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groundwater body or the water-table below which the entire soil depth is
saturated with water. The area intervened between the land surface and the
water table, is the unsaturated zone and water in this moves laterally towards
the stream and is known as sub-surface flow and is a part of run-off.
The rainfall in a catchment area is disposed off in the following manner:
1) Basin recharge
2) Direct run off
3) Precipitation down to groundwater
4) Evaporation
1.
Basin recharge :
Basin recharge has the following components :
i)
Rain intercepted by leaves of the trees and stems of vegetation.
ii)
Water held up in topographic (surface) depressions, known as
depression storage.
iii) Soil moisture as capillary water in the pore spaces of the soil. The
maximum rate at which the soil in a given condition can absorb
water is known as infiltration capacity of the soil.
Effective rainfall or excess rainfall is the amount that falls on the
ground is of interest to the agriculturist and irrigation engineers. This can be
expressed as :
Effective Rainfall or Excess Rainfall = Rainfall - Interception - Depression
storage - infiltration.
The sum total of interception and depression storage is called initial loss or
basin loss. In case of heavy rainfall the basin loss is insignificant
and is considered to be included in infiltration, i.e. Effective or Excess
rainfall = Rainfall - infiltration.
