Post-Construction Stormwater

Why Is The Control of Post-Construction Runoff Necessary?

Post construction stormwater management in areas undergoing new development or redevelopment is necessary because runoff from these areas has been shown to significantly affect receiving waterbodies. Many studies indicate that prior planning and design for the minimization of pollutants in post-construction stormwater discharges is the most cost effective approach to stormwater quality management.

There are generally two forms of substantial impacts of post-construction runoff. The first is caused by an increase in the type and quantity of pollutants in stormwater runoff. As runoff flows over areas altered by development, it picks up harmful sediment and chemicals such as oil and grease, pesticides, heavy metals, and nutrients (e.g. nitrogen and phosphorous). These pollutants often become suspended in runoff and are carried to receiving waters, such as inlets, ponds, and streams. Once deposited, these pollutants can enter the food chain through small aquatic life, eventually entering the tissues of fish and humans.

The second kind of post-construction runoff impact occurs by increasing the quantity of water delivered to the waterbody during storms. Increased impervious surfaces (e.g. parking lots, driveways, and rooftops) interrupt the natural cycle of gradual percolation of water through vegetation and soil. Instead, water is collected from surfaces such as asphalt and concrete and routed to drainage systems where large volumes of runoff quickly flow to the nearest receiving water. The effects of this process include streambank scouring and downstream flooding, which often lead to a loss of aquatic life and damage to property.

Retention Ponds 911

Does your neighborhood pond look like a green mucky mess? Does your waterfront view make you wish you had no view? Do you have a mosquito breeder in your community? If you answered yes to any of these questions then you need the retention pond 911. Please visit the Clemson Extension webpage for emergency care for your neighborhood retention pond.

Stormwater Ponds

Post-Construction Best Management Practices (BMP's)

Non-Structural BMPs

  • Begin with sound planning procedures guiding growth of communities away from sensitive areas to areas that can support it without compromising water quality.
  • Site based BMPs can include buffer strip and riparian zone preservation, minimization of disturbance and imperviousness, and maximization of open space.

Structural BMPs

  • Stormwater retention or detention BMPs control stormwater by gathering runoff in wet ponds, dry basins or multichamber catch basins and slowly releasing it to receiving waters or drainage systems. These practices can be designed to both control stormwater volume and settle out particulates for pollutant removal.
  • Infiltration BMPs: Infiltration BMPs are designed to facilitate the percolation of runoff through the soil to ground water, and thereby, result in reduced stormwater runoff quantity and reduced mobilization of pollutants. Examples include infiltration basins/trenches, dry wells, and porous pavement.
  • Vegetative BMPs: Vegetative BMPs are landscaping features that, with optimal design and good soil conditions, remove pollutants, and facilitate percolation of runoff, thereby maintaining natural site hydrology, promoting healthier habitats, and increasing aesthetic appeal. Examples include grassy swales, filter strips, artificial wetlands, and rain gardens.

Pawleys Island Drainage Improvement Project

The Pawley's Island Drainage Improvement Project installed a new pipe system under Highway 17 Bypass and along the North Causeway with a final discharge into Pawleys Creek. In an effort to add water quality improvements to the new system, the Stormwater Division incorporated Abtech's Smart Pak inserts into 16 catch basins in the improvement project.

"The Smart Pak's Smart Sponge Media remove suspended solids, including some heavy metals, absorbs oil and grease including most hydrocarbons, and provides antimicrobial treatment of the stormwater flowing through the catch basin. Once the pollutants are absorbed, the Smart Sponge transforms the pollutants into a stable solid media brick for easy disposal."

The Georgetown County Stormwater Division is pleased to introduce this innovative product to further water quality improvement.

Ref: Smart Sponge Smart Pak Catch Basin Filter Units Technical Specifications.

Catch Basin Design



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Georgetown County Stormwater Management
Old County Courthouse, Room 274, 129 Screven Street, Georgetown, SC 29440
Phone: (843) 545-3524 • Fax: (843) 545-3005 •