Water and Development
Part 4b: Dams and Weirs
Milind Sohoni
www.cse.iitb.ac.in/∼sohoni
email: sohoni@cse.iitb.ac.in
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Dams and Weirs-The Kolhapur Type Bandhara
source: http://www.maharashtra.gov.in/english/ gazetteer/
Nanded/images/kholhapur-dam.jpg
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The principle
Concrete structure within
the river bed.
Gates open in monsoons
and shut just after.
Creates a storage used for
agriculture/DW.
The storage is largely
confined to the river bed.
No land need be acquired.
Used by upstream people!
Appear in a sequence
source:
http://ahmednagar.nic.in/html docs/ Fairly cheap and useful.
images Ralegan.png Very popular in India.
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A typical caluclation
.
Height and length of KT weir: 30m × 3m.
Length: 1000m and therefore volume: 100,000 cubic meter, i.e.,
0.1MCM.
At 10cm watering, we get 100 hectares of irrigation.
About 30-40km of river gives us 4MCM per discharge.
Dimbhe Storage is 375MCM.
About 20-30 weeks of discharge gives about 100MCM through
KT weir.
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Reservoir+Earthen Dam
Objectives
Increase surface storage
in system. Increase
recharge and total GW
stored. Improve surface
water flows.
Improve drinking water
security and allow for
livelihood water.
Costs
Land acquisition, submergence. Considerable amount of earth.
Sophisticated engineering design. Labour and fuel costs.
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A Small Dam
The FSL (full storage level) of the
stream stream dam is the height at which water is
stored, in this case, 100.
The dam and the bund are higher.
The bund was needed to achieve an
100
90 main FSL of 100.
dam
bund The storage is the modified contour
100 at 100.
90 spillway
90
The spillway is at 100 and cuts into
100
the old contour at 100. Excess
100 90
water overflows from here.
The Key-wall protects the dam
from the spillway.
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Life-Cycle
Expression of Interest-GP, panchayat samiti
Need Assessment-drinking water stress, livelihood needs,
domestic needs, irrigation potential created.
Drinking W. 35 HH 0.2 person-day 200 days Rs.(L) 1.4
Buffalo 10 Rs. 500 200 days Rs.(L) 1.0
Agri. land 3 acres Rs. 10,000 1 season Rs.(L) 0.3
Dom. Use 35 HH 0.2 person day 200 days Rs(L) 1.4
Site selection. Land acquisition, forest land. Storage created.
Hydro-geological suitability.
Pre-feasibility Study. Technical report. Cost-benefit analysis.
Community Approval. Water Use agreement. Committee.
hand-over details. Labour and community contributions. Soil
and water use and other construction modalities.
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Alignment
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Storage Calculation
FSL=95
90 92 94
Storage=A90 + . . . + A95 . Height of dam=6m+safety.
Thickess=25m.
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Design Principles
Structural Stability. Sliding and Toppling. Tension and the role
of rock-toe. The two free-body diagrams. Safety and
Risk-assessment.
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Mg
Hydro-geologic analysis. Water within the dam. Drains.
Groundwater recharge. Downstream effects.
Watershed analysis. Peak rainfall. Height above FSL and
key-wall.
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Cross-Section Core
Iso−heads
Casing
Storage Water Table
Water
Drains
COT Hard Rock
Core : a wall of clay/low Casing : Muram like soil,
conductivity soil. supports the core.
COT : To insert into hard-rock. Note the water-table and the
Drains : To keep the dam dry iso-head lines.
and prevent seepage flows. Note the rapid drop in the
water table in the core.
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Section
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Section at alignment
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Overflow
H = HFL − FSL is the height or the thickness of water over the
spillway bar.
Estimate of flow in cu.m./sec is Q = 1.6 ∗ LH 3/2 , where L is the
length of the bar.
H Velocity Profile
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Overflow
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Horizontal H
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velocity
For Gudwanwadi.
Catchment was roughly 1.1 sq.km.
A peak rainfall of 50mm/hour gives Q = 15.3cu.m./s.
H = 0.8 and L = 15m gives Q = 17cu.m./s.
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Construction
Measurements and Marking. Seat of the dam. Cleaning.
Rock-toe. Drains.
Cut-Off trench. Foundation. establishing cut-off. Inspection of
strata. Corrective Action .
Filling and rolling. Two types of soil. Watering and compaction.
Checking soil conductivity.
Key Wall. Masonry structure. Horizontal wall. Connection with
earthen structure.
Pitching. Lining, clean-up.
Project Management
Procurements. Tanker, JCB, Dumpers. Soil and water. Finance.
Legal.
Weekly targets. Weekly bill payments-labour, machinery and
fuel. Community and stakeholder meetings. Visit of experts.
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Gudwanwadi Dam
85m long, 8m high, earthen.
Storage 2 acres, 20K cu.m.
Cost: 24 lakhs.
Construction time: 6 mo.
Note Spillway, and Key-wall.
Note Pitching (stones) on the
dam walls.
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Nira-Deoghar-Earthen
source: http://www.abilgroup.com/images/Nira-Deoghar.png
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The Earthen Bund at Khubi
source:
http://thdc.gov.in/Writereaddata/Projects/English/Images/PG 29
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Salient Features
Exercise: Compute rainfall intensity. Estimate Ai for various i,
average depth. Estimate irrigation efficiency.
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Budget
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Bushy Dam-Masonry
source: http://travel.sulekha.com/lovely- lovely-lonavala
maharashtra-travelogue-4508.htm
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Thanks
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