Hi,

I have a general question (or two!) for the list on the above subject:

In the abscence of field measurements, how is SWCON determined in the
DSSAT drainage equation? Ritchie and Crum (1989) list SWCON for
generalised Permeability classes. Is there something more specific? It
seems to me that the equation will give different results for different
soil layer thicknesses (the cascade taking longer for thinner layers). Is
this effect accounted for explicitly anywhere?

I also have a specific question for Ayman Suleiman:

F*C in your drainage equation seem equivalent to SWCON. How are your
constants determined? Could you possibly send me some relevant papers of
yours? It would be greately appreciated.

Regards,

Andrew

On Mon, 27 Aug 2001, Ayman Suleiman wrote:

> 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
>

________________________________
Andrew Challinor,
CGAM,
Dept. of Meteorology,
University of Reading,
Reading RG66BB
U.K.

http://www.met.rdg.ac.uk/~ajc

Tel (44) (0)118 9875123 ext 4281
Fax (44) (0)118 9318316
--------------------------------