In the late 1800s Vermont was mostly covered in farms. Even mountainous ares with thin, erodible soils and pitifully short growing seasons were cleared for farms and pastures. The effect was dramatic - severe erosion, loss of soils, loss of arable land... People began realizing around the turn of the century that it was a bad idea to farm in Vermont uplands especially when the Midwest and later California became available for farming. The floods of the 20s hit recovering, but still heavily damaged watersheds. Runoff was more intense from the thin soils and less developed forests. The Winooski river hit ridiculous heights - I think it was near 30 feet at crest from Irene but the 1927 crest was over 50 feet at Winooski (near Burlington). Irene did not get nearly as bad on main stem rivers but in some cases in the upper watershed this flood was worse, just because the rain was so heavy (and the month had already been a wet one).
Vermont does not have the immense system of levees that many other states have. In many cases Irene saw rivers abandoning their normal floodplain and cutting new courses. Buildings that survived the earlier floods (in upper watershed areas) were destroyed. This is not a case of people being unwilling or unable to avoid flooding, for the most part. This was a geologic/climactic event that is either a once in a lifetime thing or a result of climate change. Granted there is work to be done and in mill towns and rural areas we need to think long and hard about where we rebuild. In our community there has been a lot of dialog about what to do and today was an interesting day when I found an excavator in a place I did not want or expect to see one. But for the most part people here (like many places) care very deeply about their waterways and their communities. The key is finding the balance where structures and lives are protected but beyond that rivers are not over-engineered in a harmful way due to knee jerk behavior. Rebuilding will bring some interesting dialog to the table and hopefully among the destruction we DO change how we look at our rivers. Sent from my iPad On Sep 12, 2011, at 4:51 PM, "Wayne Tyson" <[email protected]> wrote: > Charlie and All: > > From Charlie's blog: > > Re: Manage for Healthy Forests > > While dealing with the current flood, there has been reference to older > floods, like theNew England Flood of 1927 . That flood dropped similar > amounts of rain to > > Irene but in many cases had much higher water flow. Why? Part of the reason > may be that in 1927 the forests of Vermont were still recovering from clear > cutting and > > hillside farming in the 1800s, and there was much less mature forest at that > time than the current day. Our forests have recovered since then, which > helped keep > > Irene's floods from being even worse. [end excerpt] > > > Why? I have zero specific knowledge of Vermont, but know a little bit about > the Southern California watersheds and flood of which Hohn speaks. The > principles, however, are the same. > > I used to demonstrate with a bunch of kitchen sponges and a big cookie-sheet. > Watersheds absorb a fraction of the precipitation, and when one takes away > that absorptive capacity, the runoff (Q) increases, creating a "spikey" > hydrograph. > > The first kind of absorption is interception; an enormous amount of water can > be held under tension on the surfaces of terrestrial features, and trees and > other vegetation hold the most. Free water flow rates are reduced by > stemflow, and the infiltration rate of undisturbed soil is much greater than > disturbed soil; in disturbed soil, smaller particles clog soil pores much as > "Stop Leak" used to stop radiators from leaking (percolating). That fraction > runs off, causing erosion (more disturbance and creation of silt loads, which > compromise stream/drainage capacity. Logging reduces the amount of water that > can be held under tension and the metering effects of stemflow. Clearcutting > compounds this phenomenon, both by removing the surface area for a fraction > of the precipitation that can be held under tension, and by reducing the > infiltration and percolation capacity through equipment disturbance. (This is > not an argument for or against logging; it is only a statement of facts that > interpreted as such by special interests who fear the facts will gore their > particular ox.) > > Urbanization tends to seal the watershed even more, including highways, > roofs, irrigated agriculture and gardens, etc. > > I'll stop here and possibly comment further on Charlie's blog. > > WT > > PS: I do not blame Vermonters for their suffering; most no doubt were > completely unaware of the hazard potential. If any flood was "unexpected" > with justification, this one, unlike the Mississippi and other well-known > flood plains and riverbottoms. > > ----- Original Message ----- > From: "Charlie Hohn" <[email protected]> > To: <[email protected]> > Sent: Monday, September 12, 2011 8:20 AM > Subject: Re: [ECOLOG-L] Flooding and stream geomorphology question from > Vermont (response from Vermont resident) > > > Hi, > > > > I study (among other things) watersheds and rivers and flood policy, and I > > live in Vermont (and in > > fact was an evacuee) so perhaps I can offer some other thoughts on this. > > > > I fully agree with the points people are making that people should not have > > built in the way they > > did in floodplains, that people should not try to control nature, and also > > feel that most floods are > > as much anthropomorphic (due to watershed degradation, etc) as natural > > disasters. > > > > That being said, the Vermont flood situation is VERY different. Our state > > is one of the most (re)- > > forested in the nation, and while we have our share of ecological problems > > like anyone else, our > > watersheds are in really good shape. In particular, most Irene flooding > > came from the Green > > Mountains, where orographic factors caused the rain to be the heaviest, and > > the Greens are almost > > entirely forest (preserved areas and timberland that is for the most part > > well managed.) > > Impervious substrates, type conversion, and so many of the other problems > > facing the United > > States are not major problems in most of these watersheds that had > > flooding. With the possible > > exception of climate change (though we can't say for sure with one specific > > storm), this is not a > > human-caused flood. > > > > I come from southern California, where the river systems are very flashy: > > most are dry for the > > entire summer, except for a few spring-fed creeks... but in winter, massive > > wet storms can dump > > 20+ inches of rain in the mountains, causing immense floods. (California > > is also dealing with lots > > of watershed degradation as mentioned above). When I moved to Vermont I > > was amazed at the old infrastructure - mill buildings, homes, etc, that > > were literally hanging into rivers. These aren't new > > buildings that keep getting rebuilt - these are buildings over 100 years > > old that did not wash away > > (except, in some cases, last month). Why? Vermont's winters have a > > well-deserved reputation for > > being cold, snowy, and harsh, but the summers are very gentle here. The > > 11+ inches of rain we > > had in Irene was a state record and a freak event... whereas in southern > > California our family cabin > > in the San Bernardino mountains got over 20 inches of rain in 24 hours, and > > the damage during > > that event was much less than the damage caused by Irene. > > > > We certainly need to change our relationship with rivers. If Irene is a > > climate change related even > > and we are going to get more storms like this, we absolutely need to > > rebuild wisely, and far from > > the rivers. But it's important to see this for what it is - a freak event > > (or sign of change) that had > > very little precedent - the massive Vermont floods of the 1920s and 1930s > > were as much a > > response to deforestation as to rainfall. Someone mentioned that 'all of > > Vermont is in a flood > > plain' but that is not actually true. Very little of Vermont is in a flood > > plain, but almost all of > > Vermont is prone to flash floods. The only places safe from flash floods > > are the immense old > > glacial lakebeds (and in part flood plains) of the Champlain and > > Connecticut valleys. Surprisingly, > > the swamps, lowlands, and flood plains that fill up with water every spring > > did not have record > > floods during Irene, and the water in some of the mainstem rivers wasn't > > much higher than during > > the spring snowmelt. This was an upper watershed event, and as such, a lot > > more complicated > > than people building in a flood plain. > > > > That being said, we absolutely need to take this crisis as also a teaching > > point, and make changes. > > I wrote a bit about that in my blog and will provide a link rather than > > posting it here since it is a bit > > long, but check it out if you're interested: > > > > http://slowwatermovement.blogspot.com/2011/08/preparing-for-or-preventing-next.html > > > > Thanks! > > > > -Charlie Hohn > > Slowwatermovement.blogspot.com > > > > > > ----- > > No virus found in this message. > > Checked by AVG - www.avg.com > > Version: 10.0.1392 / Virus Database: 1520/3892 - Release Date: 09/12/11 > >
