How do rivers and streams affect their surroundings, above and below the surface? Land system models, used to study complex ecosystems, are insufficiently configured to address the question of how water moves below the land surface. Now, scientists have developed a model that considers such waters. It captures the variable gradient of water in soils. The gradient is critical for understanding energy and water budgets, as well as biogeochemical cycling in the land surface and below. The team created the model by coupling a widely used, massively parallel multiphysics reactive transport code with the Community Land Model to create a coupled model called CP v1.0.
Rivers have a relatively small footprint on the landscape, but they have a large impact on the environment. The new open-source model lets researchers get a clear view of processes occurring along river corridors and how these processes affect watersheds. The associated data set is also beneficial. Scientists can use it as a benchmark for testing other integrated models.
The research community increasingly recognizes that rivers, despite their relatively small imprints on the landscape, play big roles in watershed functioning through their connections with groundwater aquifers and riparian zones. The Columbia River served as an ideal test case for long-term observations, as well as simulations using a coupled 3-D surface and subsurface land model. The interactions between groundwater and river water are important because they influence the volume of water in soils. However, past simulations of these processes and their impacts haven’t always mirrored the reality of field observations.
During a five-year monitoring of groundwater wells along the Columbia River shoreline, a team of researchers recognized the value of observing the layers within the subsurface rather than just what happens aboveground. The team used two open-source codes, PFLOTRAN and CLM4.5, to compare simulations to observations. They then coupled the two models to create CP v1.0. The coupled-model approach allowed the research team to estimate moisture availability, for example, particularly during changes in the river stages, and to validate the new model using data from the shoreline site.
The research shows spatial resolution matters. It’s important to refine the model resolution along river corridors that were part of this study. Scientists can also apply a coupled model like the one used in this study to larger modeling problems, such as simulating the impact of a drought on watershed functioning by explicitly considering the role of river-aquifer-land interactions.