Maryland forms commission to study sediment issues at 572-MW Conowingo hydroelectric facility

Conowingo Dam

On July 7, Maryland Gov. Larry Hogan (R) announced the state is forming a multi-agency work group to study ways to reduce sediment reaching Chesapeake Bay. Annually, sediment enters the bay by way of the 53 gates at the 572-MW Conowingo hydroelectric facility on the lower Susquehanna River in Maryland, from flow in its nine-mile-long reservoir that extends into Pennsylvania.

During his press conference on Thursday, Hogan said, "Simply put: This is a growing problem. It's getting worse, and it must be solved.”

The Conowingo Dam is a concrete gravity dam that has a maximum height of about 94 ft and a total length of 4,648 ft. Sediment in the dam's 310,000 acre-feet reservoir is at capacity, according to a study this year by the Lower Susquehanna River Watershed Assessment. The U.S. Army Corps of Engineers estimates dredging the sediment would cost billions of dollars.

The facility is the lowest of a series of dams on the Susquehanna and the last barrier between much of the Chesapeake Bay watershed and the waterway itself, and the reservoir supplies flow to 11 turbines in the Conowingo powerhouse.

According to a 2014 U.S. Geological Survey estimate, more than 160 million tons of sediment is behind the Conowingo Dam, built near Darlington, Md., in 1928. About 3 million tons arrive there each year, and about a million tons of that sloshes over the gates, according to USGS hydrologist Mike Langland.

Published reports indicate public officials took note of the increasing threat to the Chesapeake Bay in 2014 after Tropical Storm Lee produced record flows in the Susquehanna River in September of that year. The amount of precipitation from the storm forced officials to open the sluice gates at the dam releasing an estimated 4 million tons of sediment in about four days, equaling what the bay normally gets in four years.

Satellite imagery at the time showed the release discolored half of the bay’s blue-green waters.

Then Maryland Gov. Martin O’Malley (D) and Col. David E. Anderson, commander of the Corps’ Baltimore District, launched a US$1.4 million series of studies to examine how storms could undermine efforts to protect the bay from sediment and other pollution.

Conowingo is owned and operated by Chicago-based Exelon Corp., an electric and gas utility that reported $80 billion in assets and $24.9 billion in operating revenues in 2013. Exelon filed application with the Federal Energy Regulatory Commission on Aug. 31, 2012, requesting a new 46-year generation license for Conowingo.

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