OCR Text |
Show avalanche hazard evaluation and prediction in the San Juan Mountains of southwestern Colorado in association with the Colorado River Basin Pilot Project. The program uses seismic, infrasonic, and accelerometric methods in an effort to predict the occurrence of avalanches. Models are used to forecast the degree of hazard. The 1971- 72 avalanche season in the area was quite abnormal; the snowfall was well below normal, with little snow after January 1. Only the most tentative conclusions can be reached with only one abnormal season of study. Precipitation rate and total precipitation both appear to influence avalanche frequency, with rate probablyihe most important. Data from Climax, Colorado, indicate that seeding has little influence on precipitation rate, but that it extends the duration of precipitation. At Climax over two- thirds of the snowfall during a 3- year period fell at rates between .01 and .03 inch per hour. During the same period only 21 events had precipitation rates of 0.1 inch per hour or greater. These 21 events accounted for slightly less than 10 percent of the total precipitation. Erosion Erosion is a natural process which has shaped the landscape for millenia. Erosion by water is classified as sheet erosion which is caused by the overland flow of water, or channel erosion which is caused by the energy contained in concentrated waterflow. Since snowmelt usually infiltrates the soils and appears as the groundwater- induced base flow of a stream, it does not contribute to sheet erosion. Channel erosion rates depend on the hydraulics of the flow and the inherent erodability of the material through which the channel is cut. The effect on streamflow of additional snowmelt made available through cloud seeding would be to increase the height and length of the recession limb of the hydrograph. Whether the crest of the hydrograph would be increased or not depends on basin characteristics such as orientation, type of vegetative cover, etc. The increased flow would be expected to 515 |