Lecture34-36(2008)

Lecture34-36(2008) - INFILTRATION AND SURFACE RUNOFF Read:...

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INFILTRATION AND SURFACE RUNOFF Read : Chapter 14 Environmental Soil Ph ysics Water moves from high to low energy level (flow from area of high R t to areas of low R t ). The rate at which water flows through soil affects the infiltration, drainage, and water supply rate to plant roots. Infiltration : The entry of water into the soil, generally by downward flow (cumulative infiltration, I, is the total amount of water entering the soil). Infiltration rate (i) : The amount of water entering the soil per unit time (average rate over a finite time period ) (i = dI/dt). Infiltration ca pacit y (infiltrabilit y) : The amount of water per unit time which a given soil profile can absorb through its surface when it is maintained in contact with water at atmospheric pressure.
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Soil water content — In most cases, infiltration is primarily an unsaturated-flow process, although parts of the soil profile may be at or near saturation in some situations. Infiltration -- unsaturated flow process — matric forces ( R m ) dominate during early stages, and gravitational forces dominate at later stages (when soil wets). Factors Affectin g Infiltration Rates
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t 1 t 2 t 3 soil surface At t 1 R m strongly influences infiltration, thus it is nearly uniform in all directions. At t 2 and t 3 soil becomes saturated, therefore R m decreases and R g predominates. time Infiltration rate Initially dry soil Initially moist soil
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Other factors affecting infiltration 1) Pore size and distribution — The larger and more numerous the pores, the faster the infiltration rate; this depends on texture and structure.
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Lecture34-36(2008) - INFILTRATION AND SURFACE RUNOFF Read:...

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