Run-off by using infiltration characteristics

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.

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