DEEP: Impervious Cover Studies

Impervious Land Cover and Water Quality

Impervious surface or impervious land cover (IC) is defined in a variety of ways. A simple definition is any land use alteration which causes water to flow over a surface, instead of soaking into the ground.  Many studies have evaluated the relationship between the water chemistry, fish, and insects living in a stream, and the amount of development upstream. The general relationship can be described by the conceptual model below.

Impervious Cover and Biological Integrity

{impervious cover and biological integity}

This conceptual model describes the relationship between biological integrity, or how healthy a river or stream is, and the amount of IC in the watershed. This pattern of natural, very healthy biological integrity under low levels of IC, and degraded poor biological integrity under high levels of IC is very well documented in the scientific literature.

Recently, the Connecticut Department of Energy and Environmental Protection (DEEP) has tested this conceptual model with data from streams in Connecticut. The project combined the satellite based land cover data with chemical and biological data from streams across the state.

{MMI vs. impervious cover %}

This graphic describes biological health using a measure called a macroinvertebrate multimetric index (MMI) from 125 streams in Connecticut. A relatively low percentage (12%) of impervious cover upstream of a point on a stream, changes the stream dynamics so much that the biological community indicates that the stream meets aquatic life criterion goals.  It seems that the data from Connecticut fit the conceptual model very well and we are finding that this concept has spurred several ideas for further study.

In this section, we describe some of our work relating biological integrity to impervious cover. We hope that these reports will be useful to aid and assist those charged with managing the natural resources at the local, state and federal level to best protect, preserve, maintain and/or restore the integrity of our surface waters.

Multiple Stressor Presentation  This presentation was developed to present the concept of "multiple stressor syndrome" a common phenomenon in streams with developed watersheds.  The data analysis within this presentation documents that "no segment of stream in CT with > 12% Impervious Cover upstream of the sampling location was able to meet CT Water Quality Standard for aquatic life."  Following this initial finding two major projects, final reports below, were completed.


Stream Condition and Impervious Cover Factsheet (PDF)

Moderately Developed Watershed Report (PDF)

Least Disturbed Watershed Report (PDF)

Addendum to Least Developed Report (PDF)

Streams of Hope: Characterizing the Biological Potential of Moderately Urbanized Connecticut Streams (PDF)

Characteristics of Macroinvertebrate and Fish Communities from 30 Least Disturbed Small Streams In Connecticut (PDF)

Water Monitoring Main Page


Last Updated January 9, 2012