Controls of land surface and bedrock topography on the spatial
distributions of water table and storage: unifying saturation excess
runoff models
Abstract
The control of land surface topography on the configuration of
groundwater table has been recognized and well explored. However, the
control of bedrock topography on water table is much less studied,
potentially due to the limited observations of bedrock. This paper
evaluates the controls of both surface and subsurface topography on the
spatial distributions of steady-state water table and the corresponding
water storage at the catchment scale based on numerical simulations.
Numerical models with different topographic features are developed using
MODFLOW (USG). When water table is shallow, the control on the spatial
distributions of water table is dominated by land surface topography
(i.e., water table is approximately parallel to land surface); with the
increase of water table depth, the role of land surface topography
decreases; when water table is deep and close to bedrock surface, the
spatial distributions of water table is dominated by bedrock topography
(i.e., water table is approximately parallel to bedrock surface). For
land surface-dominated water table, storage capacity in unsaturated area
is spatially uniform, which is the underlying assumption of TOPMODEL;
however, for bedrock-dominated water table, water storage in unsaturated
area is spatially uniform, which is the underlying assumption of
VIC-type model. The systematical variations of the controls of surface
and subsurface topography on water table configuration provide a
framework to unify saturation excess runoff models by treating TOPMODEL
and VIC-type model as two endmembers.