Erich T. Hester, Ph.D., P.E.
AAAS Fellow, Water Power Technologies Office, U.S. Dept. of Energy
Associate Professor, Civil and Environmental Engineering, Virginia Tech

Abstract: Watershed-Scale Effects of Floodplain Restoration on Hydrologic Attenuation and Excess Nitrogen Removal
Increased peak flows and associated flood risk are common effects of human land use (e.g., urbanization, agricultural development, and certain forestry practices) and climate change.  Human land use also impacts water quality, particularly excess nutrients that lead to eutrophication of downstream waterways.  Enhancing floodplain capacity through river restoration to increase surface and groundwater storage along river networks has potential to mitigate both sets of impacts.  Yet this potential has been poorly quantified at the watershed scale.  We simulated the effect of varying the amount and location of floodplain and Stage 0 restoration on surface water storage in a series of watersheds using the U. S. Army Corps of Engineers Hydrologic Engineering Center’s River Analysis System (HEC-RAS).  We then simulated nitrate removal using an auxiliary R script.  First, we modeled a synthetic 4th-order watershed using average stream geometry and hydrology for the Virginia Piedmont with storms ranging in size from the 2-year down to monthly discharges.  Results indicate that Stage 0 techniques (simulated as low banks/shallow channel) were more effective at inducing flood attenuation (peak flow reduction) and floodplain exchange than restoring bankfull floodplains (simulated as higher banks/deeper channel).  The incremental effect of an individual restoration project varied depending on where it was in the 4th-order channel network, and on the amount of previous restoration that had already occurred in the watershed, with tradeoffs between enhancing flood attenuation and enhancing floodplain exchange.  Patterns of nitrate removal were similar to those of floodplain exchange.  Overall levels of flood attenuation (up to ~20%) and floodplain exchange (up to ~50%) were more significant than overall nitrate removal rates (up to ~1%) given kinetic-limited reactions.  Second, we simulated the cumulative effect of Stage 0 restoration (simulated as multiple/shallow channels, fully connected floodplain) in two case study watersheds, in MD and OR.  These case studies illustrated a number of limitations of the approach, including increases in peak flows due to unintentional alignment of mainstem and tributary peaks, and limitations in restoration techniques (e.g., channel filling) in certain topographic settings.  We emphasize the importance of viewing watersheds as a whole to understand the potential impacts of restoration projects, and watershed level planning to prioritize which stream reaches have the greatest benefit in supporting improved hydrologic response and water quality. 

Bio
Erich Hester is a faculty member in Civil and Environmental Engineering at Virginia Tech.  He leads a research group focused on environmental hydraulics, which studies how the flow of water through channels, floodplains, and groundwater affect flooding, water quality, and ecosystems.  This knowledge is applied to improve river management including river restoration, flood control, and hydropower.  He is currently a AAAS Fellow advising the U.S. Department of Energy’ Water Power Technology Office in Washington DC, with part of that time on detail to the Bonneville Power Administration advising on river restoration and hydropower in the Columbia River Basin.  In a prior sabbatical he studied the impact of floodplain restoration on removal of pharmaceuticals in Taiwan as a Senior Fulbright Scholar.  His service has included Associate Editor for Water Resources Research and the Board of Directors for the Consortium of Universities for the Advancement of Hydrologic Science, Inc (CUAHSI).  Prior to academia he spent nearly a decade in the private sector focused on river hydraulics, restoration, and water quality management.  He is a licensed professional engineer in Virginia and Washington State.