Clark Fork River gets closer to lagoon

The commander of the U.S. Army Corps of Engineers Seattle Division visited Plains Sunday to take a look at the progress and evaluate the erosion situation at the town's Wastewater Treatment Plant at the end of Helterline Drive.

Col. Mark Geraldi spent part of the day looking over the two sites where riprap was placed to halt erosion by the Clark Fork River. A crew was still working on the second site while the colonel was here. Since the previous Sunday, the Corps of Engineers and contractors have been working 12-hour shifts every day to keep the river from reaching the sewage lagoon. Several hundred feet of large rocks were set along the shoreline near the plant's UV facility and on property owned by Randy Garrison, which is adjacent to the town's 46-acre sewage facility. A portion of the river has already cut through Garrison's property and came within about 25 feet of one of the treatment plant's structures, although the water is near motionless and the structure is about 10 feet higher. Doug Weber, the corps' District Emergency Manager, didn't believe the water would reach the building.

The site at the lagoon was finished earlier last week, however, engineers noticed that the river was cutting a channel through a second section of Garrison's property in an old flood channel that had flooded to Helterline six years ago. Workers were in the midst of filling 1,200 feet of the secondary shoreline with riprap on Sunday and expected to be done this week.

Sanders County Emergency Manager Bill Naegeli said the river was supposed to peak on Sunday and start receding by the end of the week. Rowan checked on the water level at the lagoon Monday and said it appeared to have dropped about a foot and a half.

We're not out of danger yet, we're looking at more water next week," said Plains Mayor Dan Rowan, who got the Corps of Engineers involved by declaring an emergency. Rowan said that the National Oceanic & Atmospheric Administration – NOAA – predicted that the water would rise again Saturday before receding a second time. Naegeli said it's not so much the level of the water as it is the currents, which does the most damage to the shoreline. He believes the Clark Fork River is flowing at about seven knots.

The Corps of Engineers are not allowed to deploy to save personal property, unless by doing so it protects public property, said Bill Dowell, a public affairs specialist with the Seattle District.

Weber said they would be putting some 5,250 tons of riprap at the two sites during the course of the week. He said the first site, at the treatment plant, looked stabilized and he believes the second spot will also stop the erosion.

The crews were placing the riprap at the second site about two feet deep and at a width of 12-15 feet, some of which was placed in the water. The excavators made a slope at the river bank to help stabilize the rocks. Once the rocks were placed, the excavator used the weight of its bucket to press down on the boulders.

"I think we successfully mitigated the flood risk to the lagoon," said Geraldi, who also visited various sites in Missoula and is responsible for emergency response in Montana, Idaho and Washington. "The most impressive thing to me was the speed of the execution here," said Geraldi, referring to the high number of dump trucks that were ready to deliver the rocks from the Perma quarry and the two excavators from Alberton. The Corps of Engineers have supplied Missoula with 275,000 sandbags, he said. Because it was declared an emergency situation by the Plains mayor, the project is federally funded and there is no cost to the town. If the town would have had to flip the bill for the work, it would have cost $480,000, according to Weber.

The Town of Plains created the treatment plant 35 years ago and has been concerned about erosion ever since the river currents diverted in the mid 1990s. The town council had already approved a plan to place a steel barrier up near the UV facility at a cost of $1.1-million, but the work depended on getting government grants to cover the cost. Riprap had been used previously – and had washed away – but never at the extent of this most recent project.

Rowan believes the Corps of Engineers' actions saved the treatment plant. Geraldi told Rowan that the Corps of Engineers would work with the town to find a more permanent solution to the erosion problem.