Hello Mark

Overall, in SALUS water balance, the governing equation for upward soil water
movement due to evaporation is

SWTi  = C (SWCi-1 - SWad)

where
SWTi : is today's soil water content
SWTi-1 : is previous day soil water content
SWad : is air dry soil water content, and
C : is a conductance coefficient depends on the soil layer depth

and the governing equation for downward soil water movement due to vertical
drainage is

SWTi  = F*C (SWCi-1 - DUL)

where
SWTi : is today's soil water content
SWTi-1 : is previous day soil water content
DUL: is drained upper limit soil water content
C : is a conductance coefficient depends on DUL, and
F:  is a coefficient that depends on both saturated hydraulic conductivity
(Ksat) and incoming water flow.

I have developed a functional lateral downslope drainage model that is
based on
the vertical drainage model mentioned above. This lateral model has not
incorporated in SALUS water balance because the SALUS water balance is
one-dimensional model. However, incorporating this lateral model with SALUS
water balance can be done if needed.

The following papers explain some details of the soil water movement used in
SALUS. I will be happy to provide you or any colleague with copies.

Suleiman, A.A., and J.T. Ritchie. 2001. Modeling soil water redistribution
under second stage evaporation. Soil Sci. Soc. Am. J (In review).

Suleiman, A.A., and J.T. Ritchie. 2001. A simple model to estimate daily
vertical drainage. Soil Sci. Soc. Am. J (In review).

Suleiman, A.A., and J.T. Ritchie. 2001. Functional lateral downslope drainage
model. Water Resou. Research. J. (In review)

Suleiman, A. A., and J. T. Ritchie. 2001. Estimating saturated hydraulic
conductivity from soil porosity. Trans. ASAE. 44(2):235-239.

Ritchie, J.T., Gerakis, A., Suleiman, A. 1999. Simple model to estimate
field-measured soil water limits. Trans. Am. Soc. Agri. Eng. 42:1609-1614.


Good Luck

Ayman



Ayman Suleiman, PhD
Research Associate
Civil and Environmental Engineering Dept.
7B DANA Engineering Building
Bucknell University
Lewisburg, PA 17837
Voice: (570) 577-1692
Fax   : (570) 577-3415