Paying The Sedimentation Piper: MD Dam @ 92% Of Capacity For Toxic Mud Above Chesapeake Bay
When the Conowingo Dam opened to fanfare nearly a century ago, the massive wall of concrete and steel began its job of harnessing water power in northern Maryland. It also quietly provided a side benefit: trapping sediment and silt before it could flow miles downstream and pollute the Chesapeake Bay, the nation’s largest estuary.
The old hydroelectric dam spanning the lower Susquehanna River is still producing power, but its days of effectively trapping sediment in a 14-mile (22.5-kilometer) long reservoir behind its walls are over. Behind the 94-foot (29-meter) high barrier lies a massive inventory of coal-black muck — some 200 million tons (181 million metric tons) of pollutants picked up over decades from farmlands, industrial zones and towns.
How big a threat this sediment stockpile poses to the Chesapeake Bay or whether anything can even be done about it depends on who one talks to. With Maryland pushing to curb pollution in dam discharges, the issue has become a political football as Conowingo’s operator seeks to renew its federal license to operate the dam for 46 more years after its old license expired. And as negotiations drag on, the lack of agreement about curbing runoff pollutants following the wettest year on record imperils hard-won gains in restoring the Chesapeake Bay.
The iconic estuary famed for its blue crabs and oysters has been gradually rebounding under a federal cleanup program launched in 1983 that put an end to unbridled pollution. But the 200-mile (325-kilometer) long bay is increasingly being ravaged by runoff-triggering downpours, including record-setting rainfall in 2018 and this year’s soggy spring. Intense cycles of downpours are washing pollutants into the Chesapeake from municipal sewer overflows, subdivisions and farms where manure often isn’t effectively handled and nitrogen and phosphorous-rich fertilizers are used. Experts say climate change is accelerating the environmental decline, potentially leading to more damaging algae blooms and dead zones in the Chesapeake and coastal waters.
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https://www.apnews.com/fcc685b8e1f048eea5edd0e606493cf5
The Conowingo Dam on the Susquehanna River is at about 92 percent capacity for sediment storage according to new U.S. Geological Survey research. Since the dam’s construction in 1929, sediment and nutrients have been building up behind it, being released periodically downriver and into the Chesapeake Bay, especially during high flow events.
“Storage capacity in Conowingo Reservoir continues to decrease, and ultimately that means more nutrients and sediment will flow into the Bay,” says Mike Langland, a USGS scientist and author of the study. “Understanding the sediments and nutrients flowing into the Bay from the Susquehanna River is critical to monitoring and managing the health of the Bay.”
Previous research has shown that having excess nutrients in the Bay depletes the water of oxygen needed to maintain healthy populations of fish, crabs, and oysters. Additionally, the nutrients, along with sediment, cloud the water, disturbing the habitat of underwater plants crucial for aquatic life and waterfowl.
At full sediment-storage capacity, the Conowingo Reservoir will be about one-half filled with sediment, with the remainder--about 49 billion gallons--flowing water. That amount of sediment could fill approximately 265,000 rail cars, which if lined up would stretch more than 4,000 miles.
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https://www.usgs.gov/centers/cba/science/conowingo-dam-above-90-percent-capacity-sediment-storage?qt-science_center_objects=0#qt-science_center_objects
