There has been a lot of questioning and concerns expressed as to the “pretty ponds” at the new County Public Works Facility.
To explain the significance of “wet ponds,” Rick Green, director of engineering for the county said, “As part of the regulatory approvals required for subdivision and site developments, designs are required to take into account changes to the storm water runoff in both quantity and quality.”
This makes storm ponds significant and they are commonly used as a method of detaining flow and improving water quality before release to the natural environment.
“Generally, run-off from newly developed sites and subdivisions are required to be released at rates the same or slower than what was in place pre-development,” Green added. “The addition of hard surfaced roads, graveled sites and buildings increase the rate at which water runs off the site and depending on the site use, contaminants may be present on the runoff that require removal.”
According to Green, the entire site is graded to drain into a storm pond – often with the exception of small landscaped buffers on the perimeter – which maybe by design a “dry” or “wet” pond.
“The size of the ponds are generally designed to account for volumes associated with major storm events,” Green explained. “A dry pond, as we installed in Erskine East Subdivision, will generally detain runoff flow for a short period of time before controlled release to the natural overland drainage routes. These “dry” ponds are often grassed and can act as park space as they do not maintain normal water levels.”
In comparison, Green said that a “wet” pond, as constructed at the new Public Works Facility site is designed to maintain a certain level of water full-time, and provides surge storage for major storm events before controlled release to the natural overland drainage routes.
Explaining the significance of storm ponds further, Green said that ponds are also designed to clean the runoff by introducing the runoff in one end and releasing from the other.
“The wet ponds are designed with cells that allow water levels to build up and overflow between cells,” Green stated. “The contaminants will settle in the upstream cells providing for improved water quality as the runoff water leaves the site. The “wet” ponds can also provide for natural habitat for wetland vegetation and associated species which also serve to assist in the cleaning process of the water as it travels through the pond system.”