Connecticut Subregional Drainage Basin Town Union is 1:24,000-scale data that is the geographic combined union 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 as well as where, out of state, they do not. The geographic area covered includes the Connecticut mainland and islands along the Connecticut coastline, the Connecticut portion of Long Island Sound, and adjacent land areas in Massachusetts, New York and Rhode Island. Data is compiled at 1:24,000 scale (1 inch = 2,000 feet). This is static information that is not updated. The total geographic area covered by all polygon features is 7,201.26 square miles, larger than the area covered by Connecticut.

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. Polygon features with Connecticut Town number values of zero (0) are basin features that do not overlap a Connecticut town and are either located in Long Island Sound, Massachusetts, New York, or Rhode Island.

Connecticut Subregional Drainage Basin Town Union is derived from the union 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, particularly when analyzing subregional drainage basins located both in Connecticut and outside of Connecticut along the state boundary. As with the Connecticut Subregional Drainage Basin Town Intersect feature class, these data 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. This feature class, however, accounts for basin areas outside of Connecticut so basins along the state boundary can be analized relative to their occurence, location, and size both in and outside of Connecticut. A Connecticut town can be analyzed relative to basins, or a basin can be analyzed relative to towns and areas out of state. A polygon feature exists for each area where subregional basins and Connecticut towns occur. If a basin is located in two different parts of town, a polygon feature will exist for each. If a portion of a basin is located outside of Connecticut, a polygon feature also exists. 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 Union 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 occurence. Polygon features with Connecticut Town number values of zero (0) are basin features that do not overlap a Connecticut town and are either located in Long Island Sound, Massachusetts, New York, or Rhode Island. 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

Polygon features conform to the following topological rules. Polygons are single part. There are no duplicate polygons. Polygons do not self overlap. Polygons do not overlap other polygons. Lines are single part. Line features conform to the following topological rules. There are no duplicate lines. Lines do not self overlap. Lines do not overlap other lines. Lines intersect only at nodes, and nodes anchor the ends of all lines. Lines do not overshoot or undershoot other lines they are supposed to meet and intersect. In general, there are no duplicate features, unresolved intersections, overshooting lines, open polygons, sliver polygons, or unlabeled (unattributed) polygons. The tests of logical consistency were performed by the State of Connecticut using ESRI ArcInfo software to maintain feature topology in ArcInfo coverage format. The data is topologically clean. The ArcInfo Clean function was repeatedly used following edits to verify topology and enforce a minimum distance between vertices of 4 feet (fuzzy tolerance) and a minimum allowed overshoot length of 0 feet (dangle length).

The data reflects the content of the data source, which is a set of 1:24,000 scale mylar sheets used to compile and publish the 1:125,000-scale Drainage Basins in Connecticut Map, McElroy, 1982. All major, regional, subregional, local and smaller basin divides were digitized from these 1:24,000-scale mylar compilation sheets. This data is not updated.

The primary data source for basin information in the Connecticut Subregional Drainage Basin Town Union feature class is the Connecticut Drainage Basins layer. The Connecticut Drainage Basins layer retains the feature types and information identified on the 1:24,000-scale compilation sheets for the Natural Drainage Basins in Connecticut map, McElroy, 1981. All attributes have valid values. Values are within defined domains. There are no duplicate LBASIN_NO values except where expected (see definition of LBASIN_NO attribute).

The SBASIN_NO is derived from the first 4-digits of BASIN_NO so the accuracy of the SBASIN_NO is dependent on that for the BASIN_NO. For polygon features, the accuracy test for the BASIN_NO attribute values was conducted by visually comparing the basin number information depicted on the source Mylar overlays with 1:24,000-scale check plots or interactive displays of the digital data on a computer graphic system. These check plot maps and computer displays labeled polygon features with BASIN_NO values and differentiated line features based on DBARC_COD values for comparison with the original source Mylars. Subsequently, four additional fields (MBAS_NO, RBAS_NO, SBAS_NO, LBAS_NO) were added and populated based on the first, first 2, first 4, and first 7 columns of the BASIN_NO attribute. The MAJOR, REGIONAL, and SUBREGION attributes store drainage basin names based on MBAS_NO, RBAS_NO, SBAS_NO values, respectively. Basin names were attributed by joining basin name lookup tables to the polygon features base on MBAS_NO, RBAS_NO, SBAS_NO key values and populating the corresponding fields. These basin names are from the Natural Drainage Basins in Connecticut map, McElroy, 1981. The AREA_SQMI (area in square miles) and ACREAGE (area in acres) field were automatically calculated for each polygon feature based on computer generated feature area in square feet.

The primary data source for the town attribute information is the Connecticut Town Poly feature class. Refer to this feature class metadata for town number and name attribute accuracy report information.

The horizontal positional accuracy of this data complies with the United States National Map Accuracy Standards for 1:24,000 scale maps. According to this standard, not more than 10 percent of the locations tested are to be in error by more than 1/50 inch (40 feet) measured on the publication scale of a USGS 7.5 minute topographic quadrangle map.

Drainage basin boundaries were interpolated from 10 FT elevation contours and surface water body (hydrography) information published on a set of USGS 1:24,000-scale, 7.5-minute topographic quadrangle maps that cover the State of Connecticut. Natural drainage basin boundaries were manually delineated by interpolating elevation and water body information found on topographic quadrangle maps published by the USGS between 1962 and 1984.

Connecticut Subregional Drainage Basin Town Union

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.

Geographic information sytem (GIS), computer-aided drawing or other mapping software is necessary to display, view and access the information.

The data distributor does not provide custom GIS analysis or mapping services. Data is available in a standard format and may be converted to other formats, projections, coordinate systems, or selected for specific geographic regions by the party receiving the data.