Representing the Dupuit-Boussinesq Aquifer in the National Water Model:
Catchment-Scale Application of Hydraulic Groundwater Theory
Abstract
While hydraulic groundwater theory has been understood as a viable
approach for representing the role of the aquifer(s) in the
surface-subsurface hydrologic cycle, the integrated modeling community
still lacks a proper hydrologic structure to utilize the well-studied
theory for large-scale hydrologic predictions. This study aims to
present a novel hydrologic modeling framework that enables the
Boussinesq equation-based depiction of hillslope-channel connectivity
for applying hydraulic groundwater theory to large-scale model
configurations. We integrated the BE3S’s [Hong et al., 2020]
representation scheme of the catchment-scale Boussinesq aquifer into the
National Water Model (NWM) and applied the NWM-BE3S model to three major
basins in Texas (i.e., the Trinity, Brazos, and Colorado River basins).
Since the NWM currently relies on a single reservoir model for baseflow
estimation, theory-based evaluation was performed as the efficacies that
the Boussinesq aquifer has relative to the single reservoir model should
be consistent with hydraulic groundwater theory. We identified that the
implemented Boussinesq aquifer(s) showed ‘more’ pronouced improvements
in capturing streamflow dynamics than the original NWM as aquifers
exhibited higher nonlinearities in the observed recessions. The varying
degree of improvements in streamflow outputs according to the recession
nonlinearities demonstrates (1) the applicability of the theory-based
depiction of hillslope-channel connectivity and (2) the technical
enhancement of model structure. We also examined the river states of all
the reaches based on the represented bidirectional lateral hydraulic
connections between the stream-aquifer and thus identified the dominant
processes between the stream-aquifer (i.e., either river infiltration or
baseflow) were spatially variable roughly following climatic gradients.