Wednesday, September 28, 2011

Dam You, Tropical Storm Lee!

Conowingo Dam at flood - Photo Source
Study eyes Chesapeake Bay pollution threat from dams
Two weeks after Tropical Storm Lee flushed millions of tons of mud into the Chesapeake Bay, state and federal officials announced Tuesday they are launching a study of how to protect the estuary from sediment and other pollutants building up behind dams on the Susquehanna River.

Experts from the U.S. Army Corps of Engineers, the Maryland departments of environment and natural resources and the Nature Conservancy, a Washington-based conservation group, will team up for the $1.4 million, three-year evaluation of how to deal with sediment accumulating upriver from the Conowingo Dam and three other hydroelectric facilities on the Susquehanna.

Flooding caused by Tropical Storm Lee's torrential rains washed an estimated 4 million tons of sediment through the Conowingo Dam into the upper bay, along with large amounts of nitrogen and phosphorus. Those two plant nutrients foul the bay by feeding massive algae blooms, which subsequently rob the water of oxygen that fish, crabs and shellfish need to breathe. An even larger outpouring of sediment from the river during Tropical Storm Agnes in 1972 smothered underwater grasses and killed oyster beds.

Scientists and others have worried for years that efforts to restore the bay could be undermined by one or more storms washing sediment and accompanying nutrients down the Susquehanna from the dams now collecting it. But officials have not acted, put off by estimates that it would be extremely costly and difficult to remove the sediment and place it somewhere else that wouldn't threaten water quality.

Now, under a new push to restore the bay, the Environmental Protection Agency and the states through which the Susquehanna flows have set 2025 as a deadline for deciding how to deal with the dam sediment.
No hurry...

I was interested to see this:
Prior studies have determined that the 100-foot-high Conowingo, the dam nearest the bay, traps two-thirds of the 3 million tons washed down the river each year, but that the reservoir's capacity for capturing and storing sediment will be used up in 15 to 20 years. The latest storm, by scouring out some of the sediment stored behind Conowingo, may have extended that capacity by another two years, according to the U.S. Geological Survey.
In other words, Lee not only brought a whole lot of it's own sediment into the Bay, it brought an additional two years worth of sediment.  It will be interesting to see what changes happened on the Susquehanna Flats this spring.

I've had a few days up there like that.

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