In 1995 it was recognized that current Connecticut tidal wetland boundary information was critical to ensure the appropriate management and protection of the tidal wetlands resource. At this time the 1970's maps had become increasingly dated, with the growth of new tidal wetland areas and the restoration of others. The maps were contributing to the confusion over state versus municipal wetland jurisdiction. It was in this climate that the current project was conceived. The aim of this mapping effort was to provide current, geometrically correct tidal wetland map products that would serve as a guide to the jurisdictional boundaries for federal, state and municipal regulators and private land holders. 'Tidal Wetlands' are defined as follows: 'Tidal Wetlands' means 'wetland' as defined by C.G.S.Sec. 22a-29. C.G.S.Sec.22a-93(7)(E). 'Wetland' means those areas which border or lie beneath tidal waters, such as, but not limited to banks, bogs, salt marshes, swamps, meadows, flats, or other low lands subject to tidal action, including those areas now or formerly connected to tidal waters, and whose surface is at or below an elevation of one foot above local extreme high water; and upon which may grow or be capable of growing some but not necessarily all, of the following: (See the statute for a complete listing of tidally influenced plant species) C.G.S.Sec.22a-29(2). Thus, the actual tidal wetland boundary is determined by the application of these criteria, including identifying the presence or absence of tidally influenced plants. While the field determination of these criteria results in the most accurate tidal wetland boundary delineation, the identification of different plant types and low lying areas can also be achieved, at a high level of accuracy, through the use of large scale, stereo aerial photography. This latter method was determined as being the most efficient method to delineate vegetated tidal wetlands across the entire state of Connecticut. It should be noted that similarly to the previous tidal wetlands mapping efforts, no attempt was made to delineate those areas that were formerly connected to tidal flow, as these areas are difficult to identify by either field or photo interpretation techniques. The area mapped in the Tidal Wetlands 1990's datalayer includes all tidal, coastal and navigable waters and tidal wetlands of Connecticut with the exception of the Lower Connecticut River, which was mapped as part of the 1994 Ramsar Convention program. Between both programs, a total of 15,178 acres of tidal wetlands were mapped.
The emphasis of this mapping was to capture more detail regarding the emergent wetland areas. It provides a higher level of detail regarding emergent wetlands areas than the the 1970's mapping that combined open waters, tidal creeks and emergent wetlands into single polygons. This approach is most useful in areas such as western LIS where low marsh is gradually drowning.
ground condition
Tidal Wetlands 1990's represented as polygon features. (Source: State of Connecticut, Department of Environmental Protection)
Internal feature number. (Source: ESRI)
Description of area in terms of wetland or upland. (Source: Connecticut Department of Environmental Protection)
| Value | Definition |
|---|---|
| Upland | Upland area. |
| Tidal Wetland | Tidal wetland area. |
The code that specifies an area as either tidal wetland or upland. (Source: Connecticut Department of Environmental Protection)
| Value | Definition |
|---|---|
| 111 | Tidal Wetland Area |
| 0 | Not a tidal wetland area; upland area. |
Size of polygon in acres. (Source: Connecticut Department of Environmental Protection)
Source used when digitizing the polygons. (Source: Connecticut Department of Environmental Protection)
| Value | Definition |
|---|---|
| Null value | No source specificed |
| OLISP 1995 Air Photos | The 1995 Air Photos from the Office of Long Island Sound Programs was used as a digitizing source. |
Feature geometry. (Source: ESRI)
Area of polygon in square feet (Source: ESRI)
Perimeter of polygon in feet. (Source: ESRI)
Includes boundaries of tidal wetlands that were compiled in 1995. Information encoded about these features includes a class code, a legend field, and an acreage field. Use the AV_LEGEND attribute to symbolize features by type on a map. The Class attribute is the code that corresponds to the values in Av_Legend. The Acreage attribute denotes the size of the feature in acres.
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Tidal Wetlands 1990's is 1:12,000-scale data. Use this layer to depict the location of tidal wetlands as they existed in the 1990's. Not intended for maps printed at map scales greater or more detailed than 1:12,000 scale (1 inch = 1,000 feet.)
These photographs were used with a stereoscope to identify areas of tidal wetlands based on vegetation growth that displays on infrared images.
The precursor to the 1990's Tidal Wetlands data upon which the current data was overlaid to detect omissions and/or to reinforce accuracy in ambiguous locations.
This inventory mapping was used as an additional verification source, although it is not rectified and exists only as a series of transparent overlays to the 1981 aerial photographs.
These CAD files were produced from detailed field survey and delineation, but do not differentiate between tidal and inland wetlands. Used as a reference only.
This is an extensive area of tidal wetlands that had been drained by tide gates. A model was used to determine the upstream limits of tidal action in the absence of the tide gates under a 1 year frequency tidal flood to determine the extent of potentially restorable tidal wetlands. Used as a reference only.
Used as a base for the digitizing phase.
Preliminary digital Coverage
Final Product in ArcEdit Coverage format.
Conversion to ArcView Shapefile format, NAD 83.
Final SDE Feature Class.
Identifying Tidal Wetlands on 1995 False Color Infrared Maps Before mapping could begin it was necessary to develop skills in interpreting the 1995 aerial photographs, which were chosen as the primary data source for the tidal wetland boundary information. False color infrared imagery is particularly useful for discriminating vegetation types, and the summer date of the 1995 photographs ensured that the wetland vegetation would have a strong infrared response. Accuracy and consistency at interpreting aerial photographs was developed by looking at the color and texture characteristics of the photographs for areas known to be tidal wetlands. Photo interpretation was done using a stereoscope with either 3 or 8 times magnification lenses. In most cases the 3 times magnification lens was adequate to identify the tidal wetlands. The higher magnification lens was only used if the area was particularly difficult to interpret. The use of stereo imagery greatly assisted the interpretation of tidal wetlands, as low lying areas and vegetation textures become very distinct when viewed through a stereoscope. If the aerial photographs were difficult to interpret, assistance from other reference sources, such as previous mapping of the area (1970's Tidal Wetlands data), previous aerial photographs or site knowledge, was sought. If the boundary of the tidal wetland was not clear, after reference to all of these sources, the site was inspected in the field.
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Digitizing the Tidal Wetlands Boundaries onto Digital Orthophoto Quarter Quadrangles Digital orthophoto quarter quadrangles were displayed in ARCEDIT and overlaid with the 1970's digitial tidal wetlands coverage. The equivalent tidal wetland boundaries that were interpreted from the 1995 aerial photographs were located on the DOQQ image, and digitized on-screen or on-the-fly in ARCEDIT. The DOQQ image could be viewed and digitized at a range of scales. Generally most of the digitizing was performed at 1:6,000 scale, although larger scales were used for smaller tidal wetland polygons, or in areas where the tidal wetland boundary was less distinct. All tidal wetland areas larger than 400 square feet were identified and digitized. Large waterbodies were excluded from the mapping although creeks, streams and ditches narrower than 40 feet were included. In instances where the boundary was not visible on the digital orthophoto, the location of the boundary was interpolated from its proximity to other features that could be seen on both the aerials and the DOQQ image. The 1970's coverage was used for reference and orientation purposes, and the 1981 NWI Coastal Inventory data was used as reference material to ensure that no previously mapped areas would be overlooked. The use of the DOQQ's as a base map eliminated the usual rectification phase of the mapping process which is necessary if the wetland boundaries are mapped directly from the aerial photographs. Unlike the aerial photographs, the DOQQ's have been geometrically corrected and thus provide the best representation of topographic features for mapping purposes. The use of the DOQQ's as a mapping base saved time and increased the accuracy of the mapping process.
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Cleaning the GIS Data Once all the tidal wetland boundaries had been mapped, the ARCEDIT coverage had to be cleaned and edited to ensure all the wetland boundary arcs were closed to form area polygons. Once the wetland polygons were complete an item (class) was added to the polygon attribute table and coded. All tidal wetland polygons were given a class code of 111, consistent with the codes used in the lower Connecticut River wetland coverage. All other polygons, such as small inclusions of upland, were given a class code of 0.
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Converting the NAD 27 Coverage to a NAD 83 Shapefile The original Coverage (Source 8) was created in the State Plane Coordinate System North American Datum (NAD) 1927. This was subsequently converted to a NAD 83 Shapefile Format
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Conversion to ArcSDE Feature Class
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The TIDAL_WETLANDS_1990S layer retains the feature types and information identified by the State of Connecticut, Department of Environmental Protection and obtained from the maps & reports. All attributes have valid values. Values are within defined domains. The ACREAGE (area in acres) field was automatically calculated for each polygon feature based on computer generated feature area in square feet.
The horizontal positional accuracy of this data is unknown.
The completeness of the data reflects the feature content of the data sources, which include maps, CAD files, and previous digital data. The TIDAL_WETLANDS_1990S layer is complete in the sense that it accurately reflects the contents of the information available at the time the State of Connecticut, Department of Environmental Protection created the layer. However, compared to current conditions, the TIDAL_WETLANDS_1990S layer may not be accurate. This data is not updated.
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. Establishment of logical consistency was performed by the State of Connecticut, Department of Environmental Protection using ESRI ArcGIS software to manually create and control feature topology in SHAPEFILE format. No automated procedures or tests were performed to guarantee desired topology other than visual inspection.
The acreage from this mapping is not intended to represent the acreage of tidal wetlands which includes the open water of large internal tidal ponds and tidal creeks, which are an integral component/habitat of tidal wetland. The acreage of wetlands from this report are on the order of 2000 acres less than that computed from the 1970's mapping. When examining the two data layers, this difference should not be interpreted as wetland loss nor should the numbers from this data be used to describe the total acres of tidal wetland in CT. No restrictions or legal prerequisites for using the data after access is granted. The data is suitable for use at appropriate scale, and is not intended for maps printed at scales greater or more detailed than 1:12,000 scale (1 inch = 1,000 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. These data are suitable for planning purposes only, and should not be used to make regulatory or jurisdictional boundary determinations.
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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.
| Data format: | in format Shapefile, Feature Class (version ArcGIS) |
|---|---|
| Network links: | http://www.ct.gov/deep |
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.
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