Dredging project explained

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Jeremy Ryf with the state Department of Ecology listens to US Bureau of Reclamation representative John O'Callahan answer a question.

MOSES LAKE - People involved in a plan to remove sediment from Parker Horn in Moses Lake explained their plans.

Representatives from the firms planning the dredging, the Moses Lake Irrigation and Rehabilitation District, the City of Moses Lake and the state met and answered questions during a recent forum at Big Bend Community College. They talked about plans to remove sediment from the lake next to Alder Street.

Glenn Grette, a senior biologist and principal with Grette Associates, explained his firm became involved in the project after the district tried for several years to dredge the lake.

"The district had been trying for a couple years to permit some dredging action at Parker Horn and elsewhere," he said. "Those had not been going well through the permitting process. In addition, through some misunderstanding, the district had taken some action and started to dredge ... that created a real difficulty between the agencies and the district."

Grette's firm was hired to examine the sediment problem in the lake and how to manage it and develop a plan to protect the lake, he said.

"It was decreasing the open water habitat for fish and wildlife," Grette said. "There was an environmental component to what was going on. We saw blockages occurring to boating facilities as well as recreational boating areas. Water quality is getting degraded."

The firm's conclusion was if nothing was done the quality of the lake was going to deteriorate quickly, he said.

When the firm examined the lake, it found natural and human sources of sediment coming into it, Grette said. About 85 percent of the water running into Moses Lake comes from the Rocky Coulee Wasteway, 10 percent comes from Rocky Ford Creek and 5 percent from Crab Creek.

Grette said the sediment management plan developed for the district addresses eight different areas, and Parker Horn is one of them.

"The decision was made to go there first because it was a place where sediments were being (put into) the lake," he said. "It seemed to make the most sense to hit those areas first to short stop the materials coming into the lake."

He explained the shoal in next to Stratford Road has grown to a point where it has created a channel, which is now carrying sediment past the fill and depositing it on the other side of the fill.

"So what we see starting to happen now is a condition that occurs above the crossing starting to develop below the crossing ... because it can not stop in this portion," Grette said.

Grette and engineer Vladimir Shepsis, of P.E. Coast and Harbor Engineering Inc., Developed a plan to create a trap for the sediment. The plan calls for creating a hole in the bottom of the lake where water will slow and deposit the sediment before it goes into the rest of the lake.

Shepsis developed a range of sediment traps which could hold between 30,000 cubic yards and 240,000 cubic yards, Grette said.

"You can build that range of sizes of a hold in the mud to trap the other mud as it goes by," Grette said. "These types of options vary by how frequently you have to dredge them out and, of course, the effort it would take to construct it."

The firm received a permit for the maximum amount of 240,000 cubic yards, he said. The permit gives the district flexibility on how to implement the trap.

Shepsis explained the plan calls for dredging part of the shoal off during the first year, then possibly creating a channel on the other side of the shoal, speeding the water past both sides of the shoal.

"We said, 'Instead of chasing these particle sediments all over Moses Lake why don't we create in one location, a sediment trap - trap the sediment in one location where it's easy to extract the sediment," he said.

To create the basin, the district plans to use a hydraulic dredge, Shepsis said. The boat is able to remove 140 cubic yards of material an hour and pump it a mile away. The plans call for creating a pond to allow the sediment to settle of the water and return the water back to the ground.

Grette said the permit allows the district to dredge, starting July 1 until Nov. 30. The district is also allowed to dredge in March.

"Those are just based on trying to keep out of some of the fish and wildlife time periods that are important," he said. "It's typical practice for in-water work to have an established time period you can work in and avoid the more sensitive time periods."

Jeff Korth, from the state Department of Fish and Wildlife, said the project's impact on fish and wildlife in the area will be neutral.

"The idea here is to maintain the structure of the lake, more or less the way it is now, improve the channelization of the water through ... but maintain fish and wildlife habitat as you see it out there," he said. 

District Manager Curt Carpenter said the district has enough revenue to afford the dredging project and other projects presently planned.

"It won't raise the taxes, but it will increase the property values and also help with sustainability with the community in bringing dollars to the restaurants and gas facilities and bringing people into the community for recreational purposes," he said.

Carpenter said the dirt from the dredging will be used at Connelly Park, and the permit requires it to be used for a beneficial use. He explained the state Department of Natural Resources (DNR) owns the bottom of the lake, and the district needs to keep track of the sediment it takes.

"If it goes to a local jurisdiction, public uses, we don't have to pay DNR for that," he said. "If it does go for other uses there is a fee per cubic yard for that material."

When Grette was asked why the district can't use construction equipment to dig the sediment trap, he said the district tried it in the past.

"That's an interesting question. That's how I got involved in this project," he said. "There are a lot of rules as to how you work below the water line and the jurisdictions that are involved, depending on how you do the work."

He said any action including driving equipment onto the shoal creates problems with getting a permit, and brings in federal jurisdiction into the project.

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