The river banks along the Wynooche River at Montesano’s water treatment plant are still eroding.

Engineering studies by Parametrix, a consulting firm, found that the original plan to fix the problem, installing “rock groins” along the river in hopes of mitigating erosion, would not achieve the desired results, according to Montesano City Councilman Dan Wood.

Rock groins, structures placed in the river aimed at displacing the flow of water before it reaches the eroding banks, would do the job, but only in those immediate areas where the groins are placed. Areas to the left and right of the groins would still be problematic and would be in danger of erosion.

“It could turn the whole facility into an island,” Wood said of the erosion.

On the other hand, doing nothing is not an option.

“If nothing is done, the river will erode around the plant and would even threaten Highway 107,” Wood said.

Furthermore, Wood said, effluent would go down the Wynooche and into the Chehalis River.

“It’s just not good for the environment,” Wood said.

Aside from environmental concerns, Wood noted that the water treatment facility is a $50 million physical plant. If nothing is done, costs to repair or reconstruct the facility would be far greater than the $5 million sought for the new mitigation construction.

“Something needs to be done, and very quickly. It’s a $50 million physical plant,” Wood said.

The Chehalis River Basin Flood Authority has submitted to the Legislature a $12 million request for various projects, one of which is the $5 million water treatment plant project. The new project will entail sheet piling and the use of a relic channel of the river to mitigate bank erosion.

Sheet piling, as described by Wood, is the process of driving metal walls deep in the ground to help absorb the impact of the river, and keep it from coming any closer to the plant.

“It is not a permanent solution, but it is necessary to prevent the breach,” Wood said.

A breach of the treatment plant would send waste down the river and create an ecological disaster for Montesano and any residents downstream.

In opening the relic channel, large debris will be removed to hopefully open the channel to the flow of the river.

Wood described the process as “unclogging the drain.”

By redirecting the river’s flow, Wood says a lot of the impact will be taken off the water treatment plant.

If people saw the erosion firsthand, Wood believes they would realize that something needs to be done.

“There’s nothing like seeing something to develop a sense of urgency,” Wood concluded.