CAUSES OF FLASHY FLOODS AND MUD FLOWS IN UTAH

  • The Utah Flood Commission
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Abstract

The report of the Utah Flood Commission, of which C. L. Forsling and Reed Bailey, and R. J. Becraft of the Utah State Agricultural College are members, was forwarded to Governor Dern on December 30. The commission concluded that the flashy floods and mud flows in Utah, although due directly to heavy torrential rains on steep slopes, were indirectly the result of sparseness of vegetation due in some cases to natural barrenness of semibarrenness of the watersheds, but in most cases to denudation by overgrazing, fire, and overcutting of timber, named in the descending order of their importance. The floods in Davis County, the worst in the State, were alniost wholly the result of man-caused denudation. The floods originated on a relatively small area at the heads of the steep canyons where there has been very heavy overgrazing on privately owned land by both cattle and sheep. The study revealed that similar rains have occurred in the past and probably will continue to occiir at intervals of a few years to several decades, but there is no eviclence of a similar frequency of floods. The geological evidence shows that the floods of 1923 and 1930 mark a distinct departure from the normal geological erosion that has been going on since Lake Bonneville receded to approfimately the present level of Great Salt Lake, 20,000 years or more ago. The floods of 1923 and 1930 in places cut as great a depth in the Lake Bonneville deltas as had been cut in all the years since Lake Boiineville receded. Moreover, had erosion been going on since Lake Bonneville at a rate comparable to that during the recent floods there would have been huge alluvial fans several miles in length in front of the canyons, whereas these deposits are exceedingly small. Sand, gravel, and rocks, including bowlders up to 50 tons in weight, were deposited on rich farm lands, formerly lake bottom, where the origrnal soil was a silt. Several facts relating to erosion and deposition on the shores of Lake Bonneville, formerly overlooked by geologists, were brought to light in the study.

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  • The Utah Flood Commission

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