The Susquehanna is arguably the most important river in the Chesapeake Bay's watershed. Its two branches drain 27,500 square miles of the bay's 64,000-square-mile watershed. By the time the river reaches the bay at Havre de Grace, it has traveled 448 miles, and it will deliver 25 billion gallons of water to the bay on an average day.

But there are no average days. Water flow ranges from a record 650 billion gallons in a single day to less than 2 billion during a drought. Over the course of a year, half of the fresh water that's so vital to an estuary such as the Chesapeake comes down the Susquehanna.

Twelve miles upriver from the mouth of the Susquehanna is the Conowingo Dam. One hundred feet high and over a mile wide, the Conowingo was opened in 1928 and has been the cause of various problems since its beginning. None may be more important to the long-term health of the Chesapeake Bay than the 144 million tons of silt trapped behind the dam, with more accumulating every year.

Three and half million pounds of phosphorus and 2 million tons of dirt settle behind the dam annually. The runoff from hundreds of communities and thousands of farms, as well as numerous roads and parking lots, ends up behind the dam. It's estimated that 15 percent of the sediment is residue from Pennsylvania's coal mining history.

Hurricane Agnes in 1972 scoured out most of the sediment and created one of the largest ecological disasters in Chesapeake Bay history. Barring another Agnes-like disaster, the United States Geological Survey estimates that the remaining storage capacity behind the dam, about 30 million tons, will be filled by 2025.The sediments will have nowhere to go then but through the dam, impacting the Chesapeake Bay.

Experts say that a plan must be put in place, but even a survey of sediment management options would cost $2.5 million. Many say that the money would be better spent on erosion measures upstream to slow the volume of sediments settling behind the dam. But Michael Helfrich, the riverkeeper for the Lower Susquehanna River Valley, points out that much of the potential damage is already in the river. He believes the area behind the dam will have to be dredged to give projects upstream a chance for success, and has applied for a grant to learn if the sediment can be safely used in the construction industry.

Mr. Helfrich feels - and many others agree - that the dam's upcoming license renewal in 2014 provides the best opportunity to find a solution.

There is a precedent for using the licensing process to achieve environmental goals. Shad advocates used the dam's 1970s renewal to force Philadelphia Electric, the dam's owner at the time, to build new, improved fish ladders to allow migrating shad to move above the dam to spawn. A law judge with the Federal Energy Regulatory Commission ruled that "fish passage was a cost of doing business on a river containing anadromous fish populations."

Exelon, the current owner, needs to recognize that the problem of silt is its to deal with. The company is the beneficiary of the revenue and should bear the responsibility and costs associated with the project. It should be required to invest in the studies and outline the plans to substantially reduce the volume of sediments behind the dam in order to maintain its continued operations.

Informed citizens need to make their concerns known to the appropriate regulatory agencies over the next 4 1/2 years, because this renewal will be good for 30 to 50 years, long past the time when Conowingo's pool can no longer trap sediment.

The problem is not going to disappear by ignoring it. It's going to take a major effort from everyone involved - Exelon, the public, the states and the regulatory agencies - to reduce the threat posed by the sediments trapped behind Conowingo Dam.

David Berry lives and writes from Havre de Grace, where he also teaches sailing. He has written two books, "Maryland Skipjacks" and "Maryland's Lower Susquehanna River Valley; Where the River Meets the Bay." This article is distributed by Bay Journal News Service.

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