The City of Seattle intends to invest $57 million by 2020 to implement its Green Infrastructure Plan.
Green Stormwater Infrastructure in Seattle: Implementation Strategy 2015-2020 (Draft) released July 2015.
During the next five years Seattle is expected to invest about $57.7 million in green infrastructure across multiple city and county utilities and departments by 2020.
Seattle’s municipal departments are striving to manage 700 million gallons of stormwater annually with green stormwater infrastructure by 2025 as directed by a 2013 Executive Order and City Council resolution. By investing $57.7 million across multiple city and county utilities and departments, the city hopes to add enough green infrastructure to handle another 200 million gallons of stormwater over the next five years on top of the 100 million gallons of stormwater already managed by green infrastructure.
Seattle’s combined sewer system overflows regularly, spilling 115.6 million gallons of combined sewage and stormwater into water bodies in 2014. Not only does it overwhelm the city’s water treatment system, but stormwater also causes basement and sewer backups, localized flooding and takes pollution in urban runoff directly into surface waters.
The total volume of stormwater runoff generated in Seattle every year is about 20 billion gallons. The city’s 2025 700-million-gallon management goal means that about 1,125 acres of impervious surface (3% of the total) will function more like a native forest through implementing green stormwater strategies like rain gardens, bioswales, permeable pavement, cisterns, green roofs and other green practices.
The city plans to meet goals through carrots and sticks. Redevelopment is mandated to manage stormwater. Since about 1% of Seattle’s land is redeveloped annually and thresholds for mandatory stormwater management were recently revised, the city anticipates that stormwater code revisions will boost gallons managed by 15%. Seattle mandates stormwater management in redevelopment with disturbances of 1,500 square feet of new or replaced impervious surface or 7,000 sq. ft. of land-disturbing activity.
The city also encourages voluntary site-level stormwater management through the RainWise program that provides rebates to property owners for installing rain gardens or cisterns. RainWise also offers specialized training to landscape installers and contractors to be eligible to install RainWise stormwater solutions.
To help meet the 400-million gallon 2020 goal, the city has made an additional 40,000 properties eligible for RainWise rebates. The program is set to receive $11.7 million between 2015 and 2020.
The city encourages all private residences to manage just 1,000 gallons of stormwater runoff annually to help the city meet its goals. In their implementation strategy they provide a number of ways to do it:
- One 6’ x 6’ rain garden with sloping sides, 6” deep;
- Replacing 90 sq. ft. of asphalt or concrete with pervious pavement or compost-amended soil and mulch;
- One 140 sq. ft. green roof; or
- A 275-gallon stormwater cistern that collects at least 250 sq. ft. of roof runoff .
Trees are an important way the city sees to manage stormwater. The Urban Forest Stewardship Plan (UFSP) adopted in 2013 sets a goal to increase canopy cover from 23% to 30% by 2037, and improving the overall health and longevity of its urban forest.
From 2000 to 2012 Seattle has managed about 100 million gallons of stormwater annually through green infrastructure. Approximately 8.7 million gallons of stormwater has been managed through mandatory stormwater regulations. Another 79 million gallons are being managed by public entities through voluntary stormwater management projects and 14 million gallons are being managed through voluntary projects by commercial, residential and community groups with private funds or with rebates ($2.5 million in RainWise rebates). About 2/3 of the current capacity has been funded through utility fees.
Green Stormwater Infrastructure in Seattle: Implementation Strategy 2015-2020 (Draft) http://www.seattle.gov/Documents/Departments/OSE/GSI_Spreads_v2_July_2015_WEB.pdf
NewTerrain newsletter August 25, 2015.