Stormwater retention ponds, or basins, exist to manage runoff water surges and hold them back from flooding or overburdening an area or a waterway system. These ponds can be called either Retention or Detention ponds, depending on the purpose. Often these ponds are systematically fed runoff water from surrounding drainage systems.
Detention ponds seek merely to check the surge by filling with water, and then releasing that water at a steadier rate, until the pond itself becomes dry. The dry detention pond exists purely to detain the water for a temporary period. A wet pond, by contrast – the retention pond – seeks to retain the extra water for a longer period, gradually releasing some if necessary but never intending to empty.
Retention ponds are designed to hold some level of water permanently, and with extra capacity to take in water surges during storm flooding. Sometimes the retention pond can be dug below water level to ensure a constant amount of water, and sometimes it is filled from the community supply.
Increasingly as we lose natural wetlands to structural building and development, and thus lose some capacity to absorb and buffer stormwater surges, we find it possible to replace this loss with new wetland capacity through the retention pond. Retention ponds become the new natural feature – which presents both challenges and opportunities for communities.
The standing water of a retention pond can offer health dangers. Water can become stagnant and smell bad to the surrounding community. It can breed mosquitoes, which can carry disease. And it is a large attraction to children, who can very easily drown. Fencing or signage are important keep people out of what may look like a great swimming hole, but which can be a deadly danger.
Many retention ponds are built with a shallow floor extending a few feet into the pond from its bank, to aid maintenance workers and as a safeguard against accidentally stepping in. This ledge further away from the bank then becomes a sudden drop-off plunging to much greater depths. Swimming and playing in such structures is obviously dangerous.
Municipality health regulators and maintenance engineers must inspect retention ponds periodically to check for water quality, wildlife and vegetation accumulation, as well as the integrity of the basin banks, and the mechanical features such as the inflow and outflow components.
Even as the pond becomes a fish and wildlife habitat, it simultaneously accumulates silt and storm debris and pollutants. Algae growth is generally faster in these ponds as a direct result of contaminants brought in by storms.
Furthermore, not all stormwater retention ponds are created and maintained by municipalities. Some ponds are created in subdivision developments and must be privately maintained by, for example a homeowners association – which soon discovers the high cost of preserving such a natural feature as an attractive asset rather than a deteriorating liability.
And many ponds are simply created by nature, from the lay of the land and the run of the storm waters. A pond can exist in the back acreage of homes, without anyone having built it. But as storm intensities increase and as water management itself becomes more vital to our developed society, the balance of health maintained by such natural ponds can begin to degrade, requiring someone to deal with it.
A stormwater retention pond is created to manage runoff surges, but is designed also to be a permanent natural feature in an area. As a natural feature, it offers great scope for beautification. The surrounding trees and vegetation up to the bank provide additional storm protection and surge mitigation, and can also be managed and cultivated to create a viable and self-regulating ecosystem.
Fish will mysteriously appear in an apparently landlocked retention pond, and this can occur from numerous causes. But the right fish can help keep the insect balance healthy. Introducing native plants and wildlife can equally create a healthy balance in the system. Certain species of aquatic life can help destroy the ever-burgeoning algae that are the bane of retention ponds.
In Florida, where retention ponds have proliferated over the years from the abundant rainfall and storm surges, the drive is increasing to beautify these areas, and many good results are starting to appear. With community involvement and the guidance of experts, a stormwater retention pond close to, or in the middle of, dwelling space can become the central feature of a park setting, a gathering place made safe for children and families, and an enhancement to property values.