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Bay Blog: Conowingo Dam

Nov
13
2014

Reducing upstream pollution could ease effects of full Conowingo reservoir

A team of scientists has found that reducing pollution in the Susquehanna River watershed—which includes portions of New York, Pennsylvania and Maryland—could ease the environmental effects of an “essentially full” reservoir behind the Conowingo Dam, whose pollution-trapping capacity has diminished in recent years.

The reservoir behind the Conowingo Dam—as well as those behind the Holtwood and Safe Harbor dams—has for decades trapped particles of sediment flowing down the Susquehanna River, as well as the nutrients that are often attached. But according to research from the Lower Susquehanna River Watershed Assessment (LSRWA) team, this reservoir is full. The once-effective “pollution gate” is trapping smaller amounts of sediment and nutrients and, during large storms, sending more of these pollutants into the Susquehanna River more often.

While researchers explored strategies for managing sediment at the dam, the team found that reducing pollution loads upstream of the dam would pose a more effective solution to the “full reservoir” problem. Indeed, dredging, bypassing or other operational changes would come with high costs and low or short-lived benefits. But adhering to the Chesapeake Bay’s “pollution diet”—and taking additional steps to reduce pollution where possible—would offer management flexibility and environmental benefits.

The Chesapeake Bay Total Maximum Daily Load (TMDL) was established in 2010 to reduce nutrient and sediment loads across the watershed. Lowering these pollutants is integral to restoring the health of the Bay: excess sediment can cloud the water and harm underwater grasses, fish and shellfish, and nutrients can fuel the growth of harmful algae blooms. While the LSRWA team did find that the effects of the sediment that “scour” from the Conowingo reservoir cease once it settles to the bottom of the river, the effects of nutrient pollution linger. Green infrastructure, forest buffers and sound farm and lawn management can help businesses, landowners and individuals contribute to a restored Chesapeake.

Learn more.



Aug
30
2012

Sediment reservoirs in lower Susquehanna reach capacity, deliver more pollutants into Bay

Sediment reservoirs near the mouth of the Susquehanna River are filling up faster than researchers expected, posing a new obstacle for improving water quality in the Chesapeake Bay. 

As the holding areas behind the lower Susquehanna's three dams reach capacity, their ability to trap upriver sediment and the phosphorous that is often attached wanes, and the sediment that is held grows more and more likely to flow out of the reservoirs and into the river.

Image courtesy Jane Thomas/Integration and Application Network/University of Maryland Center for Environmental Science.

According to a report released by the U.S. Geological Survey (USGS), strong storms, severe flooding and faster-moving water have turned the one-time pollutant blockers into less effective gates.

The Susquehanna delivered more phosphorous and sediment into the Bay last year than it has in more than three decades of monitoring. The past 15 years have seen a 55 percent increase in phosphorous entering the Bay from the river and a 97 percent increase in sediment. And while nitrogen flow has dropped, it shows a jump during large storms--like Tropical Storm Lee in 2011 or Hurricane Ivan in 2004--and the flooding that follows.

Excess nutrients and sediment can harm fish, shellfish and underwater grasses. Nitrogen and phosphorous fuel the growth of algae blooms that rob water of oxygen and, with suspended sediment, cloud the water and block the sunlight that plants need to grow.

A previous USGS report cited improvements in nutrient and sediment trends as a sign of improving Bay health. The USGS has seen significant reductions in nutrient and sediment concentrations upstream of the reservoirs, which reflect the positive impacts of conservation efforts in the Susquehanna watershed. But the filling reservoirs behind the Safe Harbor and Holtwood dams in Pennsylvania and the Conowingo Dam in Maryland overshadow the pollution reduction progress that is being made.

The Lower Susquehanna River Watershed Assessment team, composed of federal, state and regional partners and administered by the U.S. Army Corps of Engineers, is exploring ways to expand the reservoirs' capacity. 

Learn more about the flow of nitrogen, phosphorous and suspended sediment from the Susquehanna River into the Bay



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