Army Corps of Engineers Conowingo Dam Report

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The Lower Susquehanna River Watershed Assessment Study, conducted by the U.S. Army Corps of Engineers in coordination with the state of Maryland, confirms that the Conowingo Dam reservoir and two dam reservoirs further upstream have essentially reached their capacity and are no longer capable of trapping sediment and associated nutrients over the long term.

The assessment also found that the sediment and nutrients swept over the dams during large storm events are among the pollution sources that should be addressed to protect water quality and aquatic life in the Chesapeake Bay.

Another major finding is that nutrients that enter the river upstream of the dams and attach to sediment particles before flowing downstream into the bay have a larger impact on water quality than sediment itself.

Modeling analysis shows that while sediments generally settle out of the water column within days or weeks, nutrients attached to the sediment can fuel algal growth and contribute to lower dissolved oxygen levels affecting water quality and underwater ecosystems.

As a result, even with full implementation of Maryland’s federally-required bay cleanup plan, it will not be enough to achieve water quality standards in the three upper and mid-bay segments without strong actions from upstream states between 2017 and 2025.

The Environmental Protection Agency has established water pollution limits, the Chesapeake Bay Total Maximum Daily Load, which must be met by 2025 by Maryland and other bay watershed states.

The EPA has said it would consider increasing its expectations for states’ progress in bay cleanup efforts if monitoring indicates that the Conowingo Dam’s capacity to trap sediment is reduced, as the newly finalized study shows.

Maryland expects that the EPA will give new consideration to these findings since it was previously assumed that the Conowingo Dam would not lose its capacity for 15 to 30 years.

source: Maryland Department of Natural Resources

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