A standardized mapping of natural drainage basins in Connecticut was completed in 1981 by the Connecticut Department of Environmental Protection (DEP). This drainage basin system divided Connecticut into 8 major basins, 45 regional basins, 337 subregional basins, 2,898 local basins, and 7,067 small drainage basin areas. The statewide mapping of natural drainage basins established a hierarchical system of basins based on drainage area size with large major basins subdivided into regional basins, regional basins subdivided into subregional basins, subregional basins subdivided into local basins, and local basins subdivided into smaller and more numerous drainage basin areas. Connecticut Drainage Basins is the most detailed delineation of natural drainage basins available on a statewide basis for Connecticut. It includes watersheds for Connecticut rivers, streams, brooks, lakes, reservoirs and ponds included on 1:24,000-scale 7.5 minute topographic quadrangle maps published by the U.S. Geological Survey (USGS) between 1969 and 1984. These basin units include smaller watersheds that drain into many of the small streams and ponds in Connecticut. These basin areas are the building blocks for the larger local, subregional, regional and major drainage basins defined by DEP. The Center for Land use Education and Research (CLEAR) at the University of Connecticut clipped these basins to the state boundary and using the 2012 statewide impervious cover dataset, calculated the area and percent of each of the three classes of impervious cover. Statistics are available per basin feature as attributes of the dataset.
Impervious Cover by Watershed Basin includes 6,953 drainage basin areas with an average size of approximately 1 square mile and make up, in order of increasing size the larger local, subregional, regional, and major drainage basin areas. Basins that cross the state jurisdiction line have been clipped to the state of Connecticut boundary. Each drainage basin is assigned a full basin number (BASIN_NO) that uniquely identifies each basin. There length of the number can be up to 13 characters long, depending on stream order of the basin. Examples include 6000-00-1+*, 4300-00-1+L1, and 6002-00-2-R1. The first digit (column 1) designates the major basin, the first two digits (columns 1-2) designate the regional basin, the first 4 digits (columns 1-4) designate the subregional basin, and the first seven digits (columns 1-7) designate the local basin. The basin number includes a few codes at the end. An asterisk sign (*) denotes a headwater basin containing a delineated impoundment into which a delineated drainage basin outlets. The letter L (for lake) denotes a reach-impoundment identifier for an impoundment basin and is followed by the reach-impoundment number. The letter R (for reach) denotes a reach-impoundment identifier for a stream reach basin and is followed by the reach-impoundment number. Refer to the Connecticut Drainage Basins GIS metadata for more information about drainage basin numbers.
Area and percent impervious area has been calculated for each of the 6,953 watershed basins using the 2012 statewide, 1-foot impervious cover dataset. Values for impervious area are included in the attributes of this dataset. Percent and Area (acres) have been calculated for total impervious cover as well as for three categories: buildings, roads, and other impervious. These data were created to support Connecticut municipalities that are required to comply with the State of Connecticut's General Permit for the Discharge of Stormwater from Small Municipal Separate Storm Sewer Systems (MS4).
This dataset was created to support Connecticut municipalities that are required to comply with the State of Connecticut's General Permit for the Discharge of Stormwater from Small Municipal Separate Storm Sewer Systems (MS4). Learn more about the MS4 General Permit on the Connecticut MS4 Guide.
Drainage basin boundaries were manually delineated by interpreting the 10 foot contour lines and hydrography features shown on USGS 1:24,000-scale topographic quadrangle maps. The horizontal positional accuracy of this information is consistent with other 1:24,000-scale hydrography related data such as Connecticut Hydrography, Connecticut Waterbody, Connecticut Named Waterbody and Connecticut Surface Water Quality Classification. Only limited field checking was conducted to verify the location of these basin boundaries. Basin boundaries may not be accurate in areas that have been diked for flood control, upland wetland and reservoirs having outlets into two basins, and areas where topographic mapping is not up to date, is inaccurate, or is not detailed enough to adequately define local drainage. Residential and commercial development, highway construction, and other changes to the landscape may have resulted in local modifications to the natural drainage pattern since the time these basin boundaries were delineated.