Establishing Volume Reduction Goals and Reducing Stormwater Runoff Using Low Impact Development to Improve Coastal Water Quality

Despite the Clean Water Act (CWA), passed by Congress in 1972, coastal water quality has continued to decline. The primary reason is the Act’s failure to adequately deal with stormwater runoff, the leading source of water pollution in coastal areas. Coastal development causes the velocity and volume of rainwater running off the land to increase, picking up pollutants in the process. Traditional stormwater systems convey that runoff directly into watersheds and coastal waters. Alternatives to the tradition stormwater systems exist that prevent runoff, instead of conveying it off the land as fast as possible. Low impact development (LID) is one option that uses a variety of techniques to mimic the lands natural hydrology by holding rainwater on the land and allowing it to infiltrate the soil. LID incorporate fairly simple measures, such as disconnecting downspouts from impervious surfaces, using rain barrels to capture runoff, and installing rain gardens, to reduce the runoff from development.

Reducing stormwater runoff can be an effective way to improve water quality in areas where waters are not meeting their designated uses established under the CWA. This can be done by bringing runoff levels back to historically acceptable volumes. This analysis uses the methods in the NC Coastal Federation’s Watershed Restoration Planning Guidebook to establish a stormwater runoff volume reduction goal by calculating the increase in runoff between 2004 and 2013 in Beaufort, NC. The study demonstrates the ease of setting reduction goals using the NCCF guidebook methods. It then presents various LID techniques as a cost effective approach to meet the reduction target.

The results for the 9-year period show a 7% increase in stormwater runoff volumes. The estimated increase in runoff volume was 423.876 acre-feet. The runoff rate went from 54% to 61%. This correlates closely with the increase seen in impervious surfaces in the study area. Impervious cover went from 29% in 2004, up to 37% in 2013, an 8% increase.