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<br />. <br /> <br />e <br /> <br />Environmental Statement [2J and the Sierra Cooperative Pilot Project <br />Environmental Assessment [8J. Both documents concluded that cloud <br />seeding produced no effect on these weather elements, or that the <br />effect was not significant. <br /> <br />b. Impacts on Hydrologic and Physiographic Phenomena <br /> <br />The 5-year San Juan Ecology Project included investigations of the <br />effect of increased snowfall on snowpack, avalanches, erosion, and <br />physiographic features of the area. In the report, nThe Influence of <br />Snow and Increased Snowfall on Contemporary Geomorphic Processes in <br />Alpine Areas,'1 Caine states: <br /> <br />'IFive years of observations in two 1-km2 alpine basins are <br />used here to estimate the impact of increased snowfall on <br />erosion above tree 1 i ne in the San Juan Mountai ns. Two <br />distinct approaches, differentiating the direct impacts <br />(those involving only the snowpack and erosion) and the <br />indirect ones (involving other components of the ecosystem <br />as intermediaries between the snowpack and erosion), are the <br />basis of the study. <br /> <br />liThe comparison of seasonal erosion rates and amounts suggests <br />that the snowpack has relatively little direct effect on alpine <br />geomorphic processes. Comparatively little sediment move- . <br />ment is produced by the action of snow glide and creep over <br />the ground surface, by avalanches or by overland flow from <br />snowmelt. Stream channel processes are more obviously <br />responsive to the seasonal snowpack, since most alpine <br />streamflow derives from snowmelt, but are relatively <br />unimportant in the alpine area of the San Juan Mountains. <br />By extension, this conclusion imolies that the 30 percent <br />increase whlcn mlont be proaucea b operationai cloua <br />seedlng shou a have itt e immediate, direct effect on <br />alolne erOSlon rates." L12, p. 145, emphasis aaaeaJ (In <br />this study, the 30 percent increase considered by Caine <br />exceeds the normally accepted "consensus increase" of 10 to <br />15 percent.) <br /> <br />Concerns have been expressed about the delay in snowpack meltout in the <br />spring as a result of increased precipitation. Climatic and meteorolog- <br />ical investigations in both the maritime-influenced Sierra Nevada and <br />the continental Rocky Mountains disclosed that temporary delays in <br />snowpack meltout could occur as a result of 10 to 15 percent increases <br />in snowfall. However, it is believed that snowmelt extension would <br />occur in protected areas, those that serve as snew traps, 3nd tnose in <br />which permanent snowbanks or glaciers exist. One of tne San Juan <br />Ecology Project studies included development of a snow CJver recession <br />model for two study basins. The model jl lus~ratea that only a small <br />area actually experienced an extended perioa of snow cover. In discuss- <br />ing the effect of a 15 percent increase in snowral I in the two San Juan <br /> <br />12 <br />