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Notwithstanding such negative impacts, construction of dams, whether major,
medium or minor, will continue for storage of water and our food security.
However, appraisal for construction of new projects of dams are made
carefully, keeping in view the negative impacts so that minimum areas are
affected. Relief and Rehabilitation measures are also taken up by the
implementing agencies.
Selection of site for a dam
Investigation on selection of suitable dam site is very important for
appropriate design of the dam. Major factors affecting the selection of dam sites
are topography, geology, availability of materials, required land for reservoir,
spillway locations, the economic impact on the local inhabitants, catchment
areas etc.
Study of the detailed topography is of vital importance for deciding the type of
dam. A narrow U-shaped valley suggests suitability of concrete overflow dam,
whereas a V-shaped valley would suggest an arch dam, provided the top width
of the valley is less than one fourth of its height with separate spillway site. A low
rolling topography will suggest construction of an earthen dam.
Geology decides the foundation of the dam. In solid hard rocks like
granite, gneiss etc. any types of dams can be constructed. The hard rocks
should, however, be devoid of fractures, fissures, faults etc. Separate
treatment like grouting etc. may be required when fracture and fissures can not
be avoided at the site. Boulder formations are suitable for earth dam, rockfill
dam or low concrete gravity dam with appropriate methods to prevent under
seepage. Silt or fine sand have the problem of settlement, seepage and
toe-erosion. In clay formation, only earth dams are suitable, but gravity dams or
rockfill dams are unsuitable.
Availability of construction materials is an important factor for selection of dam
sites. For example concrete gravity dams require sand, gravel and crushed
stone. Availability of materials in nearby area will reduce the cost of
transportation which becomes prohibitive if long distance transportation is
required.
