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Stormwater Ponds
Stormwater ponds are manmade features generally located near your
neighborhood or business. They are designed to mimic the ecological function
of naturally occurring ponds and wetlands. Water from these ponds
drains to a lake, river, stream, wetland, or may infiltrate into the ground.
Depending on the age of the pond, it may serve one or two stormwater
management functions. Older ponds were designed to slow the flow of
stormwater and discharge it at a rate to minimize downstream flooding.
Newer ponds are designed to manage water volume as well, but also provide a
water quality benefit. A
properly designed stormwater pond will remove a substantial amount of
sediment and other pollutants from stormwater before releasing this water
downstream. Some ponds are planted with wetland plants and are known
as stormwater treatment wetlands.
Next to being properly designed to store and convey stormwater,
landscaping
is the most critical component in the proper functioning of the stormwater
pond. Historically, many ponds were designed to have mowed grass edges as a
form of “sales appeal” for the developer, rather than being landscaped for
the long term benefit of the pond. Mowed grass to the waters edge on all
shorelines means the pond is not providing its full ecological value.
Unmowed vegetative buffers are essential to long term health of ponds and
waterways. Buffers should also extend into the pond where possible using
emergent wetland plants. The most important factor when designing a
buffer is to choose the proper vegetation for the slope and soils. The
buffer should include a diverse plant community that provides both habitat
and aesthetic appeal. The proper buffer will provide both a water quality
and wildlife component:
Water Quality:
The proper plant community will prevent shoreline soil erosion (bank
slumping) around the pond. It will also prevent herbicides and pesticides
from going directly into the pond. Eliminating the need for fertilizers and
frequent mowing will reduce the potential for algae blooms.
Wildlife:
A diverse plant community will provide habitat for a variety of
wildlife, including predatory insects, amphibians and birds which keep
mosquito populations in check. Tall native grasses will also discourage
Canada Geese from taking over the pond and adjacent lawns.
Trails:
Trails provide access for viewing and photographing birds, enjoying
wildflowers, fall colors and for short strolls. They can be as simple as a
footpath around the pond, or a winding mowed trail among the clusters of
planted trees and shrubs. Trails should be set well above the shoreline so
they don’t flood when the water in the pond is high, but may be designed to
get wet in large overflow events. Benches may be added as amenities for
users. Fences:
Ponds are generally designed with gentle slopes so if someone falls
into the pond, they are able to climb out. In locations were walls or
steeper slopes are incorporated into the pond, a safety fence may be added.
Many ponds have fences installed to help identify the presence of the
facility and indicate in a passive way that they are not swimming or play
areas. However, since ponds are intended to be natural areas, like
streams or natural ponds, the City avoids use of fences where possible.
Much pond maintenance, such as sediment and aquatic plant removal
requires the equipment and expertise of a professional. Some work,
like weed control or planting of approved plants can be performed by
volunteers. Native plant buffers around the pond and its discharge
waterway require maintenance to prevent non-native invasive species from
taking over. This is critical because the native plants often require more
time to become well established than the weedy species. Debris removal and
weeding will be required as small plants develop. Plant identification is
very important for this operation since it is difficult in the beginning to
distinguish between the non-native and native plants. Invasive plant removal
will be an annual task but will diminish as the native plants fill in.
Public stormwater ponds are maintained by
City crews. Private ponds are maintained by private landowners and
inspected by City staff. Regulatory required maintenance is
focused primarily on water quality benefits and ensuring that ponds have
adequate sediment storage and inlets and outlets are not blocked by plants
or debris. At times, these maintenance activities may detract from
pond aesthetics, but efforts are made to reduce any such negative impact.
Stormwater crews are limited by budget constraints, so resources are focused
primarily on functional pond attributes like storage, access, and water
quality, and less on pond aesthetics. If a local group has an interest
in improving the aesthetics of a stormwater pond, through weed control,
planting, adding trails, or other measures, the City has procedures in place
to grant permission for such activities. Contact
nr@redmond.gov for more information.
Maintenance, planting, or vegetation removal without enrollment in this
program is not permitted.
Within the limits of staff time and budgets, the City is working
with contractors and volunteer crews to convert some older ponds from the
old “mowed buffer” to the more contemporary native landscaped buffer.
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