24-hour Precipitation Depth 



Only 4 percent of the storms at the Straight Canyon 

 barometer watershed have durations longer than 7 

 hours. However, the longer duration storms are of 

 interest in the design of contour trenches and road 

 drainage devices. Storms of long duration rarely pro- 

 duce floods in this area. 



The 24-hour volumes were tabulated for the three 

 zones for recurrences of 10, 25, and 50 years and are 

 presented in table 3. As would be expected, considering 

 the penetration distance from the mountain front the 

 14-hour precipitation volumes are smaller than the 

 volumes for either Davis County or Ephraim experi- 

 mental areas. 



Average Monthly Depth and Number of Storms 



The monthly precipitation depths were determined 

 from gage catch. We hoped that these data could assist 

 in clarifying the mountain-valley precipitation relation- 

 ships when used in conjunction with intensity-duration- 

 frequency characteristics. 



Monthly precipitation fluctuates widely between 

 zones and between years. Any month during the period 

 May-October may be completely dry at one or more 



precipitation stations. Also, any month may exceed the 

 average threefold to sevenfold. 



The average number of storms during each month 

 and within each zone varies widely as does the monthly 

 volumes of precipitation (table 4). These values re- 

 semble those for the Great Basin experimental area 

 (Farmer and Fletcher 1971). The expected relation 

 between a valley station, Castle Dale, was of a relatively 

 low order. Furthermore, the most intense rains occurred 

 in zone 3 while the greatest monthly volumefell in zone 

 2. This distribution confirms the significant correlation 

 between elevation and monthly rainfall volume. Figure 5 

 illustrates the seasonal precipitation volumes for the 

 three zones and Castle Dale, which is in the valley just 

 below Straight Canyon barometer watershed. Indica- 

 tions with these incomplete data confirm the Septem- 

 ber dry season mentioned by Price and Evans (1 937) for 

 the Great Basin experimental area, but certainly there is 

 no dry spot in June although the summer season does 

 appear to be bimodal. Our analysis shows a low precipi- 

 tation volume for July and September at Straight Can- 

 yon barometer watershed as well as at Ephraim experi- 

 mental area and Davis County experimental watershed. 



Table 3.— Expected annual seasonal maximum 24-hour precipitation depths (inches) 

 by precipitation zones and recurrence intervals 



Zone 



10 



Recurrence interval (years) 



25 



50 



Straight Canyon barometer watershed 



1.50 1.83 2.08 



1.48 1.79 2.03 



1.37 1.70 1.97 



Davis County experimental watershed 



2.21 2.54 2.74 



2.04 2.38 2.45 



1.44 1.87 2.11 



1.54 1.87 1.97 



1.15 

 1.49 

 1.70 

 1.39 



Great Basin experimental area 

 1.30 

 2.16 

 2.16 

 1.66 



1.34 

 2.47 

 2.33 

 1.70 



Table 4.— Precipitation depth (inches) and number of storms by month and zone, 

 Straight Canyon barometer watershed 



Zone 



Month 



Depth Number 



Depth Number 



Depth Number 



July 



August 



September 



1.17 

 1.25 

 0.81 



5.4 

 7.9 

 3.1 



1.46 

 1.57 

 0.74 



5.2 

 10.3 

 3.9 



1.10 

 1.18 

 0.70 



6.1 

 8.0 

 2.3 



5 



