Engineers from PacifiCorp and the Oregon Water Resources Department began their inspection of the Newport Avenue Dam early Thursday, crawling along the face of the more than 100-year-old dam to search for signs of structural weakness.
The inspection comes nearly a month after the discovery of a leak in the dam that quickly dropped water level to about two feet below normal. Dam owner PacifiCorp scheduled the inspection to search for the source of the leak and to determine if other parts of the dam could be on the brink of failure. The OWRD, which regulates dam safety and oversees the distribution of irrigation water in Oregon, elected to conduct its own inspection outside of its normal inspection schedule due to the unique low water levels.
Inspectors spent most of the day Thursday on the downstream side of the dam, wading in the water and using ladders to closely examine the structure. Bob Gravely, spokesman for PacifiCorp, said inspectors were using hammers and drills to look for rot and assess the strength of the wooden “cribs” that hold tons of rock and rubble in place.
In anticipation of the inspection, PacifiCorp opened the sluice gates on the dam Monday to lower water levels even further. Gravely said Thursday that the water had come down approximately 7 feet from its normal elevation at the face of the dam.
The combination of the leak and reduced river flows brought about by the end of irrigation season has lowered water levels to a lesser degree farther upstream, creating exposed mudflats throughout Drake Park and above the Galveston Avenue Bridge.
Water levels should begin returning to about two feet below normal beginning today. Before closing the gates to refill the pond, PacifiCorp will be installing surveying equipment that will use lasers to determine if the dam shifts when water begins accumulating on the upstream side, Gravely said.
“Any sign of instability would be picked up by these, something you couldn't see with the naked eye,” he said.
PacifiCorp will not be revealing its findings from Thursday's inspection immediately, however. Gravely said the latest leak is only a small part of the equation.
While the leak appears fixable, it's the condition of the rest of the dam that will determine whether repairs are worthwhile, Gravely said. The dam's hydro generators create only enough power for 200 to 300 households, and a long list of repairs could render it unprofitable.
“It's not fixing the leak that's the big decision; it's the bigger question,” he said. “We want to have a better sense of the bigger question before we know what we're going to do.”
Gravely said he'd mistakenly given the impression that past repairs to leaks in the dam were simpler than was actually the case. In 2008 and 2009, PacifiCorp repaired three damaged sections of the dam using the heavy corrugated metal seen on the upstream side. Gravely said before he'd believed the metal panels were simply bolted to the face of the dam. In fact, the repairs used 40- to 50-foot-long sections of metal that were driven into the ground so that only 15 to 20 feet remained above the bottom of the pond.
Gravely said he was not at liberty to disclose estimates of the cost of repairing all or part of the dam. PacifiCorp officials will be weighing those costs against the dam's power generation capacity, the expense of removing the dam, and the price the dam could draw if it was sold.
“I think this inspection will probably tell us what we need to know,” he said.