I was walking north along the (east) sidewalk on Bay Street between Grosvenor and Wellesley Streets toward the subway, when this bioswale caught my eye (it's been here since 2012 - how have I missed it?!). What made me pause is the difference in appearance to other bioswales I've seen. I took the opportunity to learn more, and I hope you will, too.
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Please read the logging requirements in advance of beginning this Earth Cache. This cache is NOT available after a heavy snowfall.
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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?
Simply put: stormwater and urban runoff enters the bioswale due to a gradual slope, slowly seeping into the soil. It's then filtered twice, first through the roots of native plants, and then through rocks. 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 stones 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.The best soil type for xeriscaping is silt. Sand does not retain water very well and clay can retain water for too long to the detriment of your plants. Compost soil is a good choice as well. Mulch helps retain water and keep the plants' roots cool.
4. Wet swales function similarly to stormwater wetlands.
Questions - if you are delayed in sending your responses, please post a note. If sending responses for more than one cacher, clearly indicate the cachers' names in your submission; regardless, EACH cacher must post their own unique photo at GZ.
1. Without posting any spoilers of the bioswale, take a photo of you/your GPS/your caching name (etc) at one of the "fronds" (found on the sidewalk) along the east side of Bay St between Grosvenor and Wellesley. Post this with your log. If caching with a partner/group, each person must post their own unique photo. I've provided a spoiler photo for your reference.
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.
Thanks for visiting and I look forward to reading your responses!