On August 30, 2012, the U.S. Geological Survey (USGS) released a report indicating that the Susquehanna River delivered more sediment and phosphorus to the Chesapeake Bay in 2011 than in any year since 1978, when monitoring of this delivery began. The large sediment and phosphorus inputs resulted largely from Tropical Storm Lee in September 2011, in combination with accumulations of sediment over time in three large Susquehanna reservoirs: Safe Harbor Dam and Holtwood Dam in Pennsylvania and Conowingo Dam in Maryland. The report compared storm-delivery of sediments and nutrients from the Susquehanna over the past 34 years, and it asserts that the sediment accumulations in the reservoirs have increased the potential for sediment delivery during any given storm event. This effect threatens to counteract some of the extensive basin-wide efforts—through agricultural best management practices, wastewater-treatment plant upgrades, stormwater management, and other actions—to reduce inputs of sediments and nutrients reaching the Bay from its many tributaries. The report’s author, Robert Hirsch of the USGS’ main office in Reston, Va., stated, “In general, the changes we have observed in the reservoirs and the resulting greater impact of storms are already overshadowing the ongoing progress being made in the watershed to reduce the amount of nutrients and sediments entering the Bay.” The report, “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” (Scientific Investigations Report 2012-5185) is available online at http://pubs.usgs.gov/sir/2012/5185/; or phone USGS at (888) ASK-USGS (275-8747).
Sources: Sediment reservoirs in lower Susquehanna reach capacity, deliver more pollutants into Bay, Chesapeake Bay Program, 8/30/12; and Increased Sediment and Nutrients Delivered to Bay as Susquehanna Reservoirs Near Sediment Capacity, U.S. Geological Survey News Release, 8/30/12. Additional news source (added 9/20/12): Sediment behind a dam threatens to undermine Chesapeake Bay cleanup, Washington Post, 9/16/12.
For an earlier look at this topic, see “Changes in Sediment and Nutrient Storage in Three Reservoirs in the Lower Susquehanna River Basin and Implications for the Chesapeake Bay” (USGS Fact Sheet 003-98), a 1998 USGS report online at http://pa.water.usgs.gov/reports/fs003-98.html. The following map, showing the location of the three lower Susquehanna River dams, was taken from that publication (8/31/12).