What are Stormwater Ponds for?
Guest Article for the Tallahassee Democrat
August 9, 2013, Release for Tallahassee Democrat
Photo by Mark Tancig, Timberlake Stormwater Pond
By Mark Tancig
Many citizens notice the stormwater ponds that are constructed with new developments and question the purpose of these ponds. In Leon County, stormwater ponds are required as part of new developments to provide stormwater treatment, rate control, and stormwater volume management and reduction. Stormwater ponds are also constructed to retrofit areas that experience flooding, excessive erosion, and other stormwater related issues.
When a new road, shopping mall, or housing development is built, there is a certain amount of earth that is covered with impervious surfaces. Impervious surfaces, such as pavement and buildings, are surfaces that do not allow rain to soak into the ground. Increased impervious surface cover decreases the area available for water to soak into the ground and so increases the amount of water that runs off the property. This is what engineers and biologists call stormwater runoff. This runoff carries with it pollutants such as dirt, dust, trash, grease, animal wastes, and whatever else one may find on a roadway, parking lot, etc. Leon County’s land development regulations require stormwater ponds so that these pollutants do not enter natural waterbodies.
Stormwater treatment is achieved by the resulting runoff being collected in the stormwater ponds. These ponds filter this runoff by collecting it in one location and allowing the debris to settle to the bottom. Because this debris will eventually fill in the pond bottom, stormwater ponds need to be routinely dredged. The excavated soil and debris is properly disposed of.
Rate control is the slowing down of stormwater runoff to prevent flooding and excessive erosion. Most stormwater ponds contain special structures that control how fast the water is allowed to drain. Leon County’s regulations require that the post-development rate of runoff be equal or less than the pre-development rate so that a downstream property owner doesn’t see a change in the amount of water coming to them.
Stormwater ponds have a direct effect on the amount of water that flows downstream after a storm event. The increased volume of runoff from a new development may be held in a stormwater pond to soak into the ground. Holding this volume can reduce the potential for downstream flooding. The volume of water a new stormwater pond is required to hold depends on which stream or lake the stormwater eventually enters and whether there is a history of downstream flooding.
Stormwater ponds also play an important role, and are an important tool, in addressing stormwater problems in neighborhoods that were developed prior to current land development regulations. Requirements to address stormwater runoff rate only began in the late 1970’s and volume control requirements came along in the 1990’s. As more of the County became developed, the increased impervious surface cover and resulting runoff created or added to stormwater related concerns. Stormwater ponds are used in these instances to retrofit older developments to address these concerns. The prime example of this is the Timberlake Subdivision off Apalachee Parkway that experienced major flooding after Tropical Storm Fay came through in 2008. The new stormwater pond that was completed in 2012 now provides flood protection to the citizens in the neighborhood.
The Timberlake stormwater pond project was also an example of engaged citizens working with Leon County staff to build a stormwater pond that not only provided flood relief but also created a sense of place. This stormwater pond is now an amenity where the residents can gather for neighborhood meetings, exercise, and outdoor recreation.
Mark Tancig is a Water Resource Specialist with the Leon County Public Works. For more information about gardening in our area, visit the UF/ IFAS Leon County Extension website at http://leon.ifas.ufl.edu. For gardening questions, email us at Ask-A-Mastergardener@leoncountyfl.gov