Coupling hydrology and ocean models to forecast pathways of contaminants from land to the ocean during extreme flood events

Melissa Moulton, NCAR Boulder Colorado, United States. mmoulton@ucar.edu

John Warner, USGS Woods Hole Massachusetts, United States. jcwarner@usgs.gov

Joseph Zambon, NC State University Raleigh North Carolina, United States. jbzambon@ncsu.edu

Z George Xue, Louisiana State University Baton Rouge Louisiana, United States. zxue@lsu.edu

Ruoying He, NC State University Raleigh North Carolina, United States. rhe@ncsu.edu

Zafer Defne, USGS Woods Hole Massachusetts, United States. zdefne@usgs.gov

Donxiao Yin, Louisiana State University Baton Rouge Louisiana, United States. dyin2@lsu.edu

Daoyang Bao, Louisiana State University Baton Rouge Louisiana, United States. dbao2@lsu.edu

Christie Hegermiller, Sofar Ocean (prev. USGS) Woods Hole Massachusetts, United States. christie.hegermiller@sofarocean.com

Coastal ecosystems, infrastructure, and human health are vulnerable to extreme precipitation, flooding, and water-quality impacts. Integrating a hydrologic model (WRF-Hydro) into the Coupled Ocean Atmosphere Wave Sediment Transport modeling system (COAWST), which includes ocean (ROMS), atmosphere (WRF), surface-wave (SWAN, WAVEWATCHIII), sediment (CSTMS), and sea-ice components, offers the potential to investigate compound flooding and the dispersal of contaminants, sediments, and other material at the land-ocean boundary. Here, the new model coupling is described, along with an application to Hurricane Florence.

Extreme precipitation during Hurricane Florence, which made landfall in North Carolina in September, 2018, led to breaches of hog-waste lagoons, coal-ash pits, and wastewater facilities. In the weeks following the storm, historic freshwater discharge carrying pollutants, sediment, organic matter, and other debris was released to the coastal ocean, contributing to beach closures, algal blooms, hypoxic conditions, and other ecosystem impacts. The Cape Fear river basin, North Carolina’s largest watershed, is used as a case study. Progress in model coupling applied to this region includes (1) a two-way coupled ROMS and WRF-Hydro simulation in which fluxes between the ocean and hydrology models are computed from the pressure gradient at the ocean-land boundary, and (2) a one-way coupled simulation in which a WRF-Hydro simulation provides river point-source forcing in ROMS. The work as part of the one-way coupled simulation demonstrates how the pathways of land-sourced tracers can be tracked in the coastal ocean; a suite of different flood and wind scenarios are studied and used to map the arrival and departure times of threshold-exceeding contaminants that contribute to swimming advisories and other impacts. Next steps are described for continuing the ocean-hydrology model coupling efforts to improve forecasts of compound flooding and water quality impacts.

2022 CSDMS meeting-072

Coupling hydrology and ocean models to forecast pathways of contaminants from land to the ocean during extreme flood events