The U.S. Geological Survey (USGS), in cooperation with the National Oceanic and Atmospheric Administration (NOAA), has produced detailed maps of the sea floor in Rhode Island and Block Island Sounds. As part of this program, digital terrain models (DTMs) from bathymetry collected as part of NOAA's hydrographic charting activities are converted into Esri raster grids and imagery (primarily of 2-meter resolution), verified with bottom sampling and photography, and used to produce interpretations of seabed geology and hydrodynamic processes. Although each of the completed surveys individually provides important benthic environmental information, many applications require a geographically broader perspective. For example, the usefulness of individual surveys is limited for planning and construction of cross-sound infrastructure, such as cables between Block Island and the mainland, or for testing of regional circulation models. To address this need, we integrated 14 multibeam bathymetric DTMs into one contiguous dataset that covers much of Block Island Sound and extends eastward across Rhode Island Sound. The new dataset is adjusted to mean lower low water, is provided in Universal Tranverse Mercator (UTM) Zone 19, North American Datum of 1983 (NAD 83), and geographic World Geodetic System 1984 (WGS 84) projections, and is gridded to 4-meter resolution. This resolution is adequate for sea-floor-feature and process interpretation but small enough to be queried and manipulated with standard geographic information system (GIS) programs and to allow for future growth.

Surveyed water depths within the study area range from near sea level to more than 103 meters. Specific morphological features that indicate sea-floor geology, sedimentary processes, benthic environmental energy, and anthropogenic effects are readily identified in the DTM. Conspicuous natural features include boulder lag deposits of winnowed Pleistocene glacial drift, fields of sand waves and megaripples, and scour depressions that reflect the strength of the oscillating tidal and storm-wave-induced currents. Bedform asymmetry allows interpretations of net sediment-transport direction. Anthropogenic artifacts visible in the bathymetric data include dredged channels and shipwrecks. Together the merged data reveal a larger, more continuous perspective of bathymetric topography than previously available, providing a fundamental framework for research and resource-management activities off the Rhode Island coast.