. Does harvest in west slope Douglas-fir increase peak flow in small forest streams?. Logging Environmental aspects; Forest influences; Stream measurements. were highly significant. In a covariance analysis, slope of the regressions and the adjusted mean were nonsignificant (lines 1 and 3), indicating no difference between the two periods. We would expect this, since there was no change in cover on this watershed throughout the entire study. For the logged watershed, the rela- tionship shown in figure 4 was significant before logging (line 2) but nonsignificant after logging (line 4). As for t
. Does harvest in west slope Douglas-fir increase peak flow in small forest streams?. Logging Environmental aspects; Forest influences; Stream measurements. were highly significant. In a covariance analysis, slope of the regressions and the adjusted mean were nonsignificant (lines 1 and 3), indicating no difference between the two periods. We would expect this, since there was no change in cover on this watershed throughout the entire study. For the logged watershed, the rela- tionship shown in figure 4 was significant before logging (line 2) but nonsignificant after logging (line 4). As for the unlogged watershed, the slopes of the regressions were not significantly different, but the adjusted means were highly significantly different for the two periods (lines 2 and 4). This would suggest that logging increases the average peak flows, although any in- fluence the 30-day antecedent precipitation has on streamflow is weak in the post- logging period. In figure 4, note that there appears to be a convergence of the before and after logging curves (lines 2 and 4) for the clearcut watershed at high 30-day pre- cipitation totals. This is even more pro- nounced for the unlogged and clearcut watersheds for the 1965-69 period (lines 3 and 4). Data from our brief period of record show 30-day antecedent precipita- tion exceeded 37 inches. At this point, there is very little difference between the regressions, suggesting that logging may have relatively little influence on peak streamflow under excessively wet conditions. The influence of the 30-day antece- dent precipitation is illustrated in another form in figure 5, which shows how measured 2001- 180 - o £ ISO -. 30-DAY ANTECEDENT PRECIPITATION (INCHES) Figure 5.—Measured peak streamflow as a percent of predicted peak at various degrees of wetness as ex- pressed by 30-day antecedent Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability -
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