Dams seem to be pretty straightforward objects – they’re big things that block water – but a re-licensing effort for three dams on the Connecticut River shows that it can get complicated when electricity is added to the mix.

“This would be unique for us,” said John Ragonese of Great River Hydro, a firm that owns and operates 13 hydropower projects in the Northeast, including the three in question that it bought in 2017 from TransCanada. 

Ragonese’s title is FERC License Manager but before we plunge into acronyms, a quick recap.

Most of us think of dams as holding back or impounding so much water that rivers become lakes, and then releasing some of that water through gates as desired. The Hopkinton-Everett Flood Control dam is typical.

But many of the 4,800 dams in New Hampshire are called run-of-river. They let the river flow on without holding any of it back. If they’re hydropower dams they divert some water through channels as it goes by to spin turbines and make electricity.

By the way, that surprisingly large number of dams in New Hampshire is correct. Most are tiny, often built for long-gone sawmills, but we have a lot of bigger ones, too, including 22 on the Connecticut River.

Run-of-river dams are cheaper to build and operate and do less environmental damage than impoundment dams but also generate less electricity, since the power from water is a function of how far it falls, and provide less control over how much and when they can generate power.

The three dams in question here – Wilder, Bellows Falls and Vernon – have always been impoundment hydropower dams. Great River Hydro wants to change that and operate them instead as run-of-river dams, partly because it reduces the environmental concerns that could prevent re-licensing by the Federal Energy Regulatory Commission, or FERC. (Now you understand Ragonese’s job title.)

They made the request this month and hope to have permission by the summer.

Because these dams have pretty small impoundments, just three to five feet high, switching to run-of-river will be relatively easy, Ragonese said. “There will be no change in turbines, no modifications to the dam for the most part.”

So what’s complicated about it? The power market.

ISO-New England, the folks who run the six-state power grid, have established something called a capacity market which they say is necessary to make sure we won’t have blackouts during a polar vortex or a summer heat wave. Not everybody agrees this market is needed; some see it as a subsidy for inefficient power plants.

Power plants bid into the capacity market auction with a guarantee they can produce a certain amount of electricity on demand, no matter what. If their price is low enough, ISO-NE takes them up on it. They get paid for the guarantee whether the electricity is needed or not – that’s where subsidy claims arise – but they also face big fines if they can’t produce when their power is needed.

To my surprise, Ragonese said Great Hydro would be bidding these plants into the capacity market even after becoming run-of-river. That’s the aspect that will be unique for the company.

This sounds crazy to me. How can you be certain you can crank out enough electrons on demand during, say, a long heat wave that is part of a drought which cuts river flow? One way you differentiate between an impoundment hydropower dam and a run-of-river dam is that the former schedules its releases and electricity production while the latter doesn’t.

Despite that, Ragonese said Great River’s experience and some proprietary approaches, including the occasional use of a small amount of impounding (one foot or less), would make it work. Whether FERC agrees and grants the new operating license is yet to be seen.

Part of the company’s confidence comes from ever-better forecasting and modeling about rainfall, soil conditions, runoff and other factors that affect flow throughout the watershed, the area that drains into the Connecticut River upstream of each dam. Dams don’t just wait to see how water shows up every day; they increasingly predict future supply.

In this way, dams are like wind farms, which use ever-improving predictions of weather patterns to know in advance how much wind they’ll have and thus how much electricity they’re likely to make down the road.

A complicating factor for dams is the fact that rivers are long and skinny, which means the entire supply doesn’t change at once. It might be raining in one part of the watershed but not another, and water in river channels doesn’t move very quickly. It would take at least two days for a raindrop that falls on the Quebec border to make it to Long Island Sound even if there were no dams at all.

“The longer they are, the more there are other developments going on – water is coming in upstream but it really doesn’t hit the dam for hours and hours,” said Ragonese. “You see (the water) as more of a tilt … It’s not flat.”

I hadn’t really thought of water in rivers as tilting, but then again I haven’t had to operate a dam, either.

Great River’s change in operations is even more surprising because impoundment dams are becoming more valuable in the era of renewable energy. They can act like a big battery, holding back water when wind and solar power are abundant and releasing it to generate power when they’re not. This ability to help stabilize the grid is worth money, and it seems to me that Great River won’t be able to cash in as much.

But whatever the financial result, it shows that even big, motionless objects can be more complicated than you’d think.