Coastal Services Center

Controlling Runoff

The Goal:

Minimize nonpoint source pollution.

The Issue:

How do you identify and assess the pollution from rainfall and runoff?

The Answer:

Develop a model that predicts the potential for pollution from storm water runoff based on the physical and biological characteristics of the land derived from satellite imagery.

The Example:
Carmans River, Long Island, New York

Designated as a New York Wild and Scenic River, the Carmans is one of the most significant waterways along Long Island's South Shore. A local favorite for fishing and other recreation, this 11-mile-long river flows into Bellport Bay, the easternmost portion of Great South Bay. It is the largest undeveloped estuary system remaining on Long Island and contains vital habitat for shellfish and migratory waterfowl.

Because the Carmans River is close to New York City, its watershed is being developed as the population grows and nearby suburbs expand. As a result, nonpoint source pollution is increasing dramatically, leading to degraded fisheries and the closure of beaches and shellfish beds. Polluted storm water runoff is the most widespread water quality problem along the southern shore of Long Island.

Applying Land Cover Data:

Pollution potential models are used to predict and quantify the intensity of runoff for a particular landscape. Essentially, these models predict how much an area will contribute to pollution via storm water runoff. The amount of runoff after a storm is influenced by the ground's ability to absorb water (permeability), the type of soil, the topography of the land (i.e., relief, lowlands, hills), and cover conditions, such as vegetation types or pavement. Therefore, land cover data, combined with other physical and biological data, are an important component of a pollution potential model. The Carmans River area was selected as a test site to develop an application that determines pollution potential using land cover data developed using the NOAA Coastal Change Analysis Program (C-CAP) protocol (Dobson and others 1995).

The Carmans River is in close proximity to large expanses of high and low intensity developed land, which reduces the ability of the ground to absorb rainwater and runoff and increases the chances for nonpoint source pollution.

C-CAP land cover data have up to 22 standard classes, including two developed classes. Using ancillary data, high intensity developed (urban) and low intensity developed (suburban) classes were differentiated into three classes: high intensity, medium intensity, and low intensity developed. The distinctions between the classes were based on the amount of impervious surfaces (surfaces that cannot absorb water) in each land cover type (e.g., paved roads, parking lots). These range from 100 percent impervious (parking lots and roads) to residential developments with grass-covered lawns and trees. The model incorporated spatial information (e.g., proximity to a vulnerable body of water), physical characteristics of each class, and storm runoff prediction curves (runoff estimates based on physical characteristics of land, such as soil type and vegetation) to pinpoint potential pollution problems, or "hotspots," along the Carmans River.

The information generated from the Carmans River test site highlighted areas that may need additional management or remediation to reduce pollutant runoff. Two local governments along the South Shore have incorporated this information into townwide watershed management plans. After locating "hotspots," they can use special zoning restrictions, more stringent site reviews, and other actions to curtail nonpoint pollution and protect overall water quality.

The Result:

Many coastal managers are changing the way they manage nonpoint source pollution problems. Instead of only undertaking corrective measures, officials are moving toward prevention. Using runoff pollution potential models with land cover data, managers can create scenarios for future development, as well as permitting and land use scenarios, to estimate the impacts on sensitive water bodies.