The USGS, in cooperation with NOAA and the CT DEP, is producing detailed maps of the sea floor in Long Island Sound. The current phase of this cooperative research program is directed toward studies of sea-floor topography and its effects on the distributions of sedimentary environments and benthic communities. The data and interpretations in this report are based on NOAA survey H11251 completed during 2008 and a USGS verification cruise completed during 2009. Together these data provide a fundamental framework for research and management activities along this part of the Long Island Sound coastline, show the composition and terrain of the seabed, and provide information on sediment transport and benthic habitat.

Surveyed depths within the study area range from near sea level at mean lower low water to more than 36 m. The shallowest areas occur along shorelines and on Orient Shoal, an isolated bathymetric high. Exposed boulder lag deposits, sand-wave fields, and scour features, which reflect the strength of the oscillating tidal currents, are visible in the digital terrain model and on the sidescan-sonar mosaic. Bedform asymmetry indicates that nearshore transport is predominantly eastward, but offshore transport is primarily westward in the northern and western parts of the study area. Sand-wave asymmetry adjacent to Orient Shoal indicates clockwise sediment transport is important to shoal morphology and maintenance.

The surficial-sediment distribution is a product of the Quaternary history and modern environmental conditions. Gravel is prevalent off Rocky Point and in the shallow water along the western shoreline. These are high-energy areas characterized by sedimentary processes associated with erosion and nondeposition. Sand is the dominant sediment offshore in the western part of the study area, on top of Orient Shoal, and in the protected area between Rocky and Terry Points. Much of the sea floor in the offshore sandy areas is covered with sand waves and megaripples, and the stoss slopes of these bedforms are covered in current ripples. These bedforms reflect sedimentary environments characterized by processes associated with coarse bedload transport. Beds of shell debris and seaweed are common in and adjacent to rockier parts of the study area. These beds are ecologically important because they add considerably to the overall benthic compositional complexity.