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<br />i)-'~9~ <br />~i0~~ <br /> <br />Run No. 30 - Both the ungaged tributary inputs and downstream <br />target flows were based on month-by-month figures. Target flows <br />correspond to present modified flows at Imperial Dam. <br /> <br />Run No. 31 - This run is identical to Run No. 30, except the <br />mean monthly values were used for each month of the year for <br />the ungaged tributary inputs for the Parker-Imperial reach. Thus, <br />a single annual cycle of monthly values was repeated for each <br />year of the study. <br /> <br />Run No. 32 - This run is identical to Run No. 31, except mean <br />monthly values were also used for downstream target values. <br /> <br />Salinity results at selected stations for these runs are compared <br />to the Biennial Report values,[l, Table 18, p 149] and to the present <br />modified data of Appendix A in Table VI. As previously noted, 'values <br />in the Biennial Report are based on a mix of time- and flow-weighted <br />techniques. Only the mean concentrations are shown for these data. <br />Values for the other data include time-weighted mean concentrations <br />and standard deviations and flow-weighted mean concentrations. <br /> <br />Target flows for Runs No. 30 and 31 are identical to the present <br />modified flow at Imperial Dam in Appendix A. Salinity at Imperial <br />Dam is shown in Figures 5 and 6 for these runs. Target flows and <br />computed salinities for Run No. 32 are given in Figures 7 and 8. <br /> <br />The following observations are based on an inspection of Table VI: <br /> <br />Flow-weighted concentrations for the three runs, present modified <br />data, and Biennial Report values are not substantially different. <br /> <br />The hybrid method of the Biennial Report results in a concentration <br />intermediate to flow- and time-weighted values, but will generally <br />be closer to the flow-weighted results. <br /> <br />Variance, reflected by standard deviations, at Lees Ferry and Grand <br />Canyon are greater for present modified conditions because they are <br />based on unregulated conditions while model results are based on <br />system operations. <br /> <br />Variances below Hoover and Parker Dams and at Imperial Dam reflect <br />historic operating patterns. The addition of upstream reservoirs <br />such as Lake Powell in 1963 and other recently completed ones such <br />as Blue Mesa and Morrow Point will tend to reduce these through <br />regulation and storage. <br /> <br />Difficulties in computing ungaged tributary inputs in the Parker- <br />Imperial reach are reflected directly by the variance in results <br /> <br />23 <br />