Florida Integrated Science Center

Geomorphology and Depositional Sub-environments of Assateague Island MD/VA

Robert A. Morton, Jeremy E. Bracone, and Brian Cooke
Open File Report 2007-1388

Contents

Project Description and Purpose
Project Maps
Project Data
Project Metadata
Further Reading

Project Description and Purpose

The U.S. Geological Survey is studying coastal hazards and coastal change to improve our understanding of coastal ecosystems and to develop better capabilities of predicting future coastal change. One approach to understanding the dynamics of coastal systems is to monitor changes in barrier-island sub-environments through time. This involves examining morphological and topographic change at time scales ranging from millennia to years and space scales ranging from tens of kilometers to meters. Of particular interest are the processes that produce those changes and determining whether or not those processes are likely to persist into the future. In these analyses of hazards and change, both natural and anthropogenic influences are considered. Quantifying past magnitudes and rates of coastal change and knowing the principal factors that govern those changes are critical to predicting what changes are likely to occur under different scenarios, such as short-term impacts of extreme storms or long-term impacts of sea-level rise. Assateague Island MD/VA was selected for detailed mapping of barrier island morphology and topography because the island offers a diversity of depositional sub-environments that are representative of other barrier islands along the middle Atlantic coast. The geomorphology and sub-environment map emphasizes the origins of the surficial features and it also serves as a basis for documenting which sub-environments are relatively stable, such as the barrier island core, and those that are highly dynamic, such as the beach and active overwash zones.

Project Maps

The Geomorphology and Depositional Sub-environments of Assateague Island MD/VA map was divided up into three map tiles and are provided as is in PDF format. For users of ESRI ArcMap GIS software, ArcMap 9.2 documents are available and can be read directly from this CD. Links for the ArcMap 9.2 documents can be found below the map.

Map Tiles in PDF format:

Click on the links below or the index map to download the Map Tiles in PDF format. You will need to have the free Adobe Acrobat® Reader installed on your computer to view and print the PDF maps.

Open File Report 2007-1388 Tile 1 of 3 (841 KB PDF)
Open File Report 2007-1388 Tile 2 of 3 (3.1 MB PDF)
Open File Report 2007-1388 Tile 3 of 3 (2.9 MB PDF)

Main Map Graphic

ESRI ArcMap 9.2 Documents

Map Tile 1 (.mxd file)
Map Tile 2 (.mxd file)
Map Tile 3 (.mxd file)

Project Data

The data used as reference for the map include 0.76 meter pixel resolution 1999 Digital Orthophoto Quadrangles (DOQ), 0.25 meter pixel resolution orthorectified aerial photography from 2003, historic aerial photographs, 1 meter pixel resolution NASA Experimental Airborne Advanced Research Lidar (EAARL) survey data from 2003 and 2004, and a 1993 Assateague Island data file showing a preliminary survey of island vegetation. Spatial accuracy of class boundaries vary between 1 and 7 meters due to the variability between the data sources. Each class is stored in a standard format shapefile viewable in any GIS software.

Links to data layers:

Data Directory - The folder on the cd containing all of the shapefile data.

Accretion Mounds: Low, oblong vegetated hills formed on the margins of overwash zones by the concentric accumulation of sand.
Accretion Mound Swales: Topographic depressions within an accretion mound. May be dry or intermittently pond freshwater after heavy rain.
Barrier Core: The central part of the barrier island that commonly lies between dunes on the seaward side and marshes on the landward side. May be sparsely vegetated or covered by grasses or trees.
Beach: A mostly unvegetated strip of sand parallel to the shore that extends from the water to the seaward edge of the dunes or crest of a washover terrace. The seaward part of the beach is regularly inundated by wave run-up during high-water phases of the tidal cycle.
Beach Ridge Complex: Sets of long, continuous ridges formed parallel to the ocean shore by sand that is deposited by a combination of wave runup and the wind. May be covered by grasses or trees.
Beach Ridge Swales: Topographic depressions within a beach-ridge complex. May be dry or intermittently pond freshwater after heavy rain.
Dunes: Hills or ridges of wind-blown sand that form hummocky topography landward of and parallel to the beach. May be sparsely or densly vegetated with grasses.
Interdune Swales: Topographic depressions between dune ridges. May be dry or intermittenly pond freshwater after heavy rain.
Overwash Zones: Divided into active overwash zones and inactive overwash zones. An active overwash zone is frequently flooded by high water and ocean waves generated by storms. It is typically low lying with sparse vegetation and composed of sand with a concentrated layer of shell at the surface. An inactive overwash zone is an area that was historically overwashed by storm surge, such as during the 1962 Ash Wednesday Storm, or created by overwash such as the flats that widened the north end of the island during the 1998 storms. These areas are not flooded frequently by high water and ocean waves, but are still vulnerable to flooding from extreme storms. The former overwash sand is commonly reworked into low dunes and can be densely vegetated with low wood plants. Inactive overwash zones typically grade landward into marshes.
Marsh: Low vegetated wetlands that support plant assemblages tolerant of saltwater, brackish water, and freshwater. Typically found along the landward side of the barrier island adjacent to the lagoon or along the margins of tidal creeks.
Tidal Flats: Unvegetated transitional areas that are alternately inundated and exposed either daily by the astronomical tides or intermittently by wind-driven water.

Artificial Berm: A low linear ridge of sand, gravel, and shell constructed in the backbeach parallel to the shroe to reduce overwash of the barrier island.
Impoundments: Former water bodies or flats that have been altered by dikes to retain water, or interior water bodies created by dredging below the water table.
Jetty: An engineering structure that projects perpendicular to the shoreline. A jetty is typically composed of large blocks of rock and is designed to reduce the flow of sand into a coastal navigation channel, such as a tidal inlet.
Modified Land: Significant alterations of the land surface for residential/commercial development.
Parking Lots: Areas cleared for parking vehicles.
Reclaimed Land: Formerly low, commonly flooded land that is built up by material either dredged from adjacent submerged areas or imported from some other site.

Project Metadata

The following link straight to exported metadata text files associated with each class's shapefile. Get the more detailed XML files readable in metadata readers such as ESRI ArcCatalog in the respective data folders above.