Wednesday, September 03, 2003
Home - Local News - Bitterroot Life - Sports - Features - Classifieds - About the Valley
MORE TOP JOBS
Quick Search Classifieds
Emergency work planned for Tin Cup Dam
By BUDDY SMITH Staff Reporter
More emergency repairs are planned this month for Tin Cup Dam in the wilderness southwest of
Darby, officials said.
The work proposed by the Tin Cup County Water-Sewer District, which owns the dam, is meant to
avert a potential for the dam to fail next spring, according to the Bitterroot National Forest, which
regulates safety of privately owned dams on its lands and agrees with the irrigators that the work is
urgently needed.
Dan Ritter, acting Darby district ranger, said Tuesday the dam does not pose an immediate threat to
downstream residents in the Darby area, but a threat could come next spring with an unusually high
runoff that could cause water to overtop a notched portion of the dam and erode the structure.
Forest Service officials said members of the water-sewer district this summer informed the agency of
an urgent need to complete repairs before winter and next spring's snowmelt.
"We need to get this work done before the snow hits, which
isn't very long in that country," Ritter said.
The repairs will require using motorized equipment in the Selway-Bitterroot Wilderness, Ritter said,
though what's not been finalized is what kind of equipment or just how it will get to the remote dam,
which is 12 miles from the nearest road.
In spring 1998, a leak was found at Tin Cup Dam. The Bitterroot Forest undertook emergency repairs
to protect life and property, involving lowering the spillway and constructing a notch in the dam. The
work created a partial breach in the dam and reduced the reservoir's storage capacity.
On July 9 this summer, irrigators found and reported to the Forest Service evidence of water
overtopping the notched portion of the dam, officials said. Both the dam owners and the Forest
Service agreed that if this happened again, it could compromise the dam's integrity and possibly cause
it to fail, officials said, which, among other things, could flood homes in Darby.
"Our concern is that any kind of an unusually high runoff could cause that water to come even higher
up the notch of the dam," Ritter said.
The Tin Cup Water-Sewer District proposes starting the work from Sept. 10-15. The work would
partially fill in the notch to prevent overtopping. Additionally, a impermeable liner and rock protection
will be placed over the notch to prevent erosion. The spillway may also be modified, but the repairs
won't change the reservoir's storage capacity. The dam, about 14 miles southwest of Darby at the
headwaters of Tin Cup Creek, was built in about 1906, officials said, and is an earthen and rock
embankment structure.
Officials said to complete the repairs within the limited time frame - before winter sets in - dam
owners are proposing to use helicopters to haul in supplies and to use motorized equipment at the
site, including an excavator. Ritter said a possibility also being looked at is use of a piece of excavating
equipment with hydraulic legs that can be lifted independently and can "literally walk in" to the site on
an existing trail.
Such a machine was used to restore an area damaged by a landslide northwest of Florence, and is
lighter on the land than other equipment, he said, since it doesn't have to ride on wheels or tracks.
Officials said access plans aren't yet finalized; different options are being studied. The Forest Service
will have to put its stamp of approval on the dam owners' plans. The work cannot be done without
mechanized equipment and access, Ritter said.
http://www.ravallinews.com/articles/2003/09/03/news/news04.txt (1 of 2) [9/3/2003 8:24:43 AM]
