Soils 205- General Soils

Water flow

I.  There are three types of water flow in soils- saturated, unsaturated, and vapor

     a)  Saturated flow:

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        Saturated flow, V = K * F

                i)  hydraulic conductivity

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    b)  Unsaturated flow

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        -Volume of flow is dependent on the driving force and hydraulic conductivity, just as in saturated flow,  but the driving forces are matric and osmotic potential.

               i)  Driving force- unsaturated flow

                 Matric forces are usually the driving forces of this type of flow.  Differences in matric potentials create a GRADIENT and flow takes place in responses to this gradient.

            ii) examples of unsaturated flow

                -Water will rise above a water table in soils because of matric forces.  Capillary fringe refers to   

                 the height which water rises in the soil above the water table.

                -roads

    c)  Vapor flow

        Occurs when the soil is dry.  The matric materials hold the water so tightly (Yt < -1500 kPa or -15 bars) that it can no longer move unless it evaporates.  This type of water flow is minor in comparison to the others.

II.  flow in stratified soils