flow should be a good indicator of any alteration of watershed characteristics due to 

 trenching. A rapid recession in Halfway Creek streamflow follows the peak. After 60 

 days, the recession curve flattens to a slight downward gradient until sometime in 

 August or September. 



Evaluation of the recession flow was made by plotting daily flows for the 60-day 

 period following the peak. The average of the 12 years prior to trenching was plotted 

 as was the 4-year average after trenching and smooth curves were drawn through these 

 data (fig. 14), A greatly reduced peak and a flattened recession curve followed trench- 

 ing. Also, a general, but slight, reduction in the flow is shown. 



Summer Storms 



Runoff from summer storms does not represent a significant portion of the total 

 annual runoff. However, since control of such storms is the primary reason for trench- 

 ing, a limited analysis of their relationship to trenching was made. 



More than 100 storms were studied to determine total surface runoff, time of that 

 runoff, peak flow, and storm patterns. No two storms were alike and, more important, 

 no storm affected the two watersheds in the same manner. However, a few conclusions 

 can be drawn from the precipitation-runoff relationships studied so far. It was noted 

 that less than 2 percent of the precipitation in a storm generally left the watershed 

 as overland flow or was intercepted by the stream channel. Most of the storms analyzed 

 produced less than a half-inch of precipitation each; only a small percentage produced 

 more than an inch. 



14 



