Storage zones of reservoir
On the basis of the surface or pool level
1. Minimum Pool Level
It is the lowest level of water which is kept for normal operation of the reservoir. Water below this level can’t be used. This level is fixed by the elevation of the lowest outlet or if the dam is a multipurpose one, the minimum required to head for the generation of power governs the Minimum pool level.
2. Normal Pool Level
During the ordinary operation conditions in the reservoir, this is the maximum elevation, up to which the water surface will rise. In case of non-gated spillway, this normal pool level is determined by the elevation of the spillway crest; but in case of gated spillway, this normal pool level is determined by the top of the spillway gates. It is also known as Full Reservoir Level (F.R.L.)
3. Maximum Pool Level
The level to which the water rises in the reservoir during the design flood (or worst flood) is known as the Maximum Pool Level. It is also known as Maximum Water Level (M.W.L.)
On the basis of the functions of the water
1. Dead Storage
The volume of water stored below the minimum pool level of the reservoir is know dead storage. This storage is not of such use in the operation of the reservoirs.
2. Useful Storage
Total amount of water stored between the minimum pool level and normal pool level is called useful storage. This water is useful for irrigation purposes and power generation purposes.
3. Surcharge Storage
The volume of water stored between the normal pool level and the maximum pool level of a reservoir is called surcharge storage. The surcharge storage is an uncontrolled storage as it exists only while a flood is occurring and cannot be retained for later use.
4. Bank Storage
It is a temporarily stored water in the permeable banks of the reservoir. When any reservoir has reached the maximum pool level and has started drain out i.e. its pool level is going down, at that time only, the bank storage goes on increasing.
5. Valley Storage
It is the storage which is available in the stream channel even before the construction of the dam. In other words the volume to water stored by the river or stream in its valley before the construction of reservoir is called valley storage.
