RUN-OFF BY USING INFILTRATION CHARACTERISTICS

• The process, whereby water enters the surface strata of the soil and thus moves downward towards the water-table is know infiltration.
• In fact when water falls on the soil, a small part of it is first of all absorb by the top thin layer of soil so as to replenish the soil moisture deficiency.
• After this any excess water moves downward where it is trapped in the voids and becomes ground water.
• The amount of stored ground water mainly depends upon the number of voids present in the soil.
• The number of voids further depend upon the size, shape, arrangement, and degree of compaction of the soil.
• Hence different soils will have different number of voids and hence different capacities to absorb water.
• The maximum rate at which a soil in any given condition is capable of absorb water.
• It is evident that rain water will enter the soil at full capacity rate only during the periods when rainfall.
• When the rainfall intensity is less than the infiltration capacity, the prevailing infiltration rate is approximately equal to the rainfall rate.
• Hence the actual prevailing infiltration rate may be equal to or less than the infiltration capacity.
• This actual prevailing rate at which the water is entering the given soil at any given time is know infiltrationrate.
• If the rainfall intensity exceeds the infiltration capacity the difference is call the rainfall excess rate.
• This excess water is first of all accumulated on the ground as surface detention and then flows over land into,streams.
• The water below the water-table is know as the ground water and the water abovetable is know as soil moisture.
• When a graph is drawn between capacity and duration of rainfall in hours we get a curve know.
• This method ofcomputing run-off is use for small catchments.