Initial Loss :
In the precipitation reaching the surface of catchment, the major reduction in volume of water available for runoff is through infiltration. Apart from infiltration, there are two other processes that contribute to this reduction in volume. These two processes are
- Depression Storage.
Together they are called as Initial loss.
However, the reduction in volume of available water through initial loss is of less magnitude.
When it rains over a catchment not all the precipitation falls on the surface and becomes part of the runoff. Some of the precipitation may caught by the vegetation before reaching the surface and after that evaporated. The volume of water caught by the vegetation is called initial loss.
Depression Storage :
When the precipitation of a storm or rain reaches the surface of catchment, it must first fill up all the depressions on the catchment before it can flow over the surface. The volume of water stored in these depressions is known as depression storage.