One mechanism for the initiation of unstable flow in porous media is a condition of hydrophobicity of the solid phase. Recent continuous and nondestructive measurements of water content distribution in a 200 cm wide by 70 cm deep trench of a Netherlands' field soil containing a hydrophobic layer, reveals a complicated wetting pattern with fingered flow being quite prevalent. The soil profile consists of a humic top layer; a second layer consisting of hydrophobic sand, and a hydrophilic sandy layer at the bottom of the soil profile. In this paper we show our attempts to simulate the unstable flow pattern observed in the field using a numerical solution developed for modeling gravity-driven unstable flow. The unstable flow simulation method employs a globally mass conservative finite element solution of the Richards equation applied to the soil trench. The overall patterns of simulated saturation are similar to those of observed saturation. Statistical analysis shows that pointwise predicted saturation is reasonably close to the observed.
Bibliographical noteFunding Information:
Published as Paper No. 981120022 of the scientific journal series of the Minnesota Agricultural Experiment Station on research conducted under Minnesota Agricultural Experiment Station Project No. 12-047. Experimental work was supported by the Environment Research Programme of the European Union (EV5V-CT94-0467), Research Programme 223, ‘Physical Soil Quality’, of the Dutch Ministry of Agriculture, Nature Management and Fisheries, and the Netherlands Integrated Soil Research Programme (C3–13). The modeling part was supported by the Army High Performance Computing Research Center under the auspices of the Department of the Army, Army Research Laboratory cooperative agreement number DAAH04-95-2-0003/contract number DAAH04-95-C-0008, the content of which does not necessarily reflect the position or the policy of the government, and no official endorsement should be inferred. Collaboration on the research was supported by the NATO Collaborative Research Grant No. 960704.
- Finite element method
- Hydrophobic soil
- Unstable flow