Figure 7. — Modified 

 Venturii- trapezoidal 

 flume in a broad- 

 crested weir section 

 constructed in the 

 late 1930 's on the 

 Davis County Exper- 

 imental Watershed. 



In addition to the streamflow and precipitation records, other data have been 

 collected in Farmington Canyon that contributed to the conclusions reached here. Soil 

 moisture measurements have been made on the trenched area and on an adjacent untrenched 

 area since 1965. Vegetation measurements were taken as point samples along permanent 

 transects. Two 100-foot transects were located in the trenched area and two others in 

 an adjacent untrenched area. In addition to the regular snow courses, four snow 

 courses were established in conjunction with the contour trenches in the Halfway Creek 

 drainage. Two of the courses were so located in the trenched area that each course 

 crossed one trench. 



RESULTS AND DISCUSSION 



The relationship of three factors, streamflow from the Halfway Creek drainage, 

 streamflow from the Miller Creek drainage, and precipitation at the Rice Climatic 

 Station, was determined from records for the 12 years immediately prior to trenching. 

 Correlations of these factors for different streamflow and precipitation periods were 

 the basis used to evaluate effects of contour trenching. 



The general nature of the relationship before trenching of the Halfway Creek 

 streamflow, the Miller Creek streamflow, and the Rice Climatic Station precipitation 

 is shown in figure 8. Precipitation catch at Rice Climatic Station tended to be 

 greater than that on Halfway Creek drainage and less than that on the Miller Creek 

 drainage. The extent of this error was accentuated in wet years, primarily because 

 wet years are the result of more snow. Wind generally carries snow out of the Half- 

 way Creek drainage but into the Miller Creek drainage. The movement of snow from 

 Halfway Creek drainage into adjoining drainages is a significant factor in the actual 

 distribution of precipitation available for streamflow. 



Streamflows from Halfway Creek and Miller Creek drainages are closely correlated. 

 Based on monthly streamflow patterns, the primary difference is a shift in the spring 

 streamflow. Miller Creek streamflow is somewhat delayed relative to Halfway Creek 

 because snowmelt begins later on this north exposure. 



8 



