Investigating spatio-temporal variability of hydrological components in the Canadian Rockies (Alberta)

This thesis addresses two questions related to the broad topic of mountain hydrology: 1) How do interannual hydrological balancee and pathway components vary in complex temperate high mountain environments at various spatio-temporal scales? 2) a) Is it possible, using dedicated hydrological models, for significant errors in simulated runoff components despite good hydrograph recreations (i.e. right results for wrong reasons)? b) If so, what kinds of errors are encountered? The first question was addressed by undertaking a hydrological tracer and hydrometric study at three basin scales (Banff —2200 km2, Lake Louise —400 km2 and the headwaters —30 km2) within the Bow Valley of the Canadian Rockies from 1996 to 1999. To address question two, hydrometeorological basin properties learned from question one were used to perform two runs of the University of British Columbia watershed model for the Bow River at Banff during hydrological years 1996-1999. Simulations were evaluated using a conceptual 5\u2780 model of the hydrological balance. Seasonal geochemical patterns in runoff were similar for all basins, indicating that interannual hydrometeorological conditions play the dominant role in controlling hydrological contributions to runoff. In both seasonal baseflow and event runoff from all basins, snow was the dominant component with rainfall contributing little, even during large rainfall events. Higher rainfall contributions were evident in the runoff from glacierised basins, suggesting that impervious surfaces lead to rapid runoff but in non-glacierised basins a large volume of rainwater is probably lost to evapotranspiration. In addition, it was considered that rainfall may have appeared to be absent from the hydrograph during the large rainfall event studied as it may have shunted out older snowmelt from karst storage in the headwaters, thus masking the actual rainfall signature. For all model runs it was found that the snowmelt component of the hydrological balance was underestimated. This was generally compensated for by an overestimation of rain inputs. From the findings that rainfall was generally a minor component of annual runoff despite hydrometric observations (and phenomenological intuition) that might indicate otherwise, it was concluded that there may be a conceptual misunderstanding of the importance of rainfall contributions to runoff in glacierised high mountain basins. Rainfall occurs during summer months and is the most susceptible flow component to evaporative loss. However, rain, snow and ice are not discriminated in many model evaporation routines, and this could lead to overestimations of rainfall in the balance. In addition, orographic enhancement of precipitation varies seasonally but this is often not accounted for in models. Using a single value to represent annual conditions likely leads to overestimations of rainfall at high elevations. Automated optimisation of a model containing such process-based conceptual flaws will ultimately force the model to overestimate certain parameters (rainfall in this case) and compensate with an underestimation of hydrologically more important components (namely snow)