AGROFORESTRY DRAINAGE MANAGEMENT MODEL .3. FIELD SALT FLOW

Eucalyptus trees are being recommended as a management option for lowering the shallow ground water and reusing saline subsurface drainage water in drainage-impacted areas of the San Joaquin Valley in California. Both field and modeling studies are being carried out. To assess the efficacy of eucalyptus trees for these purposes, a finite-element method based on the Galerkin technique was used to solve the nonconservative transport governing equation. The nonconservative nature of salinity was addressed by the dissolution and precipitation of gypsum in the vadose zone. Water fluxes and volumetric moisture content needed to solve the solute model were obtained from outputs of the water-flow submodel. The present paper shows the mathematical formulation of the 2D salinity submodel as well as an example of an application during the 1990 irrigation season to an agroforestry system at the Mendota site. The measured and predicted salinity distribution was found to have good linear correlation coefficients (an average of 0.856). The sensitivity analysis of different irrigation practices on salinity distribution and shallow ground water quality are also presented.