Connecticut Subregional Drainage Basin Town Intersect is 1:24,000-scale data that is the geographic intersection of subregional drainage basins and towns in Connecticut. It includes polygon features that define where the Connecticut Subregional Drainage Basin Poly and Connecticut Town Polygon layers intersect and overlap each other. The geographic area covered includes the Connecticut mainland and islands along the Connecticut coastline. The total geographic area covered by all polygon features is 4,967.56 square miles. 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 basin number and name, town number and name, and feature size in acres and square miles. Each polygon feature includes the 1-digit major (MBAS_NO), 2-digit regional (RBAS_NO), 4-digit subregional (SBAS_NO) drainage basin number, and the Connecticut Town number (TOWN_NO). Subregional drainage basins typically are located in more than one town and a town will include more than one basin. A polygon feature exists for each subregional basin - town occurrence.

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

These data are used for geoprocessing and analysis purposes. They function as a two-way index of basins and towns, identifying the towns each subregional drainage basin is located in as well as identifying the subregional drainage basins located in each town. A town can be analyzed relative to basins, or a basin can be analyzed relative to towns. A polygon feature exists for each area where a subregional basin overlaps a town. If a basin is located in two different parts of town, a polygon feature will exist for each. Polygon feature size is available in square miles or acres so basin occurrence as a percent of town area can be determined.

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 Basin Town Intersect 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 and name, town number and name, and feature size. 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. The TOWN_NO identifies the Connecticut Town the basin feature is located in. Typically basins are located in more than one town and a town will include more than one basin so there is a polygon feature for each subregional basin - town occurrence. Use the AREA_SQMI and ACREAGE attributes to determine drainage basin - town 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.

Polygon features depict the intersection and overlap of Connecticut Subregional drainage basins and Connecticut towns (municipalities). There is one polygon feature for each subregional drainage basin - town combination, including one for each coastal island identifying both the town the island is located in and the coastal subregional basin the island is offshore of.

State of Connecticut, Department of Environmental Protection