Biophilia: For the Love of Nature, Part 3 (Rain Gardens, Barrels, Bioswales, & Permeable Pavement)

“Love of life is human nature.”

– Biophilia Network

Welcome or welcome back, nature lovers! If you're joining us for the first time, Biophilia: For the Love of Nature is a four-part mini-series that explores our affiliation with nature and the whimsical world of green infrastructure, from how it benefits us and the earth to how it is integrated into cities and urban areas around the globe. In Part Two, we delved into the intricate design, functionality, and benefits of green roofs and green walls with awe-inspiring examples from around the world. In Part Three, we will be learning about stormwater management systems that capture and recycle rainwater, such as rain gardens, rain barrels, bioswales, and permeable pavement. Rain Garden

The Ashby Grove Rain Garden in Islington, London, England is one of the first rain gardens in the United Kingdom engineered to capture return period volumes with drain down outfall based on greenfield runoff calculations. © Robert Bray Associates, 2018.

A rain garden (syn. bioretention pond) is a concave depression within a landscape designed to capture, absorb, filter and purify stormwater. Rain gardens are designed to mimic wetlands and engineered to replenish groundwater and maintain water table levels by facilitating groundwater recharge6 to aquifers. The composition of a rain garden typically contains dense perennial vegetation, thick mulches, fine-textured soils and coarse media substrates such as sand, gravel or rock.

Structural diagram exhibiting the engineered layers of a biorentention pond. © Massachusetts Department of Environmental Protection, n.d.

The Grattix (syn. “Rain Garden in a Box”) is a stormwater management device that is utilized to treat stormwater runoff by removing zinc contamination that has accumulated from galvanized metal roofs, eavestroughs and downspouts. The Grattix was invented by Matt Graves and Mary Mattix of Port of Vancouver USA in Vancouver, Washington, United States. © Port of Vancouver USA, 2013.

Stormwater planters can be designed as part of a sustainable drainage system (SuDS) for properties with zone restrictions such as offices, schools, apartments, condominiums, duplexes, townhouses or row houses. This stormwater planter is part of a rain wall designed by Wendy Allen for Action for the River Kennet (ARK) and installed by Cotswold Rainwater Services at Preshute Primary School in Manton, Wiltshire, England. © Wendy Allen, 2017.

Bioswale

A bioswale has been integrated into this street meridian parallel to Grange Avenue in Greendale, Wisconsin, United States. © Aaron Volkening, 2010.

A bioswale (syn. biofiltration swale) is a long, narrow and partly submerged trench designed to divert, channel, capture, filter and purify stormwater runoff generated from impervious surfaces such as parking lots, streets, roads, sidewalks and pathways. Bioswales are designed to facilitate large quantities of stormwater infiltration in urban cities and thus require gentle slopes (< 6%) and engineered soils7 for good drainage. Bioswale design can include an assorted configuration of botanicals, mulches, soils, rocks, drains and perforated pipes.

Structural diagram exhibiting the engineered layers of a bioswale. This schematic has been specifically designed to provide stormwater management for Xing Yuan Lake from the West Silk Road in the City of Hanzhong, Shaanxi Province, People’s Republic of China. © Green Earth Operations, 2014.

Rain Barrel

A stone rain barrel harvests rainwater from the roof of this carport in Taos, New Mexico, United States. © Jim O’ Donnell, 2015.

A rain barrel (syn. rainwater cistern) is a device that collects or “harvests” rainwater for future use to supplement irrigation during periods of reduced precipitation or increased drought. Rainwater harvesting is best performed in areas with frequent rainfall, although rain barrels can be installed in arid or semi-arid environments to help conserve water. The size of a rain barrel is relatively small to accommodate detached, single-family homes (189–227 L), whereas cisterns have tremendous capacity to accommodate office buildings, schools, businesses or communities (3,785 L–378,500 L). Cisterns may additionally incorporate water filtration and treatment systems for multifunctional purposes. Rainwater harvesting exhibits several benefits in cities, including providing a natural source of pure water and a reduced demand on municipal water services.

Rainwater cisterns are ubiquitous structures found in India, like this rainwater harvesting tank (15.3 lahk litres or 1,530,000 L) built inside the State Legislative Assembly in Thiruvananthapuram, Kerala, India. The Government of India, Ministry of Urban Development and Poverty Alleviation has amended building code bylaws to require mandatory rainwater harvesting units in all new building plots (100+ m2). Rain Water Harvesting System (RWHS) protocol can be expressed in myriad configurations, including urns, barrels, cisterns, tanks and injection wells. © S. Mahinsha, 2013.

Permeable Pavement

Permeable pavement can be incorporated into low-volume, low-speed pedestrian traffic areas such as this boulevard pad in Perth, West Australia. © Moodie Outdoor Products, 2016.

Permeable pavement (syn. pervious asphalt, porous concrete) is a specific type of high porosity asphalt, concrete or stone designed to allow percolation of stormwater through basic subgrade into a provisional subsurface reservoir. Surface designs of pervious pavement can be expressed as unit pavers with permeable polymer, porous aggregate (< ⌀ 0.075 mm), turfgrass or gravel. Unlike conventional asphalt, permeable concrete is specifically engineered from a specialized blend of polymer binders, which create a network of high porosity macropores (15–25% Tporosity) that facilitate percolation of stormwater runoff directly into subsoil instead of discharging into storm drains and river channels.

Structural diagram comparing the engineered layers of a conventional asphalt system to a permeable pavement system. © Bay Area Pervious Concrete, n.d.

Permeable pavement is often constructed from recycled concrete aggregate, like this pervious asphalt developed by scientists in São Paulo, Brazil. The scientist in the video is comparing the composition of two core samples of porous asphalt (left) and conventional tarmac (right). Permeable pavement is best suited for warm, wet or tropical climates where annual precipitation exceeds evapotranspiration (Pt > E) and there is no risk of freezing (> 0ºC). © NTD.TV, 2011.

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Stay tuned for our next & last installment in January! Biophilia: For the Love of Nature, Part 4 (Wildlife Crossings & Urban Naturalization).

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