Lower Susquehanna River Watershed Assessment

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The reservoir behind the Conowingo Dam is trapping smaller amounts of sediment and has essentially reached its limit to trap in the long term, according to a Lower Susquehanna River Watershed Assessment.

However, a large majority of the pollution to the Chesapeake Bay from the Susquehanna River comes from runoff from pollution sources from the upstream drainage area or watershed, as opposed to the sediment and associated nutrients collected behind the dam.

The Lower Susquehanna River Watershed Assessment (LSRWA) report released for public comment, Nov. 13, 2014. The inter-agency draft report was released by the U.S. Army Corps of Engineers (USACE) and non-federal sponsor the Maryland Department of the Environment (MDE).

Another major finding of the draft report indicates that nutrients that enter the river upstream of the dams and attach to particles of sediment and then flow downstream to the Bay have a bigger impact on water quality than the sediment, itself. The report includes consideration of management strategies, and recommendations for future opportunities.

Modeling in the report shows that managing sediment through dredging, bypassing or dam operational changes, alone, do not effectively offset the adverse impacts to water quality from the loss of capacity for the dam to trap sediment in the long term.

The report suggests that strategies to reduce nutrient pollution at its source from throughout the Bay drainage area are more effective at addressing impacts to the Bay.

The report underwent multiple peer reviews, including an independent, scientific peer review sponsored by the Chesapeake Bay Program partnership’s Scientific and Technical Advisory Committee.

The study area consists of the Lower Susquehanna River Watershed from Sunbury, Penn., to the confluence with the Chesapeake Bay and includes the Holtwood, Safe Harbor, and Conowingo hydroelectric dams located on the lower Susquehanna River. Much of the modeling efforts were focused on the Conowingo Dam, as it is the largest dam and reservoir closest to the Chesapeake Bay with remaining capacity left to trap sediment.

Major recommendations in the report include:

* quantifying the full impact on Chesapeake Bay water quality and living resources based on new understandings in the report;

* integrating findings from the report into ongoing analyses and development of watershed implementation plans as part of the Chesapeake Bay Total Maximum Daily Loads assessments;

* developing and implementing management options that offset impacts to the upper Chesapeake Bay ecosystem from increased sediment-associated nutrient loads;
* committing to enhanced long-term monitoring and analysis of sediment and nutrient processes in the watersheds to promote adaptive management into the future.

A public comment period on the draft report is now open until Jan. 9, 2015. Interested parties can submit comments via:

* E-mail to LSRWAcomments@usace.army.mil.

* Letter postmarked by Jan 9, 2015, to: U.S. Army Corps of Engineers, Baltimore District, Attn: Anna Compton , P.O. Box 1715, Baltimore, MD 21203.

* A public meeting and webinar held Dec. 9 at Harford Community College in Bel Air, Md., from 7 – 9 p.m.

Once the comment period closes and comments have been addressed, as appropriate, a final report anticipated for summer 2015 will be published to better inform stakeholders undertaking efforts to restore the Chesapeake Bay.

The LSRWA inter-agency team is comprised of the USACE Engineering Research and Development Center, U.S. Geological Survey, Susquehanna River Basin Commission, Nature Conservancy, Chesapeake Bay Program, Maryland Department of Natural Resources, and Maryland Geological Survey.

source: U.S. Army Corps of Engineers

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