Stormwater outlet feature location: Phase II Stormwater Mapping

As part of the City of Thomasville’s NPDES Phase II Stormwater Program, AWCK worked with the City to create a Municipal Separate Storm Sewer System Map (MS4). This MS4 map shows all outfalls, storm drains, and associated drainage areas. This was an important first step in the development of an Illicit Discharge Detection and Elimination Program (IDDE) and provides valuable information when trying to determine the source of an illicit discharge. In addition, the MS4 map makes tracking, reporting, and responding to illicit discharge much easier. To map Thomasville’s storm sewer systems as accurately and economically as possible, we proposed collecting field data using a Trimble GPS system with a hand held GIS unit.  Stormwater system information was entered on a handheld unit by a series of predefined pull-down menus and pick lists, thus increasing data entry accuracy.  The mapping was performed to a minimum relative accuracy of 0.5 meters, satisfying the North Carolina Board of Examiners for Engineers and Surveyors rules. At the same time, pre-determined attributes for each stormwater structure such as size, material, condition, etc. were collected.  The MS4 Map was provided in both AutoCAD and GIS formats for better use by the City. This gives the City the ability to easily facilitate annual permit reporting, and collect and track items such as MS4 maintenance activities, confirmed or suspected illicit discharges, and citizen complaints of flooding or water quality.