Posted on April 27, 2023
WASHINGTON – Coastlines are ever-changing. Whether from nonstop wave action, wind or storms, these landscapes constantly shift and reshape, causing challenges for coastal managers. In response, U.S. Army Corps of Engineers (USACE) researchers have created a tool to help assess the resiliency of our nation’s coastlines and improve coastal management strategies.
According to the National Oceanic and Atmospheric Administration (NOAA), the continental U.S. has almost 60,000 miles of shoreline. After observing Hurricane Sandy’s effects on beaches from Virginia to Massachusetts, a team of experts began studying the area in hopes of understanding what caused some beaches to erode rapidly and some barrier islands to breach while others did not.
“We settled on the concept that beaches that have more sand in the system — whether it’s on the beach or in the offshore — tended to respond better to the storm,” said Jennifer Wozencraft, a research physical scientist with the U.S. Army Engineer Research and Development Center. “They did not have as much storm impact, and they also tended to recover naturally after the storm.”
Without a way to quantify their findings, the team began developing the Coastal Engineering Resilience Index (CERI).
“We identified five non-dimensional factors that are based on the shape of the beach, the water levels and waves that the beach will see during a storm event,” Wozencraft said. “It’s an equation that we compute frequently — every 100 meters along the beach.”
The CERI is computed using a custom geographic information systems (GIS) toolbox that uses lidar data from the USACE National Coastal Mapping Program to extract parameters that describe the beach and dune system — measurements like the dune’s height and the beach’s slope and width. Using the data from USACE and NOAA models to extract wave and storm surge information, CERI then computes the index along the beach to estimate maximum shoreline recession and beach overtopping for specified storm events.
“It allows us to know which parts of the coastline are more resilient than others from a coastal engineering perspective,” Wozencraft said. “At the national level, USACE can use this data to prioritize beach projects for regular and post-storm sand placements – or at the project level, we can see areas within a single project that are less resilient.”
This strategy, along with other Engineering With Nature® practices, allows for the most efficient and effective beneficial use of sediment, making sure those areas of the coast that need attention get attention.
Currently, the index has been computed for pilot sites located on the northern Gulf of Mexico and North Carolina’s Outer Banks, as well as the USACE New York District’s area of responsibility in New Jersey and on Long Island. There are plans to compute CERI for most of the remaining U.S. sandy shorelines later this year.
“That would be the Gulf of Mexico and the Atlantic coasts,” Wozencraft said. “We also tested it on the Lake Ontario shoreline, but because of the bluffs there, we’re devising a different computation for CERI for bluff shorelines as compared to sandy shorelines, because the coastal processes are different. We’ll be able to start using the new CERI calculation on the Great Lakes and the West Coast shoreline next year.”
CERI can also help coastal managers understand how resilience has changed over time.
“With our national mapping program, we’re collecting data sets on a repeat basis — we’re working on our fourth time around the lower 48 states right now,” said Wozencraft. “We have a lot of data from the past, so we can use the coastal resilience index to understand over time how our management actions have improved the resilience of the coast, where our management actions haven’t been so effective, and if we need to make a change and adapt the management framework.”
From headquarters down to the project level, these data-driven approaches to decision making benefit all levels of coastal management.
“Having our data sets along with the toolbox and CERI helps us make better, more informed decisions,” said Wozencraft. “The index allows us to identify those areas of the coast that need the most attention and allows us to manage placement of sediment or other engineering works to improve the resilience of communities.”
