RESULTS 



Consistency Test 



The records were not adjusted. None of the mass curves plotted as smooth straight 

 lines and isolated points fluctuated both above and below the trend line. Even so, the 

 breaks in the lines didn't persist for a period as long as 5 years. The breaks in the 

 lines were considered to be no greater than might reasonably be expected for thunderstorm 

 data obtained from mountainous areas. 



Precipitation Zones 



Within each study area, vegetal patterns were closely related to the four precipi- 

 tation zones (table 2). This was not unexpected; however, vegetal types were not con- 

 sidered when the precipitation zones were established. On the Wasatch Plateau, the 

 major vegetal types are pinyon- juniper , oakbrush , aspen-fir, and spruce-fir. On the 

 Wasatch Range, the pinyon- juniper type disappears and oakbrush occupies sites similar 

 to those occupied by pinyon- juniper in areas south of the Wasatch Range. 



Intensity -Duration- Frequency Cliaracteristics 



The curves in figures 3a to 3d and 4a to 4d are for recurrence intervals of 2 to 

 50 years and storm durations of 2, 5, 10, 20, and 30 minutes and 1, 2, 4, and 6 hours. 

 The 50-year return period intensity is a linear extrapolation and as such must be used 

 with caution. The 10-year intensity is expected to be accurately determined because 

 one or more stations in the eight precipitation zones have records dating back more than 

 20 years. All of the curves were fitted by eye (Dalrymple 1960). In reading them, it 

 is important to remember that the recurrence interval is the average interval in which 

 an intensity of given duration will recur as an annual seasonal maximum. 



9 



