BALTIMORE (WJZ)– The build-up is relentless as millions of tons of sediment piles up behind the Conowingo Dam.

As Alex DeMetrick explains, the race is on to do something about it before it spills over and swamps the bay.

When there is simply too much water to hold back, Conowingo Dam in Harford County orchestrates controlled releases.

But more than water is passing through.

There is debris swept off the land.

After Tropical Storm Lee, it was too dangerous for watermen to start work in the dark.

“[We found] everything from firewood, to propane tanks to hot water heaters,” said waterman Tony Conrad.

But sediment that turns the water brown, also poses risk.

For every million tons that flows into the Susquehanna and the bay, two million tons is trapped behind the dam. And it is filling up.

Environmentalists put it on lawmakers’ radar this past session:

“One million goes over. Once it hits equilibrium, all three go over. Where do they go? Maryland,” said Ann Swanson, Chesapeake Bay Commission.

And that could kill off underwater grasses critical to the bay’s restoration.

Exelon Generation owns the dam, but it’s not the company’s sediment.

“Every thing from Cooperstown, New York – that’s in the watershed – all the way down to Pennsylvania down to the Conowingo Dam. That’s where the sediment comes from. It’s really dirt from human activity in the watershed,” said Mary Helen Marsh of the Exelon Generation.

Exelon has joined in a government study, perhaps to dredge that dirt.

“[Stopping the runoff] is going to require long-term solutions that address sediment at the source,” said Marsh.

Where hard surfaces have replaced plants that absorbed run-off, fueling erosion that makes dam dirt.**

The U.S. Geological Survey said sediment could reach a tipping point sometime within the next 20 years.

The cost to stop it has yet to be calculated.


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