The MMS/GOMR is supporting the development of environmental assessments in coming years that propose to use sand resources from the Federal Outer Continental Shelf (OCS) for coastal restoration and levee construction. Available sand resources are recognized on Ship Shoal, a submerged remnant of a barrier island system from a now-abandoned Mississippi delta lobe located 12 mi off the central Louisiana coast. Water depths from 3 to 9 m (9-30 ft) occur across the crest of Ship Shoal. Estimates report that the crest and flanks of Ship Shoal contain approximately 1.5 billion yd³ of sand (Figure 1). Geological and geophysical studies of Ship Shoal have identified these sandy sediments to be an ideal source material to restore and replenish the rapidly eroding barrier islands protecting coastal Louisiana.

Figure 1. Isopach (thickness) map showing high-quality sand resources on Ship Shoal over a bathymetric base (University of New Orleans, Coastal Research Laboratory).

The deltaic and coastal wetlands of southern Louisiana continue to be lost at rates estimated at between 25 and 40 mi² per year. Subsidence of the land is caused by natural processes including (1) compaction of deltaic sediments, (2) faulting with downward displacement toward the Gulf of Mexico, and (3) sea-level rise. These natural phenomena can be aggravated by human activities such as groundwater and hydrocarbon extraction. Moreover, land loss has been magnified by changes in the Mississippi River’s flow parameters and sediment load distribution after decades-long construction of upstream navigation and flood control systems.

The barrier islands along coastal Louisiana act to dampen wave energy and tidal surge during tropical storms that erode the islands as well as back-barrier wetlands and coastal lowlands. Eventually, fresh- and brackish-water wetlands are converted to salt wetlands or finally open water. The barrier island systems protecting the Barataria and Terrebonne basins, Isles Dernieres and Timbalier Islands, are eroding at alarming rates and are projected to effectively disappear by 2012 without intervention or mitigation. The recent back-to-back Tropical Storm Isadore and Hurricane Lili in 2002 served to focus attention on just how rapidly this process is occurring.

At risk are 3 million ac³ of coastal plain and wetlands that contain (1) over 1.5 million people south of Interstate 10, (2) abundant animal and plant life including many endangered species, (3) sensitive estuary ecosystems that yield 1.1 billion pounds of finfish and shellfish landings per year for the U.S. consumer, and (4) billions of dollars of infrastructure in the form of oil and gas wells, platforms, pipelines, roads, refineries, bridges, cities, towns, canals, and ports; through which perhaps 80% of the oil and gas produced in the U.S. Gulf of Mexico or transported to the U.S. from foreign markets enters or is transferred.

The 1990 Coastal Wetlands Planning, Protection, and Restoration Act (CWPPRA; also known as the Breaux Act) funds wetland creation, island restoration, and beach nourishment projects nationwide in a cost-sharing arrangement between local sponsors and the Federal Government. Since 1997, all elements of Louisiana’s coastal restoration planning were consolidated into a multiagency Louisiana Coastal Area Ecosystem Study to assist in establishing priorities for future projects. The MMS is a participant. Other Congressional actions authorize flood control structures and levees for coastal Louisiana areas, usually through the U.S. Army Corps of Engineers (COE).

The first CWPPRA projects proposing to use Ship Shoal sand are two barrier island restoration projects sponsored by the State of Louisiana on Isles Dernieres, an important barrier island arc that has undergone significant erosion (Figure 2).

Figure 2. Map illustrating over 100 years of land loss on Isles Dernieres (University of New Orleans, Coastal Research Laboratory).

Two polygons each 10 mi² in size are proposed on the crest of Ship Shoal as borrow sites for sand dredging (Figure 3). The first project is to fill a tidal channel called New Cut between Trinity and East Islands using 1 million yd³ of sand from South Pelto Blocks 12 and 19. The second project is to restore the west flank of Whiskey Island using 2.5 million yd³ of sand from Ship Shoal Block 88. A third project proposing to use Ship Shoal sand is sponsored by the COE. In the period 2004-2012 the COE proposes to use 12 million yd³ of sand from South Pelto Block 13 as the foundation material for a 72-mi flood control levee in Terrebonne Parish (the Morganza levee).

The MMS is currently carrying out the environmental analyses required by the National Environmental Policy Act for these proposals. The barrier island restoration projects are scheduled to begin during the 2^nd quarter of 2004 and last about 4 months each. The Morganza levee project is scheduled to begin late in 2004 and would involve approximately 2 years of continuous dredging and impoundment of sand in two temporary holding areas near the Houma Navigation Canal until needed for levee construction (Figure 3).

Figure 3. Map showing (1) sand borrow polygons in the Ship Shoal and South Pelto areas (2) OCS block numbers, (3) distances between sand borrow polygons, Isles Dernieres restoration projects, the project’s shore base at the Port of Terrebonne at Houma, Louisiana, and temporary sand storage areas for the Morganza levee project.

Link to MMS National Sand and Gravel Program