What is a wet pond:
Also called stormwater ponds, retention ponds or wet extended detention
ponds, these facilities are basins that have a permanent pool of water
throughout the year. The wet pond is constructed to store runoff during
and after storms. Wet ponds treat and filter stormwater runoff through
settling and through nutrient uptake by plants and other aquatic organisms.
Stormwater management basins are one of the most common methods chosen
by engineers and developers to handle stormwater runoff generated from
land development activities. Wet ponds also provide water quality benefits
dry basins can not offer. Additionally, many existing dry stormwater basins
can be converted to wet ponds through some minor adjustments to outlet
Wet ponds are usually inappropriate measures in dense urban areas due
to their space requirements. And most experts agree that in order to maintain
a permanent water elevation within the pond, they should only be used
for sites with drainage areas greater than 5 acres. Wet ponds have regulatory
limitations to where they can be placed. For example, they should not
be located within wetlands. And while they may not always be feasible
in very urban or arid climates, wet ponds otherwise have few restrictions
on their use.
There is a potential
impact to the stream that receives stormwater from the wet ponds, because
the standing water in the pond will be warmed by the sun. However, existing
dry detention basins that contain concrete low flow channels drastically
heat stormwater runoff, more so than the wet pond. The warming impact
of the wet pond can be mitigated by planting taller vegetation around
the perimeter and at the discharge point, to shade the water and provide
Wet ponds offer water quality and flood control benefits not typically
associated with dry basins. They are also among the most effective stormwater
treatment practices at removing stormwater pollutants. Water contained
in the permanent pool mixes with and dilutes the initial polluted runoff
from storm events. Additionally, plants, algae, and bacteria in the water
consume these pollutants and thereby substantially reduce the total mass
of pollutants released downstream.
The ability of a wet
pond to store runoff for longer time periods decreases stormwater peak
flows. The longer detention times can reduce stream channel erosion,
a common result of traditional stormwater practices.
Many wet ponds have
been designed as an aesthetic site amenity, to create wildlife habitat
or as a development focal point or recreational area. The results of one
study suggest that "pond front" property can increase the selling
price of a new property by 10% (EPA, 1995). Another study found that the
perceived value (value estimated by residents of a community) of homes
increased by about 15-25% when located near a wet pond (Emmerling-Dinovo,
of wet ponds can be further improved by combining them with other innovative
stormwater practices such as porous pavement and bioretention areas. Additionally,
multiple, smaller wet ponds located in a series create what is called
a "treatment train" that can better reduce pollutants and slow
the rate of flow through the system.
Wet ponds are among the most cost-effective and widely used stormwater
treatment practices. The construction costs associated with these facilities
range considerably, depending on factors such as size and landscaping
regimen. Wet ponds should be designed according to site specific requirements.
These are long-lived systems. Thus the initial investment into constructing
wet ponds may be spread over a relatively long time.
All stormwater basins, both wet ponds and dry, require regular maintenance.
Some of these maintenance activities include: annual inspections for damage,
sediment removal, ensuring the operation of inlet and outlet structures,
repairing undercut and eroded areas as needed, and clearing debris. At
some point, if the pool volume has become reduced significantly or the
pond develops high nutrient levels, wet ponds will need to be drained
& dredged. Several design features, such as sediment forebays, trash
racks, access easements for maintenance and an outlet drain hole can be
incorporated to ease the maintenance burden of wet ponds and increase
The right landscaping plan can transform a wet pond into community asset,
while enhancing its pollutant removal ability. Wetland plants should be
encouraged, as well as trees, shrubs and native ground covers. Landscaping
of this kind will also help discourage resident geese populations.
Often, homeowners and municipal officials express safety concerns as the
main deterrent to approving wet pond designs. Fencing of ponds is not
generally desirable, but may be required by local ordinances. A preferred
method is to manage the contours of the pond to incorporate shallow bench
areas around the pond and eliminate dropoffs and other safety hazards.
Vegetation can also be used to reduce public access to the basin area.