Monday, September 26, 2011

The saga of Irene continues. In the aftermath, questions arise. A story on the effects of dams on the Connecticut River and its tributaries, reprinted with permission.

Wilder -- The mighty Connecticut River might seem to operate with a force all its own -- rising in the spring, falling in the summer, naturally carving its serpentine path through fields and forest. But this behemoth in the Upper Valley's backyard is in fact a highly regulated, carefully monitored mechanism, manipulated over centuries to suit human needs and bent to human will.
Most days, the river chugs along to the Atlantic without fanfare, powering businesses and providing recreational and agricultural opportunities. But when rising waters push the limits of human control -- as happened Aug. 28 and 29 during Tropical Storm Irene -- how does the great machine function? Do the dams built over the decades protect people living and working near the river, or is it foolish to imagine that the great river can be controlled?
Those who have studied the river's rise and fall concede that the answer might be a little bit of both.
When the Connecticut and its tributaries rise dramatically, as they did during the onslaught of Irene, expertise, manpower and reams of data are called upon in an effort to get the river to run smoothly.
But the owners of the homes and businesses swamped by the chaotic rush of floodwaters in West Lebanon and White River Junction could argue that the Connecticut ran anything but smoothly last month. And some have questioned whether water released from the Wilder Dam played a role in their damaged property and lost livelihoods.
The answer to that seems to be an unequivocal no.
Experts across the board agree that, love 'em or hate 'em, the dams did what they were designed to do and, in some cases, prevented millions of dollars worth of damage.
“None of the flood flows could be attributed to the dams,” said David Deen, the Twin States' river steward for the Connecticut River Watershed Council, responding to suspicions that releases from the Wilder Dam caused flooding along the Route 12A commercial strip.
Cleve Kapala, who has worked for hydroelectric company TransCanada and its local predecessors for nearly 30 years, said that dam operation and flood control on the Connecticut went exactly as planned.
Indeed, flood-control dams helped mitigate flooding, he said, and hydroelectric dams, such as the one in Wilder, played a minimal role in fluctuating river levels.
“There wasn't any damage as a result of our operations,” said Kapala, TransCanada's director of government affairs and relicensing. “We have high-water operating procedures that kicked in. The facilities operated as they were expected to.”

‘Let the Flood Flow Through'

In the post-industrial era, the Connecticut River no longer powers mills and carries logs the way it once did. Nonetheless, 13 hydroelectric dams owned by TransCanada provide 567 megawatts of power to regional businesses, and additional private dams dot the length of the 410-mile waterway.
In Wilder, a dam was first built in 1882, at the former site of the 40-foot-tall Olcott Falls. The current dam, built in 1950, was constructed three-quarters of a mile downstream, flooding the site of the waterfall and previous dam and creating an “impoundment,” like a giant pond, behind it.
Under normal operating conditions, the Wilder Dam raises and lowers water levels by approximately two feet as it holds water back and releases it to generate electricity. About 42 megawatts of power for the New England grid -- enough to power roughly 7,500 homes -- come from the dam. Dartmouth College and Dartmouth-Hitchcock Medical Center are both major consumers, Kapala said
Because it was built as a hydroelectric dam, the Wilder facility lacks the ability to store much water and thus plays a minor role in flood control. The Wilder Dam can hold back about 4 billion gallons of water -- enough to act as a sort of speed bump to check the Connecticut's raging waters, but not enough to offer the sort of flood protection that larger facilities, like the Union Village Dam in Thetford, can.
“Hydro dams do not store water,” Deen said. “They have to just let the flood flow through. Believe me, you don't want those dams storing water. If they did, and there was a catastrophic failure, you've got much bigger problems.”
Dan Grossman, a local historian and blogger from Thetford, writes that a hydroelectric dam like the one in Wilder has a huge impact when it's first built -- stumps from flooded fields and woods can still be seen when the water is low. But after the initial shock, Grossman said, hydro dams have little effect. They “neither mitigate nor exacerbate flooding.”
The Wilder Dam was designed to handle flows of 162,000 cubic feet per second (cfs) -- the size of the infamous 1927 flood against which most other high-water events in the region are measured. Irene's waters, though dramatic, came nowhere near that. The dam's release peaked at 27,623 cfs, while the flow of the Connecticut River below the dam -- after the White River poured into it with floodwaters that had already scoured West Hartford and other communities upstream -- reached flows of 104,000 cfs.
On Aug. 25, several days before Irene's arrival, TransCanada had begun incrementally releasing water from Wilder and other dams so that the Connecticut would be as low as possible before the storm hit, Kapala said.
Cat Buxton, education coordinator at Cedar Circle Farm upriver in Thetford, credited the release with helping save farmland in Thetford and surrounding areas. “We were comparably unscathed because someone was bright enough to release the dam the day before,” she said. “Even the night of the storm, the water didn't even come close to the riverbank.”
Prior to Irene, TransCanada employees also opened the company's emergency operations center at North Walpole, N.H., for the first time in 2011. During high-water events, the logistical center employs between six and 14 people working around the clock to monitor precipitation and water levels and coordinate dam operations along the Connecticut.
By Saturday, Aug. 27, TransCanada had drained as much water as possible from behind the Wilder Dam. The rain started that night. By about noon on Sunday, enough rain had already fallen that the dam's 4 billion gallon impoundment was full, and operators were forced to open the gates partially to allow excess water to spill through.
By 3 p.m. Sunday, the dam was essentially just passing the floodwaters downstream, experts said, though it was still holding back the 4 billion gallons it had already stored.
The dam's output reached its highest flow at noon on Monday, Aug. 29, after floodwaters had already inundated the Route 12A commercial strip. Dartmouth flood ecology expert Frank Magilligan -- along with Kapala, Deen and several other experts -- all agree that the vast majority of flooding along Route 12A in West Lebanon was caused by the raging, uncontrolled waters of the White River.
“When the White River does its thing, there's nothing that can be done,” said Ken Alton, a Strafford resident with a 40-year history of working with area dams. “No controls, no flood control, no dams or anything. It's going to do its thing and it’s going to do an unbelievable thing.”

Flood-Control Dams Prepare for Irene

In addition to the 13 hydroelectric dams, the Connecticut River and its tributaries host 16 dams specifically designed for flood control. Two -- the Comerford Dam at 15 Mile Falls in Monroe, N.H., and the Moore Dam in Littleton, N.H., -- are owned by TransCanada. Neither was filled to capacity during Irene, though the water storage they provided in the northern stretches of the Connecticut helped mitigate flooding as far downstream as Massachusetts and Connecticut.
Local flood-control dams -- including those at Union Village, on the Ompompanoosuc River, and at North Hartland, on the Ottauquechee -- are operated by the U.S. Army Corps of Engineers. Under normal operating conditions, each stores only about 5 percent of its total capacity, just enough to create a small reservoir for recreation.
As with the hydro dams, operators of flood-control dams began preparing for Irene well in advance. Mike Curran, the Corps' operations manager for the upper Connecticut River basin, said all reservoirs were lowered to or below normal levels by the weekend of Aug. 28.
“We knew we were going to get a big storm,” he said. “A couple hours after it started raining we shut down to our minimum release at all our reserves and kept shut down until the situation stabilized.”
The total capacity at the 1,100-foot-long Union Village Dam is 12.3 billion gallons. During Irene, the water behind the dam reached a depth of about 90 feet, or 27 percent of its capacity. The Corps estimates that more than $15 million of property damage in Thetford, Norwich and beyond was prevented by flood control at Union Village Dam.
At the 1,640-foot North Hartland Dam, a 1,100 acre lake is capable of holding 23.2 billion gallons of water.
But though Irene dropped between 6 and 11 inches in the Connecticut River drainage area -- approaching a once-in-500-years event, the Corps reported -- the North Hartland reservoir peaked at just 61 percent of its capacity, or 126 feet. Officials said the dam prevented $38 million in damages.
Army Corps of Engineers officials estimate that the 14-plus flood-control projects in the Connecticut River basin, built with federal money, prevented $540 million in property damage in Vermont, New Hampshire, Massachusetts and Connecticut from Tropical Storm Irene.
The Corps' also estimates that in some places, the Connecticut River could have risen as much as 10 feet higher without upstream flood-control dams.
While both the rains and the floods were historic, some dams saw far less water than in 1974, when a big snowpack coupled with back-to-back springtime rainstorms caused the dams at Union Village and North Hartland to reach 100 percent capacity, Curran said, spilling over walls that stand nearly 200 feet high.
To prevent that from happening again -- and to avoid the potentially catastrophic results -- hydraulic engineer Greg Hanlon, of Lyme, said the Corps began releasing water from its dams on Monday, Aug. 29, after Irene's rains had ceased and the “downstream channel capacity” was well below flood level.
At that point, the Corps began releasing some of the water that had been stored behind the dams, to make room for the water that was continuing to flow from upstream. It continued releasing on Tuesday, after water levels began to further decrease.

‘We Can't Completely Protect Ourselves'

The problem with flood-control dams, Dartmouth's Magilligan said, is that they breed a false sense of security. Some people believe that, with the Connecticut River so thoroughly dammed, roads and buildings can be constructed with little concern about floods.
“Places that had dams still got hammered,” he said. “You can't dam the entire watershed.”
Magilligan, who studies municipal policies related to flooding, noted that planning for natural disasters is challenging because greater protection comes at a higher social and economic cost. That's particularly true on Route 12A, where PetSmart, for example, successfully sued the city of Lebanon several years ago to avoid having to build in accordance with a flood prevention ordinance that would have required a more elevated -- and more expensive -- structure.
PetSmart never built its store, but Jeff Goodrich, a civil engineer based in Lebanon, said if it had, the building surely would have been inundated by Irene. He added that retail stores built after 1980 that complied with the ordinance, such as Shaw's and The Home Depot, remained dry.
Nonetheless, Magilligan said, “we're not living in a risk-free world. When it comes to natural events, we can't completely protect ourselves.”
Deen, the river steward, noted that much of the damage inflicted by the White and the Connecticut rivers during Irene hit structures that had been built in the flood plain after the 1927 flood, including the Route 12A commercial strip.
“We've known for a long time that you shouldn't build in flood plains,” he said. “And we continue to build in flood plains. Not in the 100-year flood plain, maybe, but guess what? We build in the 500-year flood plain and that's what we ran into.”
Several of the experts interviewed for this report noted that in New England at least, the heyday of dam-building is past. Public opinion has largely turned against dams, they say, and it seems unlikely that future dams will be built. TransCanada's hydroelectric dams are all up for review in 2018, and stringent environmental reviews will accompany the relicensing process, Deen said, possibly leading to changes in the way the dams are operated.
In the meantime, though, the Twin States are rebuilding.
Deen, who has been watching the Connecticut River for 40 years, worries that some of the projects -- rebuilding in the flood plain, trying to continue manipulating the river's natural channels -- will ultimately place the region again in harm's way.
“It's really frustrating,” Deen said. “Right now, we're watching the work going on in rivers in terms of putting the river back exactly where it was, putting in bigger berms and riprap, and it's not going to work.”
The Connecticut, Deen said, has clearly shown that it can't be completely controlled.

1 comment:

  1. Hi Krista,
    We used a few of your Irene photos in our 'Then & Now' package. The change is amazing!
    All the best,


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