Visitors who expect to see clear waters at Columbia's Lake Elkhorn after a multimillion-dollar dredging is complete in December will likely find algae and vines thriving again next spring, despite rising cost estimates for removing decades' worth of sediment.
Without dredging, Columbia's man-made lakes would eventually fill in with sediment and plants, reverting over decades to the stream valleys they once were. The two largest, 37-acre Elkhorn, and 27-acre Lake Kittamaqundi, have never been completely dredged.
Despite months of tedious work, much of Elkhorn's surface is still covered with green algae and a yellow flowering vine called creeping primrose willow that has already reclaimed large sections of water where dredging has occurred. Officials say there's not much that dredging can do about that. Dredging deepens the lake bottom, but it's what is diluted in the water that causes plant growth.
"You have an ample nutrient supply," said John McCoy, the new watershed manager for the Columbia Association, which is paying for the projects. "We have rooted aquatic [plants] and a pretty good standing crop of algae," he said.
Removing or reducing the algae will be a long-term project, he said, that involves using water-management tactics to keep out trash, fertilizers, pesticides and other chemicals carried by storm runoff into the lakes. McCoy said the Columbia Association's blue harvester, a boat that cuts and collects the top inches of algae and waterborne plants, will return to Elkhorn next year.
"Our primary concern is removal of the accumulated sediment," said Bill McHugh, project manager for Chester, Pa.-based Mobile Dredging and Pumping Co., the firm doing the work at Lake Elkhorn.
The problem is that since the original measurements in 2006 when planning began, heavy storms have washed much more sediment into Columbia's lakes than was forecast. For the dredging to reach the target depths, all of that has to be removed, boosting the cost.
Measurements this year revealed higher-than-expected sediment flows into Elkhorn and Kittamaqundi over the past four years that would raise the cost at least $3.4 million above the $11.4 million estimate for dredging both lakes, CA officials reported to the association board Thursday night. Estimates on a smaller dredge project at Wilde Lake are running $700,000 under the $2.2 million budgeted. Preparations for dredging at Kittamaqundi and Wilde Lake are to begin next month, officials said.
"I appreciate they're going to be troubled by the additional money," said Dennis Mattey, the Columbia Association's director of construction.
The board can shift funding from the Wilde Lake project to the two larger lakes; other possible options are to reduce the amount of sediment removed or find more money. Since the biggest single expense for dredging is setting up the equipment staging area, Mattey said it might make sense to go ahead despite the costs. Removal of each added inch of sediment will cost about $100,000, according to a consultant, who said the muck is deepening at a rate of nearly 3.5 inches per year in Lake Elkhorn and 4.5 inches a year in Lake Kittamaqundi.
"I also don't believe it's going to be cheaper in five or 10 years to remove the sediment," Mattey said.
The Columbia Association had earlier sought to limit costs by dredging about 80 percent of the sediment that has accumulated in Lake Elkhorn since it was built in 1974. In some areas, water once 7 feet deep had filled to less than 2 feet, according to the consultant's reports.
Even after dredging, the water will be no more than 5 feet deep. No dredging is to occur in the lake's broad center section, behind the Swan Point townhouse development. Most of the work is taking place at the narrower eastern end of the lake, though the dock cove, the pond below the dam and the nearly fully silted pond behind the lake's source stream still must be dredged.
Engineers and consultants said that since a storm in June 2006 dropped 10 inches of rain, sediment has flowed into Lake Elkhorn at a rate 47 percent higher than expected. Estimates were based on calmer weather from 2001 to 2006. During the past four years, sediment flow into Lake Kittamaqundi was 97 percent higher than CA estimates. Wilde Lake, the smallest of the three, was 23 percent higher. Wilde Lake has been dredged several times, which has reduced sediment buildup.
For Elkhorn, that translates into an added 22,000 cubic yards of mud, and 37,000 cubic yards more accumulated in Lake Kittamaqundi.
Meanwhile, Elkhorn dredging has proceeded fitfully, with the dredge stopped and silent almost as often as it is operating. McHugh said the dredge scoops up sediment and pumps it to a receiving tank faster than it can be pressed dry and disposed of, which forces periodic shutdowns.
Charles Grey, the Columbia Association's project manager for dredging, expressed frustration that work has not proceeded more quickly, but the dredge must stop each time the green tank fills with sludge. Once dried and expelled, a large front-end loader lifts it into trucks. Then the barge, which uses a hydraulic device to chew and loosen the sediment before pumping it through long plastic pipes to the dredge site, can resume work. Work stopped on much of Aug. 6, for example, because of an electrical problem on the dredge, Grey said, and a hydraulic breakdown Monday delayed work again.
Some of the activity has seemed mystifying to observers.
Initially, it seemed that the dredging was depositing, rather than removing mud near the lake's shallow source. Grey said the processed remains of what was mostly sand removed from the mouth of a tributary on the lake's southern shore were pumped back into the lake's shallow source end, creating mud islands on which plants quickly began growing. But when that area was later dredged, that mud was removed, which was part of the plan.
People who live or walk around the lake watch the activity with varying levels of understanding.
David Bittner, a member of the Swan Point Homeowners Association board, said he's keeping up with the issue, especially since his development, and his house, are near the lake.
"I think we all just hunkered down to weather a year of an ugly, noisy lake," he said. "The big difference this year is that CA has not been mowing the lake" with the harvester boats.
Kevin McGill, 48, an engineering consultant whose family has lived for 16 years in a Swan Point townhouse by the lake, said he was unaware that no dredging would be done behind his home, or that the bright-green algae covering the lake won't disappear when the work is done.
"I think we all just anticipated it would be pristine, or at least much better," he said.
larry.carson@baltsun.com