Bioretention
Bioretention is a stormwater infiltration practice that treats runoff from paved areas by using the natural properties of soil and vegetation to remove contaminants. There are a number of methods being employed by communities and individuals to make use of bioretention methods to help manage store water and maintain a healthy environment
Bioretention Swales
Bioretention swales are shallow, landscaped depressions with sloped sides. They are designed to capture, treat and infiltrate stormwater runoff as it moves downstream. The depressions can be comprised of vegetation, dirt or rocks.
Rain gardens
A rain garden is a garden of native shrubs, perennials, and flowers planted in a small depression, which is generally formed on a natural slope. It is designed to temporarily hold and soak in rain water runoff that flows from roofs, driveways, patios or lawns. Rain gardens are becoming very popular in municipalities across North America to divert rain water from parking lots and roads to a curb based garden planted with drought resistant, native plants to act as a way to reduce water use to maintain a flower garden, and filter pollutants to keep them out of the water table.
Stormwater Retention ponds
Stormwater ponds have been used extensively in North America to manage runoff from urban areas. Stormwater ponds can differ significantly in the level of control provided. Ponds constructed before the late 1980s, for instance, were designed primarily to reduce peak flows, and are therefore much smaller, and often lack a permanent pool of water. Later ponds, designed to provide both water quantity and quality control, are typically larger and support a permanent pool with active storage. The added storage allows more time for sediment and associated contaminants to settle out as water is gradually released to nearby streams.
A variety of design variations of bioretention are possible. Most are designed as swales or islands and are constructed adjacent to roads, parking lots or other paved areas. Runoff from these impervious surfaces are directed into the bioretention area, where it ponds and slowly infiltrates. Flows from large rainfall events, bypass the bio-retention area and are conveyed directly to the sewer system.
While the specific components of a bioretention area may vary slightly, they generally consist of an organic mulch top layer with vegetation and filter media below. A gravel under-drain below the soil is provided in some applications. The soil underneath the mulch in bioretention areas consists predominantly of sand with smaller amounts of silt, clay and organic material, which helps increase infiltration rates and filter contaminants from surface runoff. The plants and mulch layer also help to improve infiltration and pollutant removal. The area is normally planted with native species which are tolerant to elevated contaminant levels and fluctuations in soil moisture.
The obvious benefit of these systems is that they detain, filter and infiltrate runoff as it is conveyed along the ditch, resulting in smaller volumes of runoff and associated pollutants from reaching the watercourse or stormwater management facility.
The terms swales and roadside ditches are often used interchangeably, although there are important differences between them. Roadside ditches are designed to function primarily for conveyance. Bare soil ditches may even act as a significant source of sediment. By contrast, swales and wet swales are intended both for conveyance and treatment, and are often subject to more frequent maintenance.
This practice has the potential to provide a significant improvement in contaminant removal over other stormwater infiltration practices due to the added treatment benefits of microbial activity and plant uptake. By infiltrating and evapotranspiring runoff volumes, bioretention systems also help to reduce pollutant loads to watercourses and recharge groundwater
This Earthcache
Located on the grounds of Sir Sanford Fleming College is wonderful example of bioretention techniques being used to channel water to a retention pond. After reviewing the material covered on the cache page you should be able to answer a few questions about the technique being used, and its benefits.
Logging Requirements
Parking is available in a pay and display lot on the grounds of Sir Sandford Fleming. During the school year these spots may be limited.
To Log this Earthcache
Please send me your answers within 4 days of posting your found log. If there is more than one cacher in your party, include the names in your group. Only one person needs to send me the group answers. No spoiler photo's please. Found logs posted without proof you visited the site will be deleted.
Questions
1. In your own words, explain why bioretention of stormwater is more beneficial than simply diverting all water runoff to a storm sewer?
2. Based on the information in the narrative, do you consider this a Retention Bioswale or a Rain Garden?
3. Do you see evidence that water is being diverted from the parking lot or the roadway? Please give a description to support your answer.
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