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Storage head works
- 1. STORAGE HEAD WORKS 1 ANIRUDHANK M LECTURER IN CIVIL ENGINEERING
- 2. DAMS • Hydraulic structure •Solid Impervious (or fairly impervious) barrier constructed at a suitable location across a natural stream (river), to store water in its upstream side. • A reservoir is formed due to its construction • The water in the reservoir is utilised as and when it is needed 2
- 3. TYPES OF DAM •Classification according to use – Storage Dam – Diversion Dam – Detention Dam • Classification by hydraulic design – Overflow Dam – Non Overflow Dam • Classification by Materials – Rigid Dams – Non – Rigid Dams • Classification By Mode of Stability – Gravity Dam – Non Gravity Dam 3
- 4. TYPES OF DAM •Classification according to use –Storage Dam • Constructed to store water during the rainy season, when water is available in the river. • Released gradually for intended purposes. • They may store water for hydroelectric power generation, irrigation or for Water Supply. –Diversion Dam • Used to raise water level and divert water. • No Reservoir is formed. • No or a little Storage. –Detention Dam • Flood mitigation. • Stores water in the time of flood and released after flood at safe rate. • Another type allows water to enter slowly to the ground water. 4
- 5. TYPES OF DAM •Over flow dam – Designed to carry Surplus discharge – Crest is lover than High Flood Level – Used along with Non Overflow Dam as Spillway Section • Non Overflow Dam – Top of the dam kept higher than Maximum expected high flood level – Water not permitted to overtop the dam Classification by hydraulic design 5
- 6. TYPES OF DAM •Rigid Dam – Constructed of Rigid Materials • Solid Masonry or Concrete Gravity Dam • Arched Masonry or Concrete Dam • Concrete Buttress Dam • Steel Dam • Timber Dam • Non Rigid Dam – Constructed of Non Rigid Materials • Earth Dam • Rockfill Dam • Combined Earth and Rockfill Classification by Materials 6
- 7. TYPES OF DAM •Gravity Dam – Self Weight of the Dam the major Stabilization Force • Solid Masonry or Concrete Gravity Dam • Earth Dam • Rockfill Dam • Combined Earth and Rockfill • Non Gravity Dam – Stabilises against mobilising forces using Non Gravity Methods • Arch Dam – Load Transfer by Arch Action • Buttress Dam – Load Transferred to Supporting Buttresses. Classification by Mode of Stability 7
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- 11. SITE SELECTION Factors governingsite selection • Foundation conditions • Topography • Site for spillway • Material availability • Reservoir capacity • Communication • Healthy Locality 11
- 12. SITE INVESTIGATION FORDAM CONSTRUCTION • Reconnaissance • Preliminary Surveys – Engineering Surveys – Geological Surveys – Hydrologic Surveys • Detailed Investigations 12
- 13. CAPACITY OF RESERVOIRS •Prismoidal Formula • Trapezoidal Formula 13
- 14. STORAGE ZONES OFRESERVOIRS 14
- 15. EVAPORATION LOSSES INRESERVOIRS • Losses in Reservoirs are mainly due to evaporation and seepage • The depth of water evaporated per year from the reservoir surface may vary from about 400 mm in cool and humid climate to more than 2500 mm in hot and arid regions. • Water budget method, Energy budget method etc are used for estimation of Evaporation Losses • Accurate estimation is done by using data from pan-evaporimeters or pans exposed to atmosphere with or without meshing in or near the reservoir site and suitably adjusted. 15
- 16. FORCES ACTING ONA GRAVITY DAM • Water Pressure • Self Weight • Uplift Pressure • Silt Pressure • Earthquake Pressure • Wave Load • Snow Load • Wind Load 16
- 17. FAILURES OF GRAVITYDAM • Due to Overturning • Due to Development of Tension at the Base • Due to Sliding • Due to Crushing or Compression 17
- 18. ELEMENTARY PROFILE OFA DAM 18
- 19. PRACTICAL PROFILE OFA DAM 19
- 20. FREE BOARD ANDTOP WIDTH • Practical Considerations – Roadway at top – Load due to Roadway – Freeboard • Top width is provided about 14% of the total height of dam • Free Board – Margin provided Between KFL and Top of dam – Prevent waves, unforeseen floods – Provided equal to 3/2 x Height of Waves 20
- 21. LOW DAM ANDHIGH DAM 21
- 22. DRAINAGE GALLARY • Agallery is an opening provided in the body of a dam for various purposes • Drainage gallery is a gallery extends only through the deepest portion of the dam serving purpose of drilling and draining the downstream portion of the foundation. • Inspection gallery is provided for inspection purpose 22
- 23. SPILLWAYS • Free Overfall(Straight Drop) Spillway • Overflow (Ogee) Spillway • Chute (Open Channel/Trough) Spillway • Side Channel Spillway • Shaft (Drop Inlet/Morning Glory) spillway • Tunnel (Conduit) spillway • Siphon spillway 23
- 24. FREE OVER FALLSPILLWAY 24
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- 33. EARTH DAMS • Earthdams are the oldest type of dams, as well as the most common ones. • They are always most economical type that can be constructed on soil foundations. • Can be constructed using locally available soils. • No special foundations are required for the construction of these dams. • Skilled labour is not required. • Modern earth moving equipments can be used to construct such type ofdams. 33
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- 35. SITE SELECTION OFEARTH DAM • Topography - A wide valley with deep overburden • Geology and Foundation Conditions – Gravel foundations, if well compacted is suitable for earth dams. – Silt or fine sand foundations can be used for earth dams, the main problems include settlement, prevention of piping, excessive percolation losses. – Clay foundation may be used for each dams but require flat side slopes • Material availability • Environmental Considerations • Economy 35
- 36. CAUSES OF FAILURESOF EARTH DAM • HYDRAULIC FAILURES – Overtopping – Erosion of Upstream (Wave Erosion) – Toe Erosion • SEEPAGE FAILURES – Piping – Sloughing • STRUCTURAL FAILURES – Upstream and downstream slope failure due to construction pore pressure – Upstream slope failure during sudden drawdown – Downstream slope slide during full reservoir condition Upstream slope failure during sudden drawdown Downstream slope slide during full reservoir condition 36
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