PNNL

Abstract

A fully coupled three-dimensional surface and subsurface land model is developed and applied to a site along the Columbia River to simulate three-way interactions among river water, groundwater, and land surface processes. The model features the coupling of the Community Land Model version 4.5 (CLM4.5) and a massively-parallel multi-physics reactive tranport model (PFLOTRAN). The coupled model (CLM-PFLOTRAN) is applied to a 400 m×400 m study domain instrumented with groundwater monitoring wells along the Columbia River shoreline. CLM-PFLOTRAN simulations are performed at three different spatial resolutions over a five-year period to evaluate the impact of hydroclimatic conditions and spatial resolution on simulated variables. Results show that the coupled model is capable of simulating groundwater-river water interactions surrounding a near-shore groundwater aquifer that experiences pressure changes induced by river stage vacillations along highly regulared river reaches, which are of global significance as a result of over 30, 000 dam constructions worldwide during the past half century. The dataset presented in this study can also serve as a good benchmarking case for testing other integrated models. Our numerical experiments suggested that the land-surface energy partitioning can be strongly modulated by groundwater-river water interactions through expanding the periodically inundated fraction of the riparian zone, and enhancing moisture availability in the vadose zone via capillary rise in response to pressure change induced by the river. In addition, spatial resolution is a key factor for accurately estimating the mass exchange rates at the boundaries and associated biogeochemical reactions in the aquifer, and becomes critical when surface and subsurface become more tightly coupled with groundwater table within 6-7 meters from the surface. The coupled model developed in this study can be used for improving mechanistic understanding of ecosystem functioning, biogeochemical cycling, and land-atmosphere interactions along river corridors under historical and future hydro-climatic changes.