Reservoirs are artificial lakes, which are created by the construction of dams across rivers. A reservoir may fail either due to excessive leakage of water or as a result of rapid sedimentation or rupture due to earthquakes.
Problems associated with Reservoirs:
The main geological problem connected with the reservoirs are: (i) groundwater conditions, (ii) permeable reocks, and (iii) silting.
(1). Groundwater Conditions: The amount of leakage of water from the reservoir is controlled by the depth of water table. If the water table is so near the ground surface that the water level in the reservoir does not rise above it, no serious loss by leakage will occur. On the other hand, if water table lies deep below the ground surface, the water level in the reservoir will stand above it. As a result, leakage will occur and its amount will depend on the permeability of rocks.
(2). Permeable Rocks: During the geological investigation it is necessary to locate the highly permeable rocks that are present in the reservoir area. The rocks which are highly fissured, intensely jointed, faulted or have solution channels, are likely to cause serious leakage from the reservoir.
Generally, the leakage of water from the strata that have a downstream dip, will be more than those which have an upstream dip. If a permeable rock bed outcrops on the valley slopes in the reservoir, it may not only cause leakage but may also cause land-slide. Such a landslide may produce an opening in the reservoir rim through which the stored water may escape.
(3). Silting of Reservoir: The reservoir built on rivers that carry large amounts of sediment, may silt up very soon and its water storage capacity may be reduced considerably. The amount of silt produced and supplied to the rivers depends mainly upon the lithological character and topography of the catchment area. The rivers flowing over the soft rocks and high gradient areas carry a greater amount of silt. On such rivers, silt traps maybe constructed upstream in order to check the rate of silting in the reservoir. Provisions should also be made for washing out the silt through the passage in the dam.
- Relationship of geology with civil engineering
- Geology and Building-Stones
- Most common rocks used as building stones
- Geology of Dams
- Problems associated with a dam/failure of dams