24-H Design Storm for Coastal British Columbia

Abstract

Data from the Seymour River watershed in southwestern British Columbia were used to develop a 24-h design storm for the coastal region. The study showed that there is only a small variation in the time distribution of the storm with elevation, and comparison with the results of other studies and data from other stations showed that the findings of this work are transferable to other areas of the region. Simulation of the streamflow in a watershed of the region revealed that the developed 10% time probability curve and the Soil Conservation Service Type IA curve reproduce the observed peak flows. Analysis of the spatial distribution of the annual extreme 24-h storms showed that the mean annual precipitation, which increases up to an elevation of 400–800 m, and then levels off or even decreases, can be used as an index for the estimation of the 24-h extreme rainfall. Although the study has been concentrated on the coastal British Columbia, there are indications that the results may be applicable to the greater region of the coastal Pacific Northwest.