Tamarack Lake drawn down again
Tamarack Lake in Crawford County has been closed to all public use and is being drawn down by an additional 5 feet as a safety precaution.
The Pennsylvania Fish and Boat Commission lowered the lake level by 4 feet in November because of seepage concerns in Dam A, nearest Meadville. New concerns unearthed July 31 have caused the latest drawdown.
“Failure of the dam is not imminent, but worsening conditions could change rapidly, particularly during a high pool elevation from a large storm event,” said Jack Rokavec, the commission’s chief of engineering. “In an effort to prevent the dam’s failure and protect life and property, we will lower the lake by an additional 5 feet, bringing it down to a total of 10 feet.”
The commission said its engineers started lowering the water level in the 556-acre reservoir Tuesday night. The lake will be lowered by approximately 6 inches to 12 inches per day. The additional drawdown could take a few weeks to accomplish.
Fishing, boating and walking on the lake beds is now prohibited. The commission said signs will be posted at the property and security fencing will be placed around the flood-control dams at each end of the reservoir.
Commission personnel are attempting to salvage fish and relocate them. The commission expects many of the fish in the lake to die, however.
“We will collect as many fish as we can through netting and electrofishing, but it is impossible to capture all of them,” said Dave Miko, chief of the commission’s Division of Fisheries Management. “Fish die during any drawdown and salvage effort because many hide around structures where we simply can’t reach them, and others become buried in the mud when they are slow to exit the lake with the remaining water.
“This salvage effort will be particularly challenging given the timing of the emergency drawdown,” Miko said. “The warm water temperatures will only worsen with the expected weather conditions and the loss of fish is anticipated to be greater than is typical. Anglers and the general public should expect to see this.”
The PFBC hired engineering firm Tetra-Tech in July to perform geotechnical investigations, install monitoring wells, recommend seepage/boil control measures and develop conceptual improvements at the north and south dams. Their final report is expected to be completed by November.
“Since (November) the seepage has worsened into what are termed boils,” Rokavec said. “In addition, on July 31, while geotechnical engineers were performing borings on the crest of the dam, the drill encountered an approximate 2-foot vertical void within the embankment adjacent to the outlet conduit. These conditions have confirmed previous suspicions that seepage paths and voids have developed along the outlet conduit and are eroding the dam’s embankment and foundation materials, which is a very serious situation.”
Tamarack Lake was drained in 1999 so that safety modifications could be made to the outlet structures on dams at each end of the lake. The modifications were completed in the summer of 1999 and the reservoir was fully refilled by the spring of 2000, then restocked with fish.
Friends of Tamarack Lake is keeping up with the work at the site.
0 评论: