Interaction between Storm Surge and Mississippi River Flood Flows

Stephens, T. A., Sanborn, S. C., Roy, S. S., Wallen, C. M., Savant, G. G., & McAnally, W. H. (2025). Interaction between Storm Surge and Mississippi River Flood Flows. Journal of Waterway, Port, Coastal, and Ocean Engineering. American Society of Civil Engineers. 151(5), 15. DOI:10.1061/JWPED5.WWENG-2295.

Compound flooding in coastal areas has caused substantial social and economic disruptions, emphasizing the need to accurately simulate and quantify its impacts. Advancements in modeling tools have improved the capability to simulate compound flooding; however, a need remains to advance understanding of the fundamental interaction between multiple flood sources and how it impacts flood hazards. This study investigates the interaction of riverine flood flows on the Mississippi River and coastal storm surge generated during Hurricane Barry with a two-dimensional, depth averaged hydrodynamic model, the adaptive hydraulics model. We simulate compound flooding, and individual flood drivers (storm surge and riverine flood flows) for five different flow scenarios. The results show that impacts of compound flooding can extend for more than 500 km along the Mississippi River. The increase in water surface elevations due to interacting flood sources decreases as discharge increases, because higher discharges tend to damp the impacts of storm surge. However, higher flow scenarios result in higher overall water surface elevations. Storm surge and river flows interact nonlinearly to increase or decrease water levels compared with the sum of their parts. Local discharge decreases as water levels increase with the passage of storm surge due to a shift in net momentum flux, and discharge response following storm surge depends on the availability of lateral relief to discharge stored mass. Ultimately, our findings suggest that the interaction of individual flood sources is location specific. The results of this study are transferrable and can inform compound flooding processes at additional sites; while the methods applied can serve as a template for additional research.