OSU Develops Methodology to Determine Coastal Flooding Risk

Researchers at Oregon State University have developed a new methodology for building computer models that paves the way to better understanding the flood risks faced by coastal communities.

Siletz River estuary, Photo courtesy Oregon Conservation Strategy

That’s important because towns along the coast are often situated near estuaries, which makes them vulnerable to both storm tide inundation and river flooding.

Estuaries occur where rivers flow into the ocean, meaning the rivers are influenced by tidal flooding and also experience frequent, periodic changes in salinity, sunlight and oxygen.

The study site for this research was Washington state’s Grays Harbor, but the methodology can be applied to any area subject to estuarine flooding.

“Flooding in areas like the Pacific Northwest is complicated since many processes contribute, such as tides, large waves and river flow,” said Kai Parker, corresponding author of the study published in Coastal Engineering. “We need to be able to predict water levels on several time scales.”

Grays Harbor, Photo courtesy Earthjustice

The new computer model involves “emulation” and uses statistical techniques, as opposed to traditional models that try to directly reproduce the wide collection of physical processes at play when estuaries flood.

The emulator performed well reproducing the extreme water levels of recent flooding events in Grays Harbor, Parker said.

Roughly 140 miles northwest of Portland, Oregon, Grays Harbor is a shallow bay – average depth: roughly 5 meters – with a deep-water navigation channel maintained by the United States Army Corps of Engineers.

Grays Harbor covers 235 square kilometers, is fed by five rivers that drain a watershed of greater than 7,000 square kilometers and is “subject to an energetic storm and wave climate,” Parker said, providing a solid test for the model.

“Our model is very useful since we can use it to explore an infinite variety of future flooding scenarios,” Parker said. “This allows us to better understand the risk of flooding in coastal communities as well as how this risk will change moving into the future.”

The National Oceanic and Atmospheric Administration supported this research, as did the Quinault Treaty Area tribal governments.