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The Grid

The Conowingo Dam: Keeping safety at the forefront


​It’s easy to forget about the power of power until you lose it. We depend on power grids, cable TV and even our homes’ plumbing. We don’t give these things much thought, until they aren’t available.

Hydroelectric power dams fall into an even more obscure category of “don’t-bother-me-with-it-unless-I-need-to-know.” I’ve learned this first-hand as the Community Relations Manager at the Conowingo Dam, which straddles the Susquehanna River a few miles south of the Maryland-Pennsylvania border. It is one of the oldest and largest dams east of the Mississippi River and has been Maryland’s largest source of renewable energy for 90 years. In fact, it provides more renewable energy than all other state renewable sources combined, powering more than 159,000 homes and businesses and has avoided the burning of 2.8 million tons of coal in the past 10 years – enough to fill M&T Bank Stadium four times.

Dams like the Conowingo deliver renewable power to millions of people every day. In late July, heavy rains and flood debris filled the Susquehanna and, subsequently, the Chesapeake Bay. Suddenly, the dam was on people’s radar. Even so, many of the people discussing the significant floods were — and still are — unclear about how dams work, what dam operators do and how we keep safety at the forefront.

Here are four facts about our dam that might interest you:

  1. Powerful stuff
    The Conowingo Dam is Maryland’s largest source of renewable energy. It represents over half of the state’s renewable power and has 11 turbines that generate this power. PJM is our power grid operator and it gauges energy supply and customer demand, giving us notice about how much power is needed. If there’s an unplanned outage, like a power plant going offline, other power-producing plants and dams are asked to produce more power to pick up the slack. In the event there is a regional blackout, as in 2003, Conowing Dam would be a resource to start the grid.

  2. Let it flow
    The Conowingo Dam, which was built in 1928, handles 80,000 cubic feet of water per second through the main powerhouse. This is equivalent to one Olympic swimming pool of water per second. When more water comes down the 450-mile Susquehanna, we must open our spillway or crest gates to let water through. Otherwise, these flood waters could damage the dam.

    There are 50 large gates at the top of our dam, and each one is opened with a an overhead crane. Water that passes through the gates and onto the spillway doesn’t generate power, but just continues down the Susquehanna River. If we didn’t open crest gates during times of increased river flows, the water level would rise hazardously, sending water flowing over the dams. Only twice in the dam’s existence have all 50 gates been raised. The recent heavy rains resulted in as many as 20 gates raised, which only happens about once every five years. Still, that doesn’t constitute a flood emergency; for that, we’d need to open 30 gates.


  3. Always on
    The dam’s control room is staffed 24 hours a day, every day. When one person’s shift is ending, another overlaps with that operator, ensuring that someone is always watching the dam. These operators are constantly checking water gauges to guarantee they know the river’s water flow at all times. Each gauge has a backup gauge, and operators also watch real-time cameras to keep an eye on water markers.

    We also watch for the trees, branches and debris (ranging from trash, to tires, to refrigerators) that accumulate and stretch the width of the river at the top of the dam, and we use cranes and boats to clear this debris. This year alone, we’ve removed more than 1800 tons of debris from the Susquehanna. This is the equivalent to removing an elephant a day! In cases of major flooding, we cannot attempt to capture debris carried from far upstream. The July downpours were an example of this: Susquehanna river flow was 10 times normal and water levels rose higher than they’d been in years, making conditions too dangerous to attempt debris removal.

  4. Safety first
    Conowingo Dam has a robust public safety plan, which aims to communicate with emergency management personnel who are impacted by the dam. We work closely with emergency planners and responders in downstream communities during high-flow events. We also have sirens and lights that activate whenever we turn a generator on or off, telling boaters that the downstream water level will change and could be turbulent. We post warning signs, and twice a year our safety engineers check to make sure that all of these signs are in place and readable. We also share tips about how to keep debris out of the watershed.

Though it’s easy to forget about the power of dams and how they operate, know that people like our team at Conowingo are working 24/7 to keep your homes humming with clean, reliable power and our waterways safe.

Deena O’Brien is a Community Relations Manager at Exelon Power’s Conowingo Dam.