Beach builders

February 2014 » Web Exclusive » PROGRESSIVE ENGINEERING
U.S. Army Corps of Engineers, New York District, is overseeing a 60-project, $3 billion initiative to develop long- and short-term risk-reduction strategies for coastal communities.
JoAnne Castagna, Ed.D.

On Oct. 29, 2012, Hurricane Sandy’s 80-mph winds and 30-foot-high waves pounded the East Coast of the United States. The storm made its way from Florida up to Rhode Island. New York and New Jersey, which both are within the U.S. Army Corps of Engineers, New York District’s area of responsibility, were hit especially hard. The surge of sea water inundated coastal communities, flooding roads and transportation systems and damaging electrical facilities, causing widespread power outages.

Figure 1: Locations of U.S. Army Corps of Engineers, New York District, Post Sandy dredging and beach restoration efforts

Immediately after the storm, the Army Corps was on the ground responding through its own response authorities and providing disaster response assistance for the Federal Emergency Management Agency. Army Corps-trained response teams from around the nation came to the region to assist the New York District in unwatering subway tunnels, providing temporary emergency electrical power to critical facilities, removing tons of debris, and closing barrier island breaches. Sandy is also responsible for 60 deaths, $19 billion in damages, and millions of cubic yards of sand removed from miles of coast. This sand loss makes coastal communities extremely vulnerable to future storms.

In January 2013, Congress signed the Hurricane Sandy Disaster Relief Appropriations Act of 2013 — the “Sandy Bill” — giving the Army Corps funding and authority to take steps to restore coastal projects and navigation channels impacted by Sandy and reduce risk from storms to coastal communities in the Northeast.

The Army Corps is carrying out this mission in several simultaneous steps. Districts in the Northeast are repairing and restoring previously constructed coastal projects impacted by Sandy, which includes replacing lost sand on beaches. They also are progressing on projects and studies that were underway before Sandy. In addition, the Army Corps’ North Atlantic Division, of which the New York District is part, is working on the North Atlantic Coast Comprehensive Study that will provide strategies to help reduce risk from coastal storms to coastal communities.

Bringing back the sand

Hurricane Sandy removed more than 6 million cubic yards of sand from New York District’s coastal projects in New York and northern New Jersey. The District is replacing this sand and restoring previously built dunes and beach berms, as well as repairing other risk-reduction features such as levees and tide gates.

Restoring coastal projects, including replacing lost sand, is important to reducing coastal storm risks in the future. A beach’s size, shape, and sand volume help determine how well the beach can reduce risk to a developed community during a storm. These elements of a beach offer a level of natural protection against hurricanes and coastal storms by absorbing and dissipating the energy of breaking waves and storm surge. The District is replacing the sand that was lost from Sandy, plus adding additional sand to restore beach projects back to their originally constructed designs. This means the placement of even more sand than was lost due to Sandy.

The District is dredging 16 million cubic yards of sand from navigation inlets and offshore borrow areas and placing it on five coastal projects in New York and two in New Jersey. As of October 2013, the District had placed an estimated 4 million cubic yards of sand on beaches within its area of responsibility. The District completed sand pumping operations in Coney Island, Rockaway Beach, with a second sand pumping contract scheduled to begin in January 2014, and were placing sand at Gilgo Beach. The District also was repairing a risk-reduction project in Oakwood Beach on Staten Island that involves repairing a damaged levee and tide gate. Additional work on Fire Island West of Shinnecock Inlet and Westhampton will begin in 2014.

The Army Corps pumped and spread sand onto Coney Island Beach. Photo: Chris Gardner, U.S. Army Corps of Engineers, New York District, Public Affairs

In New Jersey, the District recently completed the first of four sand pumping contracts for the Sea Bright to Manasquan Project and expected to begin work on its Keansburg Project in November 2013.The Keansburg Project, which includes Keansburg, East Keansburg, and Laurence Harbor, will include sand replenishment and repairs to levees damaged by Sandy. All of this work is expected to be completed by summer 2014.

The Sea Bright to Manasquan Project was the world’s largest sand placement project by volume when it was initially constructed from 1994 to 2001. It involved the placement of roughly 20 million cubic yards of sand along about 18 miles of New Jersey beaches, reducing risks for multiple communities. The District is replacing 8 million cubic yards of sand throughout the project area, which would be enough material to build nearly six Empire State Buildings out of sand.

Wetland protections threatened

Left to themselves, coastal wetlands can resist rapid levels of sea level rise. But humans could be sabotaging some of their best defenses, according to a Nature review paper published from the Virginia Institute of Marine Science and the Smithsonian Environmental Research Center.

Wetlands, with their ability to buffer coastal cities from floods and storms, and filter out pollution, offer protections that could be lost in the future. But according to co-authors Matt Kirwan and Patrick Megonigal, higher waters aren’t the key factor in wetland demise. Thanks to an intricate system of feedbacks, wetlands are remarkably good at building up their soils to outpace sea level rise. The real issue, they said, is that human structures such as dams and seawalls are disrupting the natural mechanisms that have allowed coastal marshes to survive rising seas since at least the end of the last Ice Age.

“Tidal marsh plants are amazing ecosystem engineers that can raise themselves upward if they remain healthy, and especially if there is sediment in the water,” said Megonigal of the Smithsonian Environmental Research Center. “We know there are limits to this, and worry those limits are changing as people change the environment.”

When marshes flood during high tide, mineral sediment settles out of the water, adding new soil to the ground. When sea level rise accelerates and flooding occurs more often, marshes can react by building soil faster. Photo: Matt Kirwan, Virginia Institute of Marine Science

“In a more natural world, we wouldn’t be worried about marshes surviving the rates of sea level rise we’re seeing today,” said Kirwan, the study’s lead author and a geologist at the Virginia Institute of Marine Science. “They would either build vertically at faster rates or else move inland to slightly higher elevations. But now we have to decide whether we’ll let them.”

When marshes flood during high tide, mineral sediment settles out of the water, adding new soil to the ground. When sea level rise accelerates and flooding occurs more often, marshes can react by building soil faster. Even erosion can work in favor of wetlands, as sediment lost at one marsh can be deposited on another. While a particular wetland may lose ground, the total wetland area may remain unchanged.

But everything has a threshold. If a wetland becomes so flooded that vegetation dies off, the positive feedback loops are lost. Similarly, if sediment delivery to a wetland is cut off, that wetland can no longer build soil to outpace rising seas.

Direct human impacts have the most power to alter those thresholds, the scientists reported. Groundwater withdrawal and artificial drainage can cause the land to sink, as is happening right now in Chesapeake Bay. Because of this kind of subsidence, eight of the world’s 20 largest coastal cities are experiencing relative sea level rise greater than climate-change projections. Dams and reservoirs also prevent 20 percent of the global sediment load from reaching the coast.

Conventional ways of protecting coastal property, such dykes and seawalls, keep wetlands from moving inland and create a “shoreline squeeze.” Photo: Jim Titus, U.S. Environmental Protection Agency

In addition to building vertically, marshes can also respond to sea level rise by migrating landward. However, human activities have hindered this response as well, the authors said. Conventional ways of protecting coastal property, such dykes and seawalls, keep wetlands from moving inland and create a “shoreline squeeze,” Kirwan said. Because rates of marsh-edge erosion increase with rates of sea level rise, the authors warned that the impacts of coastal barriers will accelerate with climate change.

Information provided by the Virginia Institute of Marine Science

While some of the coastal restoration work started during the height of beach season, the District has gone to great lengths to mitigate the impact on recreation.

“The beaches weren’t closed,” said Anthony Ciorra, chief, coastal restoration and special projects branch, New York District, U.S. Army Corps of Engineers. “We only closed off 1,000-foot sections of the beaches at a time to perform our work. Once a section was completed, we opened it up with a newly restored beach ready for the public’s enjoyment and moved to another portion. We couldn’t afford not to work because hurricane season is upon us. It’s a matter of public safety.”

Restoring navigation

As part of post-Sandy recovery efforts, the Army Corps is also restoring dozens of navigation channels and structures throughout the Northeast that were impacted by Sandy. This includes repairing breakwaters, jetties, bulkheads, and revetments, as well as dredging federal navigation channels altered as a result of Sandy.

New York District has already begun this work in its area and it is all expected to be completed by spring 2015. To reduce costs and increase efficiency, the District is combining missions by using sand dredged from navigation channels to restore beach projects where feasible.

Pre-Sandy coastal work lessened the blow

For years, the District has maintained coastal projects in New York and New Jersey. Although the massive storm overwhelmed most coastal risk-reduction projects, they still helped mitigate damages during the storm.

“Our projects are designed to reduce the level of damage from more frequent lower-intensity storms, but I do believe our coastal projects did minimize Sandy’s impact,” Ciorra said. “Areas that had our projects fared better than areas that didn’t.”

Then New York City Mayor Michael Bloomberg’s office stated that the Army Corps’ risk-reduction project at Plumb Beach along the Belt Parkway in southern Brooklyn likely prevented a breach of the adjacent highway, thus protecting a vital transportation link. Work on the first phase of the Plumb Beach Project, including building a dune and beach berm to reduce risks to the highway, was done just before Sandy hit. Work on the second phase that includes construction of groins and a breakwater to ensure the longer-term resiliency of the dune and beach berm was expected to be done by the end of 2013.

Westhampton along the south shore of Long Island, N.Y., was another area where a New York District project performed well during Sandy. Ciorra said, “In Westhampton where we had constructed a dune and berm, there was less damages to that community than in nearby areas that didn't have any projects.”

Even projects not necessarily designed to reduce risk, like the New York District’s restoration of marsh islands in Jamaica Bay, N.Y., may provide a blueprint for future approaches to coastal storm damage risk reduction (see “Wetland protections threatened”). “Marsh islands can act as a natural protective buffer to the mainland behind them during storms by absorbing wave energy,” said Lisa Baron, project manager, New York District, U.S. Army Corps of Engineers.

In September 2013, the U.S. Army Corps of Engineers was in the process of replenishing the beach in Sea Bright, N.J. Photo: Greg Kohl, AC Photos

Progressing on coastal projects and studies

When Hurricane Sandy hit, New York District also had several projects authorized by Congress for construction, but not built. Some factors contributing to this included lack of federal or non-federal funding and lack of local support or local opposition. The District also had several studies underway looking at coastal risk reduction for communities in New York and northern New Jersey.

After Sandy, and with funding from the Sandy Bill, New York District is working on coordinating with local partners and moving the unconstructed projects toward construction and advancing the ongoing studies while incorporating lessons learned from Sandy.

The next Sandy?

The Sandy Bill called on the Army Corps’ regional North Atlantic Division to study ways to help reduce risk from storms to coastal communities throughout the Northeast. The Division has assembled a team of professionals from its District offices; federal, state, and local agencies; and academia to collaborate on the North Atlantic Coast Comprehensive Study. The team is studying the 31,000 miles of coast from Northern Virginia to Maine that falls under the Division’s responsibility. Its goal is to develop a framework of strategies that can be used by agencies to protect coastal communities adversely affected by Sandy.

The team is studying 38 coastal areas to see how they can be better protected by using various measures, such as dunes, flood walls, and bulkheads. Presently, the team is considering almost 30 risk management measures, including some of the strategies proposed by the City of New York in its recently published report from its Special Initiative for Rebuilding and Resiliency.

“We are trying to place the right combination of measures in the right coastal locations based on the area’s infrastructure, population, social and environmental vulnerabilities,” said Lynn Bocamazo, engineering division, U.S. Army Corps of Engineers, New York District, who is on the team.

Donald E. Cresitello, planning division, U.S. Army Corps of Engineers, New York District , who is also on the team, said, “There is a lot of interest in this study, especially from communities severely impacted by Sandy and [that] have no federal projects or studies in their area. They want to be assured they are going to be included in the study and have some risk reduction from future storms. This study looks at those areas.”

Ciorra, who is not on the team, added, “Most of our projects are designed to reduce the level of damage from more frequent, lower-intensity storms. The study may look at storms like Sandy that may become more frequent in the future. Because of this, the team may have to develop a more robust plan for these projects because the storm that we estimated as being a 500-year storm event may now be a 100-year storm event.”

The team is doing this. The strategies it is developing will look to reduce the risk from a 100-year storm event, plus it is adding 3 feet of stormwater to account for potential 100 years of sea level rise.

“This study will provide agencies valuable information they can use to save time and resources on future studies. The environmental and economic analysis and models that will come from this study will already be prepared for others to benefit from,” said Bocamazo.

The study will be completed in January 2015. A draft of the study will be available to the public for review and comment. Sign up to receive regular study updates at www.nad.usace.army.mil/CompStudy.

Learn more about the Army Corps’ New York District’s post-Hurricane Sandy work at www.nan.usace.army.mil/Sandy.

JoAnne Castagna, Ed.D., is a public affairs specialist and writer for the U.S. Army Corps of Engineers, New York District. She can be reached at joanne.castagna@usace.army.mil.​

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