Throughout the flooding that hit the state, officials were keeping a close watch on dams. The single largest evacuation took place in Bristol when a dam on the Newfound River -- that was already in the process of being removed -- began to hold water again. NHPR's Mark Bevis spoke to Jim Gallagher, the chief engineer for the dam bureau. Gallagher says the effort to dismantle unsafe dams on the river has accelerated.
Gallagher: "There are two small hydro power dams that no longer generate electricity, and they started dismantling the lower one. And that work is ongoing right now, and after that they're gonna be moving up to the upper one, and it's my understanding that both of those dams will be largely dismantled by maybe the end of the day tomorrow."
Bevis: "I see. Now I understood also that one of the dams there, you noticed that some of the seams were coming apart, some of the welds, as we were reporting. Is that true?"
Gallagher: "That was the case, yes, and that was the upper dam, that a lot of the superstructure of the dam remained still in place. They had removed a lot of the wooden portions of the dam before, so it wouldn't impound water under normal conditions. But the superstructure remained in place - the catwalks, some of the beams, and debris had piled up against that superstructure, with high flows pressing on that superstructure caused some of the beams that remained in place to bend, breaking a few welds, and there was a concern that the whole superstructure would fail. And again, it was impounding some water because debris had piled up against the superstructure, and that would have acted like a dam - you know, dam failure and released water downstream in an uncontrolled fashion, so the determination was made that those needed to be removed."
Bevis: "Are there any other problem areas that you folks are keeping track of at this point?"
Gallagher: "Not at this point, that's the remaining one. We were concerned with a dam on the Salmon Falls River - Spaulding Pond Dam, that was earlier this week. Since then, flows in the river have receded, the pool level behind the Spaulding Pond Dam has also receded. There was some concern that the dam could get overtopped. We did some storage of floodwaters at an upstream dam - actually, a state-owned dam, the Milton Three Ponds Dam - to avoid overtopping that downstream dam, and because of that operation, and fortunately the river receded to the point where that's no longer a problem."
Bevis: "I've got to ask - are you surprised, after all this rain and all this water running down these rivers- are you surprised these dams held?"
Gallagher: "Not too surprised. There certainly was a lot of flow- the size of this flood, in the southeastern part of the state particularly, exceeded a hundred year event, which exceeded the discharge capacity of many of these dams. And so, as a result, many of them did get overtopped. They did suffer some damaged, but generally speaking are well-designed. The ones that could pose a threat to public health and safety if they were to fail, they are inspected regularly by DES and as part of that inspection process, they are generally kept in a pretty good condition."
Bevis: "Let me ask- when the water goes down, do you think you're gonna see problems down below? Do you think you'll see the possibility of problems you're gonna have to take care of?"
Gallagher: "Absolutely. After these flows have receded, we'll be doing inspection of all the dams that could pose a threat to public health and safety if they were to fail. And I expect we will be seeing some damage that will have to be repaired, some erosion damage that will have to be repaired."
Bevis: "So is the danger over in Bristol?"
Gallagher: "They're still working on it. It's gonna take them still another day and a half to finish their work there. It's still uncertain, honestly, about how long it's gonna take, but that's the best guess now, that it's gonna take about a day and a half and then the folks that were evacuated from their homes downstream can return."
Jim Gallagher is the chief engineer for the dam bureau.
He was speaking with NHPR's Mark Bevis.
