I’ve lived in New Hampshire my entire life and whenever we get ridiculous amounts of rain (Hurricane Irene, right now) I always hear about Vermont getting washed away while we have some sporadic bad flooding here in New Hampshire. Is there a reason (like terrain) that Vermont floods so much more than us? Or is it that it has happened to flood more in my short 21 years of life?
*My heart goes out to the Vermonters here right now* 💙
In: 66
When storm clouds hit the Green Mountains and start to rise up, they dump their water content. It’s the same reason why you get lots of rain and snow on the west side of mountain ranges in the Western US but the eastern side of those same ranges are almost deserts. Just on a smaller scale.
I suspect, but don’t have a good way to categorically confirm, that VT has more towns and roads built in valleys around/along rivers than NH does. And a lot more of those are located in the heart mountainous areas compared to NH.
Consider where the major mill towns are in NH. Most are in the southern part of the state and closer to the coast where the terrain is more flat, so heavy rain can spread more instead of being channeled into a couple rivers. Yes there are plenty of small towns in the white mountains, but the northern half of NH is surrounded by mountains in all it’s neighbors, which helps a ton with knocking excess water out of storms before they get to that area. NH also has more lakes that rivers drain into which helps aborb the events.
VT has a ton of towns built in the valleys of the green mountains, most built around rivers. Unlike NH there really aren’t big lakes to absorb larger rain events, instead you get all that water trying to funnel down into the valleys into the same river and it just can’t deal with the volume of water, so it over flows and takes out the roads and towns. Consider just how long the Winooski River is, and how many towns are built along it, and how many mountains funnel into it between it’s start and stop without any major bodies of water to help absorb big rain events. Same with the mad river and white river further south.
Now consider the white mountain area. There is the pemigewasset River running along side I-93, but most of that is a wider valley and it doesn’t have to go far to find lakes to empty to. 302 has the saco River, and also barely any towns built along it. 16 through the heart of the mountains also has few towns along it. Most of the larger towns in northern NH are built on the edges of the mountains where things “flatten” out a little, they aren’t tucked into the valleys of the heart of the mountains. And most of the big mountains have small lakes at their bases that can take large rainfall, like echo and profile lake at Canon, and the entire lakes region just south of the white mountains.
Basically VT takes the brunt of storms that come in from the west, often loaded with moisture from the great lakes, and their geography doesn’t allow larger rain events to drain out as efficiently. Combined with more towns in the valleys and it just works out worse.
Note, when Irene came through, up in the NH White mountains both the Kancamagus and 302 were shut down because flooding was so bad that good sized bridges washed out. 302 was out for months, I don’t remember how bad Kancamagus was.
RTE 10 in Winchester NH got hit pretty bad. It completely washed away in stretches and it’s a major north/ south rte.
The geology (and thus geography) of Vermont is somewhat different. It is more of a fold belt running north-south, so it tends to have narrow valleys between high uplands. The geology of upstate NH is dominated by intrusive rocks and lacks that linear ridge-valley system; southern NH is more like southern Maine/eastern Mass and has wider valleys or rolling terrain. The more eastern “linear system” equivalents occur up (north) toward the eastern townships region of Quebec and miss NH (those parts of Quebec got whacked pretty well too, much like Vermont). The “belt” passes n-s through Vermont before turning ne-sw through quebec (townships through Gaspé and out toward Newfoundland). A little more complicated than that, but the general idea applies.
The thing about watersheds is that narrow valleys see rise in water levels a lot faster than wide watersheds. The volume has to be accommodated somehow, and if it isn’t over a large area, it has to be by increased height. It will rise until it can spread out, basically. Well, Vermont geography has a lot of places where there isn’t a large flatland where the water can spread out easily. Not all Vermont, but enough places that particular rivers always rise a lot with heavy rain. New Hampshire does have such narrow valleys too, but it is a lot less important part of the total area, so major flooding is less common.
Latest Answers