Reservoirs are very large artificial lake formed along the course of a water when dams are constructed across it due to impounding of the natural flow of river water.
From the geological point of view, a reservoir can be claimed to be successful if it is water tight. That is if it does not suffer from any serious leakage of water and it has a long life due to a very low rate of silting in reservoir basin.
Geological consideration in Reservoirs:
Geological considerations in site investigation of reservoir are:
Influence of Rock types:
Water tightness of a reservoir is very much influenced by the kind of rock that occurs in the site. If the rocks are porous and permeable i.e, aquifers, it will cause the leakage of water and hence such rocks are undesirable at the reservoir site. Hence, it is said that the occurrence of aquifer rock is undesirable and aquifuge or aquiclude are desirable at the reservoir sites.
Influence of geological st....Show More
Reservoirs are very large artificial lake formed along the course of a water when dams are constructed across it due to impounding of the natural flow of river water.
From the geological point of view, a reservoir can be claimed to be successful if it is water tight. That is if it does not suffer from any serious leakage of water and it has a long life due to a very low rate of silting in reservoir basin.
Geological consideration in Reservoirs:
Geological considerations in site investigation of reservoir are:
Influence of Rock types:
Water tightness of a reservoir is very much influenced by the kind of rock that occurs in the site. If the rocks are porous and permeable i.e, aquifers, it will cause the leakage of water and hence such rocks are undesirable at the reservoir site. Hence, it is said that the occurrence of aquifer rock is undesirable and aquifuge or aquiclude are desirable at the reservoir sites.
Influence of geological structure:
As a consequence of the role played by tectonic force, the rock which occurs in nature often has different geological structures such as faults, folds, joints etc.The presence of such structure has a significant influence in decreasing or increasing the leakage through the rocks at the reservoir.
For example: granite is known for its impermeable character.
Water tightness and influencing factor:
As a consequence of weathering which is a natural process in general, the surface is covered by loose soil and below it lies the fracture rocks i.e, subsoil. The bedrock which is massive occurs further below. When a river flows over such loose or fractured ground, it is natural that some water of river percolates underground. Before the construction of the dam, this leakage shall be less and Limited only to the extent over which the river flow occurs. But when the dam is constructed, the impounded water accumulates in large quantities in a reservoir which covers a very large area.
Buried river channels:
Buried river channels which are more frequent in glaciated region are also a serious source of leakage when it occurs at the reserve site. This is because it is generally filled with loose and coarse sediments and allows heavy leakage of water along the course of the old channel.
Reservoir silting:
Silting of Reservoir is as harmful as the leakage of reservoir and both can cause the failure of the reservoir. The silting and leakage of the reservoir have a similar effect or result on the reservoir water quantity. In both cases, the quantity of water stored get reduced. Silting is totally different from leakage. In the case of silting, the deposition or settlement of sediments on the floor reduces the capacity of the reservoir; there by indirectly reducing the volume of reservoir water. In the case of leakage, water percolation directly causes the reduction in the volume of reservoir water.
Seismic activity in reserve areas and occurrence of landslides:
When a reservoir is put into active seismic zone, landslides are likely to occur. Hence, the possible consequences of the creation of a reservoir should be considered carefully. Due to a reservoir, large masses are likely to be waterlogged by the raising of the water table around the reservoir. This makes it necessary to determine which rock will be affected and how they will behave on the new conditions. Since, water is the single most important causes for landslide, the scope for their occurrence should be examined carefully. Further the raising and lowering of water levels in a reservoir represents the application and withdrawal of hydrostatic pressure and this could induce movement of the valley due to slipping.
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