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<br />1947 <br /> <br />"~ r" <br />'_..' '0'1.. 11 t ., . . <br />SUBJECT TO REVlSIC <br /> <br />ecific-cOndUCtaIlCe and discharge trends in the St. Charles River, which is tributary to the Arkansas River about 4.5 <br /> <br /> <br />mi upstream from station 07109500. Adequate data did exist for trend analysis a1 the other major tributary in the <br /> <br />reach, FounGlin Creek. The median specific conductance at station 07106500 (Fountain Creek at Pueblo) decreased <br /> <br />from 1,500 jlS/cm in 1969-74 to 1,380 jlS/cm in 1975-94. As previously mentioned, the median annual discharge <br /> <br />at station 07106500 increased from 45,500 acre-ftIyr in 1969-74 to 66,700 acre-ftIyrin 1975-94. The median spe- <br /> <br />cific conduct:lIlce in Fountain Creek was convened to an equivalent dissolved-solids concentration based on rela- <br /> <br />tions described by Cain (1987). The estimated median dissolved-solids concentrations was mulliplied by the median <br /> <br />annual discharge to obtain an estimate of the median annual dissolved-solids load contributed by Fountain Creek to <br /> <br />the Arkansas River in 1969-74 and 1975-94. Based on these estimates, dissolved-solids loading increased about 29 <br /> <br />percent from 65,000 to 84.000 tons per year. This increase in dissolved-solids loading from Fountain Creek is prob- <br /> <br />ably attributable to the increased volume of wastewater efflueru that is disCharged to Fountain Creek in the Colorado <br /> <br />Springs area. <br /> <br />. <br /> <br />Figure 14 near here. <br /> <br />Figure I~ near here. <br /> <br />Table 8 near here. <br /> <br />The duration frequencies of specific conductance at station 07109500 for 1969-74 and 1975-94 were com- <br /> <br />pared to the salinity-hazard classifications for irrigated crops (fig. 16). The salinity hazard is a relationship devel- <br /> <br />oped by the U.S. Salinity Lab (Richards, 1954) that describes the qualitative effect of saline waters on irrigated <br /> <br />crops. It is based on the specific conductance of the water and is divided into four classes of salinity hazard ranging <br /> <br />from low (Class CI) to very high (Class C4). Water at station 07109500 is generally Class C2 or C3. Class C2 water <br /> <br /> <br />-(250.750 j.LSlcm) is defined as having a moderate salinity hazard and can be used on crops having a moderate salt <br /> <br />27<>- <br />