Water and chloride transport in a fine-textured soil: Field experiments and modeling

Numerical models are being used increasingly to simulate water and solute m ovement in the subsurface for a variety of applications in research and soi l/water management. Although a large number of models of varying degrees of complexity have been developed over the years, relatively few have been te sted under field conditions. We tested the performance of the HYDRUS-1D com puter model to simulate variably saturated water flow and chloride transpor t: in a fine-textured Italian soil subject to a fluctuating saline groundwa ter table. The model was also used for estimating solute transport paramete rs using an inverse optimization scheme, Our results indicate that includin g the effects of immobile water produced better predictions of chloride tra nsport compared with the traditional convection-dispersion transport approa ch. Including anion exclusion as well did not improve the model predictions appreciably. Occasional deviations between model prediction and field obse rvation were attributed to unrepresented lateral groundwater flow processes and to preferential flow through macropores or other structural voids, The HYDRUS-1D model was found to be very useful for analyzing the relatively c omplex now and solute transport processes at our field site and for estimat ing model parameters using inverse procedures.