Webinar: A multiscale model for representing transport in river basins with unsteady flow

Speaker
Dr. Phong Le
Oak Ridge National Laboratory, Oak Ridge, TN, USA
Faculty of Meteorology Hydrology and Oceanography, VNU, Hanoi, Vietnam

Abstract
The movement of solutes in a watershed is a complex process with multiple interactions and feedbacks across various spatial and time scales. 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. Here, we extend a recently developed Lagrangian-based multiscale river-corridor reactive transport model to accommodate transient flow based on simplifying assumptions that streamline trajectories in the hyporheic zone have fixed geometry even when the magnitudes of hyporheic exchange and flow are time dependent.

We adopt a graph framework to represent river network topology and use hydraulic geometry scaling laws to relate channel characteristics to discharge, thus allowing the time-response function of solute fluxes throughout the entire network to be modeled. We apply the methodology to reach-scale and network-scale tracer tests at the H.J. Andrews Experimental Forest in western Cascade Mountains, Oregon, USA. Model results demonstrate that the proposed framework is able to link dynamical processes occurring at small scales into a network context to help understand how changes at reach scale cascade into network-scale effects, providing a useful tool for sustainable river basin management.