03lecture Dams

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

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Transcript of 03lecture Dams

  • DamsMehmet zger(Barajlar)Department of Civil Engineering, I.T.U

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  • 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.

  • Negative impactsImbalance of the ecosystemDecreased amount of downstream waterSpreading of some water-born diseasesReduction in the fertility of farmlands

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  • Purpose Distribution of Dams

    Source: International Commission on Large Dams (ICOLD)

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    Irrigation48.60%

    Hydropower17.40%

    Water Supply12.70%

    Flood Control10.00%

    Recreation5.30%

    Navigation and Fishing0.60%

    Others5.40%

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  • Worlds registered damsSource: International Commission on Large Dams (ICOLD)

  • Parts of a damDam body: Body forms the main part of a dam as an impervious barrier Reservoir: It is the artificial lake behind a dam bodySpillway: 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: Gerektiinde baraj gln tamamen boaltmak, dolusavak kapasitesini azaltmak, akarsu mansabna braklacak suyu salmak amacna ynelik tesisler.Diversion facilities: To redirect the streamflow from construction area

  • Parts of DamsReservoir

  • UpstreamReservoirDam bodySpillwayDownstream

  • Upstream slopeRiprapTop of damPrincipal chute spillwaySpillway training wallsDownstream slopeRight abutmentEmergency spillwayLeft abutmentToe of embankmentBermToe drain outlet

  • 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

  • Classification of dams:

  • Classification of dams:

    Based on Construction Material:Concrete / Masonry damsEarthfill damsRockfill damsEarthfill rockfill damsConcrete faced rockfill dams (CFRD)Based on Capacity:Small damsMedium damsLarge dams

  • 3.3 Planning of DamsThree steps: - Reconnaissance survey (infeasible alternatives eliminated) - Feasibility study- Planning study

  • 3.3.1 FEASIBILITY STUDY A) Determination of water demand Estimate various types of demands through the life time B) Determination of water potentialFrom available sources and available past data C) Optimal plans Check out the relation D versus S.

  • D) Determination of dam site Factors should be taken into consideration:TopographyGeology and dam foundation (faults and weak geologic formations should be avoided)Type of soil affects the overall stability of dam body Available of construction materialsFlood hazardSeismic hazardSpillway location and possibilitiesConstruction time Climate (earth fill dam is not appropriate for rainy climates)Diversion facilitiesSediment problemWater qualityTransportation facilitiesRight of way cost

  • 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

  • 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)

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

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

  • 3.4 Construction of DamsFour 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 sitesee the below figure for two possible ways to divert water:

  • 3) Foundation Treatment Concrete & Rock-fill dams hard formations Earth-fill dams most of soil conditions Highly porous foundation excessive seepage, uplift, settlementGrouting Operation is applied to solidify the foundation & to reduce seepage

  • 4) Formation of the Dam BodyFor Concrete Gravity dams: Low-heat cements to reduce shrinkage problem Concrete is placed in blocks

  • Keyways are built between sections to make the dam act as a monolith

  • Waterstops are placed near upstream face to prevent leakage

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  • *Rock formations have higher bearing capacity.Gravel have relatively high bearing capacity, however they have high permeabilitySilt and fine sand have low bearing capacity

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