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<br />Final Draft - Preferred Storage Options Plan <br />Southeastern Colorado Water Conservancy District <br />June 8, 2000 <br /> <br />The reservoir is likely to become highly eutrophic during summer months. A <br />larger Williams Creek than currently planned by CSU needs could increase the <br />potential for stratification and eutrophication. Mitigation measures have been <br />proposed by CSU for water quality management in a smaller reservoir; more <br />aggressive measures would be required for an enlarged reservoir. If Williams <br />Creek Reservoir releases are made to Williams Creek rather than to a pipeline, <br />increasing the reservoir size could aggravate downstream erosion problems and <br />increase the need for channel stabilization measures. Also, a larger reservoir <br />volume and associated releases could compromise the effectiveness of channel <br />stabilization efforts. <br /> <br />Stream Water Ouali~ Impacts <br /> <br />. All of the storage alternatives would result in lower flows during winter months <br />and higher flows during spring/summer irrigation periods, compared to historical <br />averages in the Upper Arkansas River. Decreased winter flows could lead to <br />higher constituent concentrations during those months. In addition, higher flows <br />during springs runoff periods could increase erosion and mobilization of <br />pollutants accumulated in channel sediments. Overall, it is not expected that any <br />of these possible ,vater quality changes \vould be significant. <br /> <br />. Each alternative that was modeled indicated higher mean monthly discharges <br />throughout the year on Fountain Creek. This is independent of any new storage <br />project, but is related to increased water demands in the basin. Flow increases <br />would adversely impact sediment erosion conditions along lower Fountain Creek, <br />and increased sediment and associated pollutant loads to the lower Arkans~s <br />River. <br /> <br />Based on the water quality review conducted to date, the six storage options were given scores <br />reflecting their relative performance in terms of water quality issues. The range of scores is I to <br />10, with a score of I indicating an alternative with a potential water quality fatal flaw and a score <br />of 10 indicating an alternative with no identified water quality problems. <br /> <br />Turquoise Reservoir enlargement was given the highest score (9) because it would result in <br />insignificant changes to existing water quality. Moderate scores of 7 to 8 were assigned to <br />Pueblo Reservoir enlargement and gravel lakes storage, indicating the need for possible future <br />mitigation measures, probably through managed operation of the storage facilities. <br /> <br />Low scores were assigned to the Lake Meredith enlargement and a potential enlargement of the <br />proposed Williams Creek Reservoir due to the possibly significant water quality degradation that <br /> <br />~ GEl Consultants, Inc. <br /> <br />4-4 <br /> <br />1\PROJECTS\99Q61\Rcporu\PrefCTTed SOP final_wpd <br />