Wednesday, March 27, 2013

Silver Creek plan poses big risks


Be very careful what you do to Silver Creek or be prepared to cope with potentially devastating consequences to the creek and surrounding environment. Every stream is a natural equilibrium system that will respond to any change in the channel that affects flow velocity, the channel bed, the channel characteristics (width, depth and channel length) or water discharge (i.e. groundwater). Streams have a mind of their own such that they will respond to artificial (human) changes in unpredictable ways and these responses are not trivial.

Let me give you a real-life example of the response of a stream to a human change to a stream channel. The Blackwater River in Missouri was artificially straightened as a flood control measure. The stream responded by rapidly eroding its channel, as did all the tributary streams. As the channels deepened, they also became wider, and since all the bridges were of fixed length, when the stream channels became wider than the bridges, the bridges collapsed into the channel, so most of the bridges in the county had to be replaced. One bridge that was 50 feet long had to be rebuilt to span 407 feet.

As the channels continued to erode, the water table dropped significantly and many wells went dry. Deep gullies formed in farmers’ fields and could no longer be crossed by farm equipment. Downstream, the channel changes resulted in unprecedented flooding, and two generations of fence posts were buried in floodplain silt.

All this happened immediately because of a human change to the stream channel.

One thing is certain: The proposed changes to the channel of Silver Creek will cause the stream to respond in ways undreamed of by those who are proposing the changes. Beware of disturbing the natural equilibrium of Silver Creek by artificial channel alteration—the possibility of destroying the Silver Creek preserve is very real.

Don Easterbrook

Hailey

 




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