The Channel Sediment Removal Project
Dredging the channel
October 31, 2022
Sediment is being removed from the channel between Upper and Lower Twin Lakes to improve water quality for wildlife, boaters and the overall community.
The Twin Lakes Improvement Association, a nonprofit formed in 1956 to improve and preserve the historic natural values of Twin Lakes, is working with Idaho Fish and Game, and has retained the services of Envirodredge to remove approximately 8,600 cubic yards of organic material and 330 pounds of phosphorus to improve navigation and water quality in the channel.
The Channel Sediment Removal Project will deepen the navigation corridor to 50 feet wide and up to 7 feet deep, removing 2 feet of sediment on the channel floor. No lily pads or wetlands will be removed…
While boating through the Channel between our two lakes last summer you may have noticed a plume of muddy sediment kicked up by your propeller. That plume is a clue to a problem beneath your boat we need to address. Since dredging was done in the mid-1950s, sediment and aquatic vegetation has filled the channel to the point boats can barely navigate and on occasion pass so close to each other that safety has become an issue. The shallow navigation channel is a major concern because it greatly limits boat access between the lakes late in the summer, and it can cause expensive damage to boat propulsion equipment. Also, propellers of each passing boat stir up nutrients that degrade water quality by promoting growth of aquatic vegetation.
Your TLIA Board is completing a plan to address this pressing issue. In the spring of 2022, we received permits to suction dredge about two feet of sediment across a 40-foot-wide navigation channel between the narrows at Upper Twin Lake east to the bridge at the entrance to Lower Twin Lake and north from the bridge to the channel boat launch.
The Board retained the services Envirodredge, an experienced company, to help us implement the project. The dredging phase of the project was conducted in October of 2022. Dredging removed 5,350 cubic yards of sediment. Sediment was pumped up to 2,000 feet via floating pipeline to the channel boat launch area. Polymers were then added to the slurry to help separate the water from the sediment and then pumped into two large geo-textile bags for dewatering. Dewatering of the filter bags has taken place over the past six months. In May, the residual sediment will be loaded and hauled about 3 miles to the Scarcello ranch to be used as a soil amendment. The boat launch site will then be cleaned up and restored to use by about the end of May. We expect this project to greatly improve late summer navigation through the channel and reduce nutrient loading to Lower Twin Lake.
Estimated project costs are approximately $250,000. Funding is still needed to support hauling of the dewatered sediment and for cleanup efforts this spring. If you would like to contribute to this project, you can donate under “How to help” tab on the website. We will update you on this project as more information becomes available.
If you have questions about the project, please contact Mike Knowles at (509) 863-4359, Doug Jayne (509) 710-7188, or Debbie Andrews at (724) 553-8779.