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Simulating Flood-Induced Sediment and Associated Contaminant Transport with a Coupled HEC-RAS 2D and WASP Model.
Citation:
Barber, J., B. Pluta, G. Soscia, J. Essoka, R. Poeske, M. Mehaffey, P. Whung, A. Shabani, S. Woznicki, J. Butcher, AND M. Harris. Simulating Flood-Induced Sediment and Associated Contaminant Transport with a Coupled HEC-RAS 2D and WASP Model. Chesapeake Bay Program Watershed Technical Workgroup Virtual Meeting, Virtual, January 07, 2021.
Impact/Purpose:
Extreme weather (e.g., flood, hurricane, etc.) events exert multiple stressors on communities, one of which is the possibility of contaminated water and sediment released from contaminated sites such as Superfund sites. For example, EPA requested Regions to assess the vulnerabilities of Superfund sites in the projected path of Hurricane Florence (September 2018) and during historic Midwest flooding (March 2019) for preparedness. In addition, contaminated site associated communities have expressed concerns on potential flood-induced contaminants transport, with increasing extreme weather conditions and changing climate. Some regions and states lack information needed to readily assess and determine the contaminated sites’ and communities’ vulnerabilities to flooding, and many lack site-specific flood impacts on contaminants transport data needed to inform cleanup actions to build community resiliency. In response to community concerns and in support of regional needs for data, we partner with Region 3 in framing our research and demonstrating usability of this work. The potential use of our research can include (1) remedial planning, (2) resampling strategy, (3) emergency preparedness, and (4) informing community resilience planning for severe flooding. Chesapeake Bay Program (CBP) invited me to present this work and explore opportunities to collaborate and to adopt our approaches for potential CBP use.
Description:
Increased intensity and frequency of floods raises concerns about release and transport of soil and sediment and associated contaminants to and from streams and rivers. To model these processes during flooding events, we developed an external coupler in Python to link the Hydrologic Engineering Center-River Analysis System (HEC-RAS) 2D hydrodynamic model to the Water Quality Analysis Simulation Program version 8.4 (WASP). The external coupler aggregates flow and conserves mass when transitioning from HEC-RAS 2D to WASP. We applied the coupled model to simulate soil and sediment contaminants’ (i.e., arsenic (As), lead (Pb), benzo(a)pyrene (B(a)P), chromium (Cr), dioxin, total polychlorinated biphenyls (PCBs) fate and transport for multiple flood return periods (i.e., 10, 50, 100 and 500-yr flood) in Lower Darby Creek Area, PA. The sensitivity analysis of WASP sediment transport simulation showed that shear stress is the parameter with the most influence on the erosion and deposition processes. The surface sediment volume at the end of a 48-hr flood simulation ranged from a net loss of 7,428 m3 to a net gain of 36,126 m3 for each model segment (30 m). Change in surface sediment concentrations of As, Pb, B(a)P, Cr, dioxin, and PCBs, for example in a 100-year flood, ranged from -10 to 2.1 mg kg-1, -0.47 to 3.0 mg kg-1, -4.5 to 0.9 mg kg-1, -70 to 49 mg kg-1, -70 to 48 mg kg-1, -70 to 49 mg kg-1, respectively depending on model segment. Simulated results illustrate that significant redistribution of sediments and contaminant in sediments during extreme floods. Our overall research findings include: (1) Hydrodynamic mixing of water, suspended sediment in water, and surface sediment is one of the primary drivers in redistributions of contaminants in sediment, (2) Initial spatial distribution of contaminants of concern in surface sediment plays an important role in concentration changes at the end of the flood simulation period, (3) Sediment volume changes are not a surrogate for changes in contaminants concentration in sediment, and (4) Sediment volume transport pattern is not a surrogate for redistribution patterns of contaminants in sediment. The research results can be used to inform resampling strategy and remediation planning at the study site.