In summer 2014 work will be done to enlarge the capacity for water at the point of NE 107th Street where the South Fork of Thornton Creek crosses under 35th Ave NE. Some tree removal will be required to create more space for the creek channel.

Road closure update:  As of June 2nd, 2014, 35th Ave NE is CLOSED at NE 107th Street.  Summer construction work will be done to enlarge the creek bed of the South Fork of Thornton Creek and put in new, much larger culverts under the road.

The Thornton Creek Watershed of northeast Seattle flows toward Matthews Beach at NE 93rd Street on Lake Washington. The Confluence is the flat area along 35th Ave NE between NE 107th to 115th Streets, part of the Meadowbrook neighborhood. It is the site of convergence of the North and South Forks of Thornton Creek, and many smaller tributaries join in this area, as well. The creek system flows into Meadowbrook Pond at about NE 107th Street on the east side of 35th Ave NE. The Pond collects and filters the water before it flows down to Matthews Beach and out into Lake Washington.

The vegetation-choked channel of the South Fork of Thornton Creek flows eastward into a culvert under 35th Ave NE. In the summer 2014 Confluence Project, the channel will be enlarged and new culverts put in under 35th Ave NE.

The year 2014 is the final stage of a three-year effort by Seattle Public Utilities to improve the creek and pond environments, increase capacity for water and thereby help prevent flooding in the surrounding areas.  Beginning in May, the creekbed at about NE 107th Street on both sides of 35th Ave NE will be widened, deepened and improved for more capacity, thereby preventing flooding. “Meanders” will be created with a floodplain to help absorb water. Under 35th Ave NE, going across at about NE 107th Street, new, much larger culverts will be put in, and for this reason 35th Ave NE will be closed at that point for the summer of 2014.  Buses will be rerouted over to Lake City Way NE along NE 95th and 110th Streets.

On the east side of 35th Ave NE at NE 107th Street, this willow tree is all that remains on the site of a former house, torn down to create a flood plain for the creek in 2014.

A very large number of trees will have to be removed at NE 107th Street on both sides of 35th Ave NE, because they have become too big and are choking and narrowing the creek channel. This includes the poplar trees along the creek on the west side of 35th Ave NE, going toward Nathan Hale High School; the willow tree in the empty lot on the east side at about NE 107th Street; and a few of the flame ash street trees at that point where new culverts will be put in underneath 35th Ave NE.

Why is Seattle Public Utilities doing this project?

For years, the Confluence of the North and South branches of Thornton Creek has been prone to flooding. High waters have frequently inundated nearby homes on both sides of 35th Ave NE, flowed over 30th and 35th Avenues NE and up onto the parking lot of Nathan Hale High School.

To fix the problem, Seattle Public Utilities will remove an undersized culvert under 35th Ave NE and realign the existing creek channel through a new two-acre floodplain.  Having more space for the water to spread out and be absorbed, aims to prevent flooding.  The wider channel and the floodplain connection will also help native fish habitat by spreading out and slowing the peak flows of Thornton Creek.

Annie’s Playground on Meadowbrook Field will be accessible during the summer, by coming through the Nathan Hale High School parking lot (in background.) The poplar trees lining the creek will be removed to widen the channel and create meanders.

To perform the work, it will be necessary to close a section of 35th Ave NE between Northeast 105th to 110th Streets for some months, with road closure now in effect as of June 2, 2014. There will be local access-only traffic, including access to the Meadowbrook Community Center and Swimming Pool just north of NE 105th Street.  During the construction period, Annie’s Playground at Meadowbrook will be usable. The playground will be fenced off but can be entered from the side nearest to the Nathan Hale High School parking lot.

Seattle Public Utilities is working with federal scientists (U.S. Fish and Wildlife Service and NOAA Fisheries Science Center) to measure project performance by comparing existing conditions with post-construction changes in floodplain storage, habitat conditions and biological response (abundance and diversity.)

In 2013 this enlargement of Meadowbrook Pond was created to increase its capacity for holding and filtering water. The summer 2014 creek channel and culvert work is the third and final phase of improvements.

Along with the ecological benefits of restoring stream and floodplain processes to the Thornton Creek Confluence Reach, the project will reduce the City’s operating costs at nearby Meadowbrook Pond by reducing the frequency of dredging needed at the Pond, currently averaging every three to five years.  The Pond has worked so well to filter the water, that it has had to be dredged more often than anticipated when it was created in 1996-98.  It is important that the water be filtered at Meadowbrook Pond and cleaned of sediment before the water continues flowing on down to Matthews Beach and out to Lake Washington.  This will help keep Lake Washington clean and will help prevent silt from building up and plugging up the creek, which would lead to more flooding.

At a well-attended info session on May 13, 2014, Meadowbrook residents asked questions about the upcoming Confluence work.

A private contractor, Westwater Construction, has been hired to do the creekbed-modification work in this year of Confluence improvements, as well as the new culverts to be put under 35th Ave NE at NE 107th Street.  All aspects of the work have to be coordinated with Seattle Public Utilities (SPU) and with Seattle Department of Transportation (SDOT.)  Some tree-removal work will be done by Westwater Construction and some by a logging contractor.  Some of the logs will be used for stream structures, some of the logs may be sold and some will be ground up for mulch.

The time of summer 2014 construction and the need to detour around the site will be arduous, but worthwhile.  We can look forward to recreated creek channels with scenic views, a reduction in flooding, and the planting of new trees and other landscaping to restore the area.