News Stories

Engineering the Recovery from Hurricane Sandy

US Army Corps of Engineers
Published March 2, 2015
Coastal engineers expect that large storms will induce sediment transport from the nourished beach and move sand offshore. When this happens, waves begin to break farther from the shoreline, thus weakening their force before they reach the shoreline itself. In this way, beach nourishment projects help protect dunes and property from further erosion, decrease flooding, and limit how far ashore storm surge will go. A wide, flat beach berm with a sufficient volume of sand keeps the erosive power of the waves from reaching and destroying the dunes and structures and can reduce damages significantly from waves, inundation, and erosion. Without beach nourishment, the starting point for damage would be farther onshore; a nourished beach, with sufficient sand volume and healthy dunes, absorbs the storm's energy, even during slow-moving storms, and helps prevent damages to structures and infrastructure.

Coastal engineers expect that large storms will induce sediment transport from the nourished beach and move sand offshore. When this happens, waves begin to break farther from the shoreline, thus weakening their force before they reach the shoreline itself. In this way, beach nourishment projects help protect dunes and property from further erosion, decrease flooding, and limit how far ashore storm surge will go. A wide, flat beach berm with a sufficient volume of sand keeps the erosive power of the waves from reaching and destroying the dunes and structures and can reduce damages significantly from waves, inundation, and erosion. Without beach nourishment, the starting point for damage would be farther onshore; a nourished beach, with sufficient sand volume and healthy dunes, absorbs the storm's energy, even during slow-moving storms, and helps prevent damages to structures and infrastructure.

During construction of a beach nourishment project, sand is placed so that natural coastal processes can reshape the nourished beach into the desired configuration as intended by coastal engineers The dry beach may seem "overbuilt" during construction, since sand is often placed on the shore at fairly steep slopes. After construction, it is normal for the newly nourished beach to readjust and change substantially within the first few months. Engineers expect modest waves to move and spread the sediment so that the nourished beach can begin assuming a more natural form. This sediment will continue to move offshore, so that larger waves are prevented from reaching the shore, and along the shore. This movement of sediment, while decreasing the width of the nourished beach somewhat, is not erosion; rather, it indicates that the project is performing as designed.

During construction of a beach nourishment project, sand is placed so that natural coastal processes can reshape the nourished beach into the desired configuration as intended by coastal engineers The dry beach may seem "overbuilt" during construction, since sand is often placed on the shore at fairly steep slopes. After construction, it is normal for the newly nourished beach to readjust and change substantially within the first few months. Engineers expect modest waves to move and spread the sediment so that the nourished beach can begin assuming a more natural form. This sediment will continue to move offshore, so that larger waves are prevented from reaching the shore, and along the shore. This movement of sediment, while decreasing the width of the nourished beach somewhat, is not erosion; rather, it indicates that the project is performing as designed.

Shore protection projects are designed to retain and rebuild natural systems such as bluffs, dunes, wetlands, and beaches and to protect structures and infrastructure landward of the shoreline. Shore protection not only can reduce a storm's potential physical and economic damages from waves, storm surge, and the resulting coastal flooding but also can mitigate coastal erosion and even help restore valuable ecosystems that may have been lost such as beaches, wetlands, reefs, and nesting areas.

Shore protection projects are designed to retain and rebuild natural systems such as bluffs, dunes, wetlands, and beaches and to protect structures and infrastructure landward of the shoreline. Shore protection not only can reduce a storm's potential physical and economic damages from waves, storm surge, and the resulting coastal flooding but also can mitigate coastal erosion and even help restore valuable ecosystems that may have been lost such as beaches, wetlands, reefs, and nesting areas.

In late 2012, Hurricane Sandy struck and devastated parts of the Northeastern United States, causing more than $50 billion in damage to our communities and infrastructure. The storm's effect on the coastlines was equally devastating, with millions of cubic yards of sand raked away from our coast, making many coastal communities extremely vulnerable to future storms.

In January 2013, the president signed the Disaster Relief Appropriations Act of 2013, authorizing and funding the U.S. Army Corps of Engineers to take steps to reduce that vulnerability through repairing, restoring, and constructing coastal storm risk management projects in the Northeast.

Although a lot of engineering goes into planning, designing, and constructing hard structures such as levees, walls, tidal barriers, and pump stations. Engineering is crucial to building and replenishing beaches, as well.

Beaches are important features for coastal storm damage risk management. Bluffs, dunes, berms and offshore sand bars reduce the risk of damage to property and infrastructure by absorbing and dissipating the energy of breaking waves. The Corps' beach projects are designed and engineered to work like a natural beach, allowing sand to shift continuously in response to changing wave action and water levels.

Beach nourishment will reduce but not eliminate risks because storm severity is unpredictable, and can exceed risk reduction design levels . To ensure a beach continues to meet its design criteria and purpose, additional sand must be added periodically to a nourishment project. These nourishment cycles provide opportunities to reevaluate beach performance and sea-level change.

The Army Corps' beachfill projects, authorized and funded after Hurricane Sandy, incorporate the latest science, including sea-level change, future adaptation of hard features, and lessons learned from Hurricane Katrina.

Changing sea levels throughout the Northeast, coupled with improving coastal flood risk analysis technologies can lead to changes in project planning, design, and nourishment.

To address these changes, the Corps has institutional mechanisms in place that allow for adjustments in project dimensions during the life of the project to maintain the design level of coastal storm risk management.

Beachfill projects can account for changes sea levels by adjusting elevations, widths and volumes, based on the best currently available information, explained Jeffrey Wisniewski, a Senior Engineer for the Corps' Sandy Recovery Program.

"Sandy beachfill projects funded by the Disaster Relief Appropriations Bill typically provide for periodic beach renourishment and monitoring over the life of the project," said Wisniewski. "We have the flexibility to make adjustments with regard to the height of that beach berm or dune to take into account the latest available information on sea levels."

The Corps recently completed a report designed to help local communities better understand changing flood risks associated with climate and sea-level change and to provide tools to help those communities to attain improved resiliency by better preparing for future flood risks.

The North Atlantic Coast Comprehensive Study builds on lessons learned from Hurricane Sandy and attempts to bring to bear the latest scientific information planning tools and models available for state, local, and tribal planners, as well as the NACCS Framework and technical products which can be applied throughout the North Atlantic, and to other coastlines in the United States and internationally.

The conclusions of the report, including various coastal storm damage risk management strategies communities can use to adapt to increased flood risk, can be found here: http://www.nad.usace.army.mil/compstudy