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<br />002504 <br /> <br />Withholding seeding operations early in the season results in the <br />risk of missing early opportunities with the possiblity of inadequate <br />opportunities being available later in the season. However, this risk <br />is relatively small. Model results and data analyses indicate that <br />the middle part of the winter (January and February) are the months <br />of highest potential in most years because of the frequency of storms <br />and the fact that midwinter storms are more likely to be snowstorms <br />instead of rainstorms. <br /> <br />The design study summarizes comprehensive hydrologic modeling by the <br />Sacramento River Forecast Center of the streamflow accompanying <br />projected snowpack augmentation in the Sierra Nevada. The model <br />studies considered detailed streamflow within two drainages each of <br />the Feather and Yuba Rivers; and four drainage points in the American <br />River Basin, including effects on feeder streamflow and other surface <br />and subsurface runoff. Results of modeling by the National Weather <br />Service indicate that a substantial portion of the runoff is due to <br />rain or snow that melts within a short time after falling. The snow- <br />pack contributes 20 to 30 percent of the total. Thus, water resource <br />management through use of the reservoir system is substantially <br />enhanced by an increase in the percentage of the runoff retained in <br />the snowpack. Hydrologic effects of weather modification upon the <br />snowpack are being studied by the Forest Service at the Central Sierra <br />Snow Laboratory. <br /> <br />Any multiyear hydrologic effects of seeding will have to accrue <br />primarily though the use of the reservoir system. Since most <br />immediate runoff from rainfall is not now retained at the reservoir, <br />one of the main impacts of a dry season would be to diminish the <br />effects of normal reservoir spillage. One of the objectives of <br />the SCPP is to test the feasibility of redistribution of the precipi- <br />tation to the high snowpack to increase spring snowmelt and runoff. <br />Additional studies will be made to include the control of runoff <br />with the increased storage capacity provided behind Auburn Dam. <br /> <br />29 <br /> <br />