Proceedings of the U.S. Geological Survey (USGS) Sediment Workshop, February 4-7, 1997

SEDIMENT RESEARCH IN THE MINERALS MANAGEMENT SERVICE'S MARINE MINERALS PROGRAM

As far back as 1989, the Minerals Management Service (MMS) detected a trend toward greater interest in sand resources further off the shores of U.S. coastal States. Anticipating that the Federal outer continental shelf (OCS) may become an economically viable source for sand and gravel for commercial and coastal restoration use, MMS began funding a series of studies that first evaluated the state of knowledge of the environmental impacts of sand dredging and then progressed to studies to answer critical questions needed for future decisions.

Erosion is a significant problem affecting beach or wetland areas in virtually every coastal region of the United States. State waters (generally within 3 nautical miles of the coast) and onshore areas have been the traditional sources of sand for coastal restoration projects. However, the availability of sand from these sources has been declining. Suitable nearshore sand is very limited in some areas and its use may present certain environmental risks. Many onshore sources have been depleted or face public opposition to their continued use. In some cases, source areas have proven more valuable to owners as prime commercial real estate.

In 1993, Congress recognized the potential benefits of using Federal offshore sand for coastal restoration projects and crafted legislation to remedy what was considered an impediment to State and local government access to Federal sand resources. The impediment was the competitive leasing provision of the Outer Continental Shelf Lands Act (OCSLA). Under this provision, State and local governments expressed little interest in pursuing rights to Federal sand through a lengthy competitive process that could ultimately award the resource to a another (higher) bidder. They viewed this uncertainty as an unacceptable risk. Congress remedied the situation by passing Public Law 103-426 in October 1994 which amended the OCSLA by providing the Secretary of the Interior with new authority to negotiate agreements for use of Federal sand, gravel or shell resources under certain circumstances. The passage of this law has greatly accelerated the demand for Federal offshore sand specifically for certain public works related projects

Since 1991, the MMS has invested over $1.7 million dollars through its Environmental Studies Program in environmental studies primarily related to sand dredging impacts. Relative to sediment research, the MMS has or is funding studies to address such questions as the post-dredging rates of benthic recolonization and sediment grain size changes associated with the dredging activity, the nature, extent, and effect of surface and benthic turbidity plumes from dredging operations, and the potential for wave climate changes and coastline effects resulting from sea floor alteration associated with the dredging of site-specific offshore shoal areas. A primary example of the present focus of the MMS program is an environmental study presently being conducted off the coast of Virginia. In September 1995, the MMS signed a cooperative agreement with the Virginia Institute of Marine Science (VIMS), Gloucester Point, VA and an Interagency Agreement with the United States Geological Survey (USGS), Office of Marine Geology, Reston, VA to collect environmental data and information to address environmental questions raised by the potential for mining sand from the inner continental shelf offshore Virginia. This information will directly benefit those parties charged with planning or making decisions as to the potential use of this sand for restoration of Virginia Beach or other coastal areas within the State of Virginia. The study area encompasses a coastal sector approximately 24 kilometers in length, beginning just below the community of Sandbridge and extending northward to Cape Henry at the Chesapeake Bay entrance and extends from the surf zone outward to the 15-meter depth contour. The study area encompasses the three most likely areas for sand mining: an area offshore of Rudee Inlet, Sandbridge Shoal, and an area in the vicinity of the major entrance channel to Chesapeake Bay.

The VIMS work is composed of five specific tasks:

• Benthic resource and habitat mapping using a sediment profile camera - The primary objective of this task is to assess baseline benthic ecological conditions in and around the potential sand borrow areas. This information will be used to assess the potential for biological impacts from sand dredging.
• Nearshore wave and current observations and modeling - The objective of this task is to study the potential of bathymetric modifications induced by sand mining to waves as they cross the study area.
• Bathymetric data gathering for model use - Will provide supplemental bathymetric information for the modeling effort described above.
• Shoreline processes, sediment, and sediment transport evaluation - This task will evaluate the impacts of offshore dredging and consequent beach nourishment in terms of the potential alteration in sediment transport patterns, sedimentary environments, and impacts to local shoreline processes.
• Acoustic Doppler Current Profiler (ADCP) current measurements /observations /modeling - (to be undertaken by Old Dominion University) - An ADCP will be used to define the currents at the potential sand mining sites and to define the physical regime between these sites and the shoreline. A numerical model will then be used to predict the effects resulting from alterations to the local bathymetry on the local current field.

The USGS portion of the study involves microfaunal ecology and impact assessment. USGS is investigating the ecology of benthic foraminifera and ostracods (Crustacea) from the Virginia continental shelf habitats identified as potential sites for offshor sand dredging. This information will be used to evaluate the recolonization potential of these sites on the basis of species ecology and wider zoogeographic distribution in adjacent areas.

The entire study is anticipated to take approximately 23 months from date of award. Similar field efforts are planned to take place offshore New Jersey, Maryland, Delaware, North and South Carolina, and the east coast of Florida.