Effects of slope vegetation removal on the diurnal variations of a small mountain stream

Abstract

The effect on removal of lower, mid, and upper slope vegetation on the diurnal variation in streamflow from a 46‐ha catchment was observed. The diurnal variation in streamflow of the small stream was measurable during the late‐spring‐to‐late‐autumn period. The amplitude in streamflow variation reached a maximum in early summer and declined during autumn. Observation of diurnal variations during the periods of higher flow in winter and spring showed that they may occur but were masked by much larger variations associated with storm runoff. Simulation of the characteristics of the flow measurement system showed that diurnal variations can only be studied using V‐notch weirs and float recorders during periods of low flow. No effect of the clearing of slope vegetation on the phase of the outflow could be found. However, there was evidence of a significant increase in amplitude, probably due to increased groundwater outflow from the slopes. It was concluded that the diurnal variation is due to transpiration by the riparian and near‐riparian vegetation only, and that the lower to mid slope vegetation plays little role in this variation. Simulations suggested that increased amplitude is associated with increased flow rates, and that the amplitude is not directly affected by water use of vegetation on the catchment slopes. It was concluded that the amplitude of the variation is insensitive to changes in slope hydrology and cannot be used to provide insight into deep slope processes.