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erosion, improve channel conveyance, and decrease the downstream sediment loading. Seven <br />monitoring cross sections were surveyed in a 2,000-foot river reach immediately upstream of the El <br />Viejo Diversion in May, 2000. These cross sections had an average top width of 74 feet, average depth <br />of 1.8 feet, and average width/depth ratio of 41 (Black Creek Hydrology, 2003). These dimensions are <br />used for stream classification, such as the Rosgen classification shown in Figure 2-7. There is not <br />enough information available yet to determine the effectiveness of the stabilization measures. <br />2.2.8 Gunbarrel to County Road 10 (Reach 2) <br />Between Gunbarrel and County Road 10 there are 18 ditches which have an appropriation to divert <br />456.12 cfs, which is 60 percent of the two-year event. This reach is characterized by channel <br />straightening activities, which took place in the early 1970's (C~XICB, 2000) to provide flood relief from <br />Gunbarrel Road to Highway 285. Straightening of the channel increased the bed slope, which increased <br />velocities. Increasing velocities had the desired affect of conveying more water through the reach at a <br />shallower depth. However, the higher velocities and corresponding increased stream power resulted in <br />increased bed and bank erosion. The channel straightening allowed the river to flush sediment through <br />the straightened reach. Downstream of the straightening, as meandering resumes, sediment deposition <br />occurs due to the flatter channel slope. ~Ihile flooding was all but eliminated this reach now has erosion <br />and channel instability problems. <br />The channel sinuosity of this reach is straighter than the previous two reaches at 1.2, but the average <br />channel slope is the same at 0.8%. The extensive irrigation diversions and removal of channel flushing <br />flows results in significant channel aggradation in the area. However, this has been counteracted by the <br />channel straightening. The slope appears to have adjusted to match the upstream undisturbed slope, <br />suggesting the channel is in the stage of channel evolution where channel aggradation typically occurs. <br />The photo log and description of the area show aggradation through much of this reach. Figure 2-15 <br />shows significant aggradation. As the channel adjusts, the channel bed will continue to aggrade, the <br />banks will erode, and eventually a meandering channel will form. <br />Figure 2-15. Photo Near Capulin at Straightened Channel Section (photo by Alan Millen <br />~.~ <br />~~ <br />:. <br />.'" <br />-.~ <br />° ~ N <br />r ~ ~ ~I <br />9 r _ <br />~ r-' o: <br />a <br />~ ° ~` ~ i ~~ <br />. ~ ~ <br />1R ~ '~6 <br />- ~ v._ _. - .''.. ~u <br />~r.u~ F ~ ~ ~ . ~ III S` ~E- <br />n ~ ~ ~' ~ <br />~~ a~'. ~ ~ ~ c_ ~„ 11,,,, ~' ~ iq,~. ~ _ ~~ ~ ~ ~~~. ~'d may", <br />_ ~ ~ <br />~ I ~u ~1 '!^ ~l ~" ,~ 9o- <br />r ~ _ ~ ;t~ •~ ; r <br />,~ <br />,~ .. o r <br />~ ~ ~ - ~ - ~ ~ <br />,., '~ <br />. ~ <br />~ ~~ ~ a® ~ ~~ ~. <br />Alamosa River Watershed Restoration Master Plan and Environmental Assessment Page 2-18 <br />