Conowingo Dam

CRC Director Bill Ball was recently quoted in a Johns Hopkins Magazine article about the need for increased upstream agricultural BMPs to alleviate the sediment build-up behind Conowingo Dam.

The dam has been in place, collecting sediment, for almost a century. The dam was completed in 1928 as a hydroelectric and flood control project in the Susquehanna River. For much of its life, however, the dam has served a secondary purpose as a trap for sediments before washing into the Chesapeake Bay.

As excess fertilizers wash into the Susquehanna, phosphorous sticks to silt in the runoff, and the dam retains some of this silt. This helps prevent fertilizers from reaching the Bay, which can cause algal growth and fish die-offs. However, the silt build-up in the dam is already causing performance issues, dubbed “dynamic equilibrium.”

This means that the dam has so much silt that the amount coming into the dam over ten years is about equal to the silt leaving the dam. Scientists like William “Bill” Ball, a professor of environmental health and engineering at the Whiting School of Engineering, initially thought they might have more time to seek solutions to this large and complex problem.  Although all dams that catch silt eventually lose their trapping capacity, Bay managers did not expect this Dam to fill up until at least 2020.

Episodic storm events pose huge threats to the dam. As water rises during storm events, so much water rushes into the Susquehanna that silt could be churned from the bottom of the reservoir and into the Chesapeake. Ball and CRC now use models that act as if the Dam was no longer there, as “the dam is definitely losing its performance and pretty darned close to a point where the 12-year average removal of silt and phosphorous is zero.”

To deal with this problem, Maryland Gov. Larry Hogan has started accepting bids to test whether dredging the dam would be effective. This method could provide a temporary solution, but it costs billions of dollars to implement. Instead, more needs to be done upstream. Ball notes, “in the view of many of us, you get so much more by using more sustainable practices upstream in agricultural as well as suburban and urban development.” Riparian buffers and better handling of waste will be necessary for preventing nutrients from reaching the dam and ultimately Chesapeake Bay.