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Pham, Henry Cuong

University of British Columbia

Decades of literature on forest treatment – peak flow relations have generated considerable disagreements and turned the topic into what have been regarded as enigmatic. Using the new science of causation to investigate forest treatment peak flow relations is a necessary step needed to advance the understanding and prediction of forest treatment effects on peak flows. The causes of peak flows are multiple and chancy and, hence, can only be investigated via a probabilistic approach. We analyze peak flow data using the peak flow frequency distribution framework using two pairs of control-treatment watersheds in the rain environment of Coweeta - United States Department of Agriculture Forest Service experimental forest situated in North Carolina, south eastern United States of America. We demonstrate how a wide range of forest treatments change the magnitude and frequency of all peak flows on record and how such effects can increase with increasing event size as a consequence of changes to the peak flow frequency distribution. The dominant process responsible for the changes to the parameters characterizing the frequency distribution such as mean, variance, and skewness of peak flows is the treatment-induced suppression of evapotranspiration and changes to non-vegetative factors; which alter the soil storage capacity, moisture available for runoff, and the efficiency with which such runoff is delivered to the outlet of the watershed. The dominant topographical aspect of the treatment watershed, the seasonal differences in storm types, the extent to which the storm events are in-phase or out-of-phase with high antecedent soil moisture, and lagged runoff responses and watershed memory emerged as key indicators of the sensitivity of peak flow regime to forest treatment. We call for more research on forest treatment – peakflow regime relations using the stochastic approach to physics and prediction, which is standard practice in the wider hydrology but not as commonly used in forest hydrology.

Text

2024-01-31

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/80548

Forestry

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/