water and development - iit bombay

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Water and Development Part 4b: Dams and Weirs Milind Sohoni www.cse.iitb.ac.in/sohoni email: [email protected] () October 11, 2015 1 / 22

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Page 1: Water and Development - IIT Bombay

Water and DevelopmentPart 4b: Dams and Weirs

Milind Sohoniwww.cse.iitb.ac.in/∼sohoni

email: [email protected]

() October 11, 2015 1 / 22

Page 2: Water and Development - IIT Bombay

Dams and Weirs-The Kolhapur Type Bandhara

source: http://www.maharashtra.gov.in/english/ gazetteer/

Nanded/images/kholhapur-dam.jpg() October 11, 2015 2 / 22

Page 3: Water and Development - IIT Bombay

The principle

source:

http://ahmednagar.nic.in/html docs/

images Ralegan.png

Concrete structure withinthe river bed.

Gates open in monsoonsand shut just after.

Creates a storage used foragriculture/DW.

The storage is largelyconfined to the river bed.No land need be acquired.

Used by upstream people!

Appear in a sequence

Fairly cheap and useful.Very popular in India.

() October 11, 2015 3 / 22

Page 4: Water and Development - IIT Bombay

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 throughKT weir.

() October 11, 2015 4 / 22

Page 5: Water and Development - IIT Bombay

Reservoir+Earthen Dam

Objectives

Increase surface storagein system. Increaserecharge and total GWstored. Improve surfacewater flows.

Improve drinking watersecurity and allow forlivelihood water.

Costs

Land acquisition, submergence. Considerable amount of earth.

Sophisticated engineering design. Labour and fuel costs.

() October 11, 2015 5 / 22

Page 6: Water and Development - IIT Bombay

A Small Dam

90

100

100

100

90

100

90

90

bund

maindam

stream stream

spillway

The FSL (full storage level) of thedam is the height at which water isstored, in this case, 100.

The dam and the bund are higher.The bund was needed to achieve anFSL of 100.

The storage is the modified contourat 100.

The spillway is at 100 and cuts intothe old contour at 100. Excesswater overflows from here.

The Key-wall protects the damfrom the spillway.

() October 11, 2015 6 / 22

Page 7: Water and Development - IIT Bombay

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) 1.4Buffalo 10 Rs. 500 200 days Rs.(L) 1.0Agri. land 3 acres Rs. 10,000 1 season Rs.(L) 0.3Dom. 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. Soiland water use and other construction modalities.

() October 11, 2015 7 / 22

Page 8: Water and Development - IIT Bombay

Alignment

() October 11, 2015 8 / 22

Page 9: Water and Development - IIT Bombay

Storage Calculation

9290 94

FSL=95

Storage=A90 + . . . + A95. Height of dam=6m+safety.Thickess=25m.

() October 11, 2015 9 / 22

Page 10: Water and Development - IIT Bombay

Design Principles

Structural Stability. Sliding and Toppling. Tension and the roleof rock-toe. The two free-body diagrams. Safety andRisk-assessment.

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W

N

Mg

f

N’

T

Dam

Hydro-geologic analysis. Water within the dam. Drains.Groundwater recharge. Downstream effects.

Watershed analysis. Peak rainfall. Height above FSL andkey-wall.

() October 11, 2015 10 / 22

Page 11: Water and Development - IIT Bombay

Cross-Section

� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �

� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �

� � �� � �� � �� � �� � �� � �� � �� � �� � �� � �� � �� � �� � �� � �

� � �� � �� � �� � �� � �� � �� � �� � �� � �� � �� � �� � �� � �� � �

Core

Drains

Storage Water

Water Table

Iso−heads

Hard RockCOT

Casing

Core : a wall of clay/lowconductivity soil.

COT : To insert into hard-rock.

Drains : To keep the dam dryand prevent seepage flows.

Casing : Muram like soil,supports the core.

Note the water-table and theiso-head lines.

Note the rapid drop in thewater table in the core.

() October 11, 2015 11 / 22

Page 12: Water and Development - IIT Bombay

Section

() October 11, 2015 12 / 22

Page 13: Water and Development - IIT Bombay

Section at alignment

() October 11, 2015 13 / 22

Page 14: Water and Development - IIT Bombay

OverflowH = HFL− FSL is the height or the thickness of water over thespillway bar.

Estimate of flow in cu.m./sec is Q = 1.6 ∗ LH3/2, where L is thelength of the bar.

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H

HorizontalBar

velocity

Velocity Profile

H

Overflow

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.() October 11, 2015 14 / 22

Page 15: Water and Development - IIT Bombay

Construction

Measurements and Marking. Seat of the dam. Cleaning.Rock-toe. Drains.

Cut-Off trench. Foundation. establishing cut-off. Inspection ofstrata. Corrective Action .

Filling and rolling. Two types of soil. Watering and compaction.Checking soil conductivity.

Key Wall. Masonry structure. Horizontal wall. Connection withearthen structure.

Pitching. Lining, clean-up.

Project Management

Procurements. Tanker, JCB, Dumpers. Soil and water. Finance.Legal.

Weekly targets. Weekly bill payments-labour, machinery andfuel. Community and stakeholder meetings. Visit of experts.

() October 11, 2015 15 / 22

Page 16: Water and Development - IIT Bombay

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 thedam walls.

() October 11, 2015 16 / 22

Page 17: Water and Development - IIT Bombay

Nira-Deoghar-Earthen

source: http://www.abilgroup.com/images/Nira-Deoghar.png

() October 11, 2015 17 / 22

Page 18: Water and Development - IIT Bombay

The Earthen Bund at Khubi

source:

http://thdc.gov.in/Writereaddata/Projects/English/Images/PG 291.jpg() October 11, 2015 18 / 22

Page 19: Water and Development - IIT Bombay

Salient FeaturesExercise: Compute rainfall intensity. Estimate Ai for various i ,average depth. Estimate irrigation efficiency.

() October 11, 2015 19 / 22

Page 20: Water and Development - IIT Bombay

Budget

() October 11, 2015 20 / 22

Page 21: Water and Development - IIT Bombay

Bushy Dam-Masonry

source: http://travel.sulekha.com/lovely- lovely-lonavala

maharashtra-travelogue-4508.htm() October 11, 2015 21 / 22

Page 22: Water and Development - IIT Bombay

Thanks

() October 11, 2015 22 / 22