A dam is a barrier that impounds water or underground streams.Dams generally serve the primary purpose of retaining water, while other structures such as floodgates or levees (also known as dikes) are used to manage or prevent water flow into specific land regions.Hydropower and pumped-storage hydroelectricity are often used in conjunction with dams to generate electricity.A dam can also be used to collect water or for storage of water which can be evenly distributed between locations.
A dam is a hydraulic impervious structure constructed across a river to store water on its up-stream side. Classification Of Dams By materialBy structure a. Steel dams 1 Arch dams b. Timber dams 2 Gravity dams 3 Arch-gravity dams Other types 4 Barrages a. Cofferdams 5 Embankment dams b. Beaver dams a. Rock-fill dams b. Concrete-face rock-fill dams c. Earth-fill dams d. Asphalt-concrete coreBy sizeBy use a. Saddle dam b. Weir c. Check dam d. Dry dam e. Diversionary dam f. Tailings dam
Classification of DamsDams are classified into different categories, depending on the purpose. Types of Dams Basis of classification Types ExamplesAccording to Use 1. Storage dam Gravity dam, earth dam, rock fill dam, arch dam etc., 2. Diversion dam Weir, barrage 3. Detention dam Dike, water spreading dam, debris damBy hydraulic design 1. Overflow dam Spillway 2. Non overflow dam Gravity dam, earth dams, rock fill damBy materials 1. Rigid dams Gravity dam, earth dam, buttress dam, steel dam, timer dam 2. Non-rigid dams Earth dam, rock fill dam
A weir is a dam beneath the surface of a stream. In normal conditions the stream flows over theweir but there is a pool of deeper quieter water behind the weir.
Earth-fill dams, also called earthen, rolled-earth or simply earth dams, are constructed as asimple embankment of well compacted earth. A homogeneous rolled-earth dam is entirelyconstructed of one type of material but may contain a drain layer to collect seep water. A zoned-earth dam has distinct parts or zones of dissimilar material, typically a locally plentiful shell witha watertight clay core. Modern zoned-earth embankments employ filter and drain zones tocollect and remove seep water and preserve the integrity of the downstream shell zone. Anoutdated method of zoned earth dam construction utilized a hydraulic fill to produce awatertight core.
Advantages Earth-fill dams 1.Can be constructed on any type of foundation. 2.Can be constructed rapidly 3.Skilled labor not required 4.Can be constructed with material available nearby 5.Cheaper than other type dams 6.Height can be raised without any difficulty Earth-fill dams,Disadvantages1.More vulnerable to damage by floods and fail suddenly without any warning indications2.Cannot be used as overflow dams.3.Separate spillways have to be provided to avoid overflow and damage4.Not suitable in places where heavy downpour rains are frequent5.Maintenance is very high and requires constant supervision.
AdvantagesArch Dam Particularly adapted to gorges It requires less material for construction. Construction cost is cheap Due to less base width, the problems of uplift pressure are minor. Small load of pressure load is transferred to the foundation by cantilever action, therefore an arch dam can be constructed in moderate foundations.DisadvantagesIt requires skilled labor and sophisticated form of work. It is a specialized designconstruction.Takes longer time for constructionRequires strong abutments of solid rock to resist the thrust of the arch.Only few sites are suitable for this type of dam.
Multiple Arch Dam
AdvantagesGravity Dam It is a permanent dam. It is a solid massive dam and relatively more strong and stable. Particularly suited in gorges. Requires less maintenance. Well adapted for use as an overflow spillway crest. It can be constructed of any height on strong suitable rock foundations. It suited to places where there is no excessive or likelihood of heavy downpour. It requires least maintenance DisadvantagesUnsuitable on weak foundations or weak rocks and permeable Failures of such dams is notrocks. sudden and gives warning.Initial cost is high. Deep set sluices are used toConstruction period will be more if proper infrastructure is not retard sedimentation or siltavailable. deposition.It requires skilled labor or mechanize plants for construction Trap efficiency is lessDifficult to raise the height of the dam unless specific compared to earth dams.observations are made in the initial stage..
AdvantagesIt is a less massive dam than a gravity Buttress damdam.Due to less foundation pressures itcan be constructed on foundationswhere it doesn’t support gravity dam.Water load acts normal to the inclineddeck stabilizing the dam againstoverturning.Buttress dam has a more safety factorthan for a gravity dam.Ice pressure is relatively not importantas it slides down the slope.Further raising of the dam height ispossible and convenient by extending Back of the upstream face and foundations betweenthe buttress and slab. the buttresses is accessible for periodic inspectionsIt is used where a future increase is and grouting, drilling of pressure relief holes.contemplated. The dam can be designed to accommodatePower houses and water treatmentplants can be housed between the moderate amounts of foundation movementsbuttresses. without serious damages.Concrete use is ½ or 1/3 less than that The reduction in concrete volume and increase inof the gravity dam. the surface area to volume ratio provide for better heat dissipation during construction. Increase speed of construction due to larger exposed area.
DisadvantagesRequirement ofskilled laborShuttering concreteratio > for solid damsleading to higherrates and this offsetsthe saving of theconcrete quantity.Deterioration of thethin concrete surfacein the upstream hasserious effect onbuttress dam.It is more susceptibleto willful damagewhich depends onthe thickness of theupstream face andthe facility for accessfrom the downstreamside.
AdvantagesHigher speed of construction Steel damCheaper than rigid dams.Stresses are moredeterminative can bedesigned economically withconfidence.Has greater flexibility to resistto unequal settlement withoutexcessive leakage.It is Frost resistant.Leaky joints can be fixed veryeffectively with modernwelding process.DisadvantagesSteel dams are lighter and hence not adaptable to absorb shock from the spilling water.Life is shorter than concrete dams.Requires more constant maintenance.Andhoring at foundations is difficult and precarious.There is considerable concentration of bearing stresses.
A barrage dam is a special kind of dam which consists of a line of large gates that can be openedor closed to control the amount of water passing the dam. The gates are set between flankingpiers which are responsible for supporting the water load. They are often used to control andstabilize water flow for irrigation systems.Barrages that are built at the mouth of rivers or lagoons to prevent tidal incursions or utilize thetidal flow for tidal power are known as tidal barrages. [
An embankment dam is a massive artificial water barrier. It is typically created by theemplacement and compaction of a complex semi-plastic mound of various compositions of soil,sand, clay and/or rock. It has a semi-permanent waterproof natural covering for its surface, anda dense, waterproof core. This makes such a dam impervious to surface or seepage erosion
Embankment dams come in two types: the earth-filled dam (also called an earthen dam orterrain dam) made of compacted earth, and the rock-filled dam. A cross-section of anembankment dam shows a shape like a bank, or hill. Most have a central section or corecomposed of an impermeable material to stop water from seeping through the dam. The corecan be of clay, concrete or asphalt concrete. This dam type is a good choice for sites with widevalleys. Since they exert little pressure on their foundations, they can be built on hard rock orsofter soils. For a rock-fill dam, rock-fill is blasted using explosives to break the rock.Additionally, the rock pieces may need to be crushed into smaller chunks to get the right rangeof size for use in an embankment dam.Rock Fill Dam
Type of damSaddle damRolled earth fill androck fill embankment
Frame typeTimber dam timber damRock filled timber crib dam
Rock filledAdvantages timber crib dam1.Low initial cost2.Suitable for any type of foundation3.Suitable for temporarily required dams4.Greater speed in constructionDisadvantages1.Maintenance cost is high2.Life of dam is short.3.Not suitable for high dams4.Greater seepage through the dam Beaver type timber damThe beaver (genus Castor) is a primarilynocturnal, large, semi-aquatic rodent.Beavers are known for building dams, canals,and lodges (homes). They are the second-largest rodent in the world (after thecapybara). Their colonies create one or moredams to provide still, deep water to protectagainst predators, and to float food andbuilding material.
Factors affecting selection of type of dam1.TopographyLow topography – earth dam with separate spill waysLow narrow V shaped valley – arch damA narrow stream with U shaped valley – concrete overflow damDepending on the foundation rock conditions with reference to structure etc. othersuitable type of dams can be considered2. Geology and Foundation conditionsStructural conditions and the type of rocks have to be studied in detail to go in for anymajor construction of dam.3. Materials of constructionEarth material, rocks, timber, concrete or combination of materials4. Spillway size and locationFor large spillway capacity – overflow gravity damSmall spillway capacity – earth damLarge discharges during construction of dam – concrete gravity damIf no favourable location is available for spillway – a concrete gravity dam andsometimes in inevitable conditions in earth dam with central overflow on the dam may beprovided
5. RoadwayA roadway is to be provided – earth dam or gravity dam is preferred6. Length and height of damLong length and low height – earth damLess length and higher height – gravity dam7. Life of damLong life – concrete and masonary damsTemporary dams – timber and debris dams for temporary storage of waterIntermediate life – earth dams or rockfill damsSelection of site for a dam1.Foundation2.Topography3.Site for spillways4.Materials availability5.Reservoir and catchment area6.Communications7.Locality8.Land and population