Abstract
Preferential flow processes are controlled by subsurface structures with
the hierarchical organization across scales, but there is a lack of
multiscale model validation using the field data. In this study, using a
comprehensive dataset collected in the forested Shale Hills catchment,
we tested and validated preferential flow occurrence by 2-dimension
HYDRUS-2D at the hillslope scale, and in comparison, with 1-dimension
HYDRUS-1D at the pedon scale and 3-dimension HYDRUS-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,
accounting for 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 preferential
flow (PF) 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. The
multi-dimensional modeling approaches can provide the mechanic
presentation of PF pathways to the first-order stream and the necessity
of the 3D simulation with detailed information to identify the dominant
hydrological process.