Paonia Dam repairs slated for this fall
By Tamie Meck
Published Wednesday, August 23, 2017 9:00 am
About 60 individuals attended an Aug. 15 public presentation by the Bureau of Reclamation to address ongoing efforts to minimize water storage loss at Paonia Reservoir. Attendees represented water companies, water users, commercial and recreational users, neighboring landowners, environmental organizations and other interested parties.
The earth-filled Paonia Dam and Paonia Reservoir are part of the federal Colorado River Storage Project approved in 1956 to provide needed irrigation water to the area's fruit growers. The CRSP's Paonia Project included construction of the Paonia Dam and Fire Mountain Diversion Dam, and expansion of the Fire Mountain Canal. Since completion of the project in 1962, the reservoir has stored supplemental water for Fire Mountain Canal and Reservoir Company's (FMCRC) 488 shareholders, and provided irrigation water late in the season when demand is high and creeks are running low. Water carried by the canal reaches some 15,300 acres of agricultural land around Paonia and Hotchkiss.
Ed Warner, area manager Western Colorado Area Office of Reclamation, called water "the lifeblood of this valley."
According to a 2015 Reclamation sediment modeling report, the reservoir's main water source, Muddy Creek has deposited an estimated 101 acre feet of sediment a year into the reservoir since 1962, reducing active storage capacity by about 25 percent. Three times in the past 55 years, in 1977, 2002 and 2012, supplemental water storage was depleted prior to the end of the growing season and the Fire Mountain Canal was turned off early.
Reclamation is working with the North Fork Water Conservancy District, which operates and maintains the dam, the FMCRC, the USGS and others to study both short- and long-term solutions to water storage loss. The first efforts to flush sediment date back to 1997.
Beginning in mid-September, Reclamation will undergo efforts to repair damages to the dam's water intake tower. The damage was discovered when the reservoir was drained for dam inspection in 2014. The bulkhead is encased in a trashrack at the top of the roughly 70-foot high concrete intake tower and sends water to the dam's outlet works, explained FMCRC superintendent Steve Fletcher. When properly placed, a large rubber seal at the bottom of the bulkhead works like a big sink stop to prevent water and debris from flowing into the dam's outlet works. Fletcher explained how a large air pocket formed in the outlet works forced air and water back up the intake structure, lifting the bulkhead up and dropping it back down.
Without a functioning bulkhead, in high water the intake tower can't be shut off and the dam's outlet works can't be accessed in the event of an emergency. Complicating matters, sediment now reaches the bottom of the trashrack and has filled the reservoir's dead pool. If the sediment plugs the outlet works, "Then we've got real problems, especially if it happens with a reservoir full of water," said Fletcher.
In addition, if the bulkhead breaks and falls into the intake tower during construction, it could damage or plug the outlet works, leaving the spillway the only means of releasing water and resulting in uncontrolled releases.
The project involves dismantling the damaged upper portion of the tower and replacing it with a modified aluminum support system and trashrack. The temporary fix won't fully restore the bulkhead's function, according to project representatives, but it will stabilize the intake tower until a long-term solution can be developed and implemented.
Repair work is expected to run from late September to early November. The work needs to be done between the end of irrigation season and when the reservoir begins to freeze. Freezing would affect the ability to work on the intake structure, said Fletcher.
In mid-September Reclamation will begin a drawdown of the reservoir and a release of sediment from around the tower and into Muddy Creek. The timing of the drawdown is intended to minimize impacts on users, said project lead and Reclamation engineer, Bill Dressel. To avoid further blowback through the intake structure, releases are expected to stay below 200 cubic feet per second during drawdown. Heavy equipment will be staged at the dam throughout construction.
Based on data collected during prior releases, the majority of sediment released is expected to settle within first 2,000 feet of the dam and will likely remain there until spring runoff carries it down to the Colorado River, said Dressel.
Once temporary repairs are complete, the focus will turn to long-term solutions for water storage loss and repair of the intake tower. Efforts to release sediment through drawdown would begin next spring, and are expected to increase turbidity and sediment levels in the North Fork of the Gunnison as far down a Hotchkiss. Sediment would be carried to the Colorado River during high water.
The long-range goal is to maintain future water supplies, minimize the reservoir storage loss, manage debris, minimize abrasion, and to continue monitoring and management of sediment levels in the reservoir.
Models show that about 80 percent of annual accumulation can be released into Muddy Creek through spring drawdown. Dressel said that Reclamation is "very aware" of the 15-20 percent of sediment that remains, and that the amount of federal funding -- currently $10 million for the entire project -- limits their options. "We're trying to make most of what we have available," said Dressel.
The effects of releases has raised concerns from environmentalists and ditch companies, and from local commercial fishing operations. One local outfitter said at the meeting that the effects of prior releases on fishing below the confluence of the North Fork and Gunnison rivers due to high turbidity has been felt by the industry for some time.
Potential impacts from increased turbidity and sedimentation on water quality, fish and wildlife are a concern, said Dressel. In 2016 Reclamation released a final "Finding of No Significant Impact and Environmental Assessment." Water quality testing and monitoring of sediment and its biological effects on plants and wildlife by the USGS, Colorado Parks and Wildlife and others would continue throughout the process, said Dressel.
"Everyone is trying to make best of bad situation," said North Fork Water Conservancy District president Tom Alvey. Alvey, who also serves on several ditch companies in Delta County and on the Colorado River Water District board, called the reservoir "a very efficient trap" for sediment.
Because planning is ongoing, a better solution may be found in future, said Alvey. "But for now that's a huge improvement over what we've got."
For more on the project, including the "Final Environmental Assessment and Finding of No Significant Impact" and 2015 sediment report, visit usbr.gov/uc/wcao/progact/paonia/documents.html