Agenda Item 26: Arkansas River ISF Appropriation

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Tnstream Flow Survey Data The DOW, in September of 2005 and March of 2006, collected stream cross section information, natural environment data, and other data needed to evaluate the 100 cfs instream flow recommendation proposed and supported by CWCB staff, the City of Pueblo and other local water users. The stream cross section data was analyzed using the R2CROSS program. The R2CROSS output was evaluated using the methods described in Nehring (1979) and Espegren (1996). DOW collected physical data at four different cross - section locations at three different discharges (see attached map). The observed flows ranged from a high of 260 cfs to a low of 58 cfs. The width of the Arkansas River at the four study sites ranged from 160 feet to 132 feet. Cross - Section Locations Data relating to the individual cross - sections are discussed below: • Site #1 is located approximately 1 /4 mile downstream of Pueblo Reservoir. The bank full width of this cross- section was 151 ft and had a hydraulic slope of less than 1%. Data collection flows at this site included flows of 58, 89, 155 and 260 cfs. • Site #2 is located near the eastern end of Pueblo Reservoir. The bank full width of this cross - section was 132 ft and had a hydraulic slope of less than 1 %. Data collection flows at this site included flows of 92, 155, 178 and 264 cfs. • Site #3 is located approximately 100 yards down -stream of the railroad bridge crossing the Arkansas River near Reservoir Road. The bank full width of this cross- section was 160 ft and had a hydraulic slope of less than 1 %. Data collection flows at this site included flows of 85, 155, 174 and 252 cfs. • Site #4 is located approximately %z mile upstream of the confluence with Fountain Creek. The bank full width of this cross - section was 141 ft and had a hydraulic slope of less than 1 %. Data collection flows at this site included flows of 82, 136 and 223 cfs. Table 1: Stream Flow Hydraulics and Channel Characteristics at 100 cfs Cross - section % Wetted Average Depth Average Velocity Perimeter #1 — Below Reservoir 69.8% 0.89 feet 1.06 ft/s #2 — Lower State Park 72.0% 0.76 feet 1.33 ft/s #3 — Below RR -Xing 75.9% 0.53 feet 1.54 ft/s #4 — Above Fountain Ck 61.3% 0.53 feet 2.19 ft/s A 100 cfs instream flow would provide: • Enough water to wet approximately 70% of the stream channel at 3 of the four x- section locations and 61% of the stream channel at cross - section #4; • An average depth of close to 0.5 feet at all four cross - sections and nearly 0.9 feet at cross - section #1; and • An average velocity of over 1.0 feet per second at all cross - sections. 8