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Potawot uses swales to manage and treat runoff. These swales are bioswales, because they include vegetation. [1] The swales are one aspect of Potawot’s commitment to sustainable resource usage. They use what would otherwise be a waste, runoff, for beneficial purposes. The swales use the runoff to help restore the native habitat by creating an ideal area for native plant growth. Runoff is filtered in the swales, and pollution is thus controlled. They are one part of the larger Potawot natural water treatment system. The swales empty into the treatment pond. [2]

Locations

Diagram of Potawot's waterflow. Notice the swales in the parking lots.
Diagram of Potawot's waterflow. Notice the swales in the parking lots.

The swales are positioned at the Potawot grounds to collect excess runoff and are designed to allow gravity to transport it into the treatment pond. They are located near Potawot’s parking lots, because non soil surfaces generate large amounts of runoff due to the inability for water to sink into the ground there. They are connected to each other by culverts and form a system to channel runoff into the pond. [2]

Function/Treatment

Like all bioswales, the swales have a fairly low grade, in order to slow the water as it travels. This encourages water to collect for extended periods of time, because the longer the water remains, the more sinks into the ground. Much of the water travels in the subsurface, or below the top layer of soil. This promotes the filtering of sediments and pollutants such as metals [3]. The water levels in the swales are not very deep, being 1-2 inches deep during a normal rain and 5-6 inches deep at maximum in very heavy rain.

Native plants and shrubs are encouraged to grow in the swales. They include:

  • Scirpus microcarpus - Small-fruited Bulrush
  • Cornus serecia var. stolonifera - Red-twig Dogwood
  • Juncus effuses - Juncus
  • Deschampsia cespitosa - Tuft Hairgrass
  • Alnus rubra – Red Alder
  • Acer circinatum – Vine maple
  • Salix – Willow
  • Carex obnupta – Slough sedge

These plants serve multiple purposes. They assist the filtering process as well as help collect the water in the ground through their roots, including rhizomes. Importantly, they support the larger aim of Potawot to encourage native habitat renewal. [2]

Upkeep

The swales require a mild amount of upkeep to remain functional. This mainly consists of ensuring flow by unclogging the culverts. Also, nonnative and invasive plants are removed to preserve the native habitat. [2]

References

  1. Groves, William, Phillip Hammer, Karinne Knutsen, Sheila Ryan, and Robert Schlipf. "Analysis of Bioswale Efficiency for Treating Surface Runoff." October 28, 2008. [1]
  2. 2.0 2.1 2.2 2.3 Johnson, Eric. Interview. October 27, 2008.
  3. "Bioswales Article May 2007" October 28, 2008. [2]

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