Heavy Rainfalls Send Debris, Sediment Plume Through Conowingo Dam

A DelmarvaNow article (2018-08-01) reported that the recent heavy rainfalls have sent a plume of sediment and debris down the Susquehanna River, through the Conowingo Dam, and into the upper stem of the Chesapeake Bay. Exelon, the dam’s owner, recently opened the dam’s floodgates in order to relieve pressure from the rising waters in the dam’s reservoir.

In the article, a representative from the Chesapeake Bay Foundation described the event:

“This was a fairly unprecedented event,” said Doug Myers, Maryland senior scientist for the Chesapeake Bay Foundation. “It swelled rivers and streams throughout the watershed. We saw satellite images that showed a brown plume going through the length of the Susquehanna through Pennsylvania. Then we saw that plume of suspended sediment come out into the bay.” …

“The sediment is a visible thing, but it’s not the thing the bay is most concerned with,” he said. “We’re seeing big piles of debris all along the shoreline and that has a tendency to scour over the Susquehanna flats, which is our largest seagrass bed in the bay. That debris pulled a lot of the grasses out of the mud.”

The article noted that since the dam’s reservoir has reached its capacity to trap sediment, heavy rainfall events will wash excess sediment through the reservoir and directly into the Bay. Such discharges can undermine the restoration efforts of Bay watershed states and local governments. In the article, Myers discussed the negative consequences these discharges can have on nutrient pollution and wildlife.

The article also discussed the efforts of Maryland and the Chesapeake Bay Foundation to reach an agreement with Exelon on addressing the issue posed by the Conowingo Dam. While Exelon has offered to play some role in addressing the water quality concerns posed by the dam, it remains opposed to the State’s current proposal and also argues that it cannot capture all debris washed down the Susquehanna during flood events. Multiple legal and administrative challenges are currently underway and a final solution to the Conowingo problem remains elusive.

MACo’s longstanding position on the Conowingo Dam is that the excess nutrient and sediment pollution originating from the dam’s reservoir must be addressed. That burden should not fall on Maryland’s counties, which did not generate the pollution coming through the dam. Exelon, as the dam’s owner and beneficiary of the profits generated by the dam, should play a role in addressing the dam’s water pollution situation. Bay watershed states that generate the pollution flowing down the Susquehanna and into dam’s reservoir should also work to reduce their nutrient and sediment runoff.

Useful Links

Prior Conduit Street Coverage of the Conowingo Dam

Get the latest on the Conowingo Dam and the Bay TMDL during the 2018 MACo Summer Conference panel “Charting the Next Course for the Bay TMDL.” The panel will be held on August 16.

Learn more about MACo’s Summer Conference: