Susquehanna dam’s sediment has officials fearing for the Chesapeake Bay

At the Conowingo Hydroelectric Dam in northeast Maryland, the barbarians are at the sluice gates.

Sediment, millions of tons of it, has flowed down the 440-mile Susquehanna River for more than 80 years and massed at the dam. And now a reservoir built to hold it is filling up.

Graphic

Sediment in the Chesapeake Bay.

More on this Story

• Polluted water did little damage to bay’s grasses; oysters may not be as lucky
• With oyster die-off, skipjack captain docks for last time
• Fisheries panel approves cut in menhaden harvest
• A silt road to a Chesapeake Bay eco-disaster?

View all Items in this Story

• Chesapeake Bay study finds progress against dead zones
• Trying again to eradicate swamp rats
• Maryland’s somewhat cute rodent problem
• Rockfish in Maryland making a comeback, survey says

The threat to the Chesapeake Bay came into sharp focus when Tropical Storm Lee produced record flows in the river in September, forcing officials to open the gates. Four million tons of sediment rushed through in about four days, equal to what the bay normally gets in four years. Half the bay’s blue-green waters appear as beige as coffee with cream in recent satellite images.

Worried state and federal officials are confronted with an obvious question. Could the next monster storm force even greater amounts of sediment into the bay? That could turn dirtied waters into periodic oxygen-depleted killing fields for species of marine life they are fighting to save.

Maryland Gov. Martin O’Malley (D) and Col. David E. Anderson, commander of the U.S. Army Corps of Engineers’ Baltimore District, recently launched a $1.4 million, three-year series of studies to examine how storms can undermine efforts to protect the bay from sediment and other pollution.

The District, Virginia, Maryland and four other states in the Chesapeake Bay watershed are in the first stage of an ambitious federal bay-restoration program that will cost tens of billions of dollars before it is completed in 2025.

“Tropical Storm Lee provided a vivid demonstration of the need to take steps to head off what could be a catastrophic event causing . . . enormous damage to our restoration processes,” O’Malley said. “The time to address this threat is now.”

Sediment doesn’t threaten the walls of the dam. But when Lee’s relentless rain produced near-record river flows last month, the Conowingo couldn’t stand much more water pressure. Throwing open the gates resulted in a jailbreak for the sediment.

According to a U.S. Geological Survey estimate, more than 160 million tons of sediment floats behind the Conowingo, built near Darlington, Md., in 1928. About 3 million tons arrive there each year, and about a million tons of that sloshes over the gates, said Mike Langland, a USGS hydrologist.

Environmentalists say the sediment dump during the storm was so high that it could spawn another mammoth, oxygen-depleted “dead zone” like this past summer’s.

If the storage capacity is reached in about 20 years, as Langland predicted, at least 3 million tons of sediment would wash into the bay yearly, making matters far worse.

Mixed with the sediment are large amounts of phosphorus and nitrogen from farms and cities upstream. Those nutrients are enemies No. 1 and 2 of environmentalists hoping to reduce pollution in the Chesapeake, the nation’s largest estuary.

The Susquehanna starts at Cooperstown, N.Y., flowing at about 20 miles per day in summer through Pennsylvania until it reaches Havre de Grace, Md. There it pours 18 million gallons of water per minute into the Chesapeake. It’s the biggest freshwater flow into the bay by far, supplying as much as 60 percent of the Bay’s fresh water compared with the Potomac River’s 19 percent.