Rehoboth Beach/Dewey Beach

Storm Damage Reduction Project

On February 4, 2005, after more than ten years of engineering project design, construction planning, economic analyses, and feasibility studies, the first sand from the federal project was pumped onto Dewey Beach. The dredging/beach construction stage of the Rehoboth Beach/Dewey Beach Storm Damage Reduction Project is now underway.

The Rehoboth Beach/Dewey Beach Storm Damage Reduction Project is a beach nourishment project designed to provide coastal storm damage reduction and shoreline protection along 2.5 miles of ocean front from the southern end of Dewey Beach to the northern end of Rehoboth Beach.

The U. S. Army Corps of Engineers is managing project construction, and is providing 65 percent of the $18 million cost. The Delaware Department of Natural Resources and Environmental Control (DNREC) is providing the balance of funds as the non-Federal sponsor.

Construction will start at the south end of Dewey Beach and then will proceed north to the northern limits of Dewey Beach. Once Dewey is completed, the operation will move into Rehoboth Beach. To ensure public safety, 1000-foot segments of beach will be closed off as nourishment progresses, restricting public access to the active construction zone.

Great Lakes Dredge & Dock Company, the largest dredging contractor in the U.S. and one of the largest in the world, is the prime contractor. They have successfully conducted restoration projects at beaches throughout the United States including renourishment projects in Ocean City, Maryland; Brevard County, Florida; and Fire Island, New York.

Hopper Dredging

A hopper dredge is capable of dredging material, storing it onboard, transporting it to the disposal area, and pumping it onto the project site. A hopper dredge works by dredging sand from the borrow site (usually distant from the shoreline) into a hopper (storage area) and then transporting the material to a pump-out buoy located just off-shore of the nourishment area. Once the hopper dredge arrives at the pump-out buoy, the dredge connects to the discharge pipeline on the buoy. The dredge mixes the dredged material with water to form a slurry and pumps the slurry from its discharge manifold through the hoses and pipeline. The material is pumped from the hopper, through the discharge line which runs along the ocean floor, and up onto the beach nourishment area.

The Manhattan Island is a “trailing suction” hopper dredge, and it operates much like a giant vacuum cleaner. At the designated borrow site, the dredge lowers drag arms over the side to the ocean bottom. As the dredge moves forward, the drag arms such a slurry (a water and sand mixture) from the ocean bottom. The slurry passes through the drag heads and pipelines into the hopper.

With all pumps and drag arms operating, the Manhattan Island fills its hopper with slurry in a few hours; however, pumping continues to allow sediment to displace water in the hopper and obtain a maximum load of as much as 3,600 cubic yards of sediment. Once attached to the mooring buoy and discharge line, it takes approximately 1 hour to pump the sand from the hopper onto the beach.

After the slurry of sand and water is pumped onto the beach, the material is re-worked by bulldozers so that the constructed beach meets engineering design specifications. Stakes and poles with marked survey elevations are used to ensure that correct dimensions and elevations are achieved.

The Manhattan Island – General Specifications

The 282 foot Manhattan Island dredge is well suited to work in the unprotected waters of Delaware’s Atlantic coast. With a hopper capacity of 3,600 cubic yards, her draft is 19.55 feet when loaded (9.5 feet light). The Manhattan Island’s nominal digging depth range is 70+ feet, and her loaded sailing speed is 10.5 knots (11 knots light). According to information provided by Great Lakes Dredge & Dock Company, a bow thruster augments her twin-screw propulsion system, and her shallow draft and high maneuverability allow operation in relatively tight quarters. The Manhattan Island is equipped with state-of-the-art dredging production and operations monitoring instrumentation and an electronic positioning system.

General Project Overview

• The project will cover a total length of 13,500 feet (2.5 miles).

• Project design: approximately 1.7 million cubic yards of sand will be pumped from an offshore borrow area to construct a beach and dune system.

• The source of sand for initial construction and subsequent periodic nourishment is a borrow area (Area G) located approximately 2.6 miles east of Indian River Inlet.

• Beach design:

- Rehoboth: 125-foot wide beach and 25 foot wide dune crest

- Dewey: 150-foot wide beach and 25 foot wide dune crest

• Dune design: dunes will be built to an elevation 6-foot above the beach.

• Crossovers: pedestrian, handicap and maintenance vehicle crossovers will be constructed at designated locations.

• Sand fence will be installed and beach grass will be planted.

• Storm water outfall extensions will be constructed in Rehoboth Beach only (to be constructed by others).

Estimated Project Costs (information provided by USACE and DNREC)

• Initial project construction cost is approximated at $10,324,560 and the estimated cost of periodic nourishment per cycle (approximately every 3 years) is $4.0 million.

• Total estimated project cost for the beachfill and dune system is $118 million over the 50-year project life. This cost estimate includes initial construction costs, periodic nourishment, major rehabilitation, and project monitoring over 50 years.