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The case of shallow water table

Posted: Tue Jan 19, 2010 1:36 am
by tsutchi
<font face="Arial"></font id="Arial">Numerical simulations using HYDRUS-1D for no-ponding boundary conditions do not converge when the soil column has a water table less than air-entry pressure. Is there any way to simulate water content and pressure distribution profiles in a soil column with shallow water table?
With best regards,
Mohamed Khaled

Posted: Tue Jan 19, 2010 3:38 am
by Jirka
What does that mean "the soil column has a water table less than air-entry pressure"?

J.

Posted: Wed Jan 20, 2010 2:25 am
by tsutchi
For example, if you have a soil with an air entry of 40 cm (infered from the water retention curve), you pack this soil in a 100 cm column. If the water table is set at depth less than 40 cm from soil surface the zone above it is nearsaturated because of the capillary fringe effect. In this case numerical simulations do not converge. For instance Shah and Ross (2009) quoted this problem.
Shah N. and Ross M. 2009. Variability in Specific Yield under Shallow Water Table Conditions. Journal of Hydrologic Engineering,Vol. 14, No. 12: 1290–1298. <blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Jirka</i>

What does that mean "the soil column has a water table less than air-entry pressure"?

J.
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Posted: Wed Jan 20, 2010 5:19 am
by Jirka
Are you using BC soil hydraulic model or modified VG model. Only these two models recognize air-entry value. VG model does not and thus should work fine. If you use the other two models and thus do have a fully saturated column, then obviously your boundary conditions must be such so that the system can handle that. You cannot apply flux to a fully saturated column.

J.