Wednesday, July 20, 2011

Vermont Summer Storms and Fickle Mountain Streams

The mountain streams and small rivers of Vermont are one of the state's treasures.  These streams, which hold copious water all year, are a huge draw to people looking to fish, swim, wade, dive, and explore.  These activities are an important part of the summer in Vermont and other areas with mountain streams, and by all means people should be enjoying these places.  However, they need to do so with respect for the fact that these waterways change fast, and can be quite dangerous at times.

This month a tragedy struck at the Bolton Potholes when a 12 year old boy drowned.  Another tragedy was narrowly averted when two people were rescued from Huntington Gorge.  There are many factors that can lead to danger, including dangerous cliff diving, drunken exploits into dangerous waters, or just bad luck.  One of the strongest factors, it seems, and one that is also often not well understood, is just how quickly these rivers and streams change during and after summer storms.


I live by the Middlebury River, a small river that originates in the Green Mountains.  Because the watershed is steep and prone to heavy rains, the water levels can change fast.  The floods on the river are beautiful and impressive, but also dangerous.  The part of the river I live near is full of rocks and cobbles that move and shift with every flood.  This means that the river is constantly changing, and is an adventure to explore after each time the water level rises.  It also means that one can not make assumptions about a swimming hole.  A pool that was 12 feet deep and was safe to dive into from nearby rocks can end up with a few boulders rolling into it during a summer downpour and become deadly.  Furthermore, while flash floods in Vermont are not as dramatic as those in the desert Southwest, the water level can rise surprisingly fast during and after rainstorms.

My favorite swimming hole is a small one, but one that is difficult to get to.


Friends who have lived in the area a while tell us that every year the swimming holes are different.  I have no idea if this swimming hole was even here last summer.  In fact, I don't even know if it is still here as I type this blog.

Two days ago we had heavy rains.  We had a series of thunderstorms that dropped an inch of rain, followed by more storms that dropped .3 inches more.  The mountains undoubtedly received more rain, because they do in just about every storm.


The next morning, the water had risen by at least 6 inches.  This rock, pictured below, was a dry stepping stone several inches above the water three days ago.  Two days ago, it was under 4 inches of fast moving water.  I just checked today and it is again emerging from the water.


The relaxed, slow river had swollen to fill its little channel, though it was not spilling onto the gravel bars.  It was not safe to go visit the swimming hole, because doing so involves wading downstream, and it just isn't safe to do so during high water.  Also, I didn't know if the river was still rising.  It was a warm, humid morning, and the cold water was steaming with mist.


While I wouldn't call this event a flood, the water definitely rose enough to move cobbles around.  It will be interesting to see how my swimming hole has changed.  The Middlebury River meanders through sediments deposited by the last ice age after it leaves the mountains.  While the gorge and mountain river channel is incredibly ancient, the immediate path of the river as it enters the Champlain Valley is constantly changing.

The take home message?  Vermont's rivers are beautiful, fascinating, and a great way to cool off during hot days like these hottest midsummer days.  But, they change fast, and can be quite dangerous if not respected.  Please don't go swimming during or after thunderstorms, and when you visit your favorite swimming holes after the inevitable passage of summer downpours, be aware that rocks, currents, logs, and other elements of the river may be completely different than when you last were there.  And... don't go jumping into pools when you don't know exactly how deep they are!  (I can't recommend cliff jumping at all, but if you are going to do so, be safe!)

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