Connecticut Drainage Basins is 1:24,000-scale, polygon and line feature data that define natural drainage areas in Connecticut. These are small basin areas that average approximately 1 square mile in size and make up, in order of increasing size, the larger local, subregional, regional, and major drainage basin areas. Connecticut Drainage Basins 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 information is not updated.

Polygon and line features represent drainage basin areas and boundaries, respectively. Each basin area (polygon) feature is outlined by one or more major, regional, subregional, local, impoundment, or river reach boundary (line) feature. These data include 7,076 basin area  (polygon) features and 20,945 basin boundary (line) features.

Basin area (polygon) attributes include major, regional, subregional, local, (full) basin number, and feature size in acres and square miles. The full basin number (BASIN_NO) uniquely identifies individual basins and is up to 13 characters in length. There are 7,031 unique basin numbers. 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. Note, there are slightly more basin polygon features (7,076) than unique basin numbers (7,031) primarily because a few water supply watershed boundaries split a basin into two polygon features at the location of a small dam or point of diversion along a stream.

Basin boundary (line) attributes include a drainage divide type attribute (DIVIDE) used to cartographically represent the hierarchical drainage basin system. This divide type attribute is used to assign different line symbology to major, regional, subregional, local, stream reach, and lake impoundment drainage basin divides. For example, major basin drainage divides are more pronounced and shown with a wider line symbol than regional basin drainage divides.

Connecticut Drainage Basins is the data source for other digital spatial data including the Connecticut Major Drainage Basins, Connecticut Regional Drainage Basins, Connecticut Subregional Drainage Basins, and Connectcut Local Drainage Basins.

The polygon features define the contributing drainage area for individual reservoirs, lakes, ponds and river and stream reaches in Connecticut. These are hydrologic land units where precipitation is collected. Rain falling in a basin may take two courses. It may both run over the land and quickly enter surface watercourses, or it may soak into the ground moving through the earth until it surfaces at a wetland or stream. In an undisturbed natural drainage basin, the surface and ground water arrive as precipitation and leave either by evaporation or as surface runoff at the basin's outlet. A basin is a self-contained hydrologic system, with a clearly defined water budget and cycle. The amount of water that flows into the basins equals the amount that leaves. A drainage divide is the topographic barrier along a ridge or line of hilltops separating adjacent drainage basins. For example, rain or snow melt draining down one side of a hill generally will flow into a different basin and stream than water draining down the other side of the hill. These hillsides are separated by a drainage divided that follows nearby hilltops and ridge lines.

Use these basin data to identify where rainfall flows over land and downstream to a particular watercourse. Use these data to categorize and tabulate information according to drainage basin by identifying the basin number for individual reservoir, lake, pond, stream reach, or location of interest. Due to the hierarchical nature of the basin numbering system, a database that records the 13-digit basin number for individual geographic locations of interest will support tabulations by major, regional, subregional or local basin as well as document the unique 13-digit basin number. To identify either all upstream basins draining to a particular location or all downstream basins flowing from a particular location, refer to the Gazetteer of Drainage Basin Areas of Connecticut, Nosal, 1977, CT DEP Water Resources Bulletin 45, for the hydrologic sequence, headwater to outfall, of drainage basins available at http://cteco.uconn.edu/docs/wrb/wrb45_gazetteer_of_drainage_areas_of_connecticut.pdf

Not intended for maps printed at map scales greater or more detailed than 1:24,000 scale (1 inch = 2,000 feet.). Not intended for analysis with other digital data compiled at scales greater than or more detailed than 1:24,000 scale. Use these data with 1:24,000-scale hydrography data also available from the State of Connecticut, Department of Environmental Protection.

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 printing this layer on a map: Basins - From the Drainage Basins 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.

Drainage basin information is comprised of a set of polygon and line features that together describe different types of drainage basins and drainage basin divides.  

Part 1 - Drainage Basin Polygon Features

Information encoded for drainage basin polygon features generally includes drainage basin number and name. Below is a brief explanation of the drainage basin identification number. Use the BASIN_NO attribute to uniquely identify drainage basins. The BASIN_NO is a unique number assigned to each polygon feature. However, in a few instances, two adjacent basin polygon features are assigned the same BASIN_NO when separated by a drainage basin line feature encoded as a Water diversion point divide (DBARC_COD = 10).

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).

Part 2 - Drainage Basin Divide Line Features

Information encoded for line features categorizes drainage basin divides (boundaries) for cartographic purposes. Use the AV_LEGEND or IMS_LEGEND attribute to classify and symbolize boundary lines on a map. The AV_LEGEND attribute classifies basin boundary features into the same categories as DBARC_COD and DIVIDE. It is included for convenience. Unlike the IMS_LEGEND attribute, it does not condense features into broader categories. When symbolizing drainage basins arc features on AV_LEGEND values, be sure to exclude features not intended to be shown on the map by using the following layer definition query: AV_LEGEND <> "No Show". The IMS_LEGEND attribute condenses the 9 drainage basin line feature types (DBARC_COD values) into 6 broader categories (Major, Regional, Subregional, Local, Shoreline, and No Show). When symbolizing drainage basins arc features on IMS_LEGEND values, be sure to exclude features not intended to be shown on the map by using the following layer definition query: IMS_LEGEND <> "No Show". 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.

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.

State of Connecticut, Department of Environmental Protection