APPLICATION OF A CONCEPTUAL STREAMFLOW MODEL IN A GLACIERIZED DRAINAGE-BASIN

A conceptual streamflow model which accounts for glacial cover has been developed for the Lillooet River drainage basin in the southern Coast Mountains of British Columbia, Canada. Although the model draws heavily on commonly used modelling concepts, two innovations it introduces are an algorithm for allowing the characteristics of the glacial drainage system to vary seasonally and from year to year, and the use of observed equilibrium line altitudes for nearby glaciers to help remove ambiguity from the calibration of model parameters governing glacial accumulation and ablation. Model performance as measured by the Nash-Sutcliffe criterion compares reasonably with values reported for previous model applications in mountainous snow- and glacier-fed catchments. A major problem was the necessity of extrapolating valley-bottom temperatures to higher elevations. Because of deviations of the actual from the assumed lapse rate, rainfall at higher elevations was often incorrectly modelled as snowfall. As a consequence, the modelled streamflow did not respond to many autumn-winter rainstorms. As a further consequence of the misclassified precipitation, the precipitation gradient had to be incorrectly set to a lower value than appropriate in order not to overestimate the spring-summer snowmelt response.