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<br />Hydrologic Data <br /> <br />In order to review the effects of the various alternative strategies, <br />each strategy was tested by all levels and patterns of runoff that <br />could be reasonably expected during the study period. It was, there- <br />fore, necessary to use several sets of hydrologic inputs or traces. <br /> <br />Each hydrologic data trace was characterized in two ways. First and <br />most important was the average runoff projected over the IS-year study <br />period. Traces were based on means approximating the 90, 7S, SO, 2S, <br />and 10 percentile levels of all observed IS-year means in the 78-year <br />historic record set. <br /> <br />The second characteristic used was the time distribution of runoff <br />within the projected IS-year period. The results differed signifi- <br />cantly for several runoff series which have the same mean, depending <br />on whether the individual series was wetter at the start of the <br />lS-year periOd than at the end or vice versa. <br /> <br />Three traces were chosen or developed for each of the five percentile <br />levels. Two of these traces were synthetically generated using <br />stochastic procedures for each of the five percentile levels; one <br />trace with wetter years early in the IS-year periOd and drier years <br />later and one trace with drier years early and wetter years later. <br />The third trace at each percentile was a historic based trace from the <br />78-year record set. This trace could have any time distribution. In <br />addition to the fifteen traces described above, the historic-based <br />wettest and driest traces were included. All traces reflect "natural" <br />flow conditions. These seventeen traces are believed to bracket the <br />range of what might be expected in terms of magnitudes and patterns. <br />A detailed description of these traces and their derivation can be <br />found in the main report. For purposes of summarizing the study <br />results, the median, wettest, and driest historic traces were selected <br />for viewing system impacts. <br /> <br />Depletion Data <br /> <br />Two depletion schedules are used in the study. The first schedule, <br />known as the USBR schedule, represents Reclamation's estimate of pro- <br />ject development. The second schedule, known as the "Low" or <br />"Forum" schedule, was the slowest schedule of project development of <br />three schedules developed by the Colorado River Basin Salinity Control <br />Forum in December 1983. The use of these two schedules essentially <br />provides an upper and lower bound on the expected development during <br />the next 25 years and provides an indication of the senSitivity of <br />study results to future depletion scenarios. Only the USBR depletion <br />schedule assumption is presented in the Executive Summary, <br /> <br />5 <br />