GTU. Shantilal Shah Engineering College, Bhavnagar

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Lesley O’Brien’
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1 GTU Shantilal Shah Engineering College, Bhavnagar

2 2 Around 40,000 large reservoirs worldwide used for water supply, power generation, flood control etc. About 1 % of the total storage volume is lost annually as a result of sedimentation and 300 to 400 dams would need to be constructed annually to maintain current total storage. Palmieri et al., (2003) estimated the storage loss to be approximately 45 km 3 per year.

3 3 [Source: ICOLD Report, 2004]

4 4 [Source: UNEP Report, 2004]

5 5 [Source: CWC Report, 2001]

6 6 The silting process of reservoirs is determined by several Natural causes such as: Sediment transport in the river system Bank and Shore erosion Bank and Slope sliding

7 7 Reduction of useful and economic life of reservoirs The reduction of hydro-power generation, water supply or discharge regulation capacity Additional lateral force on the dam wall exerted by deposited sediment Effect due to the action of high velocity, sediment overloaded flows The abrasion and damage of tunnels, galleries, guiding slots, turbines and other equipment

8 8 Compensate for Sediment Accumulated in Reservoir Remove Sediment from Reservoir Minimize Sediment Entering Reservoir Minimize Deposition of Sediment in Reservoir

9 9

Natural vegetation filters, Check dam, Debris basin,

10 10 Watershed Management: Vegetative Treatment Structural Intervention Operational Measures Upstream Trapping: Natural vegetation filters, Check dam, Debris basin, Sediment detention basin, Reservoir. Locate Reservoir Off- Stream:

11 11 Preserve, Enhance, Restore and Construct wetlands Sediment Control, enhance fish habitat, improve water quality etc.

12 12

13 13 Density currents can form when sediment-laden water from a stream enters the relatively clearer water of a reservoir The density current then follows down the path of the preimpoundment river channel The sediment-laden water can be discharged through lowlevel outlets (vented). If the density current is not vented, a muddy lake forms near the dam

14 14

15 15

16 16 The operational technique whereby previously accumulated and deposited sediments in reservoirs are removed by accelerated flows

17 17 Sediment flushing technique is used by two ways: Drawdown flushing Emptying and Flushing The flow velocities in the reservoir are increased to such an extent that deposited sediments are remobilized and transported through the low level outlets provided slightly above the original riverbed level with sufficient flow capacity

18 18

19 19 Raising the dam Abandon old reservoir and Construction of a new reservoir Reconstruction of dam wall New sluicing facilities Changing operation management Conjunctive management

20 20

21 21 Wide Hollow Reservoir: Location : Northwest of Escalante, Utah Sedimentation Rate: Average annual loss of 0.91% of original capacity per year ( ) or 48% lost capacity as of Management Strategies: Sediment Basin Sluice gates installed Dam Enlargement Benefit: Restore almost all of the original reservoir capacity. [Source: Utah State Water Plan, 2010]

22 22 Three Gorges Dam: Location : Yangtze River, China Normal Pool Level: 175 m. Flood Season Pool Level: 145 m. Annual Sediment Load: 532 million tons Management Strategies: During the flood season (June-Sept), when the river carries 90% of the annual sediment load the pool level is drawn down to flood season pool level (sediment sluicing) In the upstream the construction of the and Xiluodu dams trap sediment and reduce the sediment load into the TGP reservoir. [Source:

23 23 Three Gorges Dam The Xiangjiaba And Xiluodu Dams

24 24 Three Gorges Dam

25 25 Baira Reservoir: Location: Ravi River in northwest India Capacity: 3.76 Mm 3 Management Strategies: A 5m x 7m high D shaped diversion tunnel was used for flushing of sediment from the reservoir Clearing 0.38 Mm 3 in 40 hours. Benefit: Removing an estimated 80 percent of accumulated sediments from the reservoir

26 Reservoir sedimentation is a global challenge The remedial measures presented in this seminar report can prolong the live reservoir capacity Instead of adopting individual measures these

26 26 Reservoir sedimentation is a global challenge The remedial measures presented in this seminar report can prolong the live reservoir capacity Instead of adopting individual measures these may be adopted in combination for better results. Considering the alarming rates at which the reservoirs are being silted up, the sediment control practices, measures and works should be adopted

27 27 Gregory L. Morris, Jiahua Fan (2010), Reservoir sedimentation Handbook, published by McGraw-Hill. M Z Qamar, M K Verma, A P Mesharm, M. K. Pawar, Review Of Sediment Control Measures In Reservoirs, India Water Week 2012 Water, Energy and Food Security: Call for Solutions, April 2012, New Delhi. Managing Sediment in Utah s Reservoirs, Utah Division of Water Resources, Utah State Water Plan. SEE Hydropower, Sediment management and reservoir flushing in Austria, Gabriele Harb (Graz University of Technology). ICOLD. 2004, Draft final report on Mathematical modelling of sediment transport and deposition in reservoirs Guidelines and case studies. Bogdan MARCU, Iulian IANCU, Research on Silting and Desilting Of Reservoirs (Artificial Lakes), U.P.B. Sci. Bull., Series D, Vol. 75, Iss. 2, 2013

Strategies for managing sediment in dams. Iwona Conlan Consultant to IKMP, MRCS

Strategies for managing sediment in dams Iwona Conlan Consultant to IKMP, MRCS 1 Sediment trapping by dams Active storage capacity Dead storage coarse material (bed load) Fine materials (suspension) Francis