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' 5. Is driven by available records. <br />6. Reports monthly discharges in acre -feet for the Yampa River above the Maybell <br />Canal diversion and at the Maybell gage <br />CRDSS Input - Monthly Average Instream Flow Tarizets <br />' <br />If daily flows were normally distributed, they would exceed the average monthly flow as often as <br />they fall below it. Recognizing that day -to -day flow variations have occurred historically (both <br />' <br />pre- and post -human influence), we modified the flow target in the CRDSS to account for the <br />normal distribution of daily data below the mean. The CRDSS model applied these modified <br />flow targets as "demands" for fish and assigned them a priority junior to all currently existing <br />water rights. These monthly mean values were based on the 93 cfs flow target plus 1 /2 standard <br />deviation of the daily variability of the lower 20' percentile months (by volume) during the <br />entire period of record at the Maybell gage for each of the low -flow months as follows: <br />' <br />August 93+ (66) =126 cfs <br />September 93 +'/2 (44) = 115 cfs <br />October 93+ (44) =115 cfs <br />We set fish demand at zero cfs during the remainder of the year (November- July). <br />' <br />Because the CRDSS output is a monthly discharge and because daily data in the lower 20th <br />percentile months may not be normally distributed, we only used these modified flow <br />targets as screening criteria to identify those months whose minimum daily flows were likely to <br />violate the daily average flow target (93 cfs) at some time under either historic or future demand <br />conditions. Months whose average flows fell below these criteria, as well as adjacent months <br />both within and outside August- October, were examined in detail for daily transgressions of the <br />93 cfs flow target. In all cases, months failing to meet their specific screening criterion exhibited <br />one or more daily transgressions of 93 cfs. A preliminary analysis revealed that in one CRDSS <br />year (1977), daily average flows during the month of July frequently fell below the 93 cfs flow <br />target. Therefore, we expanded the low -flow period under evaluation to include July 1977. <br />CRDSS Output and Data Analysis Methodology <br />' <br />To provide continuity during the July- October low -flow period under evaluation, we reformatted <br />the CRDSS water -year output to a calendar year basis, excluding October - December 1974. Data <br />for calendar years 1975 -1990 and January- September 1991 are reported below. We distributed <br />the CRDSS monthly discharge on a daily basis in the same pattern as the gaged or synthesized' <br />historic daily flows, converted daily AF discharges to average daily flows in cfs, and compared <br />these data for July- October of each year with the flow recommendations of Modde et al. <br />e Daily flows above the Maybell Canal diversion were distributed based on the Maybell gage discharge plus <br />t concurrent <br />Maybell Canal diversions during the CRDSS period of record. <br />Appendix B <br />