News Release
| Release Number: | 06-002 |
| Dated: | 1/3/2006 |
| Contact: | Heidi Y. Helwig, 503-808-4510 |
Portland, Ore-- Fern Ridge Dam on the Long Tom River was repaired just in the nick of time, said the U.S. Army Corps of Engineers today.
The embankment dam, which was repaired in one season, is holding back the most winter water it has seen since 1996 and is filling for the first time since the repairs were completed in November 2005, said Erik Petersen, operations manager for the Willamette Valley projects.
Fern Ridge Reservoir was at elevation 371.1 feet as of midnight on Jan. 3, just 2 feet shy of the maximum summertime elevation target of 373.5 feet, Petersen said.
“Readings from more than 80 different instruments installed in the dam look good,” said Rich Hannan, the Corps’ lead geotechnical engineer. Seventy-two piezometers, which measure water levels in Fern Ridge dam’s foundation, and 12 weirs, which replaced the failing internal drainage system, show the dam to be functioning “quite well,” Hannan said.
The 10 other reservoirs in the Willamette Valley with storage capacity also were operated as designed by holding back storm waters to minimize downstream flooding. All projects were reduced to a minimum outflow to capture as much flow as possible and reduce flows at all major control points.
The Willamette River at Salem was reduced from a peak flow estimated near 260,000 cubic feet per second to an observed peak of 141,000 cfs, said Julie Ammann of the Reservoir Control Center.
“Without the dams, the flows at Salem would have exceeded the levels we saw in February 1996,” she said. “Our projects stored a lot of water.”
At the height of the rainstorm, the system of Corps Willamette reservoirs, as a whole, was just over 52 percent full, said Brad Bird of the Corps’ Reservoir Regulation Section. Dorena and Fern Ridge, in particular, had high flows coming into the reservoirs and are filled to about 85 and 80 percent full respectively, he said.
As Willamette River and tributary levels begin to fall downstream, the Corps will release water from the reservoirs to regain the flood damage reduction storage space needed for future rain events.
“We will be watching both Dorena and Fern Ridge closely and releasing as much water as possible to free up storage space for future storms,” said Bird. “When flood damage reduction reservoirs become that full, it decreases their ability to reduce the effects of future flooding,” he said. To regain adequate storage space, the Corps will make adjustments over the next several days to allow the maximum amount of water to be released while still trying to keep the rivers within their banks, he said. Bird said the Corps will release as much as 6,000 cfs and 5,000 cfs from those reservoirs, respectively.
Corps dams control 27 percent of the water that flows through the Willamette River Basin, 17 percent in the Rogue River Basin and 33 percent of the Columbia River Basin above Bonneville Dam.