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<br />flows in that version were essentially identical to those presented in the January 2000 draft. We <br />are gratified that the authors qualitatively agree with our base-flow recommendations and concur <br />on the importance of base flows to the endangered fishes of the system. <br /> <br />Comment: <br />We are unable to approve the Flow Report because the numeric range of900 to 3,000 cft (26- <br />85 cms) recommended for the mean base flow magnitudes in Reach 2 and the apportionment of <br />this range to each hydrologic category do not appear to be supported by adequate data and are <br />apparently arbitrary. We could not find supporting evidence for this specific range of base flow <br />magnitudes in the synthesis chapter of the Flow Report. We do concur that base flow <br />magnitudes should be scaled to the hydrologic conditions and the preceding peak flows (higher <br />base flows associated with higher peak flows), but there is nothing in the Flow Report that <br />substantiates the particular bounding of this scaling by the apportionment of the 900 to 3,000 cft <br />range over the hydrologic categories as presented in Table 5.5. <br /> <br />Response: The data that have been collected to date on base flows paint a very complicated <br />picture and sometimes give the appearance of conflicting results. These data indicate that it is <br />not appropriate to apply a relationship determined in a smaller subset of years to the entire range <br />of hydrologic conditions. Antecedent conditions are extremely important. We developed our <br />recommendations on the hydrologic and ecological data available for the system. Two important <br />considerations were made -- base flows should be scaled to peak flows and the range of base <br />flows should not be outside ofthe range of base flows that have been demonstrated to provide <br />suitable conditions for the endangered fish. Our recommendations are not arbitrary. <br /> <br />Comment: <br />Three background studies were offered in the Flow Report as the principal support for this range <br />and its scalingfor Reach 2: Pucherelli et al. (1990), Rakowski and Schmidt (1999) and Tyus and <br />Haines (1991). <br /> <br />Response: Another important reference used in making base flow recommendations was <br />Bell et al. (1998). This report was critical in establishing the understanding that flows that <br />optimize backwater habitat availability vary from year to year and that establishing a single <br />target base flowthat applied across a range of hydrologic conditions was inappropriate. <br /> <br />Comment: <br />Pucherelli et al. (1990) used aerial photography and GIS to examine trends in backwater size, <br />number and area over a range of base flows (5000 -1300 cft; 142-37 cms) during 1987. The <br />Flow Report (Page 3-48) summarized Pucherelli's result that "total area of backwater habitat <br />was maximized at flows between 1300 and 1940 cft (37 and 55 cms)" and that the flow level <br />thought to optimize backwater habitat in 1987 was 1800 cft (51 cms; Flow Report Page 4-32). <br /> <br />2 <br />