The average depths of the detention ponds investigated ranged from 4 to 8 feet, whereas the average depths cited by the North Carolina guidelines are 3 to 6 feet. The nutrient level in one of the detention ponds was found to be affected by the presence of urban geese. Lead and copper were not detectable in storm samples or pond effluent by flame atomic absorption spectrophotometry technique. The pollutant removal reported should be viewed as long-term average performance of Piedmont North Carolina wet detention ponds. On the other hand, the removal of particulate pollutants is achieved by sedimentation.
Fine particles require a longer detention time to settle.
The degree to which these Piedmont wet detention ponds reduce hydrographic peaks was found to be less than satisfactory because significant runoff enters near the downstream portion of the detention ponds. This is attributed to the extensive development of housing projects surrounding the detention ponds. The quality of storm runoff from the study area is better than that reported by the National Urban Runoff Program. The study site is representative of Piedmont urban settings where watershed management or maintenance activities are emphasized to reduce nonpoint source pollution. A relationship between pollutant removal effectiveness and the surface area ratio of detention ponds has been obtained to characterize the water quality improvement performance of existing wet detention ponds in the Piedmont region of North Carolina.