212th Avenue SE at Ebright Creek

Project Overview

12th Avenue SE is a north/south arterial roadway in Sammamish, currently one of only four north/south arterials for access off the Sammamish Plateau to highways and the neighboring cities of Redmond and Issaquah. This portion of 212^th Avenue SE floods during significant rain events and the roadway support infrastructure is failing. The loose wetland soils are being compacted by the weight of the road, causing it to slowly sink. The combination of the settling road and changing environment appear to be increasing the frequency of roadway flooding during the winter, and the existing gabion baskets supporting a section of roadway are deteriorating. Proactively reducing the risk for complete road failure will protect the minor arterial access route for residents, school buses, and EMT/Fire vehicles.

In 2025, a feasibility study for the project area was completed to help plan and scope the project for completion in future years. The feasibility study, often referred to as an alternatives analysis, evaluated the failing portion of the road to determine the most effective wetland crossing that proactively reduces the risk for eventual road failure due to flooding and aging infrastructure. The study analyzed three different design alternatives and prepared planning level cost estimates for each option. The three options are:

Maintaining the existing roadway and make repairs as needed
Reconstructing the roadway with lightweight cellular concrete (LWCC)
Replacing the existing roadway with a bridge that spans the Ebright Creek wetland complex

What's the latest?

2025, Quarter 2

The City is currently evaluating the three design alternatives and will select the best option to bring through the design phase.

History and Background

The 212th Avenue corridor (originally called Louis Thompson) was established in 1916 and constructed of gravel. At that time the Ebright Creek wetland was a cranberry marsh. Over the years the road has been updated and improved. The most recent update for this section of roadway was in 2003 when the Crossings at Pine Lake development was constructed. The improvement replaced the concrete barrier on the west side of the roadway with a sidewalk.

The roadway sits on top of multiple soil layers deposited by glaciers and stream activity. There is a significant layer of alluvium soils and peat - clay, silt, sand or gravel and organic soil formed by plant decay - which has been loosely deposited by running streams over thousands of years. These loose layers of material continue to slowly settle over time.

Environmental factors like weather, wildlife, and human modifications have an impact on rainwater flowing through the creek and wetland. These factors cause the water levels to rise during large storm events and combined with the settling soils, lead to increased amounts and frequencies of roadway flooding.

In 2021, the City applied for a FEMA BRIC grant (Building Resilient Infrastructure and Communities) to repair the roadway but design work had not yet been initiated and the project was not able to advance for final scoring.

Funding

This study is funded with local dollars programed in the Transportation Capital Improvements and Surface Water Capital Projects Funds

212th Ave SE at Ebright Creek

Project Engineer

What's the latest?

History and Background

Funding

Additional Information