At the center of the recently released Corps of Engineers Lower Susquehanna River Assessment findings last week was the report’s heavy reliance on a principle of physics known as dynamic equilibrium to explain the Dam’s ability to capture sediments and nutrients into the future. We suspect like most our readers, we seem to have deposited our knowledge of such laws of nature in the same dusty attic along with our high school textbooks, and therefore we thought it best to have a short tutorial on the concept.
Thanks to the good folks at Core School, a very short (30 seconds) explanation of dynamic equilibrium was available on YouTube. We’ve repeated the lesson three times, just like in high school, to encourage retention. You never know when there might be a pop quiz.
David Foster says
Thanks for that great little video. It really does provide a clear image of what would happen if sediment from upstream areas in Pennsylvania and New York were to refill the pond behind the Conowingo Dam just as fast as we removed that sediment. It really is like running on a treadmill, you spend a lot of energy but you don’t make any forward progress.
The next questions that needs to be objectively answered are:
1) Just how much would it cost each year to run on that “treadmill?”
2) Who would pay the cost of removing that sediment each year (and transporting and disposing it)?
3) Are there other alternatives that could achieve equivalent benefits at less cost?
4) How can we get EPA, the Corps of Engineers and our elected representatives to clearly lay out all of the viable alternatives, complete with their relative cost-effectiveness?
Ron Fithian says
This might be a cute little commercial, but when we are talking about the storm water pond above the Conowingo Dam and the amount of pollution that enters the Chesapeake Bay there is no relevancy at all. Let me try and explain. When there was trapping capacity left in the pond, its role was to trap the sediment before it enters the bay. And it worked ! That’s why we have 2 to 3 hundred million tons of sediment above the dam. It was estimated that 2/3 of the contaminated sediment would be trapped and 1/3 would make its way to the bay. Now that it is full, there is NO trapping capacity left which means we now have 2 to 3 hundred millions tons of contaminated sediment above the dam and now the bay receives on a daily basis, ALL of the sediment instead of only 1/3 and the next storm event will give us a portion of what we have been saving. To bad for the bay!
Andrew McCown says
Even if there were no people using the land, the watershed would naturally yield sediment. The problem is, because of incredibly intensive land use, much more sediment enters the river and it often carries a host of pollutants. What was the level of sediment behind the damn when Hurricane Agnes (1972) came along? Long before the damn was full the stage for disaster was set, as was the case with Agnes, and so dredging the damn to the levels that existed in 1996 may not get us much gain. Sooner or later we will see another Agnes type storm that will track thru the watershed and disaster will strike again no matter what the level of sediment is behind the damn, granted, less sediment behind the damn is probably better. But Agnes showed us how vulnerable we are when our land use is so intensive. It wasn’t the damn, but the condition of the land in the watershed that sent so much unwanted stuff down the river. Intensifying improvements in land use throughout the watershed will yield gains, gains in this case would be less sediment and pollution loading. I am not saying gains won’t be made by dredging, but the real gains are going to come from dramatically making improvements in how we use the land. We need to prevent the excess in the first place.
All that said, far away from the Conowingo, the entire Chester River is miserably void of rooted plants. As our land use in the watershed of the River has changed, so has the River. What is our Conowingo?
Steve Payne says
What needs to happen is to stop the erosion above the dam. Until you do that you need something to stop it (the dam) and hold it.
Then everyone can stop digging.
Andrew McCown says
If I were digging a hole and someone was shoveling dirt back into the hole at the same rate as I was digging, or even faster, then I don’t think I would call them my friend.
William Rudek says
All of this reminds me of Cool Hand Luke, when Paul Newman is forever digging and filling “the warden’s” hole. And even more relevant; it seems that “…what we have here, is a failure to communicate.”