. Does harvest in west slope Douglas-fir increase peak flow in small forest streams?. Logging Environmental aspects; Forest influences; Stream measurements. streamflow peaks. Major floods typically occur from mid-November on. Two of the postlogging peaks over 100 c. occurred early in the wet season at a time when major floods are unlikely. Later major storms that occur under thoroughly wet soil conditions would be expected to produce streamflow peaks little changed by logging. PATCHCUT LOGGING HAS MINOR INFLUENCE ON STREAMFLOW PEAKS Under current patchcutting practices, only about 1 to 2
. Does harvest in west slope Douglas-fir increase peak flow in small forest streams?. Logging Environmental aspects; Forest influences; Stream measurements. streamflow peaks. Major floods typically occur from mid-November on. Two of the postlogging peaks over 100 c. occurred early in the wet season at a time when major floods are unlikely. Later major storms that occur under thoroughly wet soil conditions would be expected to produce streamflow peaks little changed by logging. PATCHCUT LOGGING HAS MINOR INFLUENCE ON STREAMFLOW PEAKS Under current patchcutting practices, only about 1 to 2 percent of large drainages are cut at any one time. On smaller drain- ages of several hundred acres, approxi- mately one-quarter of the area might normally be clearcut within a few years. In our study, an adjacent 250-acre water- shed with 1. 65 miles of logging road (8 percent of drainage disturbed) and 25-percent clearcut showed minor in- creases similar to the clearcut and logged watersheds we have been discussing. The regression relationships of the unlogged and patchcut logged watersheds were calculated for the period before logging (fig. 6, line 1), after road construction (line 2), and after roads, logging, and burning (three clearcut units, 25 percent of area) (line 3). All these regressions were highly significant. Comparing the period after road construction (fig. 6, line 2) with the period when both watersheds were Q < O rr < Q LU iD O _i I— 3 O I u I- < 140 i- 120 100 80 B0 40 - 20. Unlogged 1953-59 95-percent confidence limits Roads 1960-62 Logging, burning,and roads 1963-68 1st fall storm each year after logging ? 20 40 B0 80 UNLOGGED LOO 120 Figure 6.—Peak streamflow relations of patchcut and unlogged watersheds on the H. J. Andrews Experimental Forest before logging, after road construction, and after logging and roads. Data points for unlogged relationship not shown. 11. Please note that these images are extracted from scanned page
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