Seattle green street project
Jan Sorby
Below is an example from Seattle’s Green Street’s program. The feel of the neighborhood is totally different (very buttoned-up and Disney Land in feeling) than BPN but like BPN they have no curbs. Let me be really clear, I don’t think every street needs sidewalks to be walkable and not every blade of grass needs to be trimmed. Look at the big concepts here not the details of the “look”.
Stormwater reduction was 99%!!!!
Jan
Seattle, Washington
Seattle, Washington also has an extensive green streets program15. Seattle Public Utilities (SPU) uses natural drainage systems (NDS), and it is currently updating its SWM codes to incorporate these technologies. Many of the pilot projects retrofitted existing residential neighborhoods that needed to improve or upgrade existing SWM.
The 2nd Ave project was the pilot street edge alternative (SEA) project for Seattle. The street and its drainage system were both completely reconstructed reducing impervious area and adding detention capacity. In this project stormwater was detained for the entire contributing drainage area (including properties and street right-of-way, 2.3 acres) with drainage improvements combining contoured swales with traditional culverts, catch basins, flow control structures and slotted pipe.
Some of the vegetated swales in this project were designed to work with a flow control structure or a sub-surface drain. Additional design was also needed to accommodate existing groundwater intrusion in residences. Detention volume gained due to the swales was 2,500 cubic feet. A complete hydrologic report was produced by the University of Washington at this site.
Two years of monitoring show that the total volume of stormwater leaving the street was reduced by 99%15.
The vegetated swales substantially reduced the width of the streets, so “flat curbs” were constructed adding 2 feet of driving space on each roadside to accommodate large trucks and emergency vehicles. Also, roadside grass-planted strips were structural grass reinforced with a lattice of material that can handle occasional traffic.
