|Rocky Zone||Rocky Zones (RZ) are rugged areas of high bathymetric relief, rising above the Nearshore Basins, ranging from rocky ledges to relatively flat, gravel-covered plains to boulder fields. Water depths range from 3 to 45 m. Although ledge and coarse-grained sediment are found within all physiographic zones defined here, they dominate the sea floor in Rocky Zones.|
|Nearshore Basin||Nearshore Basins (NB) are areas of shallow, low-relief sea floor adjacent to the mainland and separated from offshore areas by islands and shoals. Water depths range from 0 to 47 m. Along its landward margin, the basin sediment merges with the intertidal zone, often a Nearshore Ramp, in a gradational contact.|
|Nearshore Ramp||Nearshore Ramps (NR) are areas of gently sloping sea floor with generally shore-parallel bathymetric contours. Water depths range from 0 to 29 m. This zone is covered primarily with sand-rich sediment, although small rocky ledge exposures, cobbles and boulders crop out on the sea floor in places. Nearshore Ramps are mostly confined to cuspate shorelines between coastal headlands and typically grade into the Nearshore Basin.|
|Ebb-Tidal Delta||Ebb-tidal Deltas (ETD) are lobate sandy shoals found on the side of inlets that form through the interaction of waves and ebbing tidal currents flowing from Vineyard Sound. Water depths range from 1 to 14 m. The only Ebb-tidal Deltas mapped within Buzzards Bay are on the bay side of tidal passages between the Elizabeth Islands.|
|Hard-Bottom Plains||Hard-bottom Plains (HBP) tend to have low bathymetric relief, with a coarse sediment texture consisting of primarily sand and gravel.|
|Dredged Channel||Dredged Channels (DC) are anthropogenic features where the sea floor has been modified to accommodate navigation.|
|Dredge Spoil||Areas where anthropogenically derived dredged materials (DS) have been dumped on the sea floor. These areas show irregular bathymetry, roughness and acoustic backscatter that often contrast with the surrounding geology.|
|Coastal Embayment||Coastal Embayments (CE) include the coastal ponds described by FitzGerald and others (1987) along the northwest shore of Buzzards Bay and the smaller bays and harbors along the Cape Cod and Elizabeth Islands shores. Some of the shallow coastal water bodies, particularly the drowned river valleys along the northwest shore of Buzzards Bay, fit the description of coastal lagoons where these water bodies are separated from the ocean by a barrier but connected at least intermittently to the ocean with at least one restricted inlet Kjerfve (1994). Fitzgerald and others (1994) would refer to the coastal water bodies along northwestern Buzzards Bay as embayments. In this report, we refer to all partially enclosed shallow coastal water bodies along the Buzzards Bay margin as coastal embayments.|
|0||Areas of low interpretation confidence where only single beam bathymetry and qualitative sediment sample descriptions exist.|
|1||Areas of high interpretation confidence where swath bathymetry, acoustic backscatter, and seismic reflection data exist. In general these areas also contain quantitative sediment statistics and bottom photographs.|
|2||Sediment texture regions that were defined based on the highest resolution bathymetry (10m) and backscatter (1m), bottom photos, qualitative descriptions of sediment samples, and seismic interpretations were given the data interpretation confidence value of 2|
|3||Sediment texture regions that were defined based on low resolution single beam bathymetry and sediment samples descriptions were given the data interpretation confidence value of 3|
|4||Sediment texture regions that were defined based on low resolution single beam bathymetry were given the lowest (4) data interpretation confidence value of 4|
|Range of values|
These sea floor physiographic zones were created from geophysical and sample data collected from Buzzards Bay, and are used to characterize the sea floor in the area. Physiographic zone maps are important data layers for marine resource managers charged with protecting fish habitat, delineating marine boundaries, and assessing environmental change due to natural or human impacts.
Are there legal restrictions on access or use of the data?
Use_Constraints:Not to be used for navigation. Public domain data from the U.S. Government are freely redistributable with proper metadata and source attribution. Please recognize the U.S. Geological Survey (USGS) as the source of this information. Additionally, there are limitations associated with qualitative sediment mapping interpretations. Because of the scale of the source geophysical data and the spacing of samples, not all changes in sea floor texture are captured. The data were mapped between 1:5,000 and 1:20,000, but the recommended scale for application of these data is 1:25,000. Not all digitized sea floor features contained sample information, so often the sea floor texture is characterized by the nearest similar feature that contains a sample. Conversely, sometimes a digitized feature contained multiple samples and not all of the samples within the feature were in agreement (of the same texture). In these cases the dominant sediment texture was chosen to represent the primary texture for the polygon. Samples from rocky areas often only consist of bottom photographs, because large particle size often prevents the recovery of a sediment sample. Bottom photo classification can be subjective, such that determining the sediment type that is greater than 50% of the view frame is estimated by the interpreter and may differ among interpreters. Bottom photo transects often reveal changes in the sea floor over distances of less than 100 m and these changes are often not observable in acoustic data. Heterogeneous sea floor texture can change very quickly, and many small-scale changes will not be detectable or mappable at a scale of 1:25,000. The boundaries of polygons are often inferred based on sediment samples, and even boundaries that are traced based on amplitude changes in geophysical data are subject to migration. Polygon boundaries should be considered an approximation of the location of a change in texture.
Neither the U.S. Government, the Department of the Interior, nor the USGS, nor any of their employees, contractors, or subcontractors, make any warranty, express or implied, nor assume any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, nor represent that its use would not infringe on privately owned rights. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the U.S. Geological Survey in the use of these data or related materials. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government
|Data format:||WinZip version 14.5 file contains qualitatively derived polygons that define sea floor physiographic zones for Buzzards Bay, MA and the associated metadata in format Shapefile (version ArcMap 9.3.1) Esri Polygon Shapefile Size: 3.8|
These data are available in Environmental Systems Research Institute (Esri) shapefile format. The user must have software capable of importing and processing this data type.