10 r 



Figure 10. — The relationship 

 between seasonal low stream- 

 flow from the Halfway Creek 

 drainage and that from the 

 Miller Creek drainage , 

 1962-1968. 



cc 

 (J 

 > 

 < 



O Before trenching 



A After trenching 



# Mean before 



▲ Mean after 



10 



1ILLER CREEK STREAMFLOW (hiches) 



Low Streamflow Period 



As defined for this analysis, the low streamflow period includes the streamflow 

 for July through February. Streamflow during this period is almost exclusively base- 

 flow, water from deep seepage and interflow. Precipitation occurring during the period 

 contributes little water directly to streamflow. Summer storms are generally light and 

 less than 2 percent of their precipitation results in direct runoff (Croft and Marston 

 1950). Fall and winter precipitation recharge the soil mantle and build the snowpack, 

 but do not appreciably affect streamflow until snowmelt and spring runoff, March through 

 June. Consequently, the low streamflow period reflects the watershed's drainage char- 

 acteristics while the influence of concurrent precipitation is negligible (Hall 1968) . 



Soil moisture data collected at various places on the Davis County Experimental 

 Watershed (Johnston, Tew, and Doty 1969) and the fact that two-thirds of the annual 

 streamflow consistently occurs during the spring flow period indicate that the soil 

 mantle is fully recharged at the beginning of each growing season. Fluctuations in 

 streamflow, particularly on Miller Creek, sometimes occur at the beginning of the low 

 flow period due to delayed snowmelt. For the most part, however, this is a rather 

 stable streamflow period. 



The relationship between the low flow of Halfway Creek and that of Miller Creek 

 was determined for the pretreatment years (fig. 10). This resulted in an r^ of 0.46, 

 a low correlation apparently due to events on Miller Creek that effect streamflow 

 while not effecting streamflow on Halfway Creek. The most probable influence was 

 low temperatures, May through June, that delayed snowmelt longer on the Miller Creek 

 drainage with its northern exposure than on Halfway Creek with its southwest exposure. 

 A covariance analysis comparing before and after trenching data indicated no signif- 

 icant change in either the slope of the regression line nor any shift in position of 

 the line. However, a slight decrease in streamflow after trenching is indicated 

 (table 2) . 



11 



