College of Agriculture and Natural Resources
Center for Land Use Education and Research
Impervious Surfaces

Long Island Sound Regional Impervious Surface Study

Results

Long Island Sound Study

 

Summary

For the Long Island Sound study region, the amount of developed area increased from 686,039 acres (1,072 square miles), about 19.0% of the total land area, in 1985 to 768,747 acres (1,201 square miles), about 21.3% of the total land area, in 2002.  This increase of 82,708 acres (129 square miles) represents a 12% overall increase in development, when comparing 2002 levels to 1985 levels. In terms of impervious surfaces, the percent of impervious surfaces was estimated at 8.3% in 1985 and 9.7% by 2002. This represents an increase of roughly 17% when comparing 2002 to 1985 levels. The results for the Connecticut and New York portions of the Long Island Sound watershed are summarized in the table below.

 

 
1985
1990
1995
2002
1985 to 2002 % Increase
Connecticut Developed Area (acres)1
527,277
569,153
583,042
605,709
14.87%
New York Developed Area (acres)2
158,762
160,958
161,973
163,038
2.69%
LIS Study Region Developed Area (acres)3
686,039
730,111
745,015
768,747
12.06%
Connecticut % Impervious Surface
6.13%
6.75%
7.06%
7.46%
21.70%
New York % Impervious Surface
31.68%
32.68%
33.31%
34.17%
9.53%
LIS Study Region % Impervious Surface
8.30%
8.95%
9.29%
9.73%
17.23%

1 Total area of the Connecticut region is 3,296,015 acres.

2 Total area of the New York region is 306,052 acres.

3 Total area of LIS Study region is 3,602,067 acres (excludes the water area of the Sound).

Additionally, you can Download a table of IS estimates by watershed in pdf format.

Evaluation of Method

Understanding the degree and location of impervious surfaces and limiting the amount of impervious surface in a watershed is an important component of overall watershed management.  Because of this, there is a need for a consistent and replicable technique to calculate easily and quickly watershed imperviousness from readily available and cost effective remote sensing information that achieves an acceptable level of accuracy. The research reported here strives to attain that level of consistency and accuracy in regards to developing a temporal set of impervious surface estimations. The impervious surface estimates were derived through subpixel classification of Landsat image pixels that cover four dates spanning a 17 year period for the Connecticut and New York portions of the Long Island Sound watershed. The report, available below, details the sub-pixel classification procedure, impervious results for each of the four dates at a sub-regional watershed level, and an assessment of their accuracy.

Overall the Sub-pixel Classifier technique is capable of producing adequate results when compared to actual impervious surfaces derived from planimetric reference data. It has been shown that the level of error decreases as the size of the summary area increases. An advantage of this technique is the ability to identify the specific location and level of imperviousness within an analysis unit such as a watershed as opposed to only summarizing the amount of IS within an analysis unit. A limitation of the Sub-pixel Classifier, however, is that it does not detect MOIs below a 20 percent threshold increasing potential error in regions of lower imperviousness. Inclusion of land cover information for developed pixels to derive a 10 percent impervious class and also to mask erroneously detected impervious surfaces (i.e., bare fields and barren land) was a necessary step to generate a more representative estimate of impervious surfaces and to force the impervious surface information to be compatible with the land cover data. Used together, these data will improve the ability of coastal resource and land use managers to be able to identify the location and change in land cover and estimated impervious surfaces information summarized over a given analysis unit and will provide a significant advantage for the monitoring and protection of the coastal resources within Long Island Sound.

Project Completion Report

Printer-friendly pdf

Report: Mapping and Monitoring Changes in Impervious
Surfaces in the Long Island Sound Watershed

Completion report submitted to the U.S. EPA's Office of Long Island Sound Programs.

Download a copy of just the IS Watershed Summaries table in pdf format.

Interactive Map

Click the link below to go to the Interactive Map page which will allow you to explore the impervious surface estimates in map form.

Go to Interactive Map


Contact

James Hurd
Remote Sensing Specialist
James.Hurd@uconn.edu
860-486-4610