Analysis of Highflows in the Fraser River Catchment, British Columbia

Abstract

<p>Frequency characteristics of highflows in the Fraser River catchment, British Columbia, are modelled in such a way as to permit their prediction for ungauged basins.</p> <p>Two definitions of highflows, annual flood and partial duration series, are examined. The two series are shown to be stationary and serially independent. The Gumbel distribution is found to describe adequately the observed annual flood data. Following theoretical considerations a nonhomogenous Poisson distribution is used to model the time-dependent behaviour of the number and timing of highflows derived from the partial duration series. Their magnitudes and periods of duration are found to be exponentially distributed.</p> <p>The 2 year return period annual flood provides the truncation level for the regional analysis. A method of predicting partial series at other levels of interest from this base is proposed and tested. The relationship between the two highflow series is presented and a theoretical distribution for the estimation of annual flood frequencies from partial series is tested across the study area. It compares favourably with the Gumbel distribution as a means of representing the observed annual flood data.</p> <p>The estimated parameters of the probability distributions employed are entered into a regionalisation procedure that permits the definition of highflow groups. Within each of the derived groups the parametric values are related to basin physiographic and climatic variables by means of multiple regression equations. The groups are found to be defined by simple, meaningful physical variables which allow the extension of the groups to provide a regional demarcation of the study area. The regression equations are applied to test basins within the Fraser catchment and the results indicate that the method is suitable for the estimation of highflow characteristics in ungauged basins.</p>