- The effects of roadbuilding, logging and burning upon stream
runoff responses to individual storms are evaluated for the Alsea
experimental watersheds, located in the Oregon Coast Range, The
parameters analyzed are peak discharge, induced peak discharge,
time-to-peak, and storm-runoff volume. The volume parameter is
further sub-divided into total, quick, delayed, rising limb and falling
limb flows. The control-watershed approach and linear regression
method are utilized in this study.
Calibration of the main stations at Flynn Creek (502 acres) and
Deer Creek (750 acres) started in 1958. That for subwatershed DC II
(138 acres) and DC III (100 acres) started in 1962. Watershed treatments
included differing amounts of roadbuilding in the summer of 1965 and
logging in 1966. The percentages of each watershed area subject to
roadbuilding and to logging, respectively, were: Deer Creek main
station, 3.7% and 26% of area in roads and logging, respectively,
DC II, 3.1% and 20%, and DC III, 12, 1% and 72%, One small portion
on the main watershed also received burning treatment in 1967, Flynn
Creek was preserved in its natural state as a control. Data were
analyzed through 1968.
The storm-runoff responses of the treated watershed were found
to relate to the type of treatment applied and percent of area treated,
Roadbuilding resulted in significant increases in peak and induced peak
discharges on DC III, which was subjected to the most intensive treatment.
Logging generally demonstrated a more pronounced effect on
runoff than did roadbuilding, since more vegetation was removed. Although
highly significant augmentations in peak and induced peak discharges were detected after logging on subwatershed III, only minor
changes were observed at the main Deer Creek outlet,
The time-to-peak parameter was generally not affected by the
land manipulations in this study.
Separation of the annual data into the assumed recharging and
recharged periods, based on antecedent soil moisture conditions, was
selected for seasonal comparison over the use of an arbitrary cutoff
date. Changes in flow volume parameters due to roadbuilding were
insignificant. Rising limb flow on DC III as well as at the Deer Creek
main station was moderately increased after logging. Although an increase
in delayed flow and a decrease in quick flow occurred at the
main station, these are considered to be compensating errors.
Effects on design floods after treatments were indicated by the
sharp increases in peak discharges, based upon flood frequency and