The Knickerbocker Floodplain Project on Thornton Creek will include innovative subsurface restoration techniques that would be the first of its kind in the nation and part of a studied, living laboratory, according to Mike Hrachovec of Seattle Public Utilities (SPU). Mike, known to everyone as “Rocky,” is a SPU engineer who has been designing the floodplain restoration on and off for seven years as funding came in leaps and starts. He gave an enthusiastic talk Thursday night at Sacawajea Elementary School as part of SPU presentation for local residents about the project which is planned to begin construction next summer.
Nearly two dozen members of the public attended including the original Knickerbocker family the site is named after (they sold the first parcel to SPU and the Parks Department including their house just south of NE 100th which has since been demolished). Cheryl Eastberg with the Parks Department began the meeting by describing the history of the project and acquisitions of property around Thornton Creek including the Rossi property on the south side of Thornton Creek that was accessed via the wooden bridge at the end of NE 100th Street (which will be replaced by a rock ford once the project is done).
Katherine Lynch then talked about the funding that made the project happen. Although the city has been interested in creating the floodplain for the past seven years, funding had all but dried up two years ago just as plans had finally been developed. A grant from the King County Conservation District helped move the project forward, while the Thornton Creek Watershed Oversight Committee sought out further funding which finally came from the Washington State Department of Ecology, the EPA, and most importantly Sound Transit which kicked in for floodplain mitigation as part of its Northgate Light Rail station project.
The main goals of the Knickerbocker project are 1) improve instream and riparian habitat, 2) optimize floodplain storage and slow peak flows, and 3) serve as a demonstration project. “Rocky” then began describing the process of engineering which he called, “an incredibly complex design.” Using the area of the creek just west of NE 102nd as a model for what the Knickerbocker site should look like (though with more large wood), he said the city needed to correct what been engineering dogma throughout the 50s and 60s, namely taking out any large trees and installing retaining walls. “We shattered the habitat in the process,” he said. The Knickerbocker project will rip out the rockeries and retaining walls, remove 9,000 yards of dirt and replace it with logs (mainly under the surface) and create a floodplain. Restoration will not only occur on the surface (with indigenous plants and rerouting and widening the creek), but under the surface as well by rebuilding the entire subsurface, a first-in-the-nation effort. He admitted it would be “a radical experiment in stream ecology,” and “we’re just making educated guesses,” but as part of an ongoing plan the area would be monitored and studied extensively with adjustments made where needed. If you would like to see an extensive 30-page technical drawing of the project, check out this pdf from the city.
Project manager Arnel Valmonte talked about scheduling. Right now the project is at “90% design.” If any changes are to be made, now is the time. They hope to finish the design work by May 2013 and have all the permitting done. The earliest they could begin is June 2013 and wrapped up by the end of October. They need to work around the fish window giving them between July 1st and August 30th as the creek is diverted into pipes while the construction goes on. An 80 foot bridge will replace the current one over Thornton Creek (part of the 20th Ave NE walkway), and they are timing it not to interfere with the school year as many students use it to access Sacawajea from Victory Heights.
Contractors in theory work from 8 AM to 5 PM Monday through Friday but have the discretion to work past those hours and on weekends. Neighbors will be kept informed of activity if it impacts them. There will be noise and vibrations associated with the work, and the city will attempt to deal with problems with nearby residents.
Finally, Deb Hayden talked about the future of the site after construction is completed. “Our intention is to let the site grow naturally,” she said, but other than noxious weeds and invasive species being managed they want to remain hands-off. Sound Transit would assume responsibility for managing and maintaining the site (i.e. be paying the bills) for the first five years, after which it would be the domain of the Parks Department. “We’re open to feedback,” was the message.