Use of numerical modeling to evaluate the impact of hydrodynamic
pressure on hydrologic exchange fluxes and resident time for a
large-scale river section over a long-term period
Abstract
Quantifying hydrologic exchange fluxes (HEF) and subsurface water
residence times (RT) are important for managing the water quality and
ecosystem health in dynamic river corridor systems. Because of limited
field accessibility, numerical models typically have been used to
quantify HEFs and RTs. These models, however, usually are limited to
local-scale bedforms and are based on the assumption that hydrostatic
pressure drives surface and subsurface water exchanges. Previous
laboratory-scale experiments and models have shown that hydrodynamic
pressure variations on the riverbed induced by dynamic river flows can
strongly impact HEFs and RTs. In this study, the impacts of hydrodynamic
pressure on HEFs and RT for a 30 km section of the Columbia River in
Washington State over a three-year period were quantitatively evaluated
using a coupled transient three-dimensional (3D) multi-phase surface and
subsurface water flow transport approach. Based on comparisons of the
model simulations with a reference case that considered only hydrostatic
pressure, we found that hydrodynamic pressure significantly enhances
upwelling and downwelling HEFs by 2 and 1.7 times, respectively, in the
investigated river section and also leads to a reduction of the most
likely RT by one order of magnitude (i.e., from hundreds of days to tens
of days).