It's early January, and I'm driving through Durham region. My eye spies a rec centre (I'm always looking for a great pool to swim in), and I pull in the lot to see what's what. Turns out, the Audley Recreation Centre (ARC) also has a really cool skate park, a kids' park, a nice walking trail, a pond and softball diamonds (this is where the softball matches were held during the Pan Am Games in 2015). The ARC also has a series of bioswales. Well, I wasn't expecting that!
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NOTE: If working in a group/team, please note that each individual needs to submit their own response and post their own photo as part of the log.
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Dirt mounds with a purpose. You will be examining the bioswale immediately to the right (east) of the skatepark. You can't miss it - and I've WP'd it, just in case.
Please read logging requirements as set out below in order to log a find. Do not post any photos that give away the answers - they will be deleted.
What is a bioswale?
The word bioswale is a combination of the Greek prefix bio-, meaning life, with the modern word swale, meaning “a low tract of land.” A bioswale is an Earth-friendly alternative form of water drainage that filters and absorbs polluted water. In contrast to typical pipes and concrete ditches found in residential and commercial zones, bioswales are landscaped shallow troughs comprised of natural materials, such as native plants, rocks and soil. With the use of bioswales around hard surfaces like roads, buildings and parking lots, organizations can promote environmental sustainability while improving the aesthetics of their surroundings.
What is urban runoff?
Water running off impervious surfaces (e.g. roads, parking lots, sidewalks) tends to pick up gasoline, motor oil, heavy metals, trash and other pollutants from roadways and parking lots, as well as fertilizers and pesticides from lawns. Effective control of urban runoff involves reducing the velocity and flow of stormwater, as well as reducing pollutant discharges. A variety of stormwater management practices and systems may be used to reduce the effects of urban runoff. Some of these techniques focus on water quantity control, while others focus on improving water quality, and some perform both functions.
How do bioswales work?
Referring to the image below, you can see how stormwater and urban runoff enters the bioswale due to a gradual slope (1). Slowly seeping into the soil (2), it's filtered twice, first through the roots of native plants(3), and then through rocks (4). Finally, the purified water makes its way to the natural aquifer (e.g. lake, river, ocean, etc).
Environmental benefits of bioswales:
1. Filtering Pollutants: properly designed bioswales are able to achieve excellent removal of heavy metals, total suspended particulates, oil and grease, bacteria, nutrients, fine sediments and some pesticides and herbicides. Vegetation in a bioswale helps to slow water velocity and encourage deposition of fine sediment and heavy metals. These pollutants are then immobilized and no longer pose a threat to downstream water quality.
2. Retention and Infiltration: temporarily store runoff water and increase infiltration resulting in reduced runoff volumes and rates. Increased infiltration recharges groundwater and sustains stream base flows.
3. Thermal Pollution: reduce thermal pollution. Stormwater can rise in temperature as it washes across impervious surfaces such as hot parking lots in summer. Heated stormwater flowing into streams can impact fish and other wildlife that depend on cold water streams to live and breed.
Types of bioswales:
1. Grassed swales are planted with turfgrass that is mowed. These provide a more manicured look, but have been demonstrated as less effective in slowing stormwater runoff than swales with taller plants.
2. Vegetated bioswales can be planted with ornamental grasses, shrubs, perennials, or a combination of these. Mulch or stone are used to protect soils in areas not covered by turfgrass. Larger stone can also be used to break up concentrated flows of water and reduce velocity.
3. Xeriscape, or low water use, swales are useful in areas with hot summers or dry conditions. Most bioswales are designed to be dry except just after rain events.
4. Wet swales function similarly to stormwater wetlands.
The bioswale filtration system:
The picture below provides an example of a bioswale filtration system. Some key items for any bioswale is that the slope should be fairly flat, but somewhat depressed to minimize the velocity of the water and erosion, and to allow maximum in-filtration. The sloping sides should be a ratio of 2:1 and if possible planted with native species. It is best to follow the contour of the slope for a bioswale to be most effective. In order to increase the water retention capacity perforated pipe can be placed in the trench. This also allows excess flow to be directed where you want it to go. Landscape fabric is used to cover the perforated pipe to keep the soil from washing in and clogging the pipes.
https://khns.org/wp-content/uploads/2016/08/bioswale.jpg
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Please send me your responses and I will reply back. Logged finds without the accompanying appropriate and complete responses will be deleted. If you know you will be delayed, may I suggest posting a note as a placeholder.
NOTE: If working in a group/team, please note that each individual needs to submit their own response and post their own photo as part of the log.
Questions - Use the information in the lesson to guide your response.
1. Looking at the bioswale, what do you believe is its main purpose/function at the ARC and why? If you're stuck, re-read the urban run-off & environmental benefits paragraphs.
2. What type of bioswale is this and what evidence is there for your answer?
3. Describe the bioswale and explain how you think this particular bioswale functions (re: run-off, filtration, etc). Be sure to include specific on-site evidence in your response. Using measurements (e.g. depth, width, height) to describe the various elements would be very helpful, too.
4. What is the altitude when you are standing at the edge of the bioswale? To what extent would it change if you moved to the centre of the bioswale?
5. To determine that you were on site, post a photo of you/your GPS that includes the informational sign about bioswales which is at the posted coordinates.
Thanks for visiting and I look forward to reading your responses!