spillways and outlet

structures

17 IS 7365 : 1985 Criteria for hydraulic design of bucket type energy dissipators

18. IS 11527 : 1985 Criteria for structural design of energy dissipators for spillways

19. IS 13551 : 1992 Criteria for structural design of spillway pier and crest

20. SP 55 : 1993 Design aid for anchorages for spillway piers, training walls and

divide walls

21 IS 5186 : 1994 Design of chute and side channel spillways - Criteria

22 IS 11772: 1986 Guidelines for design of drainage arrangements of energy dissipators

and training walls of spillways

23 IS 10137 : 1982 Guidelines for selection of spillways and energy dissipaters

24. IS 12731 : 1989 Hydraulic design of impact type energy dissipators-recommendations

Indian Standards must be of latest version.

Chapter VII

Design of Spillway

1. Function:

The primary function of spillway is to release surplus waters from the

reservoir in order to prevent overtopping and possible failure of the dam.

The water discharged over the spillway of a dam attains a very high velocity

due to its static head, which is generally much higher than the safe non-

eroding velocity in the downstream. This high velocity flow may cause serious

scour and erosion of river bed downstream. To dissipate this excessive energy

and to establish safe flow conditions in the downstream of a dam spillway,

energy dissipaters are used as remedial devices.

2. Inflow design flood: The criteria for inflow design flood is given in IS:11223-

1985 "Guidelines for fixing spillway capacity" which has been also given

above under Chapter II “Hydrology”.

3. Factors affecting design:

a. Safety considerations consistent with economy

Many failures of dams have resulted from improperly designed

spillway or spillways of inadequate capacity. Properly designed

structure of adequate capacity may be found to be only moderately

higher in cost than a structure of inadequate capacity.

b. Hydrological and site conditions

The spillway design and its capacity depend on

Inflow discharge, its frequency, and shape of hydrograph

Height of dam, Stability of slopes

Capacity curve

Geological & topographical features and other site conditions

such as steepness of terrain, amount of excavation and

possibility of its use as embankment material , possibility of

scour, safe bearing capacity of soils, Permeability of soils etc.

c. Type of Dam

The type of dam influences the design flood and spillway. Earth

and rockfill dams have to be provided with ample spillway capacity

d. Purpose of dam and operating conditions

Normally ungated spillway should be provided, however keeping

in view submergence affected in special circumstances gated

spillway may be provided. In dams located in remote location

ungated spillway should be preferred.

4. Type of spillways & its design: Spillway can be built as part of main dam or

separately. Concrete or masonry overflow spillway can be built in the river

section where rock foundations are suitable even though adjacent section of

the dam may be embankment type. Separate spillways are required for all

types of embankment dams.

Common types, which are generally constructed, are given in detail in in T.C

No 28 “guidelines for Selection of spillway & Energy dissipators” which has

been reproduced below at end of this chapter. For design of spillway lecture

note of Director CWC may be referred enclosed as Appendix-8.

5. Type & Design of energy dissipators: Given in detail in T.C No 28 given

below & in lecture note of Director CWC “Design of Energy Dissipators”

enclosed as Appendix 9.

6. Design of side walls:

The profile of flow on spillway surface determines the height of side walls

required to retain flow on the spillway. These are designed as retaining walls

with water side face to be vertical or near vertical for perfect energy

dissipation.

The bottom width of side wall is decided as per the safe bearing capacity of

soil at foundation level.

The stability should be checked at foundation level, top of bed concrete level

and at water side floor level etc. The design loads and load combination

should be as per IS: Code 12720- 1993

Uplift pressures should always be considered at all elevations while checking

stability.

REFERENCES:

LIST OF TECHNICAL CIRCULAR

1. TC-2 CHECK LIST OF DATA REQUIRED FOR DESIGNS OF MASONRY

DAMS WITH AMENDMENT NO.1

2. TC-18 ZONING OF MATERIALS FOR GRAVITY DAM AND APPURTEMENT

WORKS

3. TC-28 GUIDELINES FOR SELECTION OF SPILLWAY AND ENERGY

DISSIPATORS

4. TC-29 TOP WIDTH OF GRAVITY DAMS

5. TC-33 SELECTION OF TYPE OF GATES

6. TC-39 GUIDELINES FOR PRESSURE GROUTING OF ROCK FOUNDATION

7 TC-41 DESIGN OF NON OVERFLOW GRAVITY DAM SECTION

LIST OF I S CODES

1. "Design of small dams" by United States Bureau of Reclamation

2. Theory & design of irrigation structures, Volume II by R S Vashney, S.C. Gupta & R.L.

Gupta

3. IS 11223 : 1985 Guidelines for fixing spillway capacity

4. IS 12720 : 1993 Criteria for structural design of spillway training walls and divide

walls

5. IS 11155 : 1994 Construction of spillways and similar overflow structures - Code of

practice

6. IS 4997 : 1968 Criteria for design of hydraulic jump type stilling basins with

horizontal and sloping apron

7. IS 12804 : 1989 Criteria for estimation of aeration demand for spillways and outlet

structures

8. IS 7365 : 1985 Criteria for hydraulic design of bucket type energy dissipators

9. IS 11527 : 1985 Criteria for structural design of energy dissipators for spillways

10. IS 13551 : 1992 Criteria for structural design of spillway pier and crest

11. SP 55 : 1993 Design aid for anchorages for spillway piers, training walls and

divide walls

12. IS 5186 : 1994 Design of chute and side channel spillways - Criteria

13. IS 11772: 1986 Guidelines for design of drainage arrangements of energy dissipators

and training walls of spillways

14. IS 10137 : 1982 Guidelines for selection of spillways and energy dissipaters

15. IS 12731 : 1989 Hydraulic design of impact type energy dissipators

Note :- latest version of I.S.Code should be referred.

Chapter VIII

Design of Canal

1. Collect existing cropping pattern & Agriculture Statistics of the village

coming under command.

2. Finalise proposed cropping pattern after irrigation with consultation of

Agriculture officer of the area.

3. Calculate crop water requirement and get it vetted by the Agriculture

Department.

4. Calculate proposed area to be irrigated from available live storage.

5. Determine C.C.A by adopting suitable intensity of irrigation & as per actual

Agriculture Statistics. Following instructions of E-in-C should be kept in mind

while finalising Intensity of Irrigation.

“It is a known fact that against the designed Kharif Irrigation actual Kharif

Irrigation is too marginal & amounts hardly to 10%. Inspite of this fact known to

everybody we are yet making provision of more than 50% of CCA as Kharif

Irrigation. In view of this except for limited areas like district Balaghat&Seoni

where still in substantial area Kharif crops are being grown, in all parts of state we

should provide not more than 20 to 25% CCA as Kharif Irrigation.”

(From E-in-C letter dt 24/01/07)

6. Survey the CCA in a grid of 30m x 30m preferably with contour interval of

0.30 m.

7. Prepare command area map by plotting grid lines on combined village map

and mark contour lines.

8. Mark proposed canal alignment on command sheet; it may be contour canal or

ridge canal as per terrain of command area. Ridge canal should be aligned to

cover area on both sides.

9. Formation of chaks including position of outlets. Chak size should be equal as

far as possible. Size of chaks should be 40 ha approximately.

10. Prepare cut off statement as per proforma enclosed, by adding seepage and

evaporation losses @ 2.5 cumecs and 0.8 cumecs per million sq mt of wetted

perimeter for unlined and lined canals respectively.( Minutes of 12th

meeting

of Canal & C.D works sectional committee WRD 13 held on 23/02/10)

11. Fix canal capacity for different reaches and design the most economical

section keeping B/D ratio as given below :-

TABLE

Bed width V/S F.S.D ratio for different discharge

Discharge in

CUMECS B/D

Ratio Discharge in

CUMECS B/D Ratio

0.30 2.90 2.25 4.0 0.40 3.00 2.50 4.10 0.60 3.20 2.80 4.20 0.85 3.40 5.50 4.60 1.15 3.60 8.50 5.00 1.40 3.70 11.50 5.30

2.70 3.80 14.50 5.70 2.00 3.90

Courtesy:-Compendium of Small Canal in MP-By MG Choubey (E-in-C)

12. Canals should be aligned as far as possible in partial cutting and partial filling.

13. Agriculture and economic development in future are likely to demand more

exacting service from the irrigation system designed today. Also to account for

any change in the cropping pattern, certain flexibility is desirable which can be

obtained by keeping a cushion over and above the calculated capacity (QR). The

following extra capacities are to be provided.

Percent

Main and branch canal 10

Distributaries 15

Minors 20

Water course 25

The increased capacity over the peak capacities required (QR) is called Q Design

(QD). The canal system would be designed for QD, while the off takes would be

designed on the basis of FSD which would be attained with reference to QR.

(From step 11 page 33 of E-in-C publication 59.)

14. Profarma for preparation of cut-off statement of Minor & Main canal is

given below.

Cut off statement of Minor canal ……..

Outlet Duty = ………..

Cha

k

No.

Area

to be

irrigat

ed in

ha

Distance

to the

next

oftake

towards

head of

canal in

metres

Dischar

ge

Require

d at

outlet in

……

Opera

tion

Losse

s

@.......

.

Total

Requireme

nt at the

outlets in

………

(Add. Col

4+5)

Transmissi

on Losses

@.........

per million

sq mt of

wetted

perimeter

Total

dischar

ge in

………

(Add.

6+7)

Cumulati

ve total

discharge

in ……

(QR)

QD

(col.

9x1.2

)

Rema

rk

1 2 3 4 5 6 7 8 9 10 11

Cut off statement of Main Canal (from 0 to Tail) of ……Project

Outlet Duty = ………..

Minor head Duty = ………..

Distributary head Duty = ………..

Cha

k

No.

Area

to be

irrigat

ed in

ha

Distance

to the

next

oftake

towards

head of

canal in

metres

Dischar

ge

Require

d at

outlet in

……

Opera

tion

Losse

s

@.......

.

Total

Requireme

nt at the

outlets in

………

(Add. Col

4+5)

Transmissi

on Losses

@.........

per million

sq mt of

wetted

perimeter

Total

dischar

ge in

………

(Add.

6+7)

Cumulati

ve total

discharge

in ……

(QR)

QD

(col.

9x1.1

)

Rema

rk

1 2 3 4 5 6 7 8 9 10 11

(from E-in-C publication 59)

15.Maximum permissible velocity for unlined canals should be ;-

S.No Type of soil Water depth in canal

Below 0.6

m

From 0.6 m - 1.20

m

Above 1.2

m

1 Light sandy soil 0.50 m/sec 0.55 m/sec 0.60 m/sec

2 B.C soil, Kanhar soil

Matasi soil or similar

soils

0.60 m/sec 0.75 m/sec 0.90 m/sec

3 Moorum& other similar

hard strata

0.91 m/sec 1.00 m/sec 1.10 m/sec

(1)Courtesy:-Compendium of Small Canal in MP- By MG Choubey (E-in-C)

(2) Technical circular no 7 -/w-6 of 61 dt 05/05/61

The maximum permissible velocities for guidance for some types of lining

are given below: (Source: - IS 10430-2000)

a) Stone-pitched lining 1.5 m/s

b) Burnt clay tile or brick lining 1.8 m/s

c) Cement concrete lining 2.7 m/s

16 For design of canal Compendium of Small Canal in MP by MG Choubey

(E-in-C) should be followed which is given below in end of Chapter

Rugosity coefficient, side slopes, free board, bank width etc. should also be

adopted accordingly.

17. As far as possible minimum number of falls should be provided.

No fluming should be provided in falls, culverts and other pucca structures

unless otherwise specified or desired in specific cases.

19. Canal may be lined in reaches of excessive seepage losses. Canal should

also be lined 15 meter upstream and 30 meter downstream of all pucca

structures.

The lining should be adopted suiting to local conditions & availability of

materials. C.C lining, Boulder lining, Tile lining etc may be considered on

merit for adoption.

20. Falls should be properly designed with proper energy dissipation

arrangements and upstream & downstream wings of suitable length should

be provided,

21. Bed level of off taking channel should not be fixed higher than 0.30 m

above the bed of parent channel (vide E-in-C letter no 340822/12 dt

06/02/13 given below).

22. It is a general tendency to irrigate only one side of the command even

when the command levels in some of the reaches permit to irrigate on the

other side by gravity flow. In such a situation E-in-Cs instruction issued

vide 348/2013(4002) dt 21/01/13 should be followed which is reproduced

below.

23. FSL in water course at head should be kept at least 0.30 metre above the

selected highest natural surface level in the irrigable area of particular

chak plus drop in the water course due to slope.

24. The water course is to be constructed upto sub chak (size 5- 8 ha).

25. Provision of Canal Siphon should only be made in unavoidable

circumstances as per E-in-Cs instruction issued vide letter no 348022/12

dt 22/02/12 ( reproduced below)

REFERENCES:

LIST OF TECHNICAL CIRCULAR

1. TC-2 CHECK LIST OF DATA REQUIRED FOR DESIGNS OF MASONRY

DAMS WITH AMENDMENT NO.1

2. TC-18 ZONING OF MATERIALS FOR GRAVITY DAM AND APPURTEMENT

WORKS

3. TC-28 GUIDELINES FOR SELECTION OF SPILLWAY AND ENERGY

DISSIPATORS

4. TC-29 TOP WIDTH OF GRAVITY DAMS

5. TC-33 SELECTION OF TYPE OF GATES

6. TC-39 GUIDELINES FOR PRESSURE GROUTING OF ROCK FOUNDATION

7 TC-41 DESIGN OF NON OVERFLOW GRAVITY DAM SECTION

LIST OF I S CODES

1. IS 5968 Guidelines for planning & layout of canal system for irrigation.

2 IS 7112 Criteria for design of Cross-section for Unlined canals in Alluvial

soils.

3 IS 4701 Code of practice for earthwork on canals.

4 IS 10430 Design of canal & selection of type of lining.

5 IS 9451 Guidelines for lining of canal in expansive soil

Note :- Latest version of IS should be referred

Chapter IX

Preparation of Cost Estimates

Under different heads/subheads provision shall be kept on the basis of detailed

estimates.

For preparation of detailed cost estimate, rates as per latest U.S.R. should be

used. For non-U.S.R. items, rates shall be got approved by the competent

authority.

Cost of land should be taken as per latest land rates of the area as decided by

the Revenue Department.

The Executive Engineer Irrigation Division after consulting the revenue record

should give certificate that no forest land is coming under the project. If forest

land cannot be avoided due to site conditions, then rates of forest land

proposed to be acquired should be obtained from concerning Divisional Forest

Officer.

1. Classification of Units:- The Project may be grouped into the following units

:-

(i) Unit-I Head Works: including main dam and auxiliary dam, dykes, spillway,

outlet works, energy dissipation devices, barrages, weirs, regulators including

intake structures and diversion works.

(ii) Unit –II Canals: Main Canals, branches and distribution system inclusive of

pucca- works (structures, lining)

2. Classification of Accounts head :- Each unit and if necessary each sub-unit

should be covered under the following Minor heads classified as direct and

indirect charge .

Direct Change :-

Following to be incorporated

I. Works

II. Establishment

Detailed Sub-heads under I-works

The provisions under I-works will be sub-divided under the following detailed

heads:

A - Preliminary

B - Land„

C - Works (For Dams only)

D - Regulator and measuring devices

E - Falls

F - Cross drainage Works

G - Bridges for canals only ( D to L)

H - Escape

L - (i) Earth work

(ii) Lining

3. Abstract of cost

3.1 Detailed Abstract of cost: - To work out the total cost of project in detail the

cost of various units given in 1 should be compiled in tabular form according to the

various accounts heads indicated in para-2.

3.2 General Abstract of cost: - On the basis of detailed abstract of cost as in

Para 3.1 a general Abstract of cost may be compiled by minor and detailed heads.

4. Detailed Estimate of cost – I Works

4.1 „A‟ Preliminary :-

The important items to be included are :-

(a) Expenditure incurred on previous investigations

(b Detailed survey for final location

(c) Contour Survey for reservoir basin ( including establishment

of permanent bench marks)

(d) Investigations for foundation, Geological surveys and geophysical

surveys;

(e) Hydrological and metreological survey

(f) Investigation for availability of construction materials

(g) Construction of access roads to facilitate investigations if found very

necessary. Maximum effort should be made to use existing

Village/District roads.

(h) Model experiments, Cost of other surveys, investigation

(i) Preparation and printing of project report

(j) Command area survey (contouring)

(k) Detailed alignment survey (cross sectional survey) of canals

(l) Taking trial pits or trenches and trial bores for foundation investigation

of structures along with alignment of canals.

(m) Taking anger holes for soil survey of command area.

(n) Field test for soil classification of command area

Normally the amount of cost of “A” preliminary should be limited to 1 to 2%

of cost of I-works.

4.2 „B‟ Land

4.2.1 Acquisition: - This sub-head should cover the following :-

(a) Compensation of Land (private & Government for works and that

coming under submergence). The probable rate for acquisition should be taken

as per collector guidelines

(b) Compensation for other properties like Houses, Wells, trees temples etc.:-

This should also be taken as per collector guidelines.

4.2.2 Rehabilitation :- Provision should be made as per guidelines of “ Madhya

Pradesh ki AAdarsh punarwas neeti 2002”

In addition to the above following charges are to be included.

(i) Interest charges on amount of award: - Necessary in view of the likely time lag

in taking possession of the land and properties and actual payment of compensation.

For estimating purpose, this provision may be considered @ 12% per annum or as per

prevailing rates.

(ii) Solatium charges for compulsory acquisition may be provided @ 30% of the

cost of permanent acquisition of private land.

4.3 C. Works. This head is intended to cover the provisions for various

components of which the Head works are composed of viz .Dam, spillway, energy

dissipation works, outlets (irrigation, power, water supply and scour sluices), pick up

weir, barrage, head regulators, waste weir, approach channel etc. The list of items to

be considered for different works is given below:

4.3.1 Embankment Dam (earth and rock fill)

This included the following important components:

(a) River Management during construction including such items

such as coffer dams and diversion tunnels.

(b) Foundations – These shall include the following.

1) Site Clearance

2) Excavations:

i) Stripping for dam seat

ii) Stripping for blanket

iii) Longitudinal, cross and toe-drains.

iv) Cut off trench.

v) Key for upstream riprap etc.

3) De-watering arrangements (with details)

4) Foundation treatment

i) Drilling in rock or in soil with casing

ii) Foundation grouting tunnel.

iii) Filling cut off trench with selected impervious materials:

- from excavated materials

- from borrow areas.

iv) Grouting (cement, bentonite, chemicals)

v) Construction of Diaphragm wall (concrete, plastic)

vi) Relief wells

vii) Upstream horizontal impervious blanket.

viii) Sheet pile,Pile driving,other treatments.

(c) Dam

1) Earthwork (in core, shell, random zones and upstream blanket)

i) Impervious

ii) Semi-pervious - Quantity to be indicated

iii) Pervious - Separately for excavated materials and borrow areas

iv) Random fill

2) Rock fill including rock toe;

i) from excavated materials

ii) from quarries.

3) Filters (at downstream toe or hearting )

i) Fine filter (sand ) – sloping vertical or horizontal.

ii) Coarse filter (gravel ) or crushed stone sloping, vertical, horizontal.

4) Upstream sealing :

i) R.C.C. membrane

ii) Blanket of special materials like geo-membrane or non-dispersive soil

layer

5) Rip rap (dumped or hand placed )

6) Downstream slope protection :

i) Turfing

ii) Rip rap

iii) Geo-textile etc. (woven fibres)

iv) Surface Drainage System (cross drains, longitudinal drains/pipes

collecting and toe drain)

7) Instrumentation, Gauge posts etc.

8) Laying of open jointed pipes for drainage, Manholes

10) Road over the dam.

4.3.2 Masonry Dam :- This will include the following items:

(a) Diversion works during construction, such as coffer dams,diversion

tunnels/channels.

(b) Foundations;

1) Clearing site

2) De-watering in foundation

3) Excavation for main dam, energy dissipation arrangements, approach

and tail channels training/divide/retaining walls in:

i) Over-burden of soft strata

ii) Over-burden of hard strata and

iii) Hard rock

4) Preparation of dam seat:

5) All works relating to shear zones/faults/weak zone treatment, wherever

applicable including grouting.

6) Drilling holes:

i) for grouting

ii) for drainage, and

iii) for anchor rods.

7) Anchor rods

c) Dam:- 1) Masonry for:

i) Hearting

ii) Upstream face

iii) Downstream face ( non-overflow section and overflow

sections)

iv) Training/divide/retaining walls

2) Cement concrete in ;

i) Filling crevices and levelling course, over-foundations

ii) training/divide/retaining walls

iii) Parapets

iv) Upstream concrete/sand-witched concrete membrane.

3) Form-work (if not included in rate for concrete) for items mentioned in

2

4) Steel for reinforcement

5) Guniting for the upstream face of masonry

6) Drilling for Anchors & Anchor rods

7) Joints and seals, Instrumentation

8) Drilling and grouting of masonry

9) Porous pipe for drainage

4.3.3 Concrete Dam:

The various items of works in the construction of concrete dams are:

a) Diversion works during construction, such as coffer dams, diversion

tunnels/channels etc.

b) Foundation (item same as under masonry dam (b)

c) Dams

1) Cement concrete in:

i) Hearting (with or without plums)

ii) Upstream facing;

iii) Downstream facing which shall include the

overflow section and non-overflow section

iv) Training/divide/retaining walls

v) Parapet

2) Form-work (if not already included in rate for concrete)

for items mentioned in (1) above.

3) Steel reinforcement

4) Joints and seals

5) Drilling for anchors & Anchor rods

4.3.4 Spillway:-The spillway structures may generally be of masonry or

concrete and the items, therefore, are respectively the same as for masonry or

concrete dam. Following additional items need to be estimated;

a) Cement concrete for:

- Spillway piers

- Bridge beams and slabs

- Tunnel lining wherever applicable.

- Spillway crest, downstream glacis, chute etc.

b) Miscellaneous items of bridge like bearings

c) Tunnel excavation wherever applicable

d) Crest gates with hoisting equipment and hoist bridge.

e) Stop logs for crest gates, and lifting arrangement.

4.3.5 Energy Dissipation Works: Same items as for concrete dam with the

addition of cement concrete for:

a) Stilling basin/bucket/apron.

b) Floor blocks, and

e) End sills and chute blocks

4.3.6 Outlets: This will include the following:

a) Excavation in soil and rock

b) Foundation treatment

i) Lean concrete in foundation

ii) Drilling and grouting

iii) shotcreting/ guniting

c) Structural concrete for:

i) Foundation, piers and abutments

ii) Conduit cut off collars

iii) Gate control structures, beams, floor slabs etc.

iv) Block outs

v) Stilling basin including chute blocks, baffle blocks and

end sills;

vi) Guide walls

d) Masonry in guide walls of approach channels or stilling

basin

e) Steel for reinforcement

f) Rubber/PVC seals at joints

g) Gates

h) Hoisting equipment and auxiliary items

i) Filters around conduit

j) Trash rack

k) Steel lining

l) Stop logs

4.4 Canal structures:The provision for canal structures is spilt up under

the following sub-heads:

D-Regulators

E-Falls

F-Cross Drainage Works

G-Bridges

H-Escapes

It is seen that provision for canal structures is generally made on lump

sum basis. This practice is not only irrational but is one of the principal causes

for steep rise in the costs of revised estimates. It is necessary that preliminary

designs are made for all important structures after proper survey and for

framing the estimates, Typical structures of different capacity (three or more

in number) should be analysed to work out unit cost for each type of structure

in each sub-head as follows:-

D-Regulators i) Head regulator – Cost per unit product of discharges of

parent and off-taking canals.

ii) Cross regulator- Cost per unit of water way width.

E-Falls -Cost per unit product of discharge and height of fall.

F-Cross Drainage - Cost per unit product of discharges of drainage and canal.

G-Bridges - Cost per meter span of bridges.

H-Escapes- Cost of structures may be worked out as mentioned above and

for escape channel procedure may be same as for canals.

Where the actual cost of similar structure constructed on other projects is

known, the data could with advantage be used in the estimate. It should

however, be ensured and justified that the structures considered are similar in

nature. The differences in leads of materials in the two structures are

accounted and escalations wherever necessary are taken into account. The

basis for premium applied as well as the reference to the project from where

such costs were realized and the year of work should be mentioned in the

estimate.

4.5 „L‟ Earth Work for Canals only:-Important items to be considered under

this sub-head are:

(a) Excavation

(b) Embankment from

i) Excavated material

ii) Borrow area

(c) Lining

(d) Pitching

(e) Miscellaneous items, such as construction of drains,

inspection & service road/path etc.

4.6. II- Establishment: - The provision under this sub head is generally

made as 11% which is inclusive of cost towards setting up of control cells at

project and head quarter level to exercise proper control over construction &

cost.

REFERENCES:

1. IS 4877 Guide for preparation of estimate for River valley projects.

Chapter X

Important Instructions, Circulars and Preparation & Submission of

DPR

Following important points should be kept in view during site selection & preparation of

DPR.

Location of waste weir & spill channel should be decided with utmost care.

Releasing of flood discharge into a smaller nalla may cause severe damage to the

adjacent fields of that nalla.

As for as possible, the spill channel should be designed to join the parent nalla

directly & not through any smaller nalla.

Construction of falls & utilisation of excavated materials of spill channel should be

done as per instructions given in detail in E-in-C letter 373/22/09/09 dt 06/06/11

reproduced in end of this chapter.

In general cost of surplussing system should be less than 10% of total cost of project.

Benefit cost ratio should be prepared on the basis of datas & rates provided by

Agriculture department.

“It has been observed that a lot of proposals of Barrages/Stop Dams without provision

of canals are being proposed, intending that stored water will be utilised by the

beneficiaries by having recourse to their own lifting arrangements. In principle this

should not be encouraged and we can go for stop dams / barrages only in cases where

there is substantial flow in river/ big nallas even in the month of February & march

and in such strams we can provide series of stop dams / barrages and not only isolated

structures, so that besides substantial irrigation actual recharging can be affected.

Even in such cases there must be a complete one proposal for the entire series of stop

dams rather than isolated structures.” (From E-in-C letter no 3433000/2009 dt

24/01/07)

For irrigation from Barrages/stop dam , the following thumb rule should be adopted. :-

Maximum Possible Irrigation (Ha) =H x F x L x (M)0.75

(10)5

Where

H = Height of the structure

F = Fetch length

L = Length of structure at crest level.

M = Catchment Area (Sq km ) [Limited to 100 Sq Km or actual whichever is less]

Before submission of DPR to E-in-C it must be checked that Report, estimate &

abstract etc. have been duly signed by higher officers.

After preparation of DPR it must be submitted to E-in-C along with all enclosures as

mentioned in E-in-C no 373/22/42/11 dt 13/02/12 & 372/22/42/11 dt 26/07/13

reproduced below. In DPR one Chapter of “Tender Related Details” should also be

added as mentioned in 22/9/2013/MI/31(1387) dt 04/07/13 enclosed below.

Following forms/proformas which are to be enclosed with DPR are attached as

Appendix.

S.No Appendix

No. List of Appendixes

1 11 Information of officers related with proposal form-133

2 12 Form-141 A “Parameters for minor storage Irrigation Projects”

3 13 Form-142 “Basic Information for Minor Irrigation Schemes”.

4 14 Proforma to accompany AA – T.C.70

5 15 Check list of according AA to Irrigation Schemes.

Guidelines for Preparation of Estimates & DPR for Minor Irrigation Projects

Index Appendix

No. List of Appendixes

1 Chapter II Survey & Investigation of Book of specifications

2 Technical Circular No - 53.-Preliminary Check Statement for General

Feasibility of Projects

3 E-in-C letter no 3332745/2011 dt 29/03/11 “estimation of Land width

proposed to be acquired for canal for Sadhyata”

4 Form-141 “Proposal for Sanction of Survey & Investigation

5 “Sample sanction order of “Sadhyata” of govt

6 Design Series TC-1- Check List for data required for design of Earth Dam

7 Design Series TC-2 - Check List for data required for design of Gravity Dam

8 Design of Spillway -lecture note of Director CWC

9 Design of Energy Dissipators -lecture note of Director CWC

10 Prescribed form of collection of Agriculture statistics - Page 353 of volume II

of book of technical Circulars

11 Information of officers related with proposal form-133

12 Form-141 A “Parameters for minor storage Irrigation Projects”

13 Form-142 “Basic Information for Minor Irrigation Schemes”.

14 Proforma of T.C.70

15 Proforma to accompany AA – T.C.70

16 Check list of according AA to Irrigation Schemes.

APPENDIX 1

(Relevant portion of chapter II Survey & Investigation of Book of specifications volume I)

2.4 GENERAL

2.4.1 Reconnaissance and study of maps

2.4.1.1. Before reconnaissance it is necessary to thoroughly understand the need, extent and

limitations of the project. And before field reconnaissance is started, all available data and

maps detailed below shall be thoroughly studied to avoid waste and repetition of effort.

(1) Previous history of the area,

(2) Projects considered, investigated or constructed in the area.

(3) Topographical features from internet (Google Earth).

(4) Topographical maps published by survey of India,

(5) Forest maps, from G.S.I and Maps and Data from Meteorological department, and

(6) Recent aerial photographs/ satellite imageries so as to furnish up-to date information on

cultivated area, natural vegetation and growth, geological reconnaissance information and

sources of construction materials. Aerial photographs may be obtained from google earth,

survey of India Dehradun and satellite imageries from Indian Institute of Remote sensing,

Balanagar, Hyderabed.

2.4.1.2 The reconnaissance for minor irrigation projects shall be carried out and its report

prepared as specified at Appendix-I

2.4.2 Guidelines for Investigation of Minor, Irrigation Projects.

2.4.2.1 In order to ensure preparation of sound and economical project, it is necessary to have

thorough and systematic investigations. The investigations shall include the study of various

alternatives regarding the layout of scheme as a whole, & also regarding details of

alternatives considered for type, and location of various features of the projects. The final

alternative recommended shall be fully justified by recording the reasons for its choice as

against the other alternatives. The minimum surveys & investigations necessary for the

purpose are as below.

(i) Topographical surveys including preparation of survey plans to cater to the requirements

of Appendix-IV

(ii) Geological and Foundation Investigations- C.W.C guide lines for foundation investigation

of major projects are appended at Appendix-V

(iii) Meteorological and hydrological studies.

(iv) Pre-irrigation soil survey and drainage soil survey.

(v) Special surveys for hydro-electric projects.

(vi) Construction Material Investigations- Guidelines for Investigations for suitability of

constriction materials are appended at Appendix-VI.

(vii) Communication investigations.

(viii) Construction planning

(ix) Other miscellaneous investigations for acquisition of land under submergence,

rehabilitation measures if any, environment and ecology.

2.4.3 For chain and compass survey generally no jungle clearance is required to be done.

However, when the alignments are passing through jungle other than the reserved forest, and

its clearance is considered necessary by the Engineer-in-charge, then ordinary, medium and

thick jungle clearance depending upon the type of jungle involved can be carried out be with

prior sanction/permission from the competent authority, But such jungle clearance in widths

not exceeding 1.5m for alignments and one metre for cross sections can only be done after

obtaining prior specific sanction of the competent authority, which shall include the type of

jungle clearance to be done in different lengths and widths as considered necessary. When it

is necessary to survey through a reserve forest, prior sanction from the competent authority

shall be required to be taken as per the Forest Conservation Act-1980.

2.4.4 Length of Survey

Length of the survey shall be measured along the lines on which particular type of survey is

done. For chain and compass survey it would be the length along which chaining and

compassing is to be done. For levelling, it would be the total length of the lines along which

levels are to be taken.

2.4.5 Use of Total Survey Station

For survey and layout of all important components & structures of Dam & Canal and setting

of curves for irrigation channels carrying discharge above one cumec the use of theodolite

shall invariably be made.

2.4.6 Chaining of Final Alignment

It shall be done with due precision after setting of curves.

2.4.7 Marking on Village Maps

The surveyed alignment and cross section shall also be marked on the concerned village

maps. In case of catchment area survey, the ridge line/lines shall also be marked on the

village maps. For command area survey, ridges and valleys shall also be marked.

2.4.8 Survey party for Double Levelling

The survey party for double levelling should invariably be headed by the sub- division officer

concerned or an officer not below the rank of an Assistant Engineer.

2.4.9 The general instructions for carrying out systematic levelling work and making entries

in the field/ level book as appended at Appendix - VII shall be followed.

2.5 DAG BAILLING IN ALL TYPES OF SOIL

Dag bailling shall only be done in all types of soil which can either yield to the

ordinary application of pick and shovel, or to spade, rake or other digging implement, and or

can be removed by this ordinary application after loosening with pick axe. This work shall

normally be done for the final alignments approved by the competent authority. The work in

single spade stroke (minimum75 mm deep) shall be carried out for all medium and minor

irrigation canal work, whereas the work in double spade 'V' shaped stroke (100 mm deep)

shall be carried out for all major irrigation projects and all dam alignments.

2.6 SUB - SURFACE EXPLORATION

2.6.1 Exploration by pits/ Trenches/ Drifts /Adits and Shafts

Open test pits, trenches, drifts and are features accessible for visual examination in

subsurface exploration and afford the most complete information on the ground penetrated.

Location of pits, trenches, drifts and shafts shall preferably be decided in consultation with an

engineering geologist; invariably to be followed for the medium and major irrigation projects.

2.6.1.1 Exploration by Test pits

2.6.1.1.1 Pits are dug manually but mechanical equipment may also be used for the purpose

up to shallow depths. In dry ground, pits are economical in comparison to bore holes up to a

depthof about 5m depending upon the location. As the depth increases, the cost of excavating

a pit increases very rapidly and it is seldom that unsupported pits are dug to a depth

exceeding 6 m except in the case of hard soils. The top of a pit shall be kept large enough so

that dimension of the pit at the bottom may be at least 1.2 m X 1.2 m which are sufficient to

provide necessary working space. Additional space for sheeting and timber supports, hoisting

arrangements and ladder, etc.shall be provided. A recommended Performa for the recording

of information obtained from trial pits is given in Appendix V(A).

2.6.1.1.2 For deep pits in soil, the walls shall be supported by timber. Typical sheeting and

bracing to be adopted in such cases is shown in plate 2-p/3 Instead of sheeting and bracing,

cribbing with 75x150 mm may be used and the arrangement is shown in plate 2-p/4. In loose

materials, it is advisable to keep the space between the pit walls and the cribbing at a

minimum and also to pack the space with hay or wood shavings, and to keep the bottom of

cribbing close to the bottom of the pit. The material from such pits is removed by buckets

operated from a hoist or windlass which should be equipped with a ratchet device for safety.

During excavation, the bottom of the pit should be kept fairly level and of full section so that

each lift may represent the corresponding portion of the deposit in quality and quantity. The

excavated material should be placed round the pits as stockpiles, separated when significantly

different materials are encountered; and marked stakes should be driven in to the stockpiles to

indicate the depth from which the materials were excavated in order to facilitate logging and

sampling latter on. The excavated material should be placed round the pits in the manner it is

received from the excavation, preferably in a clockwise direction. The deposits of excavated

material from the pit at every change in strata should be dumped separately in the manner

described above. Samples from these deposits should be taken as soon as material comes out

of the pits and the natural water content of the excavated material determined.

2.6.1.1.3 Test pits left open for inspection shall be provided with covers or barricades for

safety. Pits and trenches shall be suitably fenced. Trenches and pits should be filled back

properly when exploration and physical inspections are completed and the relevant records

have been obtained.

2.6.1.1.4 When water is encountered in a pit, suitable dewatering system may be required for

further progress. Where suction pumps are used it is desirable that the suction hose be10 mm

larger in diameter than the discharge opening of the pump and the suction head not more than

4.5m. This requires resetting the pump in the pit (on a frame attached to the cribbing) at

intervals of about 3.5 m. When an internal combustion engine is used in the pit, it would be

necessary to lead the exhaust gases well away from the pit.

2.6.1.1.5 Undisturbed samples may be obtained from open pits from each stratum if the

nature of the deposit permits. For this purpose, a pillar of suitable dimensions, say, 40 x 40

cm should be left undisturbed at the center of the pit to collect undisturbed samples of

required size from each layer showing a change of formation. If the thickness of each layer

exceeds 2m, a second sample may be taken. These undisturbed samples will be useful for the

determination of several characteristics of the in situ materials. Special care shall be taken to

preserve the natural moisture content of the samples.

2.6.1.1.6 Open pits on dam axis shall be dug at every chain up to at least 1 m inside the rock

level unless the rock level is very deep say more than 6 m in which case these shall be taken

to a depth equal to (M.W.L. - G.L.)/2 or H/3 (H is the height of dam from the lowest nalla

level to the T.B.L. of the dam) whichever is more. It is desirable to locate some pits on the

probable cut off line.

2.6.1.17 For waste weir, pits at 2 chains apart, shall be dug to rock level or to hard strata.

These shall be taken at every 2nd or 3rd chain of the spill channel. The maximum depth shall

be restricted to 6 m and if rock or suitable hard strata is not met with within 6 m depth, pits

on other alternative site shall be dug. For canals, pits shall be dug at every 150 m to a depth

equal to full supply depth of the canal or 2 metre below the designed bed level (whichever is

less). Separate pits at the location of structures shall be taken to a depth up to 1 m inside the

rock or hard strata level (maximum depth 6 m).

2.6.1.2 Exploration by Trenches

2.6.1.2.1 Test trenches are useful when a continuous exposure along a given line or section is

desired. In general they serve the same purpose as the pit but have the added advantage of

disclosing the continuity or limits of the formations or deposits in question and any vertical

faults in the rock structure.

2.6.1.2.2 The field work consists of excavating an open trench from the top to the bottom of

the slope to reach representative undisturbed material. Either a single slot trench down the

face of the slope or a series of short trenches spaced at appropriate intervals along the slope

may be excavated. Depending on the extent of the investigation required, use may be made of

picks and shovels; bulldozers, ditching machines, back hoes or dragline. A trenching layout

suitable for materials investigation is shown in plate 2-p/5.

2.6.1.2.3 All the instructions for pits given in para 2.6.1.1 shall apply to trenches.

2.6.2 Exploration by Borings and Drilling

2.6.2.1 Hand Auger Borings - Auger boring is the most common, economical and rapid

method for relatively shallow exploration of fine - grained materials above the water - table.

Hand augers become awkward and cumbersome beyond a depth of approximately 6 m. If the

work is done carefully, the layers of different soils may be accurately located, identified

classified and suitable distributed samples obtained.

In making auger borings it is often necessary to add water to soften a hard, dry,clayey soil so

that the auger will penetrate the soil. Also, if dry sands or silts are encountered, the addition

of water will make the soil slightly cohesive and easier to pick up by the auger. Cohesive

soils can be augured successfully below the ground water table. However, if clean non-

cohesive silts or sands are encountered below the water table, they are very difficult to extract

from the hole and such material will cave unless the hole is cased.

2.6.2.2 Power Auger Borings - The most suitable type of power-auger for soil investigations

is the one that will drill a hole at least 60 cm. in diameter (preferably 70 cm to 90 cm), which

is largeenough for a man to enter and make accurate inspection or sampling of the soil in

place. Theselarge-size augers will drill into slightly cohesive soils containing appreciable

quantities of gravel upto 7.5 or 10 cm in size. Power-augers ate not satisfactory for use in

bouldery materials.

Most augers permit boring of holes of about 2.5 m to 3.65 m depth. However, more recent

equipment allow boring up to 6 m or even 12 m depths.

2.6.2 Exploration with Drilling Equipment

2.6.2.3.1 This type of exploration has to be resorted where the required strata or deposit in

case of investigation of materials, cannot be reached by the methods mentioned above or

where the compaction of the soil strata or presence of boulders and rock make it necessary.

The various methods described under relevant para of chapter 22 - "Drilling and Grouting "

shall be followed.

2.6.2.3.2 Use and Extent of Use-The Use and its extent for the various types of drilling is

given below:

(a) Rotary Drilling- Rotary drilling may be used in firm clays, compact sands and silts to

estimate the extent of overburden. Such drilling can be accomplished without casing the bore

hole. A drilling fluid is forced in to the sides of the hole through the rotating drill bit. This

provides sufficient strength for the hole to be drilled without casing. The rotary drills employ

some form of hardened steel core bits with a cutting edge. After rock is reached the rotary

drilling should be replaced bydiamond core drilling. The borehole in the overburden should

be cased before commencing diamond drilling.

(b) Core Drilling-The two types of drills in common use are diamond drills and shot drills.

(i) Diamond Drill- This type is to be resorted to when rock is to be penetrated. Very deep

holes at any angle may be readily drilled and rock of any hardness can be penetrated by this

method. The cores, smaller ones also, can be recovered in good condition and cores from

softer materials can also be recovered. But in this method the holes are too small to be

explored readily with instruments and at times flexibility of rods causes deep holes to deviate

from vertical.

(ii) Small Diameter Shot Drill- Use is similar as for diamond drill. But it shall be difficult to

drill angle holes by this method and also cores are rough and not easy to examine. It shall not

core small holes and softer materials. However, holes are large enough to be explored with

instruments and this method is cheaper than diamond drilling in loose rocks and boulders.

(iii) Large Diameter Shot Drill-This is not used for the same purpose as the diamond or

small shot drill. It takes the place of hard-excavated shafts, drilling large holes to make visual

inspection easy and reliable and also leaves the rock undisturbed. But this method is not

suited for inclined holes and is expensive for small jobs.

RECONNAISSANCE SURVEY REPORT OF MINOR IRRIGATION PROJECTS

(Appendix - I of Chapter -2 survey & investigation)

1. Name of the Scheme

2. Basin/Sub-basin

2.1 District/Tehsil/Block/Village

2.2 Assembly Constituency & Parliamentary constituency (Name & Number)

3. Percentage of Irrigation in District/Tehsil/Block

4. Toposheet Study

4.1 Toposheet No.

4.2 Latitude and Longitude

4.3 Whether the scheme is covered in master plan of the basin/sub-basin (reference be

given)

4.4 Catchment area as per toposheet

4.5 Category of scheme:- Tank/Diversion/Stop dam/Lift

5. Proposed Benefits

5.1 Scheme already proposed or Contemplated on the upstream

5.2 Net catchment available at the site

5.3 Raingauge station/Average rainfall

5.4 Probable yield as per Bennie's table

5.5 Anticipated/Proposed irrigation

6. Type of Scheme : Original/Extension and Improvement / Restoration / Renovation /

Modernisation

6.1 Programme under which scheme is proposed to be taken up.

6.1.1 Plan Minor/C.D work/Tribal Welfare/Revenue sector/Tribal sub plan/T.D.P.P/D.P.A.P.

6.1.2 SC/ST beneficiaries if any.

7. Name of the Officer Inspecting Site:

(Executive Engineer for schemes irrigating 200 hact.

Superintending Engineer for schemes irrigating more than 200 hect.)

7.1 Designation

7.2 Date of inspection

8. Field Data & Feasibility

8.1 Discharge of the site on the date of inspection

8.2 Has the site been found suitable with regard to:

8.2.1 Bund site

8.2.2 Waste weir site

8.2.3 Sluice and Head reach of canal

8.2.4 Nala closure point of view

8.3 Are construction materials available in adequate quantities and within economical lead?

Earth/ Sand /Metal/Stone

8.4 Is the percentage of submergence of cultivated land to the area proposed for irrigation

less

than 10%?

8.5 Forest submergence, if any

8.6 What is the probable?

8.6.1 Tank capacity

8.6.2 Tank Percentage

8.7 Command

8.7.1 What is the crop cultivated in the command at present?

8.7.1.1 Kharif.....................................Hact

8.7.1.2 Rabi........................................Hact

8.7.2 What crop would be cultivated on availability of irrigation?

8.7.2.1 Kharif.....................................Hact

8.7.2.2 Rabi........................................Hact

9. Is the Cost per Hact Likely to be reasonable?

10. Certificate of Revenue Authorities.

11. Remarks and Recommendations’.

E.E (Field) S.E (Field)

INVESTIGATIONS FOR ESTABLISHING SUITABILITY OF CONSTRUTION

MATERIALS

(Appendix - VI of Chapter -2 survey & investigation)

1 Concrete and Masonry Dams

Following investigations shall be carried out:

(i) Geological and related characterization of aggregates including type of deposits,

classification and characteristics of rocks, chemical suitability of aggregates and strength

tests.

(ii) Investigations for the availability of natural and artificial pozzolana with their

characteristics.

(iii) The construction materials shall be tested for petrographic analysis of sand and rock

samples, grading and physical tests of sand and rock samples to assess their suitability,

presence of reactive aggregates in the area, pozzolanic materials and strength of permeability

tests.

2 Earth and Rock fill Dams

Following investigations shall be carried out :

(i) The plans and sections of the borrow area shall be made on a scale of 1:2500 with contour

interval of 0.50 m , showing the location and logs of test pits, bore holes spaced abut 150m

apart and demarcating different types of soil. The lead for different types of soil from the site

of work for different borrow areas shall also be indicated. The borrow areas shall be located

as near the dam site as possible but not less than five times the head of water (H) away from

the toe or heel of the dam for major dams and not less than 10 H away from the toe or heel of

the dam for medium and minor dams

(ii) Soil samples shall be tested for mechanical analysis, Atterberg limits, Proctor compaction,

permeability, triaxial, shear tests with pore pressure measurements under O.M.C. and

saturation conditions, and suitability tests in soils with high soluble content.

(iii) The sand and gravel to be used for filters shall be tested as for concrete aggregate.

(iv) Rock for rock fill dam shall be tested for porosity, compressive strength, durability, alkali

reaction and hammer drop test.

Appendix No- 2

Technical Circular No - 53.

-Preliminary Check Statement for General Feasibility of Projects

Appendix No – 3

E-in-C letter no 3332745/2011 dt 29/03/11

“Estimation of Land width proposed to be acquired for canal for

Sadhyata”

Appendix – 4

Prescribed form of:-

“Form-141 Proposal for Sanction of Survey & Investigation”.

Will be attached

Appendix – 5

“Sample sanction order of “Sadhyata” issued by govt”.

Will be attached

Appendix – 6

“Design Series TC-1”

“Check List for data required for design of Earth

Dam.”

Appendix – 6

“Design Series TC-2”

“Check List for data required for design of Masonry

Dams.”

Appendix – 8

DESIGN OF SPILLWAYS

1.0 GENERAL

Spillway is a safety valve provided in the dam to dispose of surplus flood waters from a reservoir after it has been filled to its maximum capacity i.e. Full Reservoir Level.

The importance of safe spillways needs no over-emphasis as many failures of dams have been caused by improper design of spillways or spillways of insufficient capacity especially in case of earth and rockfill dams which are susceptible to breaching, if overtopped. Concrete/Masonry dams can withstand moderate overtopping but this should be avoided.

Further, the spillway must be hydraulically and structurally adequate and must be so located that the overflowing discharges do not erode or undermine the downstream toe of the dam.

2.0 SELECTION OF DESIGN FLOOD

The spillway design flood is generally determined by transposing great storms which have been known to occur in the region over the drainage area. The resulting flood hydrographs are then determined by rational methods. In determining the discharge capacity consideration should be given to all possible contingencies, e.g. one or more gates being inoperative.

IS : 11223 – 1985 provides guidelines for fixing spillway capacity. Inflow design flood for the safety of the dam is guided by the following criterion:

The dams may be classified according to size by using the hydraulic head and the gross storage behind the dam as given below. The overall size classification for the dam would be the greater of that indicated by either of the following two parameters:

Classification Gross Storage Hydraulic Head

Small 0.5 to 10 million m³ 7.5 to 12 m

Intermediate 10 to 60 million m³ 12 to 30m

Large Above 60 million m³ Above 30 m

The inflow design flood for safety of the dam would be as follows:

Size of dam Inflow Design Flood for safety of dam

Small 100 years flood Intermediate Standard Project Flood (SPF)

Large Probable Maximum Flood (PMF)

Floods of larger or smaller magnitude may be used if the hazard involved in the eventuality of a failure is particularly high or low. The relevant parameters to be considered in judging the hazard in addition to the size would be:

i) Distance and location of human habitations on the downstream after considering the likely future developments

ii) Maximum hydraulic capacity of the downstream channel

For more important projects dam break studies are done as an aid to the judgement in deciding whether PMF needs to be used. Where the studies or judgement indicate an imminent danger to present or future human settlements, the PMF should be used as design flood.

2.1 Standard Project Flood (SPF)

It is the flood that may be expected from the most severe combination of hydrological and meteorological factors that are considered reasonably characteristic of the region and is computed by using the Standard Project Storm (SPS). While transposition of storms from outside the basin is permissible, very rare storms which are not characteristic of the region concerned are excluded in arriving at the SPS rainfall of the basin.

2.2 Probable Maximum Flood (PMF)

It is the flood that may be expected from the most severe combination of critical meteorological and hydrological condition that are reasonably possible in the region and is computed by using the Probable Maximum Storm (PMS) which is an estimate of the physical upper limit to maximum

precipitation for the basin. This is obtained from the transposition studies of the storms that have occurred over the region and maximizing them for the most critical atmospheric conditions.

3.0 FLOOD ROUTING

The process of computing the reservoir storage volumes and outflow rates corresponding to a particular hydrograph of inflow is known as flood routing. It is used for arriving at the MWL for the project. The relationship governing the computation is essentially simple – over any interval of time the volume of inflow must equal the volume of outflow plus the change in storage during the period. If the reservoir is rising, there will be increase in storage and change in storage will be positive, if the reservoir is falling, there will be decrease in storage and the change in storage will be negative.

For an interval of time Δt, the relationship can be expressed by the following expression:

I . t O. t S

Where, I = Average rate of inflow during time equal to Δt

O = Average rate of outflow during time equal to Δt ΔS = Storage accumulated during time equal to Δt

The following three curves are required for carrying out the computations:

a) The inflow flood hydrograph b) The reservoir capacity curve

c) The rating curve showing the total rate of outflow through outlets and over the spillway against various reservoir elevations

Flood routing in gated spillways is generally carried out assuming the flood to impinge at FRL assuming inflow equal outflow to at that level. For ungated spillways this would correspond to the spillway crest or a little above this.

The methods generally adopted for flood routing studies are:

i) Trial and Error Method ii) Modified Puls Method

3.1 Trial and Error Method

This method arranges the basic routing equation as follows:

I1

I 2

2

. t

O1

O2

2

. t S 2

S1

The procedure involves assuming a particular level in the reservoir at the time interval Δt, and computing the values on the right side of the above equation. The computed value on the right side of the equation, corresponding to the assumed reservoir level, is compared with the known value on the left side of the equation. If the two values tally, then the assumed reservoir level at the end of the time interval is OK; otherwise a new reservoir level is assumed and the process is repeated till the required matching is obtained.

This method gives quite reliable results, provided the chosen time interval is sufficiently small, so that the mean of the outflow rates at the start and the end of the interval may be taken as the average throughout the interval.

3.2 Modified Puls Method

This method arranges the basic routing equation as below so that the knowns are placed on the left side and unknowns are placed on the right side of the equation.

I I S

O S O 1 2

1

1

2

2

2 t 2 t 2

Since this equation contains two unknowns it cannot be solved unless a second independent function is available. In the modified Puls method, a storage-indication curve viz. outflow O versus the quantity (S/Δt+O/2) is constructed for the purpose.

In the above equation, it may be noted that subtracting O2 from

(S2/Δt+O2/2) gives (S2/Δt-O2/2). This expression is identical to (S1/Δt-O1/2)

on the left side of the equation except for the subscripts. Since the subscript 1 denotes values at the beginning of a time increment and subscript 2 denotes values at the end of a time increment, it is apparent that (S2/Δt-O2/2) at the end of one time increment is numerically equal to

(S1/Δt-O1/2) for the beginning of the succeeding time increment.

The detailed routing procedure is as follows:

i) Compute the numerical value of left side of the equation for given values of I1, I2, S1 and O1 for the first time increment.

ii) With this numerical value, which equals (S2/Δt+O2/2), refer storage- indication curve and read outflow O2 corresponding to this computed

value of (S2/Δt+O2/2). The O2 thus read is the instantaneous outflow at the end of the first time increment.

iii) Subtract this value of O2 from (S2/Δt+O2/2), which gives the value for

(S2/Δt-O2/2). The value of (S1/Δt-O1/2) for the second time increment is equal to (S2/Δt-O2/2) for the first time increment. Consequently the left side of the equation can be computed for the second time increment and the entire procedure is repeated.

4.0 TYPES OF SPILLWAYS

Spillways can be classified as controlled or uncontrolled depending upon whether they are gated or ungated. Further they are also classified based on other prominent features such as control structure, discharge channel or some such other components.

The common types of spillways used are: i) Overfall or Ogee ii) Orifice or sluice iii) Chute or trough iv) Side channel v) Tunnel/Shaft or Morning Glory vi) Siphon

4.1 Overfall or Ogee Spillway

The overfall type is by far the most common and is adapted to masonry

dams that have sufficient crest length to provide the desired capacity.

This type comprises a control weir which is ogee or S-shaped. The ogee shape conforms to the profile of aerated lower nappe from a sharp crested weir. The upper curve at the crest may be made either broader or sharper

than the nappe. A broader curve will support the sheet and positive hydrostatic pressure will occur along the contact surface. The support sheet thus creates a backwater effect and reduces the coefficient of discharge. The sharper crest on the other hand creates negative pressures, increases the effective head and thereby the discharge.

These spillways are generally provided in Masonry/Concrete dams and also in composite dams as central spillways located in the main river course. Examples are Bhakra dam, Rihand dam, Sriram Sagar dam, Nagarjunasagar dam, Jawahar Sagar dam, Tenughat dam, Srisailam dam, Tawa dam, Ukai dam etc.

A typical ogee spillway is shown in figure below:

4.2 Orifice Spillway

Low crested spillways with either breast wall or sluice type arrangements are now increasingly being provided for flushing out the silt and controlling the silt entry in the power intake which is kept above the spillway crest. These spillways are called orifice or sluice spillways (See figures below).

The orifice spillways have the advantage of having high discharging capacity due to the high water head. At sites where only a limited area and relatively short length of suitable foundation material are available for the spillway structure, the orifice spillway offers the most economic means of passing the design flood. However, the orifice spillways result in high flow concentration, which increases the size and cost of energy dissipation work below.

Orifice spillways are being provided in many of our diversion dams recently in rivers carrying heavy silt load. The power intake is kept above the spillway crest and as close to the spillway as possible. This kind of spillway arrangements thus performs the dual function of passing the flood and managing the sediment in the reservoir.

Examples of spillways with breast wall type arrangements are in Ranganadi H.E. Project (Arunachal Pradesh), Chamera H.E. Project Stage-I (Himachal Pradesh), Rangit H.E. Project Stage-III (Sikkim) etc. and that of sluice spillways are in Tala H.E. Project (Bhutan), Nathpa Jhakri H.E. Project (Himachal Pradesh), Myntdu H.E. Project Stage-I (Meghalaya) etc.

4.3 Chute Spillway

A spillway where discharge is conveyed from the reservoir to the downstream river through an open channel or chute along a dam abutment or through a saddle is called a chute or trough spillway. The chute is the commonest type of water conductor used for conveying flow between control structures and energy dissipators. Chute can be formed on the downstream face of gravity dams, cut into rock abutments and either concrete-lined or left unlined and built as free-standing structures on foundations of rock or soil. These are mostly used with earth/rockfill dams and have the following main advantages:

i) Simplicity of design ii) Adaptability to all types of foundations and iii) Overall economy by using large amount of spillway excavation in

dam construction

Examples of chute spillways are Beas Dam, Ram Ganga Dam, Kolar Dam, Tehri Dam etc.

A typical chute spillway is shown in figure below:

4.4 Side Channel Spillway

The distinctive feature of side channel spillway which distinguishes it from chute spillway is that whereas in the chute spillway the water flows at right angle to the axis of the dam, in the side channel spillway, the flow is initially in a channel parallel to the axis of the dam and thereafter it flows in a discharge channel at approximately right angle to the dam axis.

This type of spillway is suited to narrow canyons with steep sides which rise to a considerable height above the dam. This type of spillway is also provided at sites where the overfall type is ruled out for some reason and where saddle of sufficient width is not available to accommodate a trough (chute) type spillway. It is assumed that all the energy of the overfalling water is dissipated in turbulence in the side channel. Example of side channel spillway is Pancheshwar Project.

A typical layout of a side channel spillway is illustrated in figure below:

4.5 Tunnel/Shaft or Morning Glory Spillway

In this type of spillway water enters over the lip of a horizontal circular crest and drops through a vertical or sloping shaft and then flows downstream through a horizontal conduit or tunnel. The spillway is suitable to dam sites in narrow canyons where room for a spillway restricted.

In some instances advantage of the existing diversion tunnel has been taken for conversion into tunnel spillway. A disadvantage of this type is that the discharge beyond a certain point increases only slightly with increased depth of overflow and therefore does not give much factor of safety against underestimation flood discharge as compared to the other types.

Examples of Tunnel/Shaft spillways are Tehri Dam, Itaipau Dam etc. A typical Tunnel/Shaft Spillway is shown in figure below:

4.6 Siphon Spillway

Siphon spillways are based on the principle of siphonic action in an inverted bent pipe. If such pipe is once filled with water, it will continue to flow so long as the liquid surface is higher than the lower leg of the pipe unless of course, the upper leg gets exposed earlier.

Siphon spillways are often superior to other forms where the available space is limited and the discharge is not extremely large. They are also useful in providing automatic surface-level regulation within narrow limits. The siphon spillways prime rapidly and bring into action their full capacity. Therefore, they are especially useful at the power house end of long power channels with limited forebay capacity where a considerable discharge capacity is necessary within a very short time in order to avoid overflow of the channel banks.

However, siphon spillways are not very common mainly because of:

i) Possibility of clogging of the siphon passage way and siphon breaker vents with debris, leaves etc.

ii) The occurrence of sudden surges and stoppages of outflow as a result of the erratic make and break action of the siphon, thus causing fluctuations in the downstream river stage.

iii) The release of outflows in excess of reservoir inflows whenever the siphon operates, if a single siphon is used. Closer regulation which will more nearly balance outflow and inflow can be obtained by providing a series of smaller siphons with their siphon breaker vents set to prime at gradually increasing reservoir heads.

iv) Vibration disturbances which are more pronounced than in other types of spillways.

A siphon spillway through a dam is shown in figure below:

5.0 HYDRAULIC DESIGN OF OVERFALL OGEE SPILLWAYS (Refer IS: 6934)

Overfall ogee spillway has its overflow profile conforming, as nearly as possible, to the profile of the lower nappe of a ventilated jet of water over a sharp crested weir. These spillways are classified as high and low depending on whether the ratio of height of the spillway crest measured from the river bed to the design head is greater than or equal or less than 1.33

X

respectively. In the case of high overflow spillways the velocity of approach head may be considered negligible.

5.1 Shape of Ogee Profile

i) Spillways with vertical upstream face

Upstream Quadrant

The upstream quadrant of the crest may conform to the ellipse:

2

X 2

Y 1

A1

1 1

B1

The magnitude of A1 and B1 are determined from the graph P/Hd vs A1/Hd

and B1/Hd respectively in fig.2 of IS:6934, where,

P = Height of crest from the river bed

Hd = Design Head

Downstream Quadrant

The downstream profile of the crest may conform to the equation:

1.85

2

K 2 .H d

0.85

.Y2

The magnitude of K2 is determined from the graph P/Hd vs K2 in fig.2 of IS:6934.

ii) Spillways with sloping upstream face

In the case of sloping upstream face, the desired inclination of the face is fitted tangentially to the elliptical profile described under (i) above, with the appropriate tangent point worked out from the equation. The profile of the downstream quadrant remains unchanged.

Figure 2 – IS:6934

iii) Spillways with crest offsets and risers

Whenever structural requirements permit, removal of some mass from the upstream face leading to offsets and risers as shown in fig.1 of IS:6934 results in economy. The ratio of risers M to the design head Hd i.e. M/Hd

should be at least 0.6 or larger, for the flow condition to be stable. The shapes of u/s and d/s quadrants defined for spillways with vertical upstream face are also applicable to overhanging crests, for the ratio M/Hd

> 0.6.

5.2 Discharge Computations

The discharge over the spillway is generally computed by the equation

Q 2 3

2 g C.L.H 3 / 2

where, C = Coefficient of Discharge L = Effective length of crest H = Head over crest

i) Effective Length of Overflow Crest

p

The net length of overflow crest is reduced due to contraction caused by abutment and crest piers. The effective length L of the crest may be calculated as follows:

L L'

2H ( N .K

where,

K a

)

L’ = Overall length of the crest excluding piers H = Head over crest N = Number of piers

Kp = End contraction coefficient of piers Ka = End contraction coefficient of abutment

The pier contraction coefficient, Kp is affected by the shape and location of the pier nose, thickness of pier, the actual head in relation to the design head and the approach velocity. The average pier contraction coefficients may be taken as follows:

Type Kp

Square-nosed piers with rounded corners of radius about 0.1 times pier thickness

0.02

Round-nosed piers 0.01

Pointed-nosed piers 0.0

The abutment contraction coefficient, Ka is affected by the shape of the abutment, the angle between the upstream approach wall and the axis of flow, the actual head in relation to the design head and the approach velocity. The average abutment coefficient may be taken as follows:

Type Ka

Square abutments with head wall at 90o to direction of flow

Rounded abutments with head wall at 90o to direction of flow, when 0.5Hd > R > 0.15Hd

0.2

0.1

Rounded abutments where R > 0.5Hd and head wall not more than

45o to direction of flow

0.0

ii) Coefficient of Discharge

The value of coefficient of discharge depends on the following:

a) Shape of the crest b) Depth of overflow in relation to design head c) Depth of approach d) Extent of submergence due to tail water e) Inclination of the upstream face

Fig. 3 of IS:6934 gives the coefficient of discharge C for the design head as a function of approach depth and inclination of upstream face of the spillway. These curves can be used for preliminary design purposes.

Fig. 4 of IS:6934 gives the variation of coefficient of discharge as a function of ratio of the actual head to the design head (i.e. H/Hd). This curve can be used to estimate C for heads other than design head.

The coefficient of discharge is reduced due to submergence by the tail

water. The position of the downstream apron relative to the crest level also has an effect on the discharge coefficient. Fig. 5A and 5B of IS:6934 give the variation of C with the above parameters.

iii) Design Head

When the ogee crest is formed to a shape differing from the ideal shape or when the crest has been shaped for a head larger or smaller than the one under consideration, the coefficient of discharge will differ.

A design head grater than the actual head will push the crest surface into the theoretical nappe and result in greater pressure along the curved surfaces and in lower discharge capacities. Conversely, a design head lower than the actual head pulls the crest surface below the theoretical nappe, resulting in sub-atmospheric pressures over some portion of the crest curve. At the same time the discharge capacity of such a crest curve is increased.

Excessive sub-atmospheric pressures can result in pulsating, inefficient spillway operation, and possibly damage to the structure as a result of cavitations. A certain amount of sub-atmospheric pressure can be attained without undesirable effects. Figure provides a guide for determining the minimum pressures on the crest for various ratios of design head and actual head on the crest.

Designing the crest shape to fit the nappe for a head less than maximum head expected often results in economies in construction. The resulting increase in unit discharge may make possible a shortening of the crest length, or a reduction in freeboard allowance for reservoir surcharge under extreme flood conditions.

Because the occurrence of design floods is usually so infrequent, the spillway crests are fitted to the lower nappe of a head which is 75% of that resulting from the actual discharge capacity. Tests have shown that the sub- atmospheric pressures on a nappe-shaped crest do not exceed about half of the design head when the design head is not less that about 75% of the maximum head. An approximate diagram of the sub-atmospheric pressures, as determined from model tests, is shown by figure. The design head is normally kept as 80% to 90% of the maximum head corresponding to MWL.

The minimum crest pressure must be greater than cavitation pressure. It is suggested that the minimum pressure allowable for design purposes be

20ft of water below sea level atmospheric pressure and that the altitude of the project site be taken into account in making the calculation. For example, assume a site where the atmospheric pressure if 5ft of water less than sea level pressure, and in which the maximum head contemplated is

60ft; then, only 15 additional feet of sub-atmospheric pressure is allowable.

Appendix -9 DESIGN OF ENERGY DISSIPATORS

1.0 General

The waters flowing down the spillway have very high energy. The same if not dissipated can cause considerable erosion/scour downstream which can endanger the dam stability. It is, therefore, necessary to provide adequate downstream protection work or energy dissipation arrangements (EDA) for dissipating the energy downstream of the spillway and minimize erosion of natural river bed.

As per IS : 11223 – 1985 “Guidelines for fixing spillway capacity”, the energy dissipation works should be designed for a flood which may be lower than the inflow design flood for the safety of the dam. The E.D.A. should be designed to work most efficiently for dominant floods. The designs are invariably checked for lower discharges which would correspond to various percentages of the dominant flood.

The problem of designing energy dissipators is one essentially of reducing the high velocity of flow to a velocity low enough to minimize erosion of downstream river bed. This reduction in velocity may be accomplished by any or a combination of the following, depending upon the head, discharge intensity, tail water conditions and the type of the bed rock or the bed material.

The Energy Dissipation Arrangements generally adopted consist of : i) Stilling Basin

a) Horizontal apron type b) Sloping apron type

ii) Bucket Type Energy Dissipators a) Solid Roller Bucket b) Slotted Roller Bucket c) Flip/Ski Jump Bucket

2.0 Stilling Basin

These are one of the most efficient and commonly adopted Energy Dissipation Arrangements. In stilling basins, the energy is dissipated

through the well known phenomenon of hydraulic jump which is the most effective way of dissipating the energy of flowing water. The simplest kind of protection could be used if a jump would form at all stages on a horizontal floor, at the stream-bed level, extending from the dam to the downstream end of the jump. The height of the tail water for each discharge seldom corresponds to the height of a perfect jump. In some cases the sloping apron will permit a hydraulic jump to form at proper depth within the limits of the apron throughout the entire range of spillway discharges and corresponding tail water depths.

IS : 4997 – 1968 (reaffirmed 1995) gives the criteria for design of hydraulic jump type stilling basins with horizontal and sloping aprons.

2.1 Stilling Basin with Horizontal Apron

When the tail water rating curve approximately follows the hydraulic jump curve or is slightly above or below it, then hydraulic jump type stilling basin with horizontal apron provides the best solution for energy dissipation. In this case the requisite depth may be obtained on an apron near or at the ground level which is quite economical. For spillways on weak bed rock and weirs and barrages on sand or loose gravel, hydraulic jump type stilling basins are recommended.

Hydraulic Jump type stilling basins with horizontal apron may be classified into the following two categories:

a) Stilling basin in which the Froude number of the incoming flow is less than 4.5. This case is generally encountered on weirs and barrages. The basin is called Basin-I.

b) Stilling basins in which the Froude number of the incoming flow is

greater than 4.5. This case is generally encountered in dams. This basin is called Basin-II.

2

Design Criteria

Factors involved in the design of stilling basins include the determination of the elevation of the basin floor, the basin length and basin appurtenances.

Determination of Level of Basin Floor

Knowing HL and q; Dc, D1 and D2 can be determined from the following formulae or from fig.7 of IS:4997:

D D 3

1 / 3

q H

L

2 1

4D1 D

2

D

2q

2 D

2

Dc

g

D2

where,

1

2

D1 g

1

4

HL = Head Loss

D1 = Prejump depth D2 = Post jump depth q = Discharge per unit length g = Acceleration due to gravity

Having obtained D1 & D2, the elevation of basin floor may be calculated.

Basin – I

Requirements of basin length, depth and appurtenances for basin-I are as under:

Basin Length and Depth: Length of basin may be determined from the curve in Fig. 8A of IS:4997. The basin is provided with an end sill preferably

dentated one. In the boulder reach the sloping face of the end sill is generally kept on the upstream side. Generally the basin floor should not be raised above the level required from sequent depth consideration. If the raising of the floor becomes obligatory due to site conditions, the same should not exceed 15% of D2 and the basin in that case should be further

supplemented by chute blocks and basin blocks. The basin blocks should not be used if the velocity of flow at the location of basin blocks exceeds 15 m/s and in that case the floor of the basin should be kept at a depth equal to D2 below the tail water level. The tail water depth should not generally exceed 10% of D2.

Basin Appurtenances: Requirements for basin appurtenances, such as chute blocks, basin blocks and end sill are as below:

a) Chute blocks: Height and top length of chute blocks should 2D1 while width should be D1. The spacing of chute blocks should be kept as 2.5D1 and a space D1/2 should be left along each side wall.

b) Basin blocks: Height of basin blocks in terms of D1 may be obtained from fig.9B of IS:4997. Width and spacing should be equal to their height. A half space is recommended adjacent to the walls. Upstream face of the basin blocks should be vertical. The blocks should be set at a distance of 0.8D2 downstream from chute blocks.

c) End sill: Height of the dentated end sill should be 0.2D2. Maximum width

and spacing should be 0.15D2. In the case of a narrow basin, the width

and spacing can be reduced but in the same proportion. A dent is recommended adjacent to each side wall.

Basin – II

Requirements for basin length, depth and appurtenances for Basin-II are as

under:

Basin Length and Depth: Length of the basin will be determined from the curve in Fig. 9A of IS:4997. The basin should be provided with chute blocks and end sill. The maximum raising of the basin floor shall not exceed 15% of D2 and basin in that case will be further supplemented by basin blocks.

However, when the velocity of flow at the location of basin blocks exceeds 15 m/s, no basin blocks are recommended and in that case the floor of the basin should be kept at a depth equal to D2 below the tail water level. The

tail water depth should not generally exceed 10% of D2.

Basin Appurtenances: Requirements for basin appurtenances, such as chute blocks, basin blocks and end sill are as below:

a) Chute blocks: Height, width and spacing of chute blocks should be kept as D1. The width and spacing may be varied to eliminate fractional

blocks. A space D1/2 should be left along each side wall.

b) Basin blocks: Height of basin blocks in terms of D1 may be obtained from

fig.9B of IS:4997. Width and spacing should be equal to three-fourth of the height. A half space is recommended adjacent to the walls. Upstream face of the basin blocks should be vertical. The blocks should be set at a distance of 0.8D2 downstream from chute blocks.

c) End sill: Same as Basin I.

2.2 Stilling Basin with Sloping Apron

When the tail water is too deep as compared to the sequent depth D2, the

jet left at the natural ground level would continue to go as a strong current near the bed forming a drowned jump which is harmful to the river bed. In such a case, a hydraulic jump type stilling basin with sloping apron should be preferred as it would allow an efficient jump to be formed at suitable level on the sloping apron.

Hydraulic Jump type stilling basins with sloping apron may be classified into the following two categories:

Basin – III: This is recommended for the case where tail water curve is higher than D2 curve at all discharges.

Basin – IV: This is recommended for the case where tail water depth at maximum discharge exceeds D2 considerably but is equal to or slightly

greater than D2 at lower discharges.

Design Criteria

The slope and overall shape of the apron are determined from economic consideration, the length being judged by the type and soundness of river bed downstream. The following criteria should be used only as a guide in proportioning the sloping apron designs.

Basin III

a) Assume a certain level at which the front of jump will form for the

maximum tail water depth and discharge.

b) Determine D1 from the known upstream total energy line by applying

Burnoulli’s theorem and calculate F1.

c) Assume a certain slope and determine the conjugate depth D’2 and

length of jump for the above Froude number from fig.5 and fig.3 of IS:6977 respectively. The length of apron should be kept 60% of the jump length.

d) Compare the available tail water depth with D’2. If they do not match,

change the slope or the level of upstream end of the apron or both. Several trails may be required for arriving at final figures.

e) The apron designed for maximum discharge may then be tested for lower discharges, say 25%, 50% and 75% of maximum discharge. If the tail water depth is sufficient or in excess of the conjugate depth for intermediate discharges, the design is acceptable. If not, a flatter slope at the lower apron level should be tried or Basin IV may be adopted.

f) The basin should be supplemented by a solid or dentate end sill of

height 0.05 to 0.2D’2 with an upstream slope of 2:1 to 3:1.

Basin IV

a) Determine the discharge at which the tail water depth is most deficient.

b) For the above discharge, determine the level and length of horizontal portion of apron by criteria for horizontal apron.

c) Assume a certain level at which the front of jump will form for the maximum tail water depth and discharge.

d) Determine D1 from the known upstream total energy line by applying Burnoulli’s theorem and calculate F1. Then find out the conjugate

depth D2 from equation 3.3 of IS:4997.

e) Determine a suitable slope (by trial and error) so that the available tail water depth matches the required conjugate depth D’2

determined from fig.6 of IS:4997.

f) Determine the length of jump for the above slope from fig.3 of IS:4997. If the sum of the lengths of inclined and horizontal portion is equal to about 60% of the jump length, the design is acceptable. If not, fresh trials may be done by changing the level of upstream end of jump formation.

g) The basin should be supplemented by a solid or dentate end sill of

height 0.05 to 0.2D2 with an upstream slope of 2:1 to 3:1.

3.0 Bucket Type Energy Dissipators

The bucket type energy dissipators generally used are: i) Solid Roller Bucket ii) Slotted Roller Bucket

iii) Ski-Jump/Flip Bucket

IS:7365–1985 “Criteria for Hydraulic Design of Bucket Type Energy

Dissipators” is normally used for carrying out hydraulic design.

3.1 Solid Roller Bucket

An upturn solid roller bucket is used when the tail water depth is much in excess of the sequent depth. The dissipation energy occurs as a result of formation of two complementary elliptical rollers, one in bucket proper called the surface roller, which is anti clockwise (if the flow is to the right) and the other downstream of the bucket called the ground roller, which is clockwise.

The hydraulic design involves determination of a) Bucket invert elevation b) Radius of bucket c) Bucket lip shape and lip angle

a) Bucket Invert Elevation

Normally the invert level of a roller bucket is so fixed that the difference in the design maximum tail water level and the invert level (d3) is between 1.1

to 1.4 times the sequent depth (d2). It has been seen that a satisfactory

energy dissipation is obtained when the roller height (hb) is between 75 and 90 percent of the tail water depth (d3). If the aforesaid two criteria are satisfied, then the surge height (hs) measured above the invert level is 105 to 130 percent of the tail water d3, that is, hs/d3 = 1.05 to 1.3.

Charts at fig.4 and fig.5 of IS:7365 are used for determining the roller depth (hb) and the surge height (hs) respectively.

D D

3

b) Radius of the Bucket

The values given in fig.4 of IS:7365 shows the range of H1/R for which good roller action can be expected. One formula which has been found to be widely applicable for a bucket lip angle of 45o is as under:

R 8.26 X 10

2 2.07 X 10

3 F

H1

1.4 X 10 5

F 2

where, FD = Discharge parameter

q

gH1

X 103

H1 = Reservoir Pool Level – Bucket Invert level

There are many other empirical formulae available for calculating the radius of bucket. The bucket radius is chosen to fall within the recommended

ranges (fig.4, IS:7365) consistent with economical and structural considerations.

c) Bucket Lip

A flat topped lip tends to lower the jet after it leaves the lip and the size and strength of the ground roller would reduce. This is not desirable from the point of view of prevention of erosion near the lip. Therefore, a downstream slope of 1 in 10 or slightly steeper than that may be given to the bucket lip. The width of the lip should not be more than one tenth of the radius of bucket. However the minimum width may be kept as one metre.

A 45o bucket lip angle with the horizontal is generally found to be satisfactory for most cases where the discharge parameter lies between 30 and 80.

Model studies are desirable for finalizing the parameters/arrangements.

3.2 Slotted Roller Bucket

This is an improvement over the solid roller bucket arrangement. In the slotted roller bucket, a part of the flow passes through the slots, spread laterally and is lifted away from the channel bottom by a short apron at the downstream end of the bucket. Thus the flow is dispersed and distributed over a greater area resulting in a less violent flow concentrations compared to those in a solid roller bucket. The height of boil is also reduced in case of

slotted roller bucket. The slotted roller bucket provides a self cleaning action to reduce abrasion in the bucket.

Although a slotted roller bucket is an improvement over the solid roller bucket, experience has shown that bucket teeth are vulnerable to damage on account of various reasons like boulders rolling down the spillway, unsymmetric gate operation causing heavy discharge intensities etc. Slotted roller buckets are not recommended in bouldery stages of the river.

The hydraulic design involves determination of a) Bucket radius b) Bucket invert elevation c) Bucket lip angle

d) Tooth dimensions

a) Bucket Radius

Calculate q, the discharge per meter width of bucket.

Calculate vt , the theoretical velocity of flow entering the bucket using the formula,

vt

2 gH 3

where, H3 is difference in reservoir pool elevation and tail water level.

From fig.7 of IS:7365, find va, the actual velocity of flow entering the bucket.

Find d1=q/va and F1.

From fig.8 of IS:7365, find minimum allowable bucket radius.

b) Bucket invert elevation

Find the minimum tail water depth Tmin and maximum tail water depth

Tmax from fig.9 and fig.10 respectively of IS:7365. Set such bucket invert elevation for which tail water elevations are

between tail water depth limits.

c) Bucket lip angle

Same as solid roller bucket.

d) Tooth dimensions

Width of tooth is kept as o.125R and spacing of tooth is kept as 0.05R, where R is the radius of the bucket.

Detailed tooth dimensions are given in fig.12A and fig.12B of IS:7365.

Model studies are desirable for confirming the design parameters. It shall

be ensured that the teeth perform cavitation free.

3.3 Ski Jump Bucket

This bucket is used when the tail water depth is insufficient for the formation of hydraulic jump and when the bed of the river channel downstream consists of sound rock capable of withstanding the impact of high velocity jet. The flow coming down the spillway is thrown away from the toe of the dam to a considerable distance downstream as a free discharging upturned jet which falls on the channel bed downstream. There is no energy dissipation within the bucket. The device is used mainly to increase the distance from the structure to the place where the jet hits the channel bed. In the ski jump bucket, only part of the energy is dissipated through interaction of the jet with the surrounding air. The remaining energy is imparted to the channel bed below.

Design Criteria

The principal features of hydraulic design of trajectory bucket consist of the following:

a) Bucket shape b) Bucket invert elevation c) Bucket radius d) Bucket lip elevation and exit angle e) Trajectory length f) Estimation of downstream scour

a) Bucket shape

The performance of the trajectory bucket is judged mainly by the trajectory height and length of throw. Generally a circular shape is preferred from practical consideration.

b) Bucket invert elevation

This depends on the site and tail water condition. For a clear flip action, the lip should be kept above the maximum tail water level. However this may not always be possible. Some of the various considerations which are taken into account while fixing bucket invert elevation are as under:

i) A minimum concrete cover of 1.5 metes over the bed rock

ii) A submergence of not more than 70% of the sequent depth over the lip of the bucket

iii) A safe maximum submergence equal to critical depth over the bucket lip elevation

An attempt is made to keep the bucket invert of the trajectory bucket as high as possible consistent with economy. The hydraulic performance is normally verified in a model.

c) Bucket radius

The radius of bucket should not be less than 3 times the maximum depth of flow (d1) entering the bucket to avoid separation tendency.

The formula generally used for determining the radius of bucket is as under:

R 0.6to0.8 H .H 5

where, H = Depth of overflow over the spillway crest

H5 = Reservoir Pool Elevation – Jet Surface Elevation at bucket invert

d) Bucket lip elevation and lip angle

The lip angle affects the horizontal throw distance. The factors affecting the horizontal throw distance also include the initial velocity of the jet and the difference in elevation between the lip and the tail water. Normally

adopted lip angle is between 30o and 40o. Greater the exit angle grater will

be the distance of throw. However the jet impinges on the tail water at a steeper angle which results in deeper scour. For submerged lips the lower

lip angle of 30o may be adopted to minimize sub-atmospheric pressures on the lip.

The lip shall be made flat in case tail water level is lower than the lip level. However, if the tail water level is higher than the lip level, the lip shall slope downstream about 1 in 10. In some cases necessity of aeration may arise which may be finalized after model studies.

e) Trajectory length

The following expression may be used for calculating the horizontal throw distance:

X Sin2 2Cos Sin

2 Y

H v

H v

where, X = Horizontal throw distance from bucket lip to the

centre – point of impact with tail water

Y = Difference between the lip level and tail water level, sign taken as positive for tail water below the lip level and negative for tail water level above the lip level

Hv= Velocity head of jet at bucket lip

Φ = Bucket lip angle with the horizontal in degrees

For the conditions when Y is negative, model studies may be carried out to confirm the value of horizontal throw distance (X) and vertical distance of throw (a).

Vertical distance of throw above the lip level may be calculated from the following formula:

a v

a

2 Sin

2

2 g

where, a = Vertical distance from the lip level to the highest

point of the centre of jet Va = Actual velocity of flow entering the bucket Φ = Bucket lip angle

214

s 4

g = Acceleration due to gravity

f) Estimation of downstream scour

The factors governing scour below trajectory buckets are the discharge intensity, height of fall, water level, lip angle, mode of operation of spillway, degree of homogeneity of rock, type of rock, time factor etc. However, restricting the analysis of correlating the scour depth with two dominant factors, namely discharge intensity (q) and the total head (H4), the scour depth can be worked out by the following

equation:

d m qH 0.5

where, ds = depth of scour

m = constant (0.36 for minmum scour, 0.54 probable scour under sustained operation, 0.65 for ultimate scour)

q = discharge intensity H4 = reservoir pool elevation – bucket endsill elevation

Experience has shown that erosion upto the ultimate scour level will take place irrespective of the type of rock etc. The process is merely a function of time. In case of mega projects, pre-formed plunge pool upto the scour level is being invariably considered.

215

Appendix 10

Prescribed form of

Collection of Agriculture statistics –

(Page 353 of volume II of book of technical Circulars)

Agriculture Statistics for the Year …… of Area Commanded by the … Irrigation Project in the District …..

Seri

al N

o.

Nam

e o

f V

illag

e

Po

pu

lati

on

Cu

ltu

arab

le a

rea

in v

illag

e

Area under

kharif in

whole

village

Area under

Rabi in

Whole

Village

DETAILS OF AREA COMMANDED

Are

a d

ou

ble

cro

pp

ed in

wh

ole

villa

ge

Tota

l vill

age

area

Tota

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mm

and

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area

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lus

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fo

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Area

under

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Area

under

rabi

Are

a d

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ed

Net

cro

pp

ed

are

a

Area Under Rice

Trans-

planted

Broad

Casted

Dry

Irri

gate

d

Dry

Irri

gate

d

Dry

Irri

gate

d

Dry

Irri

gate

d

Dry Irrigat

ed Dry Irrig

ated

1 2 3 4 5 6 7 8 9 1

0

1

1

12 1

3

14 1

5

1

6

1

7

18 19 2

0

21 2

2

216

Are

a u

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ted

su

garc

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and

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d g

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Soils of area commanded

Pro

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in a

rea

irri

gate

d

Pro

po

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ns

of

ligh

t so

ils in

are

a ir

riga

ted

Revenue Officers opinion as

to the extent of expansion of

the Rice area in the area

commanded that will be

secured with irrigation

Rem

ark

Ten

yea

rs a

fter

com

ple

tio

n o

f p

roje

ct

Twen

ty y

ears

aft

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Thir

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aft

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ple

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n p

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ct

23 24 25 26 27 28 29 29 30 31 32 33 34

(From page 353 of book of technical circulars volume II)

217

Appendix 11

Prescribed form of

“Information of officers related with proposal form-133”

will be attached

218

Appendix 12

Prescribed form of

“Form-141 A - Parameters for minor storage Irrigation Projects”

will be attached

219

Appendix 13

Prescribed form of

“Form-142 -Basic Information for Minor Irrigation Schemes”

will be attached

220

Appendix 14

Prescribed form of

“Proforma of T.C.70”

will be attached

221

Appendix 15

Prescribed form of

“Proforma to accompany AA – T.C.70”

will be attached

222

Appendix 16

Prescribed form of

“Check list of according AA to Irrigation Schemes.”

will be attached