Seattle Stormwater Runoff Remediation by Jimmy Mounivong
What is storm water runoff? • Storm water runoff – the flow of water that is not absorbed into the ground, intercepted by vegetation, or evaporated. It flows into surface waters such as rivers, canals, and coastal water. natural environment vs urban environment “Stormwaterrunoff would not be a problem if people like you and I didn't do things to the land, but we do," said Robert Chandler, a senior environmental analyst at Seattle Public Utilities. "We clear timber, build homes, put up storefronts, set up businesses, pave roads and drive on them. . . . And every time it rains, we are dismayed at what we see coming out of pipes and going into our creeks, our lakes, our bays and our own Puget Sound.” • A typical city block produces nine times more runoff than an equivalent woodland area, where forest soils act like a sponge. • As more land is paved and rain has fewer places to soak in, water runs off faster.
Problems with stormwater runoff • Increase the magnitude of floods • Alters the amount, quality and temperature of water in our rivers and creeks • As rain washes over the developed landscape, it may be contaminated by oil and grease, heavy metals, pet waste, sediments, chemical fertilizers and pesticides. • The speed and volume of water coming out of pipes erodes stream channels. • These problems decrease water quality, disrupt marine food chains, and negatively impact wildlife habitat.
Strategies to minimize stormwater runoff • Slow down water, allow it to infiltrate and evaporate • Natural drainage systems limit the negative impacts of stormwater runoff by redesigning residential streets to take advantage of plants, trees, and soils to clean runoff and manage stormwater flows. • Vegetated swales, stormwater cascades, and small wetland ponds allow soils to absorb water, slowing flows and filtering out many contaminants.
bioswale • Along with native plantings, soils amended with compost and sand may be needed to facilitate infiltration. • Native vegetation is planted in the bioswale that optimizes characteristics for water absorption, lengthy root systems that prevent soil erosion as well as require a minimum of maintenance. • They are hearty plants that can manage well during periods of dry, hot weather, yet manage to make use of and manage the flow of water from unexpected storms.
SEA Streets case study • Location: Seattle, WA Broadview neighborhood Piper’s Creek watershed • Alternative street edge from conventional curb and gutter system to vegetated swales, bioretention areas, and infiltration trenches • Cost: $800,000 • natural drainage systems generally cost 15 to 25 percent less than traditional street redevelopment, which requires curbs, gutters, catch basins, asphalt, and sidewalks. • The SEA Street design cleanses stormwater through a series of natural functions. • DrainageReduce impervious surfaces by narrowing the road; create more space for plants and soil to absorb rain water; control flooding and move stormwater away from the roadway. • Water QualityUtilize a combination of soils and plants to filter rain water and allow it to seep into the ground • The plants and soils filter pollutants as rainwater moves through the swales, preventing them from traveling downstream to sensitive water • Bacteria within healthy soils can also help break down carbon-based pollutants like motor oil. • Grasses, sedges and rushes physically filter pollutants out of stormwater.
Other examples • Seattle City Hall Green Roof • estimated to reduce annual storm water runoff by 50 to 75 percent. • The growing media consists of pumice, sand, compost and nutrients. • 110th St Cascade Project • is a series of stair-stepped natural pools that slow damaging stormwater flows, reduce flooding, and trap pollutants before they reach Pipers Creek. • Northgate Parking Lot vegetated swales retrofit • Growing Vine St.
citations • http://findarticles.com/p/articles/mi_m0HTO/is_3_34/ai_n25120965/ • http://www.seattlepi.com/local/95881_model20.shtml • http://www.seattlepi.com/specials/sound/day3.asp • http://www.ci.seattle.wa.us/util/About_SPU/Drainage_&_Sewer_System/GreenStormwaterInfrastructure/index.htm • http://www.greenroofs.com/projects/pview.php?id=310