The Davis County Experimental Watershed and the Great Basin Experimental Area are 

 located on the Wasatch Range and the Wasatch Plateau, respectively. These two mountain 

 ranges form the high-elevation midrib of the northern two-thirds of the State of Utah. 

 The Wasatch Range forms the northern half of this midrib and is characterized by steep 

 slopes, deep canyons, and ridges that rise to about 12,500 feet m.s.l.--some 3,000 to 

 6,000 feet above the adjacent valleys. The high-plateau section of the Colorado Plateau 

 province extends southward from the Wasatch Range to form the southern half of this mid- 

 rib. The Wasatch Plateau extends 75 miles from north to south and has a very narrow 

 summit, usually less than 6 miles wide. The western front is a great monoclinal flexure 

 whose strata bend upward to the summit in a single sweep. The summit is about 10,500 

 feet m.s.l.--some 4,000 to 5,500 feet above the San Pitch Valley to the west. The rim 

 of the plateau has been notched by erosion and the streams have trenched back toward the 

 summit giving the plateau a dissected appearance. 



These two mountain ranges have a relatively long history of land use--particularly 

 grazing- -dating back to about 1847. Summer convective storms delivering very high- 

 intensity rainfall have been the source of destructive debris floods. Summer debris 

 floods emanating from the Wasatch Range were particularly destructive [Bailey et al . 

 1934; and Bailey et al. 1947). These summer-flood flows took lives, destroyed property, 

 and disrupted communities. 



On both mountain ranges, summer precipitation contributes very little to streamflow. 

 However, it is important to the production of mountain vegetation that is vital to soil 

 stability (Packer 1951; Orr 1957; Packer 1963; and Croft and Bailey 1964). However, 

 vegetal cover is only one factor that affects the hydrologic performance of a watershed. 

 Storm characteristics also have a major effect on the processes of soil erosion and flood 

 production, especially when the land becomes barren of vegetal cover due to fire, road 

 construction, overgrazing, or urban development. 



A storm was defined for this study as a period of precipitation, uninterrupted for 

 a period exceeding 1 hour, delivering at least 0.10 inch of water. Most of these storms 

 were convective thunderstorms and frontal thunderstorms aided through orographic lifting. 

 Summer convective cells, often associated with lightning, usually approach from the 

 south or southwest, which is the direction of the prevailing wind of that season. Some 

 of the storms that delivered the greatest intensity of rainfall were probably of a type 

 that has been termed orographic-convective . The primary source of summer moisture aloft 

 comes from the Gulf of Mexico (Humphrey 1962). A small proportion of the total storms 

 comes from large frontal systems. 



4 



