SEASIDE The Seaside City Council heard a proposal Monday night that could reinforce the deteriorating bank where the citys wastewater treatment plant sits south of the Necanicum estuary.
Public works Director Neal Wallace estimated that only 8 feet of a sand bank sits between the fence on the north side of the plant and the Necanicum River, which has already significantly undercut the bank.
Although the sewage plant itself is not yet in immediate peril, Wallace said, the fence and auxiliary buildings are threatened by winter storms that push the river into the bank.
He introduced Evan Engber, president of BioEngineering Associates, a Charleston-based company that specializes in stabilizing eroding riverbanks.
Engber showed a short video that displayed how the company reinforced 1,300 feet of a 40-foot high riverbank on the Mad River in McKinleyville, Calif.
Layers of boulders, and dirt were placed where the erosion had occurred, and each layer was wrapped in special cloth designed to hold it in place. Live willow tree trunks were laid over each layer. Then more layers of rocks and dirt, covered by the cloth and the willows were placed on top of the first layer, until the layers reached the top of the bank.
Eighteen months after the projects completion, the riverbank was covered in willows, and it was difficult to tell any construction had occurred. Engber said the shade from the willows hanging over the river attracted shelter-seeking fish to the water, and a new habitat had been created.
Engber showed photos of a similar riverbank restoration project on the Russian River in California.
Estimating that at least 1,000 feet of Seasides riverbank along the Necanicum estuary needed to be reinforced, Engber called the erosion near the wastewater treatment plant kind of a dire situation.
The fence and auxiliary buildings sit only about 25 feet on top of a sand dune, which is coming apart pretty badly, Engber said.
He noted, however, that the nearest homes, at 800 feet away, arent in immediate danger.
Cam Parry, an engineer and Engbers associate, said the Seaside project was challenging because of the tidal exchange and the river, which changes course and force in the winter.
Wallace agreed that, in winter storms, the river slams into the bank.
Every time it comes at us, we lose 40 to 50 feet of ground, and we dont have 40 feet of ground to lose, Wallace said.
When asked by City Councilor Jay Barber if the bank could last another winter, Wallace replied, I dont know if it can.
The major erosion is caused not by the ocean, but by the river channel. We have a meager area there.
To protect the area immediately, Engber suggested taking the trees that have already fallen on the bank because of the erosion and placing them into a monumental pile with rock placed on top of them as an anchor.
That pile would be removed when the permanent project begins, Engber said.
Although an estimated cost to stabilized the riverbank wasnt discussed, Engber said the Mad River project cost close to $1 million. Parry said funding would be sought from state and federal agencies, and Oregons congressional delegation would be consulted.
A major cause for the river to approach that area of the estuary so forcefully is a build-up of rock that was placed in the estuary by a developer in the 1960s who wanted to build homes there. Although the development never occurred, the rock foundation remained, and the river hasnt been able to follow its natural course since, Wallace said.
Depending on how the sand shifts at any given time, the rock could be within the Seaside city limits or it could be within Gearharts city limits, and, therefore, unavailable to be removed, Wallace said.
In 2004, the U.S. Army Corps of Engineers studied the ongoing erosion and decided that the revetment it had placed along the bank in 1949 was enough at the time. The Corps said it would do more work if damage was sustained, Wallace said.
Once the fence is undermined, that means the plant is sustaining damage. It may be that were looking at emergency funding, he said.
In the next few weeks, BioEngineers will submit a proposal for a stabilization project to the city, said City Manager Mark Winstanley. The proposal will be submitted to the City Council to consider.