PHYSICAL CHARACTERISTICS OF ALLUVIAL FANS
ARMY NATICK LABS MA NATICK
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In this study a new technique is developed for analyzing available world maps and aerial photographs in terms of frequency of occurrence of terrain obstacles as related to capabilities of various types of military vehicles. Employing this technique, an areal quantification of the geometry of alluvial fans was completed for a total of seven 1-degree quadrangles 1 degree Latitude x 1 degree Longitude of representative desert terrain in the United States and West Pakistan. The greatest development of alluvial fans is associated with mountainous desert regions having wide valleys. Alluvial fans are not related to high mountainous areas or to areas where the mountain mass has been deeply dissected by steep, narrow valleys. Within desert regions it was noted that landform data in one physiographic province were very similar to those in the same type of province such as a folded-faulted type and climate elsewhere. Except for similar provinces the agreement was not close. Approximately 70 percent of all alluvial fans studied were 1 to 5 miles miles in length and had total slope gradients of 1 to 5 degrees. Gradients up to 600 feet per mile have been measured on the upper slopes of small alluvial fans. Nearly all alluvial fans have deep washes with vertical walls which may be located near their apices or their aprons.