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<br />Draft Final Completion Report to UDWR for Contract #93-1070, Amendment 3 <br /> <br />Vi <br /> <br />create nursery habitat. The typical shape of HAC' s is multi-modal for specific sites which may explain why Pucherelli <br /> <br />and others (1990) found a poor relation between discharge and available habitat in this reach. Further research is <br /> <br />necessary in order to evaluate the degree to which site-specific discharge-dependent HAC's can be extrapolated to <br /> <br />longer reaches. <br /> <br />At the detailed study site. the discharge that maximized nursery habitat in 1992 was lower than the mandated <br /> <br />base flows and was higher than the mandated base flows in 1993 and 1994. These data are only for the detailed study <br /> <br />site and cannot be extrapolated throughout the 10-Ian study reach. However. they demonstrate that the use of the same <br /> <br />value for mandated base flows in years of high and low annual floods probably does not actually achieve its intended <br /> <br />goal. <br /> <br />A conceptual model was developed illustrating the response of secondary-channel nursery-habitat availability <br /> <br />over a three-year period during which one large flood occurs (Fig. ES2). This model is based on the field and numerical <br /> <br />modeling results of this study. Lvge floods increase the topographic relief of secondary channels and increase the range <br /> <br />of discharges at which nursery habitat is available. The discharge at which secondary channel habitat availability is <br /> <br />maximized also increases in years of high flood peaks. Subsequent lower floods reduce the secondary channel <br /> <br />topographic relief and therefore decrease the range of discharges over which this habitat is available. The discharge at <br /> <br />~ ~ W 100 IW I~ <br />DISCHARGE. IN CUBIC METERS PER SECOND <br /> <br />FIGURE ES2. Conceptual model of secondary channel habitat cwve. The shape of the cwve and the discharge <br />associated with the maximum area of available habitat changes in response to flood passage. Lvge floods rebuild <br />topography, shifting the peak for available habitat to the right as the overall elevations of the secondary channel is <br />increased. The peask shifts to the left in subsequent low peakyears as the upper end of the secondary channel erodes. <br />The width narrows as the total relief within the secondary channel is reduced. <br /> <br />~ <br />t:: 0.9 <br />~ 0.8 <br />>- <br />~ 0.7 <br />~ <br />en <br />~ 0.6 <br />t.t. 0.5 <br />o <br />< 0.4 <br />~ 0.3 <br /> <br />~0.2 <br />< <br />~O.I <br />o <br />o <br /> <br /> <br />LARGE FLOOD <br /> <br />YEAR I <br /> <br />PEAK <br />SHIFTED <br /> <br />YEAR 2 <br /> <br />20 <br /> <br />I~ <br /> <br />180 <br />