The Plan for Conowingo Pollution Releases

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. 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, studies conducted over the last several years demonstrated that the reservoir has reached dynamic equilibrium (i.e., the reservoir is near full capacity).

The Conowingo Dam will no longer be able to trap sediment in the Susquehanna River and prevent them from entering the Chesapeake Bay. 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 will have to come from somewhere else.

The Chesapeake Bay Program’s has developed a separate Conowingo Watershed Implementation Plan (WIP) that outlines the programmatic and numeric commitments that need to be taken to reduce the adverse water quality impacts to the Chesapeake Bay resulting from Conowingo Dam infill, as well as a timeline at which those reductions could be achieved. The Conowingo WIP strategy primarily focuses on the even more implementation of agricultural BMPs to reduce 6 million pounds of nitrogen in the Susquehanna River Basin.

A draft Watershed Implementation Plan (WIP) was developed by a committee consisting of representatives from the Chesapeake Bay Commission and each Chesapeake Bay watershed jurisdiction – Delaware, the District of Columbia, Maryland, New York, Pennsylvania, Virginia and West Virginia – and supported by the Center for Watershed Protection to assign the additional reduction of 6 million pounds of nitrogen and 0.26 million pounds of phosphorus needed to mitigate the water quality impacts of Conowingo Dam infill.

EPA states in their news release that it “recognizes that the Conowingo WIP will continue to evolve based on implementation successes and challenges,” but noted that “critical to the successful implementation of the Conowingo WIP is to ensure that the plan complements and does not compete with the jurisdictions’ Phase III WIPs in terms of opportunities for BMP implementation and resources, including technical assistance, staffing, and funding.”  The evaluation states that “it is currently unclear” how the two efforts will be distinguished and recommends that the final CWIP “provide more detail on where exactly implementation will be targeted and the affected stakeholders.”

The EPA evaluation also recognizes that the Conowingo WIP financing strategy is still under development, but notes “there is currently little confidence that the Conowingo WIP will be fully implemented to meet the necessary nitrogen reductions without dedicated funding mechanisms in place and the commitment from the public sector to provide an initial investment to initiate Conowingo WIP implementation.”

Unlike the individual state WIP III,  EPA does not approve or disapprove the Conowingo WIP. However,  EPA does provide its evaluation and provide recommendations for strengthening the Conowingo WIP. The EPA has completed its evaluation of the draft Conowingo WIP to mitigate and additional 6 million pounds of Chesapeake Bay pollutants no longer being trapped in a reservoir behind the Conowingo Dam. The EPA has expressed concerns that there is no way to distinguish Conowingo WIP restoration actions from others already pledged, as well as the need for a dedicated funding mechanisms and public sector financial commitments for the additional work.

Let’s be honest here. Implementation of Agricultural BMPs in the Susquehanna River Basin has lagged even without these additional goals, and 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. Recent research has shown how global warming can alter atmospheric circulation and weather patterns such as the jet stream, affecting the location, frequency, and duration of these and other extremes,”  says the Fourth National Climate Assessment.

The bottom line here is no matter what mankind does, in the next couple of decades the expected impacts from climate change are going to happen. At this point, Human's actions can only have impact  on the second half of the 21st century. 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 to capacity 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. Dredge it. Just put the bill into one of the multitrillion dollar spending plans. The senators from Virginia, Maryland, New York, and Delaware could simply come together to require the inclusion of the restoration of the Conowingo Dam in one of the bills. Long term capital improvements are the sorts of things that should be financed.

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.