As the Snoqualmie River shifts and erodes the riverbank, the risk of collapse becomes a threat to the safety of the community and to the river itself. To combat erosion, the city of Snoqualmie has partnered with King County to install 400 feet of riverbank stabilization.
The city council authorized the city to enter an agreement with King County to install revetments along a county-owned portion of the Snoqualmie River that had been the site of a riverbank collapse in 2016. The collapse, at the corner of Southeast River Street and Park Avenue Southeast, exposed city utility pipe that has since been moved.
Per the agreement, the city will manage design, permitting and bid solicitation for the project and King county will fully reimburse related expenditures for a total of more than $509,000. The council also approved an agreement with Northwest Hydraulic Consultants (NHC) to conduct design and permitting for more than $360,000, which falls within King County’s funding.
Senior planner Nicole Sanders said the city took on the work of design and planning despite it being county land because that area is part of the riverwalk project, a multi-phase trail plan to create a walkable path through the city along the river. Because that site was already in need of riverwalk improvement, the city can design and integrate riverwalk considerations into the bank stabilization.
With the agreement approved, the city will hold a kickoff meeting with stakeholders to review the project and will begin data collection efforts to inform the design process. A geotechnical assessment of the soils is needed, Sanders said, to determine if pilings need to be put in to the bank. NHC will also do a bathymetric survey, a method of mapping and examining the bottom of the river, to determine how the river flows and what type of stabilization is needed.
The data collection process will begin now, with conceptual design work expected to start in three to four months.
As for the stabilization work itself, Sanders doesn’t expect the project to go out to bid for contractors until 2021 due to the time expected to receive permits. Getting a Corps of Engineers permit can take as long as a year on its own, she said.
When asked about the cost of the next phase, the actual development of the revetments, Sanders said she expected the cost to come in at about $700,000.
The council voted unanimously to approve both the agreement with King County and the contract with NHC.