Compound Fluvial-Coastal Flood and Climate Adaptation: A Transferable Framework of Engagement, Modeling and Cost-Benefit Analysis

Compound flooding is the combination of rainfall-induced flooding with storm surge

induced flooding, and is currently inadequately considered nationwide in both flood risk

assessment and forecasts. It is well-established that coastal floods are becoming more

frequent, and the U.S. Northeast has seen a substantial increase in intense rainfall events in

recent decades, likely as a result of climate change. In many U.S. cities, coastal and fluvial floods

merge in estuaries, causing a compounded problem, and the coincident occurrence of extreme

rain and surge is growing at many locations. However, little research has been performed to

improve our understanding of compound flooding.

An ideal location to investigate this problem, Eastwick is a low-lying neighborhood in South

Philadelphia situated near the Delaware River at the confluence of Darby and Cobb's Creeks. It

is in close proximity to the 1.2 km2 John Heinz National Wildlife Refuge, two federal Superfund

sites, a series of oil refineries, and the Philadelphia International Airport, and meets the EPA

criteria for an Environmental Justice community, with a majority (76%) of its population being

African American, and pockets of low income residents. Triggered by rainfall, coastal surges

pushing up the tidal portion of the Delaware River, or some combination of the two, flooding

has long been one of the biggest problems facing this community.

The proposed research will inform climate risk management and adaptation decision-making

regarding flooding in Eastwick, and will be performed by researchers from two universities and

the Philadelphia Water Department (PWD). The project will include four core areas of science,

as well as a community engagement process, strong coordination with decision makers and a

specific focus on two ongoing city planning initiatives. The core compound flood science

research areas include flood modeling, extreme value analysis, climate-impact assessment, and

adaptation benefit-cost analysis. The engagement process will consist of two community

workshops, including collaborative design of flood adaptation scenarios and a socially-sourced

validation of the flood modeling. Coordination with decision makers will occur through an

advisory panel, project webinars, and the activities of our team members at the PWD.