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<br />I <br />.. <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />. <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />(' <br />I <br /> <br />I - 17 <br /> <br />entirely new channel. With the abandonment of the existing channel there would be <br />a variety of bridges and hydraulic structures that would also be abandoned at great <br />expense to the public. <br />The clear-water diversion into South Boulder Creek in Colorado is another <br />example of river development that affects bridge crossings and encroachments as <br />well as the environment in general. Originally the North Fork of South Boulder <br />Creek was a small but beautiful scenic mountain stream. The banks were nicely <br />vegetatedj there was a beautiful sequence of riffles and pools which had all the <br />attributes of a good fishing habitat. Years ago, water was diverted from the <br />Western Slope of the Rockies through a tunnel to the North Fork of South Boulder <br />Creek. The normal stage in that channel was increased by a factor of 4 to 5. The <br />extra water caused significant bank erosion and channel degradation. In fact, the <br />additional flow gutted the river valley, changing the channel to a straight raging <br />torrent capable of carrying large quantities of sediment. Degradation in the system <br />had reached as much as 15 to 20 feet before measures were taken to stabilize the <br />creek. <br />Stabilization was achieved by flattening the gradient by constructing numerous <br />drop structures and by reforming the banks with riprap. 1 he system has stabilized <br />buL it hi a different system. 1 he channel is straight, much of the vegetation has <br />been washed away, and the natural sequence of riffles and pools has been destroyed. <br />1 he valley may never again have the natural form and beauty it once possessed. It <br />is necessary for us to bear in mind that diversions to or from the natural river <br />system can greatly alter ilts geometry, beauty and utility. The river may undergo a <br />complete change, giving rise to a Inultitude of problems in connection with the <br />design and maintenance of hydraulic structures, encroachments and bridge crossings <br />along the affected reach. <br />In the preceding paragraphs possible immediate and long -term responses of <br />river systems to various types of river development have been described. Nothing <br />has been indicated about how to determine the magnitude of these changes. This <br />important aspect of response of rivers to development will be treated more <br />objectively in later chapters. <br />