Seven Myths about the Conowingo Dam and its Impact on the Bay By David Foster


 The impact of the Conowingo Dam, particularly during storm events, continues to be one of the most serious and contentious issues associated with the clean up the Chesapeake Bay and its tributaries.  Despite the importance of this issue, much of the current debate is founded on mythology:

1)    “Most of our pollution comes from the Conowingo Dam and until we clean that up there is no use in trying to implement other pollution control programs.”

While the Conowingo is a very serious problem and the Susquehanna is the largest single source of nutrients and sediment flowing into the Chesapeake Bay, these are by no means the only problems we face in our waterways.  In fact, most of the pollution in the Chester and Sassafras, particularly on the upper reaches of these rivers, is actually home grown and is generated right here on our farms, lawns and septic systems.

2)    “The fact that Chester River still fails to meet EPA standards even after several years in which farmers have implemented Best Management Practices further proves that the Conowingo is the real source of our problems.”

It is certainly true that most of our farmers are now doing a better job of controlling pollution but we are also dealing with a legacy of nitrogen and phosphorous that was once applied excessively and still remains in the ground water from years ago.   The U.S. Geological Survey estimates that it could take 10 to 30 years of sustained good practices before all of those excess nutrients have been washed out of the ground water and we have overcome this pollution legacy.

3)    “Funk & Bolton and the Clean Chesapeake Coalition are the only organizations trying to stop pollution from the Dam.”

While these organizations have played a valuable role in helping to bring attention to the problems associated with the Conowingo Dam, they are certainly not the only such organizations involved.  The Corps of Engineers; EPA; MDE; DNR; and Michael Helfrick, Riverkeeper on the Lower Susquehanna River and Rich Batuik from the Chesapeake Bay Foundation, have all been seeking to promote better controls for many years.  Furthermore, Waterkeepers Chesapeake, an organization serving as an umbrella for all the Riverkeepers in the area recently filed a motion to intervene and the Chesapeake Bay Foundation also plans to file a motion this month.

4)    “The flood of sediment and nutrients that came down the Susquehanna and through the Conowingo Dam in 2011, following Hurricane Irene and Tropical Storm Lee, undid all of the work that had been done to clean up the Chesapeake and set us back 100 years.”

Those two storms in 2011 not only brought down a new torrent of mud and trash from New York and Pennsylvania but they scoured out 3 or 4 million tons of the mud that had been accumulating in the reservoir behind the Conowingo Dam during the past several years.  This cloud of sediment could be seen from the Susquehanna to the Potomac immediately after that storm and yet, fortunately, very little of that sediment went up the Chester, the Sassafras or other tributaries of the Chesapeake.  Furthermore, while 2011 was a setback for all of us who care about the Bay, by 2012 the overall index of water quality was even slightly better than it had been back in 2010 before those storms.

5)    “Sediment from the Conowingo destroyed the once thriving oyster industry in the Chesapeake Bay.”


Sediment has certainly been a factor in the destruction of the oyster industry, especially in that portion of the Bay above the Bridge.  However, sediment is only one of many factors and analysis by the University of Maryland Center for Environmental Science at Horn Point indicates that the most important factors were over-harvesting and disease.  Before these recent storm events the oyster population in the Chesapeake had already declined by 99%.  Furthermore, the heaviest sediment deposits actually occurred north of the traditional oyster beds and many of the oysters killed in the upper Bay during the recent storms were more likely killed by the sudden influx of fresh (non-salty) water rather than by the sediment itself.


6)    “If we can control the Conowingo, then we will not have to implement the TMDLs (Total Maximum Daily Loads) and the WIPs (Watershed Implementation Plans).”

The Blueprint for the Chesapeake Bay composed of TMDLs and Watershed Implementation Plans was designed by Federal, State and local agencies to reduce pollution going into the Chesapeake and its tributaries.  The best available models and the most knowledgeable scientists recognize that the pollution; primarily the excess nitrogen, phosphorous and sediment; is created throughout the Chesapeake watershed, including right here on the Eastern Shore.  Consequently, if we are to restore and protect the Chesapeake, all of us will have to continue to do our part.

7)    “The only solution to the Conowingo is to dredge the sediment that has built up behind the Dam.”

The Conowingo Dam and reservoir are currently operated as a “catch and release” facility, trapping nutrients and sediment during times of low flow (when the impact would be comparatively small) only to release them in huge quantities during storm events (when the impacts can be catastrophic).  Somehow we have got to change this process.

While it may be true that some sediment can be removed from behind the dam “for only pennies a pound,” there are approximately 4 billion pounds of sediment that flow into the dam each year.  The 348 billion pounds that have accumulated there over the years since the dam was built in 1928 is roughly the equivalent of 2 million freight cars.  Just to dredge the annual accumulation would cost at least $40 million per year and the cost of transport and disposal would be on top of that.  Therefore, although dredging the sediment may have seemed attractive at first, it is clear that we must begin studying all potential viable alternatives.  A range of potential options include but are not limited to:

a) Dredging, followed by:

i.     Making marketable products from the dredged material, if possible, and/or

ii.     Transporting and disposing of non-marketable material in abandoned mines or by creating new islands in the Chesapeake Bay or in the Atlantic;

b) Sediment-bypassing, so that the reservoir would operate in “steady state” allowing the daily load of sediment and nutrients that flows down the Susquehanna to be dispersed daily rather than filling up the reservoir (only to be scoured out during storms) and reserving space for some form of “catch and hold” for the storm events;

c) Sluicing the sand and gravel through the dam on a regular basis into areas of the bay where it is needed while reserving storage space within the reservoir for trapping the fine particles that are so damaging;

d) Sediment-fixing, so that the sediment (and nutrients attached to it) would be stabilized and/or capped so that it is less susceptible to scouring during storms;

e) Modifying dam operations (including operating gates in advance of and during storms), in a manner designed to minimize scouring during storms; and

f) Any other potentially viable option that the creative readers of this article can propose.

Anyone interested in continuing this discussion or in developing additional options of their own is encouraged to forward comments to David Foster at the following address:

Letters to Editor

  1. Editor,

    Thanks for this solid and accurate article, based on solid evidence and science. One correction, Rich Batiuk is the Sr. Science Director for the Chesapeake Bay PROGRAM, the broad federal/state partnership that provides the peer reviewed science from which policy decisions can be made.

    • David Foster says:

      Hi Margaret,

      Thanks for catching my error regarding Rich Batiuk’s official title and employer. Any other comments or corrections would be gratefully appreciated.

  2. A.Stuart Baldwin says:


    Excellent coverage of the Susquehanna/Conowingo concerns.

  3. Ken Noble says:


    Thank you David and thank you on a job well done in your years as the Chester River Riverkeeper. We also can wonder how and why it seemed necessary to pay an Annapolis lobbying firm with offices in Chestertown to misinform the public on earth science dynamics. The money that Kent County paid for “experts” to transmit fear of “big government” in the form of opposition to a well established pollution diet calculation (read Judge Rubio’s recent decision) could have been used in the Kent County public schools to teach… science for instance.


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