Water Resources Engineering (WRE) connects engineering hydrology and hydraulics with global, economic, environmental, and societal issues. Our student Matt DeLuca makes this connection here…

The news entitled, Flood cresting lower, earlier, was reported by the newspaper company, The Baltimore Sun on September 10, 2011.  The news relates to the WRE on both hydrology and hydraulics.  This article is specifically referring to the Conowingo Dam on the Susquehanna River in Maryland (figure 2).  The Conowingo Dam is the last and largest dam on the Susquehanna.  In fact when it was completed in 1928, it was the second largest hydroelectric dam behind Niagara Falls in the entire United States, producing 252 MW (Exelon).  The dam is owned and operated by Exelon and is now capable of generating up to 500 MW of electricity with its 11 turbine generators (Exelon).  This article deals with hydrology since the Susquehanna River runs through this dam, and the Susquehanna is the largest tributary of the Chesapeake Bay.  The article also deals with hydraulics in that the Conowingo Dam is a hydroelectric dam using the water’s potential energy to create electricity.  The article interviews dam operators and residents living near the area.  The dam operator was expecting to have to open all 50 flood gates but only 43 flood gates were open because of Tropical Storm Lee on the night of the 8th (figure 1) (Baltimore Sun).  The water reached a height of 32.41 feet early on the 9th making it the third-highest recorded height behind Tropical Storm Agnes and the winter storm in January 1996 (Baltimore Sun).  Although there was mandatory evacuation downstream, 40 people stayed  in their homes.  The article touches on how the sediment washed downstream would threaten the health of different plant and animal species in the Chesapeake Bay.  A CBS story confirms this statement and gives an estimate of 4 million tons of sediment from the Susquehanna River were wash into the bay by the back to back storms.  This story left out a very important part of the story, as every article conveniently left out relating to the 2011 flooding, and that was that the flood gate side of the dam was wired to blow up if the water rose above the height needed to open all 50 flood gates.  I found this out the next summer when the dam employee, giving my friend and me a portage around the Conowingo Dam, told us this “minor” detail during the car ride.  The reasoning behind this is to save the powerhouse since it is a lot more expensive to rebuild.  I feel that this fact is left out of in all the news stories as to not induce panic into the public and avoid possible protests.

Although this is one specific example, I can only imagine that this process of wiring dams that are at risk of cresting is a common practice.  Using a cost-benefit analysis, it is clearly better to lose the part of the dam where the flood gates are located than to lose the powerhouse side or even the whole dam altogether.  If the explosives were detonated due to water exceeding the cresting height, massive amounts of sediment would be released with all the water added tremendously to the estimated 4 million tons of sediment that already passed through the dam (CBS). 

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Figure 1. Conowingo Dam during normal water level conditions

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Figure 2. Conowingo Dam with flood gates open from flooding during the 2011 storms

 Video of open flood gates during 2011 flooding in September

References

Baltimore Sun. http://www.exeloncorp.com/powerplants/conowingo/Pages/profile.aspx

 CBS. http://baltimore.cbslocal.com/2011/09/27/susquehanna-sediment-focus-of-new-chesapeake-study/

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