Dam-notching project costs balloon
JACKSONVILLE — Notching of the Jacksonville Reservoir dam and clearing sediment from the basin may be two years away as the city looks for funds to carry out the project that has grown with detailed engineering studies.
“We’ve got to find the money. Our hope would be doing it next summer,” said City Administrator Jeff Alvis. But the following year is more likely, he added.
The dam has been labeled a hazard for people and property below it on Jackson Creek, according to state dam safety experts. Failure is likely in a major flood. Use of the dam — built in 1912 — was discontinued in the 1950s, and sediment has filled most of the reservoir, which lies within the town's Forest Park.
Plans developed by Applied Geotechnical Engineering of Medford and other contractors are now being reviewed the state’s dam safety officer prior to submission to the Army Corp of Engineers, which must issue a joint work permit for the project with the Division of State Lands.
City cost estimates for the project are $528,310, including a 15 percent contingency. Major expenses include $200,000 to excavate sediment, $126,000 to dig and construct a new stream bed, and $50,000 to plant riparian and slope areas.
“I had no idea it would be this expensive,” said Mayor Paul Becker. The city set aside $200,000 toward the work in the current fiscal year budget. Grants may be available to help with planting.
A preliminary study done by the Rogue Valley Council of Governments in 2010 estimated less work, but that study did not include detailed engineering.
An initial project description estimated that 30,000 cubic yards of sediment would need to be removed. That figure has grown to 50,000 yards. Studies determined the material could be left on site with proper handling.
“The one advantage we have is leaving the dirt on site,” said Alvis. Hauling materials away would have increased costs. The material will be placed on slopes adjacent to a new stream bed.
Containment of the sediment is critical, said citizen volunteer Tony Hess, who is assisting the city. Hess had supervisory experience with dam and mining projects while he worked for a Salt Lake City engineering firm.
“The Corps of Engineers is very concerned about slope stability,” said Hess. “They will want to know what will stay.”
Revegetation of the slopes to prevent erosion will include an estimated 10,000 trees, shrubs, flowering plants and grass plugs over six acres, according to Northwest Biological Consulting.
Initial plans also envisioned a narrower dam notch. The notching may now be larger.
“We’ll be removing the biggest portion of the dam,” Alvis told City Council in early September. An exact amount has not been determined, because the state is still reviewing the plans.
A meandering rip-rap stream channel would be created when sediment is removed. The channel would be about 800 feet long and 3 feet deep, with a 5 percent slope.
Jackson Creek is a fish-bearing steam up to the toe of the dam, but not above. Because anadromous fish cannot get past a culvert at Hanley Road, no funds for restoration would be available from the Oregon Watershed Enhancement Board to help with the work, Hess said.
Others working on the plans include the city’s engineering firm, KAS Engineering, Cascade Stream Solutions and K & C Environmental Services. About $50,000 has been spent on engineering and plans, said Alvis.
“This is not a cookie-cutter project,” Hess told the council. “You have a construction project, and you have to consider the safety of it. In the end, a professional engineer puts his PE stamp on it.”
Tony Boom is a freelance writer living in Ashland. Reach him at firstname.lastname@example.org.