Task Force on dredging starts work

A 13-member task force convened to ponder the future of the South Fork Rivanna Reservoir met Tuesday to take its first step toward understanding the impact of dredging the silt-filled reservoir that supplies drinking water to Charlottesville and Albemarle County.

The task force — which is made up of local government officials, environmental advocates, property owners and other stakeholders — spent the bulk of its inaugural meeting engaged in what might be called Reservoir 101.

The panel heard state and local experts describe the various recreational uses of the waterway (namely, fishing and rowing) and they got reports on the current status of the reservoir’s sediment and its overall water capacity.

There was little talk among the task force about the specifics of maintenance dredging, a move that proponents say would improve and expand the local water supply, as well as preserve recreation and wildlife habitats.

Charlottesville and Albemarle’s long-term water supply plan calls for construction of a dam at the Ragged Mountain Reservoir to increase the water storage capacity from 464 million gallons to 2.19 billion gallons. A pipeline would be built to connect the two reservoirs to fill the newly expanded Ragged Mountain Reservoir.

During the next four months, the task force will try to learn what would happen over the next 50 years if no maintenance of the South Fork Rivanna Reservoir is performed.

The panel will collect data, hear testimony and gather input from the public. By the end of the year it will present its findings and make a majority recommendation of what the task force believes ought to be done.

At Tuesday’s meeting, Jennifer Whitaker, an engineer with the Rivanna Water and Sewer Authority, explained the history of “bathymetric” studies of the reservoirs, meaning an investigation of sedimentation and its impact on the reservoir’s water capacity.

When the South Fork Rivanna Reservoir was built in 1966, its designers anticipated that it would have an annual sedimentation rate of 19.6 million gallons per year. In fact, the average rate has turned out to be 15.14 million gallons of sedimentation annually. Since its creation, the sediment has lowered the reservoir’s storage from 1,700 million gallons to 1,115 million gallons in 2002.

“The sedimentation rate is actually slower than was anticipated at the time of construction,” Whitaker said.

A detailed study of the reservoir’s bed would likely be an expensive endeavor, she said.

The composition of the reservoir’s silt is a bit of a mystery, said Bob Wichser, the Rivanna Water and Sewer Authority’s director of water and wastewater operations. Sampling was conducted in 1996 and 2002, but a current and detailed test has not been conducted.

Past samples suggested that the silt had normal levels of metals, though it is not known if it contains herbicides, pesticides or organic matter.

The reservoir is highly popular with anglers from throughout Central Virginia, said John Kauffman of the Virginia Department of Game & Inland Fisheries, as they are drawn by the abundant large mouth bass and channel catfish.

It is also heavily used by rowers from the University of Virginia and community groups. Increasing sedimentation has taken away a mile-and-a-half of water available to rowers, said Mark Fletcher, UVa’s executive director of intramural/recreational sports.

On the horizon, the task force will seek the answer of the why or why not dredging should occur. And it will also consider what alternative strategies might be used to keep silt from getting into the reservoir.