Enough was enough. After record floods of 1936 were backed up by historic flooding from the Great Hurricane of 1938, everyone knew this couldn't just keep happening for riverside communities in western Massachusetts to survive. The federal government heard this plea as well, and through an act of congress, called upon the Army Corps of Engineers to help.

What weather brings record flooding?

According to Dave Vallee, Hydrologist- in-Charge at the Northeast River Forecast Center, based in Taunton, MA, there are essentially two distinct weather events that can cause record flooding in a New England river basin. One of them is obviously a storm of tropical nature, but the other one lurks more in the late Fall or early Spring. Here, a storm of particularly high water content would rain down on a watershed, and simultaneously temperatures that happen to be above freezing rapidly melts a well-established snow-pack. This has the additive effect of introducing several inches of falling precipitation, and several inches of newly melted liquid equivalent, to a river at the same time. In March of 1936, one such flood devastated many areas of Western Massachusetts, and even remains the flood of record on parts of the Connecticut River and on several tributaries in the watershed. September 1938's hurricane brought destruction a second time to the area, and many feared a susceptibility to the same on a much too frequent basis. In an era of massive construction and works projects, it seemed only logical to come up with some way to help communities in Western Massachusetts.

Flood Control Dams

Paul Marinelli oversees the flood control dams in the Connecticut River watershed. "Congress authorized the corps to build flood control dams as a result (of these earlier floods)...the first of which was completed in 1941," he says, as he stands atop the Littleville Dam in Huntington, MA. "This here was completed in 1962." The concept of these dams are relatively simple, according to Marinelli: "Inflow equals outflow." That is to say, locations are chosen for these dams in areas that are prone to flooding, but most often, the rivers are permitted to behave as if the dam isn't there at all. The dam works by being able to control the flow of water through it, and in therefore in flood situations, by not permitting the full flow of water downstream. This would naturally cause a backup on the other side of the floodgates, where a waiting valley of space is ready for use.

"We're responsible for real time water management. Data collection equipment is scattered downstream and upstream from the dams. We digest it. We know what the water levels are, the flows, etc. Then in concert with the National Weather Service, we see where the stage forecasts are. If the rivers rise, we'll start ordering some cut-backs...to help mitigate those rises (the river downstream will not rise as fast if the water is not permitted to flow as fast out of the dam)...If they continue to rise, then we really cut back. We don't go to zero...we still maintain a target so we sustain fish life."

"We can't prevent flooding...we can help keep the crests from being as high," Paul explains. "Then, when the threat has passed and things improve...we start gradually releasing water that has stored up behind the dam, to free it up for the next time."

Not Flood Proof

There are 15 such flood control dams within the Connecticut River watershed. "If you add up all the dams, we control about 14% of the watershed. It shows you we can't stop flooding." Marinelli goes on, "If all the water from a rainstorm were to fall downstream from a dam, there's not much we can do about it...that's the uncontrolled part." There is also a limit to how much water the dam can hold back, relative to the area designed to contain it. Each dam in the watershed has a different maximum, but they're all governed by a 'spillway'. A spillway is part of a dam system that perhaps resembles the overflow segment of a bath-tub drain. When the water level gets high enough, it would flow down that upper part instead of continuing to fill to the point of overflowing into the bathroom en masse. A flood event causing a dam to 'spill', even as its gates are permitting water to flow downstream anyway (just not at a flooding level), is truly a dangerous situation. "If we see water rising to our spillway crest...right away we know we're in a critical situation, as communities downstream may be surprised by a rush of excess water into the system from the spillway. We would contact emergency operation centers...informing for possible evacuations." Since the dams have been in place, many of them have actually never spilled, which means they have worked successfully to do their job for citizens downstream, and have not been overcome by the weather through all those years. Some indeed have spilt, which is a testament to the storm that brought the event. Any given year has about a 1% chance or less of having a storm capable of doing such a thing. In fact, I asked him about the Great Hurricane of 1938, and how the dam system would have fared. When deciding where to build a dam, and how big to build it, engineers would often use past storms as test cases to make sure they're designing the proper capability. If we had another storm with the exact similarities to the 1938 event, we would have less flooding today as a direct result of the flood control dam network. "In fact," Marinelli says, once again looking toward the containment pool behind the Littleville Dam, "we wouldn't have spilled here at all."

Possibility for Dam Failure

Now that there is a series of dams along the waterways of Western Massachusetts, there is always this vastly remote possibility that the water held back by one could all spontaneously flow forward during some cataclysmic dam failure situation. Paul Marinelli also talked about this. "All the dams in New England that the Corps built are simple: earthen dams with an impervious core, with sloped banks that are protected against erosion." It's not the same as a perhaps more famous wall-of-concrete holding back a torrent. Its simplicity adds to it's staying power. "If the corps dams weren't inspected, we might be surprised with some structural compromise. But because we seriously review the dams every 5 years with a multi-disciplinary team, we're careful to detect and repair so we don't have these problems."

The truly catastrophic, a dam failure at maximum capacity, a scenario that would unleash a fury unequaled by nature, has also been  been analyzed for each dam installed. The impacts of these studies are never pretty, but the prospects of the worst case scenario, in light of the rigorous safety measures and the rarity of the weather event necessary to trigger it, are utterly remote. Nevertheless, for example, if the Littleville Dam were to fail at maximum capacity, the town of Westfield, MA would experience a 50' - 60' wall of water (!) within a couple of hours. The local emergency management teams have copies of all these reports for each dam, so they can attempt to react with the short amount of time given.

This very scene played out in Alton, NH in 1996, on a private (non-flood control) earthen dam. The 38' high meadow pond dam failed, causing 8 million dollars in damage and killing one person. Another flood in October 2005 caused another failure, with localized devastating proportions. So far, none of the flood control dams built by the corps have suffered similar fates.

After the Rain Stops

"The most critical element of flood regulation," Paul Marinelli says, "is not so much holding water back, but how do you release after the flood, and when." By knocking the crest down off a major water event, the pool builds up behind the dam, and would need to be released to lower the pool in time for the next event. Careful consideration must be taken in these instances, so that they don't release too much water after a flood...or else they end up causing a secondary rise on the river. What results is instead of a devastating event of short duration, we'd have a more innocuous near/at flood stage river level downstream from the dam for several days.

Local Flood Mitigation Projects

In response to record flooding on a local level, cities and municipalities often want their own specific flood protection effort, designed for certain areas, and not for watershed management. Paul explains it this way: "The city of Springfield would say 'we need flood protection in this residential area'...they would come to us. The corps would design and construct the appropriate project, and then turn them over to the city. The city would have to pay a percentage of the costs for these projects, and then be responsible for maintaining them." These local flood control projects have taken a variety of forms and materials, as the Army Corps of Engineers have build close to 100 projects in the Connecticut River watershed. There are earthen levees, concrete flood walls, channelizing, flood gates, dikes with no moving parts, stop-loss structures, pumping stations, all in attempts to provide a continuous line of protection to vulnerable areas, based on prior flood experience.

There comes an interesting post script to local flood protection, and that there hasn't been any flooding since they've been installed, so they haven't come into use much. It begs the question: "How long has it been since these things have been stressed or tested?". Marinelli responds, "Testing and inspecting (these projects) are very important. The Corps is supposed to inspect them every 2 years or so, but the city is responsible for their upkeep. It can be reasonable to wonder...for example...here's a hole for a lock...but where are the locks (talking about a theoretical flood mitigation structure)? It's only natural that things can break down when not in use...that's the whole point of inspections." Consider a floodgate for example. Some of them are across heavily traveled roads along the Connecticut River. They are not easy to test, and its certainly easier to allow to sit. After all...how bad can it be? Hopefully we don't find out.

As of 2005, $538 million dollars have been spent on flood control projects in New England, and, according to the Army Corps of Engineers, prevented an estimated $3.2 billion in losses at the hands of flooding.

Related Links:

Army Corps of Engineers - New England Region
New England District Resevoir Control Center
Advanced Hydrologic Prediction Service - Boston