15
Water Movement in Soils
The general equations governing unsaturated flow in porous media
are the continuity equation and Darcy's Law. Hi11 el (1980) presented a
combined flow equation which incorporates the continuity equation
36
_= v-q S (1)
3t
where q = flux density of water,
0 = volumetric water content,
v = differential operator,
t = time, and
S = a sink or source term,
with Darcy's equation for unsaturated flow
q = K(h) vH (2)
where K = hydraulic conductivity,
H = the total hydraulic head and defined as
H = h z, and
h = capillary pressure head.
The resulting combined flow equation for both steady and transient
flows is also known as Richards equation
39
= v*(K(h>v H ) S (3)
3t
For one-dimensional vertical flow, equation (3) becomes
36 3 3h 3K(h)
= ( K(h) ) - S(z,t) (4)
3t 3Z 3Z 3z
where z = the vertical dimension.