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2.
Direct Run-off
Run-off that reaches directly or through stream is called direct run off or stream
discharge. It has two components :
i)
Water that flows directly over the ground surface, called True
Surface run-off.
ii)
When the soil is permeable, water infiltrates part of which flow
laterally and joins the adjacent stream, through sub-surface
run-off.
iii) Some amount of rainfall also adds to run-off.
3.
Percolation down to groundwater
Rainfall that infiltrates downward vertically joins the groundwater body (Fig. 1.5)
recharges groundwater, as a result of which water table rises. When the stream
water level is lower than the adjacent water level groundwater will flow into the
stream. Such streams are known as effluent streams. Groundwater inflow to
the stream is known as baseflow. In dry period, many perennial streams are fed
by base flow.
Fig. 1.5 :
Constituents of Surface runoff and of runoff
(Source : Garg, 1988)
