Dual porosity modeling of agricultural groundwater movement

Thermodynamic principles were applied to the problem of saturated/unsaturated flow in fractured porous media to develop a model based on the dual porosity conceptualization. The development was based on assumptions that the system was isothermal, that all phases were chemically inert, and that the solid phase was rigid. A general procedure was developed for incorporation of microscopic interfacial effects, where the interfacial properties were treated as volumetric average quantities. These quantities then appeared in the global constraints on interphase exchanges. It was proposed that the soil moisture characteristic curve should be decomposed into macropore and micropore components, which could then be used to develop the interphase mass exchange functions. The soil moisture characteristic curves could also be used to supply information relating equilibrium moisture content to specific surface free energy. The model was developed to handle two fluid phases in each of the void domains, allowing either saturated or unsaturated flow in either domain. The resulting equations were simplified to approximate the near-surface conditions encountered in agricultural situations