Types of reservoirs :
In general there are two types.
Impounding reservoirs :
An impounding reservoir is a basin constructed in the valley of a stream or river for the purpose of holding stream flow so that the stored water may be used when supply is insufficient.
They have the following two functions :
- To impound water for beneficial use.
- To retard flood.
These two functions may be combined to some extent by careful operations.
An impounding reservoir presents a water surface for evaporation. This loss must be considered. Possibility of large seepage loss must also be considered. If it is economically impossible to prevent them, the project may have to be abandoned or move it to a more favorable site. There will be some loss by seepage through and under the dam itself.
- Distribution reservoirs :
The basin constructed to equalize the supply and demand of the community or used for treated water and to provide supplies in emergency, is known as distribution reservoir.
Difference between distribution and impounding reservoirs :
The main difference between these two is that the impounding reservoirs hold untreated water white distribution holds treated water. The water held by an impounding reservoir may not all used as treated water but may be used for other purposes such as irrigation.
Size of reservoirs :
The most important function is that water should be available at all times. It does not mean that largest reservoir must be constructed. Size of reservoirs must be adequate. It must not be too large and it must not be too small. For this purpose, the rate of water consumption of the community or users should be known. In case of impounding reservoir, the stream flow during drought conditions should be calculated.