| Summary: | The Mecham River is a stream near Resolute, Cornwallis I., N.W.T., which has an arctic nival regime. It flows only in summer, from June or early July to late August or early September. Discharge begins shortly after the snowpack becomes fully ripe under the influence of increasing temperature and radiation. Over a period of about two weeks it rises rapidly to a spring snowmelt peak from which there is a gradual recession through the rest of the summer. Superimposed on the recession there are (in most summers) occasional rainstorm responses. These floods are rapid to rise and to fall, because the bare terrain with shallow underlying permafrost has little capacity to detain or retain water. Diurnal fluctuations are also superimposed on the seasonal pattern of discharge; they can be related to diurnal fluctuations of incoming radiation, and although they are sometimes subdued late in the season they can be very pronounced before rainwater runoff begins to drown them out. The most important findings of the study concern the annual water balance of the Mecham River basin. Several terms of possible importance in the water balance can be eliminated. Changes in frozen water storage and in lake storage may be neglected because the basin contains very few snowbanks and lakes. Annual changes in the moisture content of the active layer may also be neglected, although more understanding of how the active layer behaves hydrologically would be valuable for other purposes besides the solution of the water balance. The flux of windblown snow across the drainage divide has been suspected to be large, at least potentially, but an analysis of basin topography shows that this is unlikely to be so in basins as large as that of the Mecham River. The remaining terms in the water balance are snowfall, rainfall, evaporation and discharge. Three of these are measured at Resolute or on the Mecham River itself. The fourth - evaporation - must be calculated indirectly. The method chosen in this study was an application of the combination model to the weather data collected routinely at Resolute. The hardest problem encountered in developing the model was the accurate estimation of surface wetness, although improvements would also be desirable in measurements of the wind speed profile, the soil heat flux perhaps in the estimation of basin snow cover. Nevertheless, comparisons of the results with pan evaporation measurements suggest that the model performs well. Comparisons with Priestley and Taylor's approach to the estimation of the vapour flux are also encouraging: their empirical coefficient is larger at Resolute (1.47) than elsewhere (1.26), probably because Resolute is a windy place. An accounting of the water balance reveals gross discrepancies between inputs (precipitation) and outputs (evaporation and discharge). A small numerical allowance for unrecorded trace precipitation does not come near to removing the disparity, which is such that on average outputs exceed measured inputs by 400 percent. Most of the disparity must be attributed to underestimation of precipitation, which is thus about four times greater than has been supposed in this "arid" locality. Measurements of sediment concentration in the Mecham River suggest that, if the amount of water in hydrologic cycle has been underestimated, so too has its effectiveness as a geomorphic agent. Having a gentle slope and a coarse-grained channel bed, the Mecham River carries little bed load, but its suspended sediment load is comparable with those measured in compared physiographic and lithologic situations at lower latitudes. The largest fraction of its sediment load is made up of dissolved Ca, Mg and HCO3. In comparison with warmer waters draining better-vegetated carbonate terrains, the Mecham waters have low solute concentrations, though the solute load is by no means negligible. Average Ca concentrations in the Mecham River and its basin are those which would be expected (allowing for an inverse relationship with discharge) in waters at equilibrium with atmospheric CO2 and near saturation with respect to calcite. Even moderate admixtures of biogenic CO2 can be shown to increase the aggressivity of these High Arctic waters towards calcite, and the notion that more limestone is dissolved at lower temperatures (sc., in cold periglacial regions) can now be considered dispelled. Doctor of Philosophy (PhD)
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