Conowingo Dam Agreement Reached (again)

Last Thursday, Governor Wes Moore announced an agreement with Constellation Energy to fund and implement operational improvements and some environmental projects at the Conowingo Dam. The total commitments are valued at more than $340 million and were negotiated in partnership with Waterkeepers Chesapeake and Lower Susquehanna Riverkeeper Association. A previous $240 million agreement with the former dam operator was challenged in court by the Riverkeepers and Waterkeepers.

“The Chesapeake Bay is the keystone to Maryland’s prosperity,” said Gov. Moore. “This agreement will lead to real improvements in water quality in the biggest tributary of the Chesapeake Bay, while securing the future of one of our state’s largest clean energy producers. By bringing everyone to the table, we have struck an agreement that is good for the environment, good for energy production, and good for Marylanders.”

The agreement clears the way for the re-licensing and continued operation of the dam’s hydroelectric facility on the Susquehanna River, which is the largest source of renewable energy in the state. The terms of the agreement, announced today at the dam, include operational improvements and upfront and ongoing annual payments: 

• Water quality and resiliency: $87.6 million for pollution reduction and resiliency initiatives, including shoreline restoration, forest buffers, fish passage projects and planting underwater grasses that produce oxygen, stabilize sediments and provide habitat for countless species.

• Trash and debris removal: $77.8 million to improve trash removal program that currently clears an average of about 600 tons of debris each year.

• Aquatic life passage: More than $28 million for fish and eel passage improvements and protections at the dam, helping American shad, river herring, and freshwater mussels rebound while reconnecting habitats across the Susquehanna.

• Freshwater mussel restoration: $23.3 million to build and operate a hatchery that will seed the river with mussels, which are natural filters that clean the water and reduce pollution flowing into the Bay.

• Dredging: $18.7 million for additional studies on dredging.

• Invasive species management: $9.4 million to control destructive species like snakeheads and blue catfish, protecting the river’s ecosystem.

• The Lower Susquehanna Riverkeeper Association and Waterkeepers Chesapeake will have an ongoing role in aspects of the implementation of the certification and settlement agreement.

“This historic agreement ensures that our children and grandchildren will inherit a Chesapeake Bay and Susquehanna River that are cleaner and healthier than they are today,” said Attorney General Anthony G. Brown. I do not know if this is indeed a historic agreement, but it does seem better than the last one that failed.

“This deal ensures we balance the importance of generating renewable energy while protecting water quality standards and the broader ecosystem,” said Maryland Department of Natural Resources Secretary and Chesapeake Bay Program Principals’ Staff Committee Chair Josh Kurtz. “The settlement will allow us to apply the innovative strategies we developed restoring oysters in Chesapeake Bay tributaries to bring back water-filtering mussels in the Susquehanna River basin and other freshwater rivers in Maryland. Thank you to everyone who helped us reach this agreement.”

The Conowingo Dam is a large hydroelectric dam on the Lower Susquehanna River about 10 miles upstream from where the river flows into the Chesapeake Bay at Havre De Grace, Maryland. Not only is the Conowingo Dam the largest source of renewable energy in Maryland, the three dams at the downstream end of the Susquehanna River have been important in mitigating the downstream transport of nitrogen, phosphorus, and suspended sediment from the Susquehanna River watershed to the Chesapeake Bay. The Conowingo, the last dam in a series of three traps polluted sediment from the Susquehanna River in its 9,000-acre reservoir.

When the Chesapeake Bay Total Maximum Daily Load (Bay TMDL) was established in 2010, it was estimated that the reservoir behind the Conowingo Dam would trap sediment and associated nutrients through 2025. However, the reservoir reached dynamic equilibrium (i.e., the reservoir is near full capacity) more than a decade earlier than thought

The Conowingo Dam can no longer trap additional sediment in the Susquehanna River and prevent them from entering the Chesapeake Bay. That is what dredging studies are about. If it is feasible, the dredging could allow the Conowingo Dam to once more capture the nitrogen, phosphorus and sediment washed into the river by rainstorms.

The Susquehanna River flows 464 miles from Cooperstown, New York to Havre De Grace, Maryland collecting sediment and nutrient runoff along the way. The Susquehanna drains an area of more than 27,000 square miles and is the single largest source of fresh water flowing into Chesapeake Bay. The river currently provides nearly half of the Bay’s freshwater, 41% of its nitrogen, 25% of its phosphorus and 27% of its sediment load. Without the Conowingo removing sediments containing nitrogen and phosphorus the reductions in sediment, nitrogen and phosphorus necessary to meet the goals of the Chesapeake Bay Agreement will have to come from somewhere else.

Let’s be honest here. Implementation of the various state’s watershed plans to reduce nitrogen, phosphorus and sediment in the Chesapeake Bay failed to meet the targets set in 2012. In addition, climate projections for our region forecast that on average, precipitation in the region  is projected to increase by around 8% by 2040, and temperature is projected to increase by 2.16 °C (3.9 °F). “Because warmer air can hold more moisture, heavy rainfall events ...are projected to increase in frequency and severity as the world continues to warm. Both the intensity and rainfall rates of Atlantic hurricanes are projected to increase with the strongest storms getting stronger in a warming climate. …”  says the Fourth National Climate Assessment.

The bottom line here is the Conowingo Dam cannot be left full. It will not exist in some gentle equilibrium. The Conowingo and its sister reservoirs will not be constantly filled with sediments because of short-term changes from severe storms that cause scour and a subsequent reduction in exported sediments until the scoured amount is refilled. Therefore, the amount of sediment transported out of the reservoirs will not always be in equilibrium with the amount of sediment transported into the reservoirs. Dredging does seem to be the answer, but there are so many problems with the source water for the region; we need to indeed study the issue.  

See Also: Hirsch, R.M., 2012, Flux of nitrogen, phosphorus, and suspended sediment from the Susquehanna River Basin to the Chesapeake Bay during Tropical Storm Lee, September 2011, as an indicator of the effects of reservoir sedimentation on water quality: U.S. Geological Survey Scientific Investigations Report 2012–5185, 17 p.