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Table 2-4. Alamosa River Channel Geometry Data <br /> Width Depth Slope <br />Location Location Description Reach Ift) (ft) Ratio (ftlft) <br />1 Upstream of County Road 15 1 40 3.5 11.4 0.0064 <br />2 Below Ortiz Ditch 2 85 4.0 21.3 0.0033 <br />3 Downstream of San Jose Ditches 2 65 4.0 16.3 0.0108 <br />4 Upstream of Rodriquez Bridge 3 58 4.0 14.5 0.0599 <br />5 Downstream of Terrace Main Canal 3 98 3.5 28.0 0.0082 <br />6 Downstream of Gomez Bridge 4 58 5.5 10.5 0.0045 <br />7 Upstream of campground 6 72 4.0 18.0 0.0108 ' <br />8 Near Lieutenant Creek 7 57 4.0 14.3 0.0199 <br />9 Upstream of steep reach 8 78 7.0 11.1 0.0037 <br />10 Downstream of Wightman Fork 10 40 2.3 17.4 0.0080 <br />11 Upstream of Alum Creek 11 45 4.0 11.3 0.0105 ~ <br />Source: July 2004 Field Measurements <br />Stream classifications for the river upstream of Terrace Reservoir were performed using the principles <br />described in David Rosgen's report "Applied River Morphology." Rosgen described the river between <br />Terrace Reservoir and Highway 285 according to his classification scheme in 1999 based on field <br />observations. Field checks were conducted during the July 2004 site visit to evaluate the Rosgen stream <br />classifications. No changes were made to Mr. Rosgen's 1999 classifications based on the data collected <br />during the site visit. The Alamosa River stream classifications are shown in Figure 2-6. Figure 2-7 <br />depicts the Rosgen stream classification methodology. <br />The following sections describe channel characteristics on a reach by reach basis. The 2-year flowrate is <br />discussed in each reach compared to the appropriated irrigation diversions in that reach. The 2-year <br />flowrate is considered the channel forming flow and is important when analyzing channel stability and <br />future changes. The 2-year flowrate is a peak flow with a 5o percent probability of occurring in any <br />given year. This comparison is meant to show the potential that diverted flow can have on channel <br />forming characteristics. <br />2.2.1 Upper Watershed (Reaches T1, 12, and 11) <br />The upper Alamosa River originates at the continental divide. Treasure Creek's headwaters are at <br />elevation 13,300 feet with a slope of 9.5% and sinuosity of approximately 1.1. Many of the channels in <br />the upper watershed are characterized by steep narrow valleys consisting of highly weathered and <br />erodible material. Natural processes including landslides and debris flows occur in these upper <br />tributaries (the high sediment loading from the upper watershed tributaries will be described in more <br />detail in Section 2.7). <br />Alamosa River Watershed Restoration Master Plan and Environmental Assessment Page 2-10 <br />