SEA (Street Edge Alternative) Street was a Seattle Public Utilities Natural Drainage System project, and was completed in April of 2011. The location of this roadway improvement project is relatively small, with it only spanning one city block on 2nd Avenue NW, from NW 117th Street to NW 120th Street. The purpose of the project was to provide a drainage system that would more closely resemble the natural environment before construction began, as well as be able to completely contain a 2 year, 24 hour storm event. This was done in a variety of ways, including changing the drainage, water quality control, landscape, as well as pedestrian and car mobility.
Drainage is improved by using a combination of plated swales as well as routing techniques. This helped contain all run off and moderates its flow. The landscaping also helps create a longer Time of Concentration, which is an important factor when using the Rational Method.
Water quality control is important, because if it is not attended to then the water runoff can have many pollutants from the roadway such as oil, dirt, grease, and pesticides. SEA Street addresses this issue by using the plants and soils as a natural buffer to remove the toxins, and this improves the water quality downstream and the ecosystems that it goes through. The landscape was redone on the road to serve two purposes: the aforementioned drainage purposes, as well as to ignite a sense of community among the residents. One of the main reasons that the community involvement is critical is because they take it upon themselves to maintain the environment around them. The landscaping has nearly 100% of all plants still alive from 2001 and this helps to maintain the saturation of flood waters.
SEA Street was a good Guinea Pig project for this type of sustainable design meant to simulate the built environment, but for runoff contamination to truly be significantly reduced, more communities will need to start using this construction plan. The technology is now there, and there is this case study to reference, so hopefully SEA Street becomes a mainstay in the area in the coming decade.