Watershed Assessment & Modeling

Watershed Assessment

The 1st step in a WIP is completing an assessment. A watershed assessment is like a checkup. The watershed is examined to learn about its current condition. Once problems have been identified proper steps to be taken to deal with them. During the assessment engineers examined information about many features of Ellerbe Creek including:
  • Development patterns
  • Floodplains
  • Land contours
  • Land use
  • Soil types
  • Structures designed to protect water quality
  • Water quality
Scientists even walked 35 miles of streams and visited 107 locations in the watershed to evaluate them for the installation of stormwater control measures (like ponds and filters).

Factors Affecting Water Quality

The assessment found 2 major factors affecting water quality in Ellerbe Creek. The 1st was development. Studies show that water is less healthy when as little as 10% of its watershed is covered with impervious surfaces (such as roads, roofs, and parking lots). The assessment determined that almost 80% of the land in the Ellerbe Creek watershed has been developed. Most of the development in this watershed is older. This means there are a lot of impervious surfaces in the watershed that do not have stormwater management.

The 2nd problem is clay soil. This soil drains poorly and doesn’t let rain sink into the ground. It also erodes easily and gets carried along with stormwater into Ellerbe Creek.

Development Problems

These problems combine to cause others. The poor natural drainage, along with large amounts of man-made impervious surfaces, has made Ellerbe Creek prone to flooding. Stormwater control measures, such as filters and constructed wetlands, can help improve water quality. However, poor drainage means many types of control measures won’t work. Few undeveloped areas mean that there aren’t many places to put the measures that will work.

Ellerbe Creek also has problems with old sewer pipes. Old pipes tend to need repairs and can be a source of leaks. Another problem is that there are not records or maps of many of the pipes in this area. This makes it hard to connect to pipes properly, as well as to repair and maintain them. Between 1999 and 2007 there were 180 sanitary sewer overflows. Since sewer pipes often run along low lying areas, as do streams, this is a real water quality problem.


Once the assessment was completed, all of the collected information was put into several computer models. These models examined ways to improve water quality in Ellerbe Creek. The models consider both current development levels and how Durham will look in the future.

Top priority was given to projects that improved water quality the most. Projects that enhanced the community also had high priority as residents indicated this was important to them in public meetings. Priorities were discussed at a public meeting in April of 2008. The 2nd meeting gave an update on how priorities had been set and went over the model. The information presented at each meeting is available below.

Public Meeting April 2, 2008

Public Meeting October 22, 2008