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<br />1942 <br /> <br />:.)K~UMiNARV REPO::S:'-;- <br /> <br />.." ,~ '~""T T"" C:-..' <br />'-.. : - . ::::~, -, . '..:' - <br /> <br />. <br /> <br />Figure 9 near here. <br /> <br />Table 5 near here. <br /> <br />Specific conductance at station 07099400 has changed markedly since the construction of Pueblo Reservoir <br /> <br />(fig. 10). The median specific conductance decreased significantly (p<0.01) from 625 !-,Sfcm in 1966-74 to 496 !-,Sf <br /> <br />cm in 1975-94. The most obvious change in specific conductance was a narrowing of the range in specific conduc- <br /> <br />tance that occurred after 1974 (fig. 10). Since 1974, the annual maximum specific conductance has tended to <br /> <br />decrease and the annual minimum specific conductance has tended to increase. The annual maximum specific con- <br /> <br />ductance decreased from about 800-1.000 ~lS/cm in 1966-74 to about 500-750 !-,Sfcm in 1975-94 (fig. 10). The <br /> <br />annual minimum specific conductance increased slightly from about 200-400 !-,Sfcm in 1966-74 to about 300-400 <br /> <br />. <br /> <br />I-lSlcm in many years during 1975-94 (fig. 10). Specific conductance tended to decrease during the low-flow <br /> <br />months of September-April and increased during the high-flow months of May-August (fig. II). These differences <br /> <br />in specific conductance were statistically significant for the months of January, March, April. May, June, Septem- <br /> <br />ber, October, November, and December (table 6). Historically, before the construction of Pueblo Reservoir, 5pe- <br /> <br />cific conductance was highest during periods of low discharge in the winter months. With the closure of the dam. <br /> <br />the high specific-conductance inflow (October-April) began to mix with and be diluted by lower specific-conduc- <br /> <br />tance water within the reservoir, thus, resulting in decreased specific-conductance water flowing Out of the reser- <br /> <br />voir during the low-flow months. A decrease in the specific conductance of the reservoir inflow, as indicated by <br /> <br />the 19 percent decrease in the median specific conductance at Canon City, also contributed to the decreased specific <br /> <br />conductance at station 07099400. Additionally, before the closure of Pueblo Dam, the annual minimum specific <br /> <br />conductance occurred during the high-flow months of May-August. Following the closure of Pueblo Dam. the spe- <br /> <br />cific conductance at station 07099400 increased in the high-flow months, because of mixing of low specific-con- <br /> <br />. ductance inflow with higher-conductance water within the reservoir (fig. II). <br /> <br />22"'- <br />