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ARMY CORPS OF ENGINEERS Jacksonville receives permit to modify unsafe dam Comment By Tony Boom for the Mail Tribune MailTribune.com By Tony Boom for the Mail Tribune Posted Jan. 11, 2016 at 12:01 AM By Tony Boom for the Mail Tribune Posted Jan. 11, 2016 at 12:01 AM » Social News JACKSONVILLE — Creation of a larger spillway for the city’s reservoir dam on Jackson Creek to prevent its collapse in a catastrophic flood has been given a go-ahead by the U.S. Army Corps of Engineers. Enlarging the existing spillway will be less costly than other proposals considered, such as notching the dam and reconstructing a stream bed in the reservoir. A variety of scenarios were considered, one estimated to cost up to $767,000. City Manager Jeff Alvis said he hopes the spillway work can be done for about one-third of that figure. “There have been about 15 different designs,” said Alvis. “We are breaching it and then putting in the riprap (piled stones or chunks of concrete) so it won’t erode the face of the dam.” The dam was constructed in 1910 to serve the water needs of Jacksonville. Use was discontinued in the 1950s, and much of the reservoir has filled with sediment. A 1999 inspection by the state’s Dam Safety Division led to its classification as a high-hazard dam. Alvis has directed City Engineer Scott Pingle to prepare a request for proposals to perform the work. He hopes to have the project completed next summer. In-water work can be done only between June 15 and Sept. 15. Up to 873 cubic yards of material can be placed in the creek to create the new spillway. “Most of the material is being imported. It will come from a fresh source. Primarily it's riprap,” said Omar Ortiz, project manager with the Corps’ Eugene office. Some of the concrete from the demolished old spillway will be used. Sediment in the reservoir will not be removed, said Ortiz. “My understanding is that just wasn’t an affordable option for the city," said Ortiz. While much of the current dam will remain, the project is regarded as a breaching. Project specifics include: Demolition and removal of the old concrete spillway, to be replaced with a 10-foot-wide channel capable of passing storms that exceed FEMA’s 500-year flood flow figures. Placement of removed material and debris from the spillway in designated areas. The material would be compacted and planted with vegetation to provide slope stability. Placing a log-boom in the impoundment to catch large logs and other debris that might clog the newly configured spillway. At its deepest, the new spillway would be approximately 12 feet below the current dam face slope. A scour hole below the new riprap spillway would be filled with concrete from the old spillway. Work won’t begin until the water level in the reservoir drops. Under the permit, a sump pump can be placed in the reservoir to help drain the site, said Alvis. Alvis hopes to place all removed materials below the dam in areas designated in the permit. But the permit also allows placement adjacent to the reservoir and in an old quarry site across a road from the dam’s west end. The Oregon Department of Environmental Quality, Oregon Department of Fish and Wildlife, National Marine Fisheries Service and Oregon’s Division of State Lands have consulted on the project. Planning to correct the situation began in the fall of 2013. The city has $200,000 set aside for the project, with additional money set aside for engineering. Tony Boom is an Ashland freelance writer. Reach him at [email protected] By Tony Boom for the Mail Tribune MailTribune.com By Tony Boom for the Mail Tribune Posted Jan. 11, 2016 at 12:01 AM » Comment or view comments Reader Reaction » STAY INFORMED Email NewsLetter Sign Up Today Sign up for our newsletter and have the top headlines from your community delivered right to your inbox. Southern Oregon Directory Featured Businesses Loading... 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