Explosive population growth (24 million increase from 1985 to 2005) and development in the coastal zone continues and demographic projections show that people will continue moving to the coast to live and recreate, placing more people and development at increasing risk. With the prospects of global climate change likely causing increased storminess and accelerating global sea-level rise in the near future, coastal regions will be more dynamic, experiencing even greater vulnerability to erosion, inundation, and storm-surge flooding.
Beach nourishment, a method of dredging sand from offshore areas and pumping it ashore to widen and elevate beaches and dunes to mitigate erosion has been in use since the 1920s when Coney Island was created. Nourishment is often viewed as a cost-effective and environmentally acceptable method for use on developed coasts to mitigate erosion, reduce storm and flooding risk, enhance recreation, and restore degraded ecosystems. Over the past 80 years about 650 million cubic meters of sand have been used throughout the U.S. coastal zone for beach nourishment. For beach nourishment to be viable, however, large volumes of high quality sand are necessary. Also, the sand deposits must be located reasonably close to the beaches being considered for nourishment and in water depths ranging typically from approximately 10 m, an approximate close-out depth for sediment transport, to 40 m, an approximate current limit of U.S. commercial dredging.
Continental shelf regions adjacent to the mainland are products of a complex geologic history and dynamic oceanographic processes, dominated by the Holocene marine transgression (>100 m sea-level rise) during the past 20,000 years. The area of the Exclusive Economic Zone, which extends 200 nautical miles seaward from the coast, is larger than the continental U.S. and contains submerged landforms that provide a variety of natural functions and societal benefits, such as: critical habitats for fisheries, ship navigation and home-land security, and engineering activities (i.e., oil and gas platforms, pipeline and cable routes, potential wind-energy-generation sites). Some parts of the continental margins also contain unconsolidated hard-mineral deposits such as sand and gravel that are regarded as potential aggregate resources to meet or augment needs not met by onshore deposits. As demonstrated recently by Hurricanes Katrina, Rita and Wilma, coastal erosion resulting from a combination of natural processes (i.e., storms, sea-level rise, sediment starvation, land subsidence) and anthropogenic activities (i.e., dams, flood control, dredging, coastal engineering structures), is pervasive for all coastal regions.
Marine Sand Bodies
Sand bodies on the inner continental shelf are often the most attractive sand sources for beach nourishment. Demand for offshore sand and gravel is likely to increase in the near future as accelerated sea-level rise and increased storminess increase coastal erosion and the vulnerability of coastal development to natural hazards. In addition, growing shortages of onshore supplies of aggregate in some parts of the country might be met using marine aggregates. However, for many regions offshore aggregates are sparse or unknown, and sand volumes needed to meet requirements (e.g. 50 yrs) and sustain long-term beach nourishment are uncertain.
Examples of the variety of marine sand bodies present on continental shelves are shown in the following figure.
GIS Maps and Marine Mineral Assessments
Because offshore areas of the are increasingly important for a variety of purposes, knowledge of the framework geology and processes is critical and comprehensive, up-to-date and integrated computer databases are needed by a variety of users. Products of greatest value are GIS-compatible base maps displaying thematic information such as seafloor physiography, geology, sediment character and texture, seafloor roughness, and geotechnical engineering properties. Digital geologic maps, based on unified national datasets showing the sedimentary character of continental margins, are critical for scientists to better understand and interpret the geologic history and sedimentary processes that formed and continue to modify the sea floor. These map products are useful to planners and managers for regulating, protecting, and managing coastal and offshore environments.
The U.S. Geological Survey in collaboration with other federal agencies (Navy/ONR, MMS, USACE, NOAA), coastal states, and universities, is leading a Nation-wide program to gather existing marine geologic data into the usSEABED system. This new data base is being used to conduct regional-scale assessments of offshore sand and gravel resources and for producing interpreted GIS maps that can serve a variety of needs. Sand and gravel assessments are in-progress for offshore New York and New Jersey and Louisiana and similar assessments are planned for other regions. Figure 2, a gridded map of New York Bight depicting the seafloor sedimentary character, is one example a GIS map product resulting from the assessment study.
The GIS seafloor maps for New York Bight and Louisiana, scheduled to be completed in 2006, are providing fresh scientific insights into the geologic character and development of continental margins and the assessments are providing useful information about the potential availability and quality of offshore sand and gravel deposits. The GIS maps and the usSEABED data they are based on may also provide useful information on benthic character and habitats useful for fisheries research and management.
Bliss, J.D., Williams, S.J., and Bolm, K.S., Modeling and assessment of marine sand resources, New York Bight, USA, Chapter M in Bliss, J.D., Moyle, P.R., and Long, K.R., eds., Contributions to Industrial-Minerals Research: U.S. Geological Survey Bulletin 2209-M.
Bliss, J.D., Williams, S.J., and Arsenault, M.A., Mineral resource assessment of marine sand resources in cape- and ridge-associated marine sand deposits in three tracts, New York and New Jersey, United States Continental Shelf, Chapter N in Bliss, J.D., Moyle, P.R., and Long, K.R., eds., Contributions to Industrial-Minerals Research: U.S. Geological Survey Bulletin 2209-N.
Buczkowski, B.J., Reid, J.A., Jenkins, C.J., Reid, J.M., Williams, S.J., and Flocks, J.G., 2006, usSEABED: Gulf of Mexico and Carribbean (Puerto Rico and U.S. Virgin Islands) Offshore Surficial Sediment Data Release: U.S. Geological Survey Data Series 146, Version 1.0, CD-ROM. ONLINE
Goff, J.A., Jenkins, C.J., and Williams, S.J., 2008, Seabed mapping and characterization of sediment variability using the usSEABED data base, Continental Shelf Research, 28, 614-633.
Poppe, L.J., Paskevich, V.F., Williams, S.J., Hastings, M. E., Kelly, J.T., Belknap, D.F., Ward, L.G., FitzGerald, D.M., and Larsen, P.F., 2003, Surficial sediment data from the Gulf of Maine, Georges Bank, and vicinity, U.S. Geological Survey Open-File Report 03-001, CD-ROM. Online at http://pubs.usgs.gov/of/2003/of03-001.
Poppe, L.J., Williams, S.J., and Paskevich, V.F., Editors, 2005, USGS East-coast sediment analysis: procedures, database, and GIS data, U.S. Geological Survey Open-File Report 2005-1001, DVD-ROM. Online at http://pubs.usgs.gov/of/2005/1001/.
Reid, J.M., Reid, J.A., Jenkins, C.J., Hastings, M.E., Williams, S.J., and Poppe, L.J., 2005, usSEABED: Atlantic coast offshore surficial sediment data release, U.S. Geological Survey Data Series 118, Version 1.0, CD-ROM. Online at http://pubs.usgs.gov/ds/2005/118.
Reid, J.A., Reid, J.M., Jenkins, C.J., Zimmermann, M., Williams, S.J., and Field, M.E., 2006, usSEABED: Pacific Coast (California, Oregon, Washington) offshore surficial-sediment data release: U.S. Geological Survey Data Series 182, version 1.0. Online at http://pubs.usgs.gov/ds/2006/182/
Williams, S.J., Arsenault, M.A., Buczkowski, B.J., Reid, J.A., Flocks, J., Kulp, M.A., Penland, S., and Jenkins, C.J., 2006, Surficial sediment character of the Louisiana offshore Continental Shelf region: a GIS Compilation, U.S. Geological Survey Open-File Report 2006-1195, online at http://pubs.usgs.gov/of/2006/1195
Williams, S.J., Arsenault, M.A., Poppe, L.J., Reid, J.A., Reid, J.M. and Jenkins, C.J., 2006, Surficial sediment character of the New York-New Jersey offshore Continental Shelf region: a GIS Compilation, online at http://pubs.usgs.gov/of/2006/1046/
Williams, S.J., Bliss, J.D., Arsenault, M.A., Jenkins, C.J., and Goff, J.A., 2007, Geologic characterization of shelf areas using usSEABED for GIS mapping, modeling processes and assessing marine sand and gravel resources. In: N. Kraus and J. Rosati, eds., Coastal Sediments ’07, American Society of Civil Engineers, p. 2473-2486.
Williams, S.J., Reid, J., and Manheim, F., 2004, A Bibliography of Selected References to U.S. Marine Sand and Gravel Mineral Resources, U.S. Geological Survey Open-File Report 03-300. Online at http://pubs.usgs.gov/of/2003/of03-300.
Williams, S. J., Jenkins, C., Currence, J., Penland, S., Reid, J., Flocks, J., Kindinger, J., Poppe, L., Kulp, M., Manheim, F., Hampton, M., Polloni, C., and Rowland, J., 2003, New digital geological maps of U.S. continental margins: insights to seafloor sedimentary character, aggregate resources and processes, Proceedings of the International Conference on Coastal Sediments 2003,: Corpus Christi, Tex., World Scientific Publishing Corporation and East Meets West Productions, Corpus Christi, Tex., 11 p., CD-ROM.
Williams, S.J., 1992, Sand and gravel - an enormous offshore resource within the U.S. Exclusive Economic Zone, in DeYoung, J.H., Jr., and Hammarstrom, J.M., eds., Contributions to Commodity Geology Research, U.S. Geological Survey Bulletin 1877, p. H1-H10.