10 



Figure 14. — The recession 

 stream flow from the Halfway 

 Creek drainage based on 

 daily flow periods before 

 and after trenching. 



1 - 



10 20 30 40 50 60 



NUMBER OF DAYS SINCE PEAK STREAMFLOW 



Hydrographs of two storms are illustrated (figs. 15 and 16) to show the relation 

 between precipitation and runoff from summer storms on the Halfway Creek and Whipple 

 Creek drainages. Figure 15 is the hydrograph of a storm that produced a total of 1.3 

 inches of precipitation, but had a maximum 5-minute intensity of 6.0 inches. Peak 

 runoff exceeded 18 c.s.m, from Halfway Creek within an hour. Whipple Creek peaked an 

 hour later at 11 c.s.m. The initial smaller peak on Whipple Creek is the result of 

 a rainburst lower on the watershed. This also occurred on Halfway Creek and appeared 

 on that portion of the hydrograph not shown. Figure 16 illustrates a storm 1 year after 

 trenching. This storm produced 1.6 inches of precipitation, but had a maximum 5-minute 

 intensity of 2.5 inches. Halfway Creek peaked at 6.7 c.s.m. Whipple Creek peaked at 

 7.5 c.s.m. an hour later. In comparison to pretrench conditions, the peak on Halfway 

 Creek was greatly reduced. Also, the flow was distributed over a longer period of time, 

 whereas the untrenched Whipple's flow period was about the same as before. How many of 

 these differences can be attributed to trenching and how many to storm patterns is 

 difficult to say. 



15 



