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Research

USGS Research Contributes to Assateague Island Restoration—Mitigating 70 Years of Coastal Erosion Due to Ocean City Inlet Jetties


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map of changes in the shorelines of Fenwick Island and Assateague Island between 1849 and 1980
Changing shoreline: Changes in the shorelines of Fenwick Island and Assateague Island between 1849 and 1980 illustrate the effects of the two large jetties at Ocean City inlet on coastal sediment transport along the adjacent coast.
Coastal erosion, a serious and widespread societal issue affecting all the coastal regions of the United States, results from complex geologic and oceanographic processes, such as storms, changes in sediment supply at the coast, and sea-level rise. During the past century, however, manmade alterations in the coastal zone have become increasingly responsible for a share of the erosion. All of this erosion is taking place at the same time as explosive population growth and development along all coasts.

Ocean City inlet, MD, is one of the most striking examples of the unintended consequences of engineered inlets causing increased erosion of adjacent barrier islands downdrift from the jettied inlet.

The Ocean City inlet opened during a 1933 hurricane, and soon after, the twin stone jetties were built by the U.S. Army Corps of Engineers (USACE) to maintain the inlet for navigation. However, the jetties also severely disrupted littoral-inlet processes, trapped sand on the north side of Fenwick Island (site of the Ocean City amusement park and parking lot), and severely starved Assateague Island National Seashore to the south of sand.

The result of almost 70 years of disrupted sand transport along the coast has been an offset in the two barrier islands—Fenwick and Assateague—by approximately 1 km, along with accelerated erosion, reduction and alteration in beach-berm heights, and loss of critical beach and dune habitats. The effects attributable to the jetties have extended about 15 km southward from the inlet.

To mitigate the effects of Ocean City inlet, a bold plan of coastal restoration began in August 2002, with a price tag of $63 million. The restoration is a partnership between the National Park Service (NPS), the USACE, and the Minerals Management Service (MMS).

The plan to restore Assateague consists of an initial, short-term phase in which 1.8 million cubic yards of sand dredged from Great Gull Bank, a linear shoal on the shelf, will be added to Assateague Island beaches.

A longer-term phase will follow over the next 25 years, in which sand will be mechanically dredged and bypassed from the Ocean City inlet area and placed on Assateague Island beaches on spring and fall schedules, in a phased approach intended to replicate natural processes.

This plan of restoration could become a model for other coastal regions where engineering structures have disrupted littoral processes, causing increased erosion and land loss.

Assateague Island Restoration Map
Assateague Island: Sand dredged from Great Gull Bank will be added to Assateague Island beaches (shaded black) to mitigate the erosion effects of the Ocean City inlet jetties.

Science has been instrumental in understanding the connection between inlet processes and erosion of Assateague Island and in designing the restoration plans. The USGS' role, in cooperation with the Maryland Geological Survey and the NPS, has been to

  1. map the geology and sedimentology of the sea floor and subsea floor;
  2. identify potential sand-borrow sites, including linear shoals, such as Great Gull Bank;
  3. map historical shoreline change, including recent use of lidar (light detection and ranging) technology (an airborne system that uses laser light to measure elevation); and, most recently,
  4. use Assateague Island, as one of a dozen sites nationwide, to evaluate the risk and vulnerability of coastal regions to future sea-level rise.

Related Web Sites
Assateague Island National Seashore
U.S. National Park Service
Maryland Department of Natural Resources
State of Maryland

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in this issue: Fieldwork cover story:
Seagrass Restoration in Tampa Bay

Tracking Pintail-Duck Population Decline

Remote Sensing of Coral Reefs at Biscayne National Park

Exploring the Puerto Rico Trench

Research Assateague Island Restoration

Outreach Dedication of New Lake Mead Research Vessel

Meetings Sea-Level Change Workshop

The Need for Better Scientific Understanding of Sea-Level Change

Remote-Sensing at Cape Cod National Seashore

Familiar Faces at Fall Meetings

Giving Interns a View of Science Career Paths

Staff & Center News Visiting Engineer Brings Modeling Expertise

Parsons Succeeds Lee as Acting Chief Scientist for WRCMG Team

Publications November Publications List


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Updated April 15, 2014 @ 01:53 PM (THF)