Montesano, WA is a town of around 4,000 located 40 miles southwest of the state capital. For years, the City’s wastewater treatment plant has been peacefully located along the banks of the Wynoochee River. However, now movement of the river threatens to overtake the treatment plant. The bank continues to erode at an alarming rate of 17 feet per year. If this pattern were allowed to continue, the river could breach the plant, sending millions of gallons of raw sewage spilling down the Wynoochee, into the Chehalis River, affecting many communities along the way and eventually making its way to Puget Sound.
Parametrix is working with the City to implement a multi-faceted sustainable solution that takes into account the river’s ecosystem and the longevity of the wastewater treatment plant.
Log jacks have been placed in and near the river to deflect the flow away from the plant. The log jacks, composed of lengths of tree trunks and large boulders, are an innovative method of streambank protection that mimics natural processes and provides aquatic habitat while minimizing more typical hard armoring techniques.
The first phase of the project to address upstream scour and erosion was completed in 2018. A series of launchable log jacks were constructed on the upstream bank above the ordinary high water line. The log jacks naturally fell into the Wynoochee River as the bank continued to erode. With this innovative approach to the project, the first phase was able to address the immediate need of scour abatement, while buying time to develop a permanent solution to address river velocity deflection.
The second phase of the project, which involved placing in-river log jacks adjacent to the treatment plant’s sheetpile wall, was recently completed. This phase was designed and permitted so the log jacks could be placed in the river during the Wynoochee River’s 2019 summer in-water fish work window, when low water conditions greatly reduced the amount of in-water work needed.
The permanently placed log jacks are already creating a noticeable change to the flow path of the river. It is anticipated that the log jacks will ultimately protect and improve the quality and quantity of essential fish habitat, as well as create additional channel complexity.
Improvements to the wastewater treatment plant include moving sludge handling and effluent piping away from river encroachment, UV disinfection upgrades, electrical and SCADA upgrades, building modifications, process piping modifications, effluent pump station upgrades, and conversion of a lime slurry feed system to magnesium hydroxide.
This project has led to an innovative and cost-effective long-term solution to protect and upgrade the City of Montesano’s wastewater treatment plant in addition to providing valuable habitat. This multi-benefit project is a prime example of how critical community infrastructure within the floodplain can be protected while providing valuable opportunities for habitat protection and uplift.
About the Author
Matt leads Parametrix’s community building division in the Puget Sound region and also serves as a project manager. He began his career as a land surveyor and then moved into construction management. He now has 20 years of experience managing and coordinating various construction projects.