INITIAL RESULTS FROM A DISTRIBUTED, PHYSICALLY-BASED MODEL OF GLACIERHYDROLOGY

This paper describes the development and testing of a distributed, phy sically based model of glacier hydrology. The model is used to investi gate the behaviour of the hydrological system of Haut Glacier d'Arolla , Valais, Switzerland. The model has an hourly time-step and three mai n components: a surface energy balance submodel, a surface flow routin g submodel and a subglacial hydrology submodel. The energy balance sub model is used to calculate meltwater production over the entire glacie r surface. The surface routing submodel routes meltwater over the glac ier surface from where it is produced to where it either enters the su bglacial hydrological system via moulins or runs off the glacier surfa ce. The subglacial hydrology submodel calculates water flow in a netwo rk of conduits, which can evolve over the course of a melt season simu lation in response to changing meltwater inputs. The main model inputs are a digital elevation model of the glacier surface and its surround ing topography, start-of-season snow depth distribution data and meteo rological data. Model performance is evaluated by comparing prediction s with field measurements of proglacial stream discharge, subglacial w ater pressure (measured in a borehole drilled to the glacier bed) and water velocities inferred from dye tracer tests. The model performs be st in comparison with the measured proglacial stream discharges, but s ome of the substantial features of the other two records are also repr oduced. In particular, the model results show the high amplitude water pressure cycles observed in the borehole in the mid-melt season and t he complex velocity/discharge hysteresis cycles observed in dye tracer tests. The results show that to model outflow hydrographs from glacie rized catchments effectively, it is necessary to simulate spatial and temporal variations in surface melt rates, the delaying effect of the surface snowpack and the configuration of the subglacial drainage syst em itself. The model's ability to predict detailed spatial and tempora l patterns of subglacial water pressures and velocities should make it a valuable tool for aiding the understanding of glacier dynamics and hydrochemistry. (C) 1998 John Wiley & Sons, Ltd.