. Effects of defoliation by Douglas-fir tussock moth on timing and quantity of streamflow. were made on peak discharge, and total runoff during snowmelt (April - June) , during summer months (July-September), and during the autumn months (September-November). The test indicated no significant change during snowmelt or the summer months. Runoff during the autumn months of water year 1974, however, was significantly greater than the pre- dicted value. Actual runoff during these months was compared to the predicted value of cm. This was about cm greater than the upper end point of t
. Effects of defoliation by Douglas-fir tussock moth on timing and quantity of streamflow. were made on peak discharge, and total runoff during snowmelt (April - June) , during summer months (July-September), and during the autumn months (September-November). The test indicated no significant change during snowmelt or the summer months. Runoff during the autumn months of water year 1974, however, was significantly greater than the pre- dicted value. Actual runoff during these months was compared to the predicted value of cm. This was about cm greater than the upper end point of the confidence band (95-percent level) for the base- line data. Peak discharge data were highly variable, and no change could be detected. This result was expected because even on small watershed studies where runoff is measured much more accurately than is possible on rivers, complete clearcutting produces only small increases in peak flow rates (Harr 1976). Plottings of annual runoff for the North Fork and the South Fork of the Walla Walla River revealed no detectable change in runoff after the defoliation (figs. 4 and 5). E o â¢ââ 1 be 1 1 2. â *â o o c CO C C < 90 r 80 70 60 50 40 30 20 10 o lnh. 0 30 40 50 60 70 80 90 100 110 Annual runoff, Mill Creek (cm) Figure 4.âAnnual runoff from the North Fork of Walla Walla River compared to annual runoff from Mill Creek. The number beside each solid dot is the year of measurement for that point. 9. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Helvey, J. D; Tiedemann, Arthur R; Pacific Northwest Forest and Range Experiment Station (Portland, Or. ). Portland, Or. : Pacific Northwest Forest and Range Experiment Station, Forest Service, U. S. Dept. of Agriculture
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