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<br />The present report summarizes extensive hydrologic <br />modeling of the streamflow accompanying projected snowpack augmen- <br />tation in the Sierra Nevada. These studies have considered detailed <br />streamflow within two drainages of the Feather, Yuba, and four drainage <br />points in the American River, including effects on feeder streamflow and <br />other surface and subsurface run-off. The results of the modeling <br />indicate that most of the run-off is due to rain or snow that melts within <br />a short time after falling. Thus, the total seasonal run-off is only <br />increased approximately one-tenth as much as the increase in the <br />snowpack. Dr. James Smith of the U. S. Forest Service, Pacific <br />Southwest Forest and Range Expe riment. is conducting a detailed inves- <br />tigation of the impact of augmentation on snowpack structure. <br /> <br />Any multi-year hydrologic effects of seeding will have to <br />accrue through the use of the reservoirs in the American and Feather <br />River Bas ins. Since most immed iate run-off from rainfall is not <br />retained at the reservoir, one of the main impacts of a dry season <br />would be to diminish the effects of normal reservoir spillage. Since <br />one of the objectives of a seeding program would be to redistribute the <br />precipitation so that spring, snowmelt will contribute a greater portion <br />of the run -off, modification could help alleviate the impact ove r the <br />rest of the year. However. due to the total system operation, multi- <br />year effects are expected to be minimal. <br /> <br />3.4 <br /> <br />Soc iological Cons ide rations <br /> <br />The re we re three recommendations that can effectively be <br />classified as sociological. These have to do with highway operations <br />and safety and the numbe r of people who will be directly exposed to <br />the effects of snow augmentation. Since this report has no impact <br />on the past numbers of visitors to the Sierra Nevada that recommendation <br />is not discussed further. The recommendations concerning highway <br />operations and safety are restated and discussed below. <br /> <br />. A study should be made involving careful recording <br />of times of various road surface conditions, accidents. and continuously <br />recorded traffic counts.. Much of this information is already available <br /> <br />12 <br />