Flood-Inundation Grids and Shapefiles for the Lower Pawcatuck River in Westerly, Rhode Island, and Stonington and North Stonington, Connecticut

A series of 11 digital flood-inundation maps were developed for a 5.5 mile reach of the Pawcatuck River in Westerly, Rhode Island and Stonington and North Stonington, Connecticut by the U.S. Geological Survey in cooperation with the Town of Westerly, Rhode Island and the Rhode Island Office of Housing and Community Development. The coverage of the maps extends from downstream from the Ashaway River inflow at the Westerly, Rhode Island and North Stonington, Connecticut State border to about 500 feet (ft) downstream of the U.S. Route 1/Broad Street bridge on the state border between Westerly, Rhode Island and Stonington, Connecticut. A hydraulic model was used to compute water-surface profiles for 11 flood stages at 1-ft intervals referenced to the U.S. Geological Survey Pawcatuck River at Westerly, Rhode Island streamgage (01118500) and ranging from 6.0 feet (3.32 ft, North American Vertical Datum of 1988), which is the National Weather Service Advance Hydrologic Prediction Service flood category "action stage", to 16.0 ft (13.21 ft, North American Vertical Datum of 1988), which is the maximum rated stage at the streamgage and exceeds the National Weather Service Advance Hydrologic Prediction Service flood category "major flood stage" of 11.0 ft. The hydraulic model reflects the removal of the White Rock dam during 2015-16. The hydraulic model was calibrated using the stage-discharge relation at the streamgage, and documented high-water marks from the March 30, 2010 flood, which had a peak flow slightly greater than the estimated 0.2-percent annual exceedance probability flood flow. The simulated water-surface profiles were combined with a Geographic Information System digital elevation model derived from light detection and ranging (lidar) data with a 1.0-ft vertical accuracy to create flood-inundation maps. The flood-inundation maps depict estimates of the areal extent and depth of flooding corresponding to selected 11 flood stages at the U.S. Geological Survey Pawcatuck River at Westerly, Rhode Island streamgage (01118500).