Hemmingwood Way was renovated in the Spring of 2021 and there’s something new that has been implemented here: bioswales. The posted coordinates bring you to one of the bioswales that has been built, and there are 5 others located further west along this road as well. The bioswales are listed as additional waypoints, so you can find them easily.
Initially, I thought the roadwork was just to implement "traffic calming" measures, but then I noticed that this was something else altogether (although the bioswales do have that added benefit).
What is Ottawa Doing?
Green infrastructure – the use of natural and built systems to slow down, soak up and filter stormwater – is an exciting new area of focus for many cities around the world. Green infrastructure can be used to manage wet weather impacts in a way that enhances water quality and strengthens resilience to impacts from climate change. Ottawa has started experimenting with green infrastructure with a number of pilot programs, and has begun collecting data.
Green infrastructure can be defined as the use of natural and built systems to slow down, soak up and filter stormwater. It can include living systems (e.g., trees, wetlands, green roofs, bioswales, rain gardens) as well as green technologies (e.g., porous pavements, rain barrels and cisterns). Whereas more traditional “grey infrastructure,” such as piped drainage and water treatment systems, is designed to move urban stormwater away from the built environment, green infrastructure reduces and treats stormwater at source while delivering environmental, social, and economic benefits.
Why is Ottawa Doing This?
The city's Infrastructure Master Plan indicates three specific trends: 1. Ottawa’s average temperature is rising. 2. Precipitation in the form of rain and snow is increasing. 3. The frequency of major one-day rainfall events is increasing. In short, the Ottawa area is experiencing more frequent multi-day precipitation events, with a 25% to 30% increase in the number of days with precipitation. Expanding Ottawa's green infrastructure is one of the ways of beginning to deal with these trends. The City of Ottawa’s initial efforts on green infrastructure were concentrated on three experimental pilot projects: the Sunnyside Avenue Rain Gardens, the Stewart Street Green Infrastructure Project, and the Former Canadian Forces Base Rockcliffe Low Impact Development Demonstration Project. The Hemmingwood Way bioswales are the next project being undertaken.
What Exactly is a Bioswale?
A bioswale is an 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, or larger storm water collection ponds (such as the one nearby in Centrepointe Park), bioswales are landscaped shallow troughs comprised of natural materials, such as native plants, rocks and soil.
Bioswales are typically linear, shallow, vegetated channels that convey stormwater from one point to another. Sometimes they are used to guide runoff from an entry point on a property (downspouts, uphill properties, etc.) towards a nearby rain garden, dry well or other structure. In some cases, street-side bioswales can replace curb and gutter systems, as well as storm sewers. Bioswales are not just ditches under another name, and they must be carefully designed and maintained to function properly.
What is Urban Runoff?
Water running off hard surfaces (e.g. roads, parking lots, sidewalks) tends to pick up gasoline, motor oil, heavy metals, trash and other pollutants, 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, you can see how stormwater and urban runoff enters the bioswale due to a gradual slope (1). Slowly seeping into the soil (2), it is filtered twice, first through the roots of native plants (3), and then through rocks (4). The vegetation in swales helps to trap pollutants (suspended solids and trace metals), reduce the velocity of stormwater runoff, and encourage infiltration. Finally, the “purified” water makes its way to the natural aquifer (e.g. lake, river, ocean, etc. ) (5).
The use of bioswales around hard surfaces like roads, buildings and parking lots can promote environmental sustainability while improving the aesthetics of the surroundings. Another of the key advantages of bioswales is that they can be squeezed into smaller locations, where new construction is taking place, thereby supplementing the existing water management infrastructure.
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. Low water use, or “Xeriscape”, swales are useful in areas with hot summers or dry conditions. These bioswales are designed to be dry except just after rain events.
4. Wet swales retain water for longer periods and function similarly to stormwater wetlands.
To Qualify For This Earthcache
Please send your responses using the “Message this owner” link at the top of the cache page. Don’t put your answers in your log. I do check the responses and I will reply back. Logged finds without the accompanying appropriate and complete responses will be deleted. If you need extra time to respond, just let me know. This isn’t meant to be tough, and nobody expects geocachers to be expert geologists!
- Looking at the bioswale at the posted coordinates, as well as the 5 others further west on Hemmingwood Way, what do you believe is its main purpose and why?
- What type of bioswale is this and what evidence is there for your answer?
- Describe the bioswale (width, depth, length, features etc.) and explain how you think this particular bioswale will work.
- Photos are not mandatory but are highly encouraged and welcomed.
Thank you for visiting. I look forward to reading your responses!
Credits
ARC Bioswale (GC94PAT) - I saw this EC in Whitby and it prompted me to do some research on the topic. Some of the images and content here are “borrowed” from that EC.
Green Infrastructure in Ottawa: A State of the City Report
https://www.watershedcouncil.org/
Bioswale – Wikipedia
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