An Integrated Framework to Assess Compound Flood Potential in Coastal Areas: Concurrence of River Discharge and Storm Surge Extremes

Abstract:

Climate change is anticipated to significantly impact the frequency and severity of compound flooding events, resulting from coincidence of river discharge and storm surge extremes. Situated in a low-lying coastal delta, power grid substations may be particularly exposed to certain types of extreme weather events. The degree to which the network may prove resilient in the presence of these events is an open question. The objective of this study is to characterize the return period of compound flooding due to the concurrence of storm surge and river peak discharge and demonstrate the methodology at selected coastal areas in Connecticut, USA. We base the analysis on coastal flood events identified according to the National Centers for Environmental Information (NCEI) for the time period 1979-2019. For each storm event, we simulate river discharge time series using a physically-based distributed hydrological model, Coupled Routing and Excess Storage–Soil–Vegetation–Atmosphere–Snow (CREST-SVAS)¹, forced with atmospheric reanalysis data generated from the National Land Data Assimilation System (NLDAS). For the same storm events, we retrieve the surge time series from the National Oceanic and Atmospheric Administration (NOAA) total water level and tide time series. To simulate the compound effect of the two flood drivers, these time series are used respectively as upstream and downstream boundary conditions in a two-dimensional hydrodynamic model, Hydrologic Engineering Center’s River Analysis System (HEC-RAS). For quality control, the hydrodynamic model simulations are validated against the surveyed high-water marks in Connecticut collected by the United States Geological Survey (USGS) since the storm Sandy. The outcome of the study is to characterize the compound flooding in terms of maps of return periods (100-year, 50-year, 10-year) and maps of correlation to the return periods of the two individual flood drivers. The findings of the study will be a better understanding of the potential impacts of compound flood hazard on flood risk management strategies for spatial exposure e.g. impact on critical infrastructure situated in flood prone coastal zones.

References

1. Shen, X. & Anagnostou, E.N., Journal of Hydrology (2017).