Understanding km- to Reach-Scale Hydrological Exchange Flows along a Large Dam-Regulated River Corridor

Department of Hydrology & Atmospheric Sciences
Weekly Colloquium
Thursday, November 15, 2018
4:00 pm in Harshbarger 206 ~ Refreshments at 3:45 pm

Xingyuan Chen

Scientist

Atmospheric Management and Data Sciences
Pacific Northwest National Laboratory, Richland, WA

Abstract:

Xingyuan Chen*1, Xuehang Song1, Pin Shuai1, John Zachara1, Glenn Hammond2, Patrick Royer1, Huiying Ren1

 1Pacific Northwest National Laboratory, Richland, WA

 2Sandia National Laboratories, Albuquerque, NM

This study seeks to understand how the hydrological exchange flows (HEFs) at the river water and groundwater interface are impacted by the dynamics of river flow and the heterogeneity in hydrogeologic properties in dynamic river corridor systems. We used a combination of field observations and 3D numerical simulations (PFLOTRAN) to understand the complex spatial and temporal dynamics of HEFs from the km- to reach-scale (10s of km) along the regulated river corridor of the Hanford reach. Multiple numerical tracers are introduced at selected segments of river boundary to track the contribution of river water in the groundwater system. Particle tracking is run to reveal exchange pathways and estimate the distributions of river water residence time. At the km-scale, the exchange pathways exhibit strong heterogeneity along the river shoreline within a given flow window as impacted the physical heterogeneity in riverbed substrate and in the aquifer. The riverbed permeability (or conductance) and its spatial heterogeneity are identified as the most sensitive parameters of the HEF model. The exchange patterns also vary substantially across different flow regimes. Consequently, the residence time distribution of river water in the groundwater system is featured by long tails and multiple modes. The reach-scale HEF model encompasses multiple hydromorphic features of the entire reach, which showed increasingly more complex spatial and temporal patterns of HEFs as the scale grows. The HEF studies at both the km and reach scales fill in a critical need in bridging the gaps between hydromorphic-scale process understanding and robust predictions of the watershed hydrobiogeochemical function.

Bio:

Dr. Xingyuan Chen is a research scientist at the Pacific Northwest National Laboratory. She is a co-PI on a DOE science focus area project that studies Influences of Hydrologic Exchange Flows on River Corridor and Watershed Biogeochemical Function. Her main research expertise is in multiscale hydrobiogeochemical modeling and data assimilation. She got her PhD degree in Civil and Environmental Engineering and a Master’s degree in Statistics from University of California, Berkeley.