Impervious Cover

From 1985 to 2023, in the entire watershed, impervious cover increased from 588 square miles to 712 square miles, a 21 percent increase. More specifically, the greatest increase was in the lower watershed where Connecticut experienced a 23 percent increase and New York experienced a 9 percent increase. Furthermore, in the 300-foot riparian buffer area, an especially sensitive area as it is critical to providing protection to the adjacent waterway, an increase of 24 square miles of impervious cover was in the lower watershed, and an increase of 125 square miles in the entire watershed. The total area of land in Connecticut that lies in the Long Island Sound watershed is 5,150 square miles. In New York, the total area that lies in the Long Island Sound watershed is 478 square miles.

The degree of impervious cover, particularly near water bodies, has been shown to be associated with degradation of water quality in rivers and streams. Impervious surfaces—like roads, rooftops, and parking lots—are important to water quality because they prevent rainwater from soaking into the ground, causing polluted runoff to flow directly into streams, rivers, and lakes. As this runoff moves across hard surfaces, it picks up contaminants such as oil, fertilizers, and trash, which degrade water quality. The lack of natural infiltration also reduces groundwater recharge and impacts resiliency for flooding. Managing impervious surfaces is therefore a key part of protecting clean, healthy water resources. Additionally, land area with impervious cover (e.g., paved surfaces such as roads, and high-density development) limits the supply of land available for  open space preservation.

To meet both the healthy watersheds and conserved open space objectives, the Partnership is focusing on restoring and protecting riparian buffers and open space (i.e., forest cover), implementing nature-based solutions or other practices like enhancing urban forestry and using pervious pavements (i.e., green infrastructure), and promoting stewardship and sustainable behaviors.

Implementing these practices to restore impervious to a natural or natural like hydrology is most effective at the local level; however, there are some challenges associated with implementation of these types of projects. For example, creating large scale change through collective small-scale efforts is always complex to coordinate and sustain. However, through partnership and collaboration, local organizations can work with property owners and their own public works departments to encourage implementation of these practices.

Limiting additional impervious area is also complex. As new development is often synonymous with growth and opportunity, it can be difficult and more costly to take a slower methodical approach to the design and use of  less traditional materials to promote  less impervious surface. Cost also inevitably drives much of the decision making in new or re-development. Thus, the limited availability of materials, skillsets, funds, and land often create complexities for limiting the expansion of impervious area.