Bioswales by Mark Menz

Author: Gladwyn d'Souza | Category: Environment | Date: 01-16-2021

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Written by Mark Menz

Bioswales are a creative alternative to standard sewage piping during the aftermath of storms. A different mechanism of storm drainage that has pathways of vegetation soak the water. They funnel the water through groves of grasses and water plants, slowing the flow and allowing them to be filtered, leading eventually to traditional sewage inputs. Aside from being aesthetically pleasing, this allows an easy purification method that irrigates through thick clumps of plants that will suck in the nutrients and filter the water. The Low Impact Development Stormwater Management Planning and Design Guide depicts how “Research has shown the pollutant mass removal rates of grass swales are variable, depending on influent pollutant concentrations (Bäckström et al., 2006), but generally moderate for most pollutants (Barrett et al., 1998; Deletic and Fletcher, 2006). Median pollutant mass removal rates of swales from available performance studies are 76% for total suspended solids, 55% for total phosphorus, and 50% for total nitrogen.”

This comes with the cost of installation, carving the earth and planting the vegetation. Bioswales take up different amounts of space and different types of areas, meaning pipes can’t just be taken out with plants to replace them, there must be a slope of sorts in order for water to be drained in, and if this is not present then it must be dug. It should also be mentioned that they are not as useful in compact urban areas. There is also maintenance, which isn’t costly but definitely necessary. The build-up of debris or lack of plants in certain spots causes the system to fail to properly filter the water. However no gardener is required, only a pattern check up to make sure it functions properly after a large storm or every few months. Grasses of plants that are more native to the area will often take less attention to manage as they require no fertilizer or special needs. Floods themselves are not a large problem, but frequent flash floods could destroy the vegetation, which is much more open to damage than metal pipes, although they also come with similar maintenance costs, because when broken, pipes are much harder to fix than just planting new seeds. In fact, floods themselves are reduced by large numbers of bioswales, which are more able in their handling of large inputs of water through soil and plant intake of water, protecting homes, streets and environments.

Bioswales create multiple benefits to the surrounding area, creating a healthier ecosystem. The National Association of City Transportation Officials labels how “Bioswales are the most effective type of green infrastructure facility in slowing runoff velocity and cleansing water while recharging the underlying groundwater table. They have flexible siting requirements, allowing them to be integrated with medians, cul de sacs, bulb outs, and other public space or traffic calming strategies.” Grass swales can be used as snow storage areas. Standing water is a breeding ground for mosquitoes and other insects, but valleys of grasses eliminate large pools and let water pass through more naturally. Unlike grass fields or planted trees, bioswales are diverse in nature, usually consisting of native plants that might have trouble growing elsewhere. They make little communities of animals that rely on more vegetation, along with providing more plants to help collectively pull carbon out of the atmosphere. But aside from any side benefits, they’re just a more efficient possibility, a better option that has been overlooked because of its installment costs and odd nature in concept. But a natural and innovative funnel and filter system for stormwater treatment pushes for a community to be more optimized than it could have been before.

Sources:

nacto.org/publication/urban-street-design-guide/street-design-elements/stormwater-management/bioswales

cvc.ca/wp-content/uploads/2014/04/LID-SWM-Guide-v1.0_2010_1_no-appendices.pdf

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