Stormwater Ponds

What are stormwater ponds?
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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.

What should a pond look like?
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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.

How are ponds maintained?
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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.

Who maintains Redmond ponds?
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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. Maintenance, planting, or vegetation removal without enrollment in this program is not permitted.

Are existing ponds being improved?
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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.  

How can I help?
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The biggest impact homeowners and businesses can have is to prevent pollutants from entering these ponds. Ponds are designed to remove pollutants, but they are not able to remove all pollutants.

In particular, soaps used to wash cars cannot be removed by ponds and actually suspend other pollutants to reduce the effectiveness of ponds. Don't wash your car in a place that drains into a pond. Using natural yard care practices and limiting the use of chemicals around the home are good measures everyone can take to reduce the source of pollutants, rather than relying on imperfect pond facilities to remove those pollutants.

Contact:   nr@redmond.gov