Knickerbocker Floodplain Work Begins July 1st

The Knickerbocker Natural Area as seen in May 2014. In three months time, it will look much different.

The Knickerbocker Natural Area as seen in May 2014. In three months time, it will look much different.

Construction work on the long-planned Knickerbocker Floodplain Restoration Project will begin in July on Thornton Creek. Last night at the Knickerbocker Natural Area (NE 100th Street and 20th Avenue NE), staff at Seattle Public Utilities (SPU) and the Parks Department met with neighbors to update them on the work. The project will relocate about 600 feet of Thornton Creek, create a 1.5 acre vegetated floodplain, and upgrade the pedestrian bridge over the creek. The new floodplain will store more water, wood, and sediment during storms and provide benefits to properties further down the creek (e.g. less flooding). It will also improve the habitat for fish and wildlife in the creek.

Related: Knickerbocker Restoration Would Be First In the NationKnickerbockerPlans

Some construction work will begin in June, while work in the creek will take place during July 1st and August 31st in an effort to protect fish populations. During that time, the creek will be diverted into two 12″ pipes, and the pedestrian path across the area will be closed for those two months. Once the new 80 foot bridge is installed, access will be reopened in time for the school year to begin.

The two and half million dollar project is a joint effort between the two Seattle departments (SPU & Parks) that have purchased parcels over the past several years. Some of the wetlands creation is being paid by Sound Transit as mitigation for construction at Northgate of the Link Light Rail station. After the contractors finish their work this summer, both departments will be responsible for maintaining the floodplain.

Just a mile east of Knickerbocker, another section of Thornton Creek is being updated when 35th Avenue NE is closed at Meadowbrook beginning Monday to install a larger bridge over the creek. The Seattle Times describes the project.

Visit the SPU website about the Knickerbocker project.


Knickerbocker Site History


Knickerbocker Floodplain site circa 1960. Photo courtesy Jay Amena.

Seattle Public Utilities (SPU) has created a page detailing the history of the Knickerbocker Floodplain site (aka Thornton Creek at NE 100th Street and 20th Avenue NE).  Resident Jay Amena has provided a number of historic photographs that show the houses that once existed on NE 100th, the soon-to-be site of the Floodplain Restoration Project that begins works this summer.

Related articles: Knickerbocker Restoration Would be First In The Nation

SPU Outlines Knickerbocker Project Status

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Knickerbocker Floodplain Project Meeting November 15

The next in a series of community meetings (read about the first here) about the Knickerbocker (Thornton Creek) Floodplain Project will be held Thursday, November 15th at Sacajawea Elementary School beginning at 6:30 PM. Seattle Public Utilities (SPU) and Seattle Parks & Recreation are restoring several hundred feet of the south branch of Thornton Creek at the downstream end of the Kingfisher Natural Area, now dubbed the Knickerbocker site (where the 20th Ave NE footpath crosses Thornton Creek just south of NE 100th Street). This project also will create a 1.5 acre vegetated flood plain and replace the pedestrian bridge across the creek.

SPU and Parks will review the project designs and timeline at this meeting, and invite you to express your concerns, ask questions and make suggestions. Visit their official website for more details.

Sacajawea Elementary School is located at 9501 20th Avenue NE, the meeting will be held in the school’s lunchroom between 6:30 PM and 8 PM.

SPU Outlines Knickerbocker Project Status

Click for larger image

Tuesday night, employees of Seattle Public Utilities (SPU) met with local residents to discuss the status of the Knickerbocker Floodplain Restoration Project at the site location (the walkway at 20th Ave NE and NE 100th Street). They outlined the funding, construction timeline, work, and goals of the project.

Contrary to what Sound Transit officials said last month, funding for the project is coming from a Capital Improvement Project grant of SPU that will be voted on in November 2012. Sound Transit’s interest is to increase the wetlands area as mitigation for the work at the Northgate Link Light Rail station, but the Knickerbocker project is not dependent on that money.

Construction would need to be done between July 1, 2013 and August 31st, 2013 due to impact to fish migration. During the work, Thornton Creek would be diverted into pipes via pumps (possibly generating some noise, although the possibility of using quieter electric pumps was mentioned). As can be seen in the map above, the channel of the creek would be moved slightly north with a much wider floodplain added to collect runoff during storms.The pedestrian bridge that is part of the 20th Ave NE walkway would be replaced by a larger prefabricated bridge 80 feet long and five feet wide just west of where the current one is located. The existing bridge at the west end of NE 100th Street would be replaced with a rock crossing similar to the one on the 17th Ave NE trail.

The main objectives of the project are flooding and fish (less of the former, more of the latter). The project is of scientific interest as well and will be studied to see if the Hyporheic Zone (an aquatic environment that exists within the stream bed sediment) can be improved in an urban area.  The test wells that were sunk last month were the first part of that study.

Invasive plants within the project zone (the dotted line on the map) such as ivy and blackberries would be removed and replaced by native plants and trees.  When completed, only two parking spots will be at the location. SPU was worried garbage trucks might lose their turn-around area but were reassured that those vehicles always back down the many dead-end streets of Victory Heights so they can easily access bins and then drive straight out.

Residents seemed mostly positive about the project, the only hesitation was about the name. Apparently “Knickerbocker” was a woman who owned part of the property for only a year, never built on it, and then sold to the city. SPU seemed amenable to a name change although there was no consensus on a better one. (For my money, I say keep it unique. If you do a search online or call up SPU and say “Knickerbocker” they instantly know what you are talking about; a more generic name runs the risk of obscurity. Feel free to discuss this in the comments section.)

Curiously, nobody at SPU has the least idea what was going on near the Les Schwab on Lake City Way on Tuesday as dozens of trees were removed on the south side of Thornton Creek by a large crane (a small bulldozer was also spotted on the north side across from Summa).

Further public meetings will be scheduled in the autumn to discuss the final design stages of the Knickerbocker Project. Stay tuned for announcements when it happens.

Knickerbocker Floodplain Construction Friday

Residents around the Knickerbocker site of Thornton Creek (the intersection of 20th Ave NE and NE 100th Street) received a notice late today from Seattle Public Utilities,

There will a construction crew working at the Knickerbocker site tomorrow, June 22, 2012, from approximately 8 a.m. to 5 p.m. They will be drilling seven (7) groundwater wells 6-8 feet deep using an excavator with a small drill rig. It will generate some construction noise. The wells will be capped when they’re done.


There will be another crew there next week to hand-dig three (3) additional shallow wells, approximately 2-3 feet deep, for devices that will show the elevation of the stream. All work will be done next to the stream and not in the water itself

More information is available at the SPU site.