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Dams

Dams. ( Barajlar ). Mehmet Özger. Department of Civil Engineering, I.T.U. What is a dam?. A dam is a barrier built across a stream, river or estuary to hold and control the flow of water for such uses as drinking water supplies, irrigation, flood control and hydropower generation etc.

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Dams

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  1. Dams (Barajlar) Mehmet Özger Department of Civil Engineering, I.T.U

  2. What is a dam? • A dam is a barrier built across a stream, river or estuary to hold and control the flow of water for such uses as drinking water supplies, irrigation, flood control and hydropower generation etc.

  3. Drinking water Irrigation Flood control Hydropower Navigation Recreational purposes

  4. Negativeimpacts Imbalance of the ecosystem Decreased amount of downstream water Spreading of some water-born diseases Reduction in the fertility of farmlands

  5. Purpose Distribution of Dams Source: International Commission on Large Dams (ICOLD)

  6. World’sregistereddams Source: International Commission on Large Dams (ICOLD)

  7. Parts of a dam • Dam body: Body forms the main part of a dam as an impervious barrier • Reservoir: It is the artificial lake behind a dam body • Spillway: is that part of a dam to evacuate the flood water from reservoir. • Water intake structures: is a facility to withdraw water from a reservoir. • Sluiceway: Gerektiğinde baraj gölünü tamamen boşaltmak, dolusavak kapasitesini azaltmak, akarsu mansabına bırakılacak suyu salmak amacına yönelik tesisler. • Diversion facilities: To redirect the streamflow from construction area

  8. Water intake structures Dam body Sluiceway Flow Spillway Parts of Dams Reservoir

  9. Upstream Reservoir Dam body Spillway Downstream

  10. Classification of Dams • According to dams height • If crest elevation and foundation level is greater than 15 m then it can be considered as a Large Dam. • If dam height is less than 15 m then Small Dam. • If dam height is greater than 50 m then High Dam

  11. Classification of dams: Dams are classified on several aspects, some of the important aspects are as follow: • Based on Hydraulic Design: • Over flow dams (e.g. concrete dams) • Non over flow dams (e.g. embankment dams) • Based on Structural Design: • Gravity dams • Arch dams • Buttress dams • Based on Usage of Dam: • Storage dams • Diversion dams • Detention dams

  12. Classification of dams: • Based on Construction Material: • Concrete / Masonry dams • Earthfill dams • Rockfill dams • Earthfillrockfill dams • Concrete faced rockfill dams (CFRD) • Based on Capacity: • Small dams • Medium dams • Large dams

  13. 3.3 Planning of Dams • Three steps: • - Reconnaissance survey (infeasible alternatives eliminated) • - Feasibility study • - Planning study

  14. 3.3.1FEASIBILITY STUDY • A) Determination of water demand • Estimatevarioustypes of demandsthroughthe life time • B) Determination of water potential • Fromavailablesourcesandavailablepast data • C) Optimal plans ◘ Check out the relation D versus S.

  15. D)Determination of dam site ◘ Factors should be taken into consideration: • Topography • Geology and dam foundation • (faultsandweakgeologicformationsshould be avoided) • Type of soilaffectstheoverallstability of dam body • Available of construction materials • Flood hazard • Seismic hazard • Spillway location and possibilities • Construction time • Climate(earthfill dam is not appropriateforrainyclimates) • Diversion facilities • Sediment problem • Water quality • Transportation facilities • Right of way cost

  16. e) Determination of dam location • Characteristics of dam location: • Geologic formation • Spillway location and capacity • Diversion conditions • Sediment condition • Transportation facilities • Structural design • Availabilty of meterials

  17. f) Project design ◘ involves the computation of dimensions of the dam. 1.Hydrologic design (max. lake elevation + spillway cap. + crest elevation) 2.Hydraulic design (static & dynamic loads + spillway profile + outlet dimensions) 3.Structural design (stress distribution + required reinforcement)

  18. Failure of the dam  “Dam Break” • It is rapid for a concrete dam. See the textbook for the examples.

  19. Ç.Ü., İnş.Müh.Böl.

  20. 3.3.2PLANNING STUDY • ◘ Followings need to be done, since dimensions are already determined: • Topographic surveys (1:5000 scaled map) • Foundation study (seepage permeability, bearingcapacityetc. tests) • Materials study (quantity of materials) • Hydrologic study (measurements of hydrologic parameters) • Reservoir operation study (is to be performed periodically)

  21. 3.4 Construction of Dams • Four principal steps are followed during the construction: • 1) Evaluation of Time Schedule and Equipments • ◘ a work schedule is prepared using CPM. • 2) Diversion • ◘ before the construction, river flow must be diverted from the site • see the below figure for two possible ways to divert water:

  22. 3) Foundation Treatment • ◘ Concrete & Rock-fill dams  hard formations • Earth-fill dams  most of soil conditions • ◘ Highly porous foundation  excessive seepage, uplift, settlement • “Grouting Operation” is applied to solidify the foundation • & to reduce seepage

  23. 4) Formation of the Dam Body • For Concrete Gravity dams: • ◘ Low-heat cements  to reduce shrinkage problem • ◘ Concrete is placed in “blocks”

  24. “Keyways” are built between sections to make the dam act as a monolith

  25. “Waterstops” are placed near upstream face to prevent leakage

  26. Ç.Ü., İnş.Müh.Böl.

  27. Ç.Ü., İnş.Müh.Böl.

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