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Becoming a good upstream neighbor
By Randy Graves
The recent flooding and associated widespread property damage caused by Hurricane Irene are perhaps unprecedented since the Mad River Valley was originally settled in the mid 18th century. But the geologic history of both the rivers and streams of our area tells a story of continuous and frequent fluctuation in the location of the stream channel as it literally meanders within the valley floor. Warmer rainwaters and colder snowmelts give the river channel volumes of water and, succumbing to the demands of gravity, it all immediately begins to flow down valley.
Rivers and streams are dynamic bodies of water and sometimes, as we enjoy the rivers and streams for our pleasure, we forget that they can, at times of flood stage, be quickly and surprisingly destructive. These active bodies of water seem to have a mind of their own at times and this notion is actually truer than you might expect or imagine.
Simply because water flows downhill, all the while seeking a path of least resistance, a river’s course and purpose is dynamic; it is constantly undergoing change. Regardless of what attempts man can make to confine a river’s course or to modify its behavior, the energy derived from its flow downstream cannot be abated. At best, it can only be redirected. In fact, often is the case whereby when trying to contain a river’s channel, we mistakenly create situations where the contained waters actually gain more energy and, as a consequence, gain more destructive capacity.
There is a simple balance that stream and river scientists study that evaluates a river’s volume of water, its speed and the amount of debris or sediment that the same water can contain. Rivers with more volume and greater speed can, of course, move greater and heavier objects. When the river channel is more confined (narrow) the water must flow even faster, making the ability to carry and move heavier objects even greater. If you think of this in another way, though, if you allow the river to widen, then the volume and energy of that same river is then more spread out. Even though immediate flooding may occur, the potential for more large-scale damage is reduced greatly at early flood stages.
Part of the job of a river is to move sediments: rocks, gravel, sand and silt. The instant that the river’s flow (speed) lessens these sediments are then “dropped” by the river. A river certainly does not discriminate between a large rock or a gas tank, a tree trunk or a section of retaining wall. It all goes downstream carried by the momentum of the water and directed by the channel’s course. How often do we all catch ourselves gazing at the calmness of a river or stream and when in flood stage, we then marvel at the destructive power of that very same channel. The same river but with very different personalities.
The state of Vermont, supported by riverside communities, has begun an evaluative and educational program targeting the FEH or Fluvial Erosion Hazard. This is a state-funded initiative to, in very practical terms, help all Valley (floodplain and fluvial area) landowners become better examples of “good upstream neighbors” through a better and more fundamental understanding of stream dynamics. There simply could not be a better time to have this discussion than during the aftermath of Irene. Through talking with our neighbors and sharing stories, opinions, information and concerns, we can, as a community, minimize the overall impact of the next flood. For surely, the next Irene is not a matter of “if” but a matter of “when.”
Graves is a member of the Warren Planning Commission.