Estimation of Design Snowmelt Floods
Abstract
A Large number of different methods are available for estimating snowmelt, though few procedures are directly applicable to the practical estimation of design floods in catchments with sparse data. This paper presents a methodology for the estimation of snowmelt design floods in which particular attention is given to ensuring that the exceedance probability of the snowmelt flood is the same as the concomitant rainfall. The method used to estimate snowmelt is based on a water budget approach developed by the U.S Bureau of Reclamation. The method tracks changes in pack density with time due to changes in energy input and incident rainfall, and provides hourly estimates of the amount of water released from storage. The procedure was incorporated into the RORB runoff-routing model and used to provide estimates of snowmelt floods resulting from rainfalls of a specified exceedance probability. All inputs used to derive the snowmelt floods were selected to be representative of the correlations expected during extreme events. The influence of the antecedent snowpack depth was found to have an appreciable impact on the magnitude of the design flood, and accordingly a simple joint probability approach was adopted to avoid the introduction of bias.