A Multiscale Integrated Hydrology Model for Transport in River Basins


Phong Le1* (lepv@ornl.gov), Saubhagya Rathore1, Ethan T. Coon1, Scott L. Painter1, J. David Moulton2


1Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN; 2Los Alamos National Laboratory, Los Alamos, NM



Solute movement in a watershed is a complex process with multiple interactions and feedbacks across various spatial- and timescales. Understanding how solute moves along diverse hydrologic pathways through watersheds—from hillslopes to channels and in and out of the hyporheic zones—is challenging but critically important since these processes integrate and contribute to the biogeochemical functioning of the river corridor up to the river network scale. In partnership with Oak Ridge National Laboratory’s Watershed Dynamics and Evolution science focus area (SFA), the IDEAS-Watersheds project is developing a multiscale integrated modeling framework for transport at the river basin scale. The framework combines a fully integrated surface/subsurface flow model with a multiscale transport model in which the dynamics of transport and reactions in the hyporheic zone adjacent to stream channels are described in Lagrangian form as a subgrid model. The framework is implemented in the Advanced Terrestrial Simulator model, which provides great flexibility in simulating flow and transport over multiple interacting meshes. It also links to biogeochemical reaction capabilities in the PFLOTRAN code, thus enabling multiscale reactive transport models. Researchers demonstrate multiscale models where flow dynamics are simulated over the entire watershed, but reactive transport is localized to the stream network and associated hyporheic zones. This greatly reduces computational cost without losing the effect of biogeochemical hot spots on downstream water chemistry. The research team first demonstrates the model using the synthetic tilted open book catchment. Then they simulate a long-term network-scale test at the H. J. Andrews Experimental Forest in the western Cascade Mountains, Oregon, and successfully compare it to observations. Model results demonstrate that the proposed framework can link hydro-biogeochemical processes occurring at small scales into a network context to help understand how small-scale processes cascade into network-scale effects, a common scaling challenge across ESS SFAs.