Silting of the reservoir starts from the day it is created.
When reservoirs are created some of its capacity is left unused.
This is the capacity of the reservoir lying below the crest level of the bottom most under sluices.
This storage capacity which remains unused is know dead storage.
This dead storage capacity is used to accommodate deposited silt so that effective storage of the reservoir is not affected.
So long as dead storage capacity of the reservoir is not silted completely, effective storage or useful storage capacity is not affected.
The process of silting continues even after complete silting of dead storage.
The further silting affects the effective storage of the reservoir and the reservoir does not have enough water to fully fulfil its obligations.
Generally useful life of the reservoir is considered terminated when its effective storage is reduced by 20% of the designed capacity of the reservoir.
