Benchmarking of numerical models for simulating flow and transport in unsaturated soils

Accurate model predictions of water flow and solute transport in unsaturated soils re- quire a correct representation of relevant mechanisms in a mathematical model as well as correct solutions of the mathematical equations. Due to the complexity of boundary conditions, the vertical variations of model parameters in the soil profile, and the non- linearity of the considered processes, solutions of the mathematical equations rely on numerical approximations. We evaluate a number of numerical models (WAVE, HY- DRUS_1D, SWAP, TRACE/PARTRACE, 3D_LEWASTE, MACRO, DUALP_1D, SIMULAT) and check the accuracy of the numerical solutions against analytical so- lutions. All considered models use the Richards and the convection dispersion equa- tions to describe, respectively, water flow and solute transport in unsaturated soil. The MACRO, DUALP_1D and SIMULAT models, can also simulate preferential flow and transport through macropores. The models represent different numerical strategies to solve flow and transport equations: finite differences (WAVE, SWAP, MACRO), fi- nite elements (HYDRUS1D, TRACE, DUALP_1D), particle tracking (PARTRACE), and method of modified characteristics (3D_LEWASTE). The following scenarios are considered in the benchmarking: infiltration in uniform and layered soil profiles, evap- oration from a soil profile with a fixed groundwater table depth, solute transport for steady state flow conditions in uniform and layered soil profiles, solute transport dur- ing water infiltration, and water flow and solute transport in an uniform soil profile during one year with climatic boundar