Soils 205- General Soils

Lecture 11- Soils and the hydrologic cycle

I.  Water supply

II.  Hydrologic cycle

    a.  Interception

    b.  Infiltration-  Infiltration is the movement of water into a porous media (soil).  The rate of infiltration decreases with time and is also a function of soil texture and structure.

coarser texture =

finer texture =

well structured =

II.  fate of infiltrated water

    a.  Evaporation

    b.  Transpiration

        Evapotranspiration (ET)

        PET- potential evaporation

        Determined by:

        1)

        2)

        3)

        Measurement of PET using a class A evaporation pan

        PET is calculated by applying a correction factor to the amount of water evaporated from an open pan of water of standard design.

PET = 0.65 * pan evaporation

c.  leaching- once water gets past the root zone it is unrecoverable.  This water carries dissolved constituents with it such as nitrate (NO₃^-) which leaches readily.  Water remaining (not evapotranspirated or leached) is called soil storage.

III.  hydrologic balance equation

P = ET + SS + L + R

IV.  enhancing drainage- required for saturated soils to reduce the amount of water in the soil or to lower the water table.  Conditions for outflow:

1)

2)

    a.  Methods of drainage

    i. 

    ii.