Coastal infrastructureRising seas may force coastal communities to “strategically retreat”: Corps of Engineers

In response to Hurricane Sandy, the October 2012 storm that caused $65 billion in damages, the U.S. Army Corps of Engineers has conducted a two-year study on 31,200 miles of coastal, back bay, and estuarine areas in ten states. The Corps has identified nine high-risk areas for future flooding along the North Atlantic coast.

The study, known as the North Atlantic Coast Comprehensive Study, looked at four sea-level rise scenarios with three time horizons (2018, 2068, and 2100) and predicts that under the worst scenario, Atlantic City would experience almost three feet of sea-level rise by 2068, and more than five feet by 2100. The dune systems along New Jersey’s ocean side could handle the sea-level increase, but the bayside along the state’s barrier island communities will suffer a great deal.

“The back bays in several of the areas become highlighted as high-risk areas particularly with sea level rise. These areas are already low. The challenge is flooding could come from multiple directions,” said Amy Guise, the chief of the Army Corps command center in Baltimore that drafted the report. Guise adds that most of the dune system on the ocean side was initiated by Army Corps projects.

The dune system protecting Long Beach Island in Ocean County could keep the ocean at bay under a six-foot sea-level rise scenario, but the west side of the island has engineers concerned. According to PressOfAtlanticCity, a one-foot increase in sea level means that storms that currently bring in back bay waters and flood 20 percent of the roads would end up flooding 70 percent of the roads. The average depth of that water would increase from one-foot to about four-feet. “At a 3-foot sea level rise, the road network becomes unusable,” the study says.

U.S. Representative Frank Pallone (D-New Jersey), who helped secured $20 million in funding for the study, said it will be made available to federal, state, and local agencies including transportation departments, community planners, and emergency managers. It should help communities prepare for future storms and floods, he said.

“I am hopeful that this report will help federal, state and local governments mitigate the adverse effects of future disasters. The study builds on lessons we learned from Superstorm Sandy and allows officials to use the latest science and tools to ensure that coastal communities are resilient to the impacts of climate change, as well as future storms,” Pallone said.

Global sea levels are rising roughly 1.7 millimeters per year, but the rate is expected to accelerate over the next 100 years due to warmer ocean waters and melting polar ice. The study offers a nine-step planning process on how to identify risky areas and develop strategies to reduce the risk. It also recommends several ways communities can deal with rising sea levels, including bulkheads, seawalls, levees, elevation of homes and roads, dunes, breakwaters, living shorelines made of natural materials, groins, deployable floodwalls, and reefs. “Some communities looking out twenty years or more may consider strategic retreat and relocating people to higher ground. Each community has to evaluate which measures will work for them,” Guise said.