Connecticut Subregional Drainage Basins for Clipping is 1:24,000-scale polygon data used to clip point, line and polygon features to Connecticut subregional drainage basin areas. These medium size basins mostly range from 5 to 70 square miles in size and make up, in order of increasing size the larger regional and major drainage basin areas. Connecticut Subregional Drainage Basins for Clipping includes drainage areas for all Connecticut rivers, streams, brooks, lakes, reservoirs and ponds published on 1:24,000-scale 7.5 minute topographic quadrangle maps prepared by the USGS between 1969 and 1984. Data is compiled at 1:24,000 scale (1 inch = 2,000 feet). This is static information that is not updated.

Polygon feature attributes include major, regional and subregional basin number, and feature size in acres and square miles. The subregional basin number (SBAS_NO) uniquely identifies individual basins and is 4 characters in length. There are 335 unique subregional basin numbers. Examples include 6000, 4300, and 6002. The first digit (column 1) designates the major basin, the first two digits (columns 1-2) designate the regional basin, and the first 4 digits (columns 1-4) designate the subregional basin.

Connecticut Subregional Drainage Basins for Clipping is derived from the geometry and attributes of the Connecticut Subregional Drainage Basin Polygon and Connecticut State Polygon feature classes.

The clip geoprocessing function extracts input features that overlay clip features. This feature class is intended to be used as a clip feature class when clipping other point, line and polygon features to Connecticut subregional drainage basin areas. It differs from the original Subregional Drainage Basin Polygon feature class because subregional basins 2000, 5000, and 7000 along the Connecticut coastline are intentionally enlarged, extending beyond the Connecticut coastline to the state boundary between Connecticut and New York in Long Island Sound. These enlarged coastal basin areas ensure clip input features located along both the landward and seaward sides of the 1:24,000-scale Connecticut coastline are included in the clip output feature class and associated with subregional coastal basin 2000, 5000, or 7000. Using this feature class when clipping information by subregional drainage basins often eliminates discrepancies caused by differences in the shape of the Connecticut coastline, source map scale and feature accuracy between the clip input and clip feature classes. Input features located along the Connecticut coasline expected to be associated with coastal subregional drainage basins may not be included in the resulting clip output feature class unless Connecticut Subregional Drainage Basins for Clipping is used as the clip feature class. Using the original Connecticut Subregional Drainage Basin Polygon feature class as a clip feature class may produce different results with clip input features along the Connecticut coasline.

These data are intended for analysis with other digital data compiled at 1:24,000 scale or greater.

A standardized mapping of natural drainage basins in Connecticut was completed in 1981 by the Connecticut Department of Environmental Protection. 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. Major basins are subdivided into regional basins. Regional basins are subdivided into subregional basins. Subregional basins are subdivided into local basins. Local basins are subdivided into smaller drainage basin areas for impoundments and river reaches. 

A pair of 1:24,000-scale polygon and line feature classes is available for all basin levels. These data are named Connecticut Major Basins, Connecticut Regional Basins, Connecticut Subregional Basins, Connecticut Local Basins, and Connecticut Drainage Basins. Connecticut Drainage Basins includes the most detailed information upon which the other basin datasets are based.

A hierarchical drainage basin number was assigned to uniquely identify drainage basin areas. Drainage basin areas are numbered sequentially beginning upstream and proceeding downstream. The first digit (column 1) identifies the major basin, the first two digits (columns 1-2) identify the regional basin, the first 4 digits (columns 1-4) identify the subregional basin, and the first seven digits (columns 1-7) identify the local basin. Below are examples of the hierarchical drainage basin numbers.

Basin Numbers:

4 = Major drainage basin number, MBAS_NO (column 1)
43 = Regional drainage basin number, RBAS_NO (columns 1-2)
4302 = Subregional drainage basin number, SBAS_NO (columns 1-4)
4302-04 = Local drainage basin number, LBAS_NO (columns 1-7)
4302-04-1-R12 = Basin drainage identification number, BASIN_NO (columns 1-13)

Stream Order (column 9):

4304-00-1 = Stream order value of 1 represents a headwater basin.
4304-00-2 = Stream order value > 1 denotes the complexity of the drainage basin morphology.

Mapping Status Element (column 10):

4302-00-2- = Ending with minus sign (-) denotes detail mapping at 1:24,000 scale for entire basin.

4302-00-2+ = Ending with plus sign (+) denotes detailed mapping not performed at 1:24,000 scale for the entire drainage basin. The Stream Order value will not reflect the complexity of the drainage basin morphology.

4302-00-1* = Ending with asterisk sign (*) denotes a headwater basin containing a delineated impoundment into which a delineated drainage basin outlets.

Reach-Impoundment Identifier (column11) and Number (column 12-13):

4302-00-1-L1 = The value for the Reach-Impoundment Identifier for an impounment basin is L (for lake). It is followed by the Reach-Impoundment Number (1).

4302-04-1-R12 = The value for the Reach-Impoundment Identifier for a stream reach basin is R (for reach). It is followed the Reach-Impoundment Number (12).

Tom Nosal, State of Connecticut, Department of Environmental Protection, for the final compilation and delineation of 1:24,000-scale drainage basin boundaries, assignment of drainage basin numbers, and conversion to digitial format. Basin boundaries were manually delineated at 1:24,000-scale by visually interpreting the 10 feet contour elevation lines and waterbody features appearing on 1:24,000-scale 7.5 minute USGS topographic quadrangle maps for Connecticut published between 1969 and 1984. The metadata abstract includes a brief description of a drainage basin obtained from material written by Jim Murphy in an article entitled Reading the Landscape published in the Citizen's Bulletin, a CT DEP monthy magazine.

publication date

None. The data is in the public domain and may be redistributed.

No restrictions or legal prerequisites for using the data. The data is suitable for use at appropriate scale, and is not intended for maps printed at scales greater or more detailed than 1:24,000 scale (1 inch = 2,000 feet). Although this data set  has been used by the State of Connecticut, Department of Environmental Protection, no warranty, expressed or implied, is made by the State of Connecticut, Department of Environmental Protection as to the accuracy of the data and or related materials.  The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the State of Connecticut, Department of Environmental Protection in the use of these data or related materials. The user assumes the entire risk related to the use of these data. Once the data is distributed to the user, modifications made to the data by the user should be noted in the metadata. When printing this data on a map or using it in a software application, analysis, or report, please acknowledge the State of Connecticut, Department of Environmental Protection as the source for this information. For example, include the following data source description when this layer is used in analysis or when printed on a map: Basins - From the Subregional Drainage Basins for Clipping layer, compiled and published by CT DEP. Source map scale is 1:24,000.

Gazetteer of Drainage Basin Areas of Connecticut is organized by the eight major drainage basins covering Connecticut. The individual basins that comprise each major basin are listed in hydrologic sequence, headwater to outfall, with drainage basin number, description, basin area, and cummulative drainage area listed for each individual basin.

Information encoded for drainage basin polygon features generally includes drainage basin number, name and size. Below is a brief explanation of the drainage basin identification number. The SBAS_NO uniquely identifes subreginal drainage basins and uniquely identifies each polygon feature. It represents the first 4 digits of the 13 digit BASIN_NO. The drainage basin numbering system is hierarchical. Use the MBAS_NO and RBAS_NO attributes to identify the major and regional drainage basin for each subregional drainage basin feature. Use the AREA_SQMI and ACREAGE attributes to determine drainage basin polygon feature size. These values reflect the area of the respective polygon feature. They do not reflect the cumulative (upstream) drainage area for each basin. Note, ACREAGE and AREA_SQMI values are not automatically updated after modifying feature geometry (shape). These values must be recalculated after features are edited, simplified, generalized, clipped, dissolved, etc.

Basin Numbers:

4 = Major drainage basin number, MBAS_NO (column 1)
43 = Regional drainage basin number, RBAS_NO (columns 1-2)
4302 = Subregional drainage basin number, SBAS_NO (columns 1-4)
4302-04 = Local drainage basin number, LBAS_NO (columns 1-7)
4302-04-1-R12 = Basin drainage identification number, BASIN_NO (columns 1-13)

Stream Order (column 9):

4304-00-1 = Stream order value of 1 represents a headwater basin.
4304-00-2 = Stream order value > 1 denotes the complexity of the drainage basin morphology.

Mapping Status Element (column 10):

4302-00-2- = Ending with minus sign (-) denotes detail mapping at 1:24,000 scale for entire basin.

4302-00-2+ = Ending with plus sign (+) denotes detailed mapping not performed at 1:24,000 scale for the entire drainage basin. The Stream Order value will not reflect the complexity of the drainage basin morphology.

4302-00-1* = Ending with asterisk sign (*) denotes a headwater basin containing a delineated impoundment into which a delineated drainage basin outlets.

Reach-Impoundment Identifier (column11) and Number (column 12-13):

4302-00-1-L1 = The value for the Reach-Impoundment Identifier for an impounment basin is L (for lake). It is followed by the Reach-Impoundment Number (1).

4302-04-1-R12 = The value for the Reach-Impoundment Identifier for a stream reach basin is R (for reach). It is followed the Reach-Impoundment Number (12).

Drainage basin polygon features cover the geographic area of the State of Connecticut, plus the entire headwater upstream areas of all rivers and streams that drain into Connecticut from New York, Massachusetts, and Rhode Island, with the exception of the Connecticut River. The drainage basin area for the Connecticut River starts at the mouth of the Connecticut River and extends upstream into Massachusetts to just over the Connecticut-Massachusetts state boundary. Subregional basins 2000, 5000, and 7000 along the Connecticut coastline have been enlarged to encompass the coastal waters, extending beyond the Connecticut coastline to the state boundary between Connecticut and New York in Long Island Sound.

State of Connecticut, Department of Environmental Protection