Sand replenishment work taking place on Rockaway Beach New York. This beach had no dunes and was totally inundated with water after Hurricane Sandy. Photo credit: USACE.
After analyzing the success and failure of its beaches post-Hurricane Sandy the U.S. Army Corps of Engineers estimated that beach nourishment projects in the States of New York and New Jersey saved $1.3 billion in avoided damages. Now the Corps New York District is taking these findings to improve future beach nourishment projects.
The Corps is responsible for the coasts along New York City Long Island New York and the New Jersey coast as far south as Manasquan. In addition it’s responsible for the portions of the Passaic River Rahway River South River and the Raritan and Sandy Hook Bayshore that are affected by the coastal tides.
Anthony Ciorra senior program manager New York District U.S. Army Corps of Engineers said “The forces of Hurricane Sandy eroded approximately 6 million cubic yards of sand from the coasts of New York and New Jersey where the District has responsibility.”
The Corps has replenished these coasts with approximately 15 million cubic yards of sand. Ciorra said that some of the projects that were replenished in New York include Coney Island Beach Rockaway Beach Gilgo Beach west of Shinnecock and Westhampton Beach. In New Jersey Sea Bright to Manasquan and Keansburg were replenished.
HURRICANE SANDY ANALYSIS
After Hurricane Sandy the Corps examined its beach nourishment projects across the northeast U.S. many of which faced the greatest intensity of the hurricane.
The Corps performed an analysis along the northeast that identified what beach nourishment projects were more effective in reducing storm risk to the shore communities and the analysis showed that beach nourishment and dunes were important in some areas.
Ciorra said “The beaches that had previously received beach nourishment and dune construction sustained less damages and saved an estimated $1.3 billion in avoided damages along the New York District’s shorelines.”
One of the beach nourishment projects that demonstrated a great reduction in damages was Coney Island Beach in the Borough of Brooklyn New York City. The beach was designed to protect against storm surge and erosion. Hurricane Sandy’s surge pushed sand up and over the beach’s boardwalk but the impacts behind the constructed project were minimal and this was due to the beach’s high elevation. “As a result there was an estimated $494 Million in avoided damages to houses and structures” Ciorra said.
Another project was the Fire Island to Montauk Point – Westhampton Interim beach nourishment project on Long Island New York.
Lynn Bocamazo senior coastal engineer and chief of the New York District’s Engineering Division’s Hurricane Sandy Branch visited this beach after Hurricane Sandy and witnessed how the high dunes resulted in an estimated $107 million in avoided damages.
Bocamazo said that the dunes have grown to different heights along the project area and the shorter dunes in one location were the only ones topped by water during Hurricane Sandy. This showed that a dune and beach fill project significantly acted as a protective barrier to the water.
According to Bocamazo beaches that did not have beach nourishment and dunes prior to Hurricane Sandy experienced much more coastal damage. Some of these beaches sit right next to beaches that had been constructed and the comparison was striking.
Bocamazo also saw this in New Jersey. The Sandy Hook to Barnegat Project stood up well after Hurricane Sandy and resulted in an estimated $323 Million in avoided damages.
Within the Sandy Hook to Barnegat Project is a three-mile area in Deal to Loch Arbour New Jersey that never had beach nourishment where she saw one building completely demolished standing near a house that had minimal damage.
It was a similar situation in New York City at Rockaway Beach in the Borough of Queens where it didn’t have dunes and was totally inundated with water.
BEACH NOURISHMENT PROCESS
A sand replenished beach with dunes can prevent elevated ocean waters due to storms from inundating coastal communities. Beaches lose their sand over time due to wave action and longshore currents. When hurricanes and coastal storms occur like Hurricane Sandy the fierce breaking waves and elevated water levels can change the width and elevation of beaches and accelerate erosion.
Ciorra said “The Army Corps tries to match the sand to the native sand of the beach that is being nourished. This is done for environmental habitat consistency to be in balance with the forces of waves tides and currents and for the community beachgoer experience.”
The sand can be placed in different areas of a beach depending on the project design. Sand can be placed to increase the height and width of a berm of the beach. The berm is a flat area of the beach between the landward shore and the ocean where beach goers typically sun bathe.
The sand can also be placed offshore in an underwater berm or stockpiled on a feeder beach where the sand can naturally distribute to other parts of the project. The sand can also be used to create sand dunes. Sand dunes are areas of the beach where sand is elevated several feet to act as a buffer between the waves and stormwater levels and the structures landward of the beach.
Determining whether dunes are needed has become a more pressing question in the last few years especially after Hurricane Sandy.
Constructing a dune has to be necessary and cost effective. Ciorra said “For example one project area had a high backshore elevation. In this case a dune is not necessary if the land be-hind the beach is more than 18 feet above sea level. And in another project the beach already had a seawall that was more than 21 feet above sea level which acted as a de-facto more permanent dune.”
If it’s determined that a dune is necessary the dune’s sand volume itself isn’t very costly but how a dune is situated on a beach berm can make it a more costly project. Creating dunes pushes out the beach berm more oceanward because of the footprint of a dune.
If a berm is 75 or 100 feet wide and a dune is created that has a footprint of 50 feet wide this will reduce the size of a berm. It will then be necessary to add sand to that berm to increase its full design width.
Additional structures may be constructed to help maintain the beach nourishment work. For example groins are designed to retain sediment moving along the shore and help maintain the wide beaches by minimizing or slowing down erosion. Groins are shoreline structures that are perpendicular to the beach that are made of large boulders concrete steel or wood.
Beach renourishment is also a continual process. Sand on beaches naturally erodes and needs to be replenished with sand every few years depending on the location.
With these findings from Hurricane Sandy the New York District is re-examining areas that originally didn’t include dunes.
Atlantic hurricanes may occur every season from June to November but what is steadily occurring is sea level rise associated with climate change and the Corps believes that beach nourishment and dunes are an answer to dealing with this.
Ciorra said “Addressing this is straightforward the dunes can be made higher each time sand replenishment is done on a beach. The Army Corps performed a study and found out that it is cost effective to create a dune foundation now on a beach in anticipation of having to raise the dune in the future because of climate change.”
Dr. JoAnne Castagna is a public affairs specialist and writer for the U.S. Army Corps of Engineers New York District. She can be reached at email@example.com. Follow her on Twitter at http://twitter.com/writer4usacenyc