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<br />b. Impacts on Hydrologic and Physiographic Phenomena. - The 5-year <br />San Juan Ecology Project included investigations of the effect of <br />increased snowfall on snowpack, avalanches, erosion, and physio- <br />graphic features of the area. In the report, liThe Infl uence of Snow <br />and Increased Snowfall on Contemporary Geomorphic Processes in Alpine <br />Areas," Caine states: <br /> <br />"Five years of observations in two 1-km2 alpine basins are <br />used here to estimate the impact of increased snowfall on <br />erosion above treeline in the San Juan Mountains. Two distinct <br />approaches, differentiating the direct impacts (those involving <br />only the snowpack and erosion) and the indirect ones (involving <br />other components of the ecosystem as intermediaries between the <br />snowpack and erosion), are the basis of the study. <br /> <br />liThe compari son of seasonal erosion rates and amounts suggests <br />that the snowpack has relatively little direct effect on <br />alpine geomorphic processes. Comparatively little sediment <br />movement 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 respon- <br />sive to the seasonal snowpack, since most alpine streamflow <br />. derives from snowmelt, but are relatively unimportant in the <br />alpine area of the San Juan Mountains. By extension, this <br />conclusion implies that the 30 percent increase which might <br />be produced by operational cloud seeding should have little <br />immediate, direct effect on alpine erosion rates." L12, p. 145, <br />emphasis addedJ (In this study, the 30 percent increase con- <br />sidered by Caine exceeds the normally accepted "consensus <br />increase" of 10 to 15 percent.) <br /> <br />Concerns have been expressed about the delay in snowpack meltout in <br />the spring as a result of increased precipitation. Climatic and <br />meterological investigations in both the maritime-influenced Sierra <br />Nevada and the continental Rocky Mountains disclosed that temporary <br />delays in snowpack meltout could occur as a result of 10 to 15 <br />percent increases in snowfall. However, it is believed that snowmelt <br />extension would occur in protected areas, those that serve as snow <br />traps, and those in which permanent snowbanks or glaciers exist. <br />One of the San Juan Ecology Project studies included development <br />of a snow cover recession model for two study basins. The model <br />illustrated that only a small area actually experienced an extended <br />period of snow cover. In discussing the effect of a 15 percent <br />increse in snowfall in the two San Juan study basins, the report <br />conc1 uded: liOn on1 y 1 percent of the Will i ams Forks Lakes catchment <br />is the delay in seasonal melting likely to be of more than 7 days, <br />while only 3 percent of the E1 Dorado Lake Basin would be similarly <br />affected." [12, p. 179J <br /> <br />Snowpack me1tout dates must be <br />seeding program <br /> <br /> <br />12 <br />