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DRAFT DRAFT DRAFT <br />B. Current Management Hydrographs <br />This section presents a composite hydrograph for four McPhee release <br />scenarios: baseflow releases only, and small, average, and large spills. <br />Baseflow only conditions (30,000 AF) are defined as those years in which there <br />is no excess supply available for downstream releases. Based on the modeled <br />hydrology, an average spill is approximately 187,000 AF. The standard deviation <br />from the average spill was used to define a specific release for the small and <br />large spills. One standard deviation was approximately 123,000 AF, so a small <br />spill was defined as the average minus one standard deviation (187,000 AF - <br />123,000 AF = 64,000 AF). A large spill was approximately 310,000 AF (187,000 <br />AF + 123,000 AF). <br />Figure 2 presents a composite plot of these four hypothetical hydrologic <br />scenarios. Notable features that have bearing on the expected ecological <br />outcomes are the relative magnitudes of peak flows, duration of a flow that <br />performs work on the channel (raftable flows > 800 cfs generally provide this <br />amount of stream power), and the rate at which peak flows taper to the <br />baseflows (the `recession limb' of the hydrograph). These are not actual <br />operations hydrographs, but represent a coarse integration of management <br />objectives and water availability given the range of scenarios described above. <br />Composite Hydrographs of Current Management Scenarios <br />4500 <br />4000 <br />3500 <br />3000 <br />N <br />w <br />V <br />~ 2500 <br />a~ <br />L <br />~ 2000 <br />N_ <br />1500 <br />1000 - <br />500 <br />0 <br />N D J F M A M J J A S O <br />Baseflow Only 64,000 AF -Small Spill 187,000 AF -Ave Spill 310,000 AF -Large Spill <br />Figure 2. Composite Hydrographs for the four current management scenarios <br />being discussed in this section. The small spike October 1 is the 12-hour, 400 <br />cfs release for fish stocking between McPhee Dam and Bradfield Bridge. <br />9/5/06 7 <br />