A NOVEL COMPUTATIONALLY EFFICIENT HYDROLOGIC MODELING FRAMEWORK TO SIMULATE WATER, SOLUTE, AND SEDIMENT TRANSPORT AT THE HILLSLOPE SCALE

Interactions of water and solutes at the surface-subsurface boundary strongly affect water quantity and quality in the environment, but little attention has been given to water and solute mass transfer at this boundary. Herein, an innovative framework was developed to sequentially couple water flow, solute, and sediment transport processes at the surface-subsurface boundary into a simple, physically-based, and computationally efficient hydrological model at the hillslope scale. The KINEROS2 (K2) model solves the 1D kinematic wave equation for water flow and the advection-dispersion equation for non-absorbing solute (or sediment) transport at the surface, whereas the HYDRUS-1D (H1D) model solves the Richards equation for water flow and the advection-dispersion equation for solute transport in the subsurface. The coupled H1D-K2 model can simultaneously simulate the advection flux caused by infiltrating water and diffusive mass transfer from the contaminated soil to runoff. Three benchmark problems are conducted to verify, evaluate, and analyze the performance of the proposed model. The simulated hydrographs, chemographs, water balance components, and solute balance components are all in excellent agreement with results from HYDRUS-2D, analytical solutions, and experimental data. For the homogeneous cases, the relative differences in water and solute balance components between the H2D and coupled H1D-K2 models are less than 1%, whereas, for the heterogeneous cases, the differences are within 4%. Alternatively, the proposed model accurately captures the soil erosion and sediment transport processes induced by rainfall and overland flow.