Simulation in Preferential Flow by Multi-dimensional Modeling Approach

Abstract:

Watershed hydrological processes controlled by subsurface structures that have hierarchical organization across scales, but there is a lack in multiscale model validation using the field data. In this study, using a comprehensive dataset collected in the forested Shale Hills catchment, we tested preferential flow simulation using a multi-dimensional modeling approach based on widely-used HYDRUS codes (i.e., 1D at the pedon scale, 2D at the hillslope scale, and 3D at the catchment scale). There was good agreement between the 1D simulations and measurements of soil moisture in the soil profile, which was mainly affected by the vertical change in porosity/permeability with depth and precipitation characteristics; however, short-term fluctuations due to preferential flow were poorly captured. Notably, 2D and 3D simulations, which accounting preferential flow controlled by slope positions and shallow fractured bedrock, provided better results than the 1D simulations. Furthermore, a dual-porosity or anisotropic model provided more accurate predictions of soil moisture than a single-porosity or isotropic model due to a more realistic representation of local soil and fractured shale structure, which is also the premise of subsurface preferential flow occurrence. Consequently, our study reflected the central importance of multi-dimensional model approaches, while highlighting the quantification of the soil structure and fractured nature of the bedrocks itself is essential to the simulation of preferential flow. Our multi-dimensional modeling approaches can provide the mechanic presentation of subsurface preferential flow pathways to the first-order stream and the necessity of the 3D simulation with detailed information to identify the dominant hydrological process.