Abstract:River flow from glacierized areas in the Himalaya is influenced both by intra-annual variations in precipitation and energy availability, and by longer term changes in storage of water as glacier ice. High specific discharge from ice melt often dominates flow for considerable distances downstream, particularly where other sources of runoff are limited, providing a major water resource. Should Himalayan glaciers continue to retreat rapidly, water shortages might be widespread within a few decades. However, given the difference in climate between the drier western and monsoonal eastern ends of the region, future warming is unlikely to affect river flow uniformly throughout.A simple temperature-index-based hydro-glaciological model, in which glacier dimensions are allowed to decline through time, has been developed with a view to assessing, in data-sparse areas, by how much and when climate warming will reduce Himalayan glacier dimensions and affect downstream river flows. Two glaciers having the same initial geometries were located (one each) in the headwaters of two identical nests of hypothetical catchments, representing contrasting climates in the west and east of the region. The hypothetical catchments were nested such that percentage ice cover declined with increasing basin area. Model parameters were validated against available but limited mass-balance and river flow measurements. The model was applied for 150 years from an arbitrary start date (1990), first with standard-period climate data and then with application of a 0Ð06°C year 1 transient climatic warming scenario.Under this warming scenario, Himalayan rivers fed by large glaciers descending through considerable elevation range will respond in a broadly similar manner, except that summer snowfall in the east will suppress the rate of initial flow increase, delay peak discharge and postpone eventual disappearance of the ice. Impacts of declining glacier area on river flow will be greater in smaller and more highly glacierized basins in both the west and east, and in the west, where precipitation is scarce, for considerable distances downstream.  Crown

ABSTRACT. Two components of discharge through the internal hydrological systems of Alpine glaciers were separa ted on the basis of chemical composition of water. Some surface melt waters reta in low solute contents after fl owing without delay through conduits in whi ch no chemical enrichment occurs, whereas those flowing slowly at the glacier b ed h ave increased io ni c concentrations. A simple mixing m odel was used to investigate te mporal variations in the quantities ofw a le r routed through each of the two sub-sys tems. Electrical conductivity was taken as an indicator of melt-water composition and was monitored fo r p e riods during the summer ablation season of 1975 at Gornergletscher and of 1977 at Findelengletscher. At both g laciers, conduct ivity of melt waters varied diurna ll y inversely with discha rge flu ctuations, depending o n the proportion of tota l discharge routed through the two sub-syste ms. TOlal discharge and the flow component routed rapid ly through conduits within the glacier, a large proportion (50-80% ) of total discharge, exhibited in-phase rhythmi c diurnal hydrogra phs at the two glaciers. Distinctive subglacial hyd rologi cal reg imes are contrasted. At Findelengletschcr, the hydrographs of total discharge and of subglacial chemically enriched flow were in phase. At Gornergletscher, the subglacial hydrogra ph occurred with reverse asymm etry and out of phase. A possible interpretation is that water was tempo ra rily stored in basal cavities during high total discharge. During the night, stored water was released, contributing much of the total discharge at times of low fl ow. RESUME . D etermination quantitative de l'hydrologie sous-glaciaire de deux glaciers alpins. Les deux composantes du debit a trave rs le reseau hydrologique interne de glaciers alpins ont ete distinguees sur la base de la composition chimique des eaux. Quelques eaux de fusion d e surface n'ont qu'un e fa ible teneur e n matiere dissoute a pres avoir coule sa ns reta rd dans des cheneaux ou il n'y a pas d'enrichissement chimique, tandis que celles qui ont coule lentement le long du lit du glacier ont accru leur concentration en ions. Un. simple modele de melange a servi pour rechercher les va riations dans le temps des quantites d'eau empruntant l' un des deux sous-resea u x. La conductivite electrique fut choisie comme indi cateur de la composition de I'eau d e fusion et fut surveillee pour des p eriod es de la sa ison es tiva le d'a bla tion d e 1975 a u Gornergletscher et de 1977 a u Findelengle tscher. Sur les d eux glaciers, la conductivite des eaux de fusion variait journelle m e nt en raison inverse des debits selon la proportio n du debit total transitant da ns les deux sous-reseaux. Le debit tota l et la co mposa nte de l'ecoul ement empruntan t rapidement le reseau intra-glaciaire, une large part (50-80% ) du d e b it tota l, montre pour les deux glaciers des hydrogrammes quotidiens rythmes e n phase. L es regimes hydro logiqu es sous-glaciaires distincts sont opposes. Au Findelengletscher, les ...

Suspended-sediment concentrations in melt waters from the Gornera, Gornergletscher, Switzerland, were determined at hourly intervals for periods during the ablation seasons of 1974 and 1975. Rapid erratic fluctuations of suspended-sediment concentration produced peaks which occurred both before and after highest daily flows. Clockwise daily hysteresis rating loops between sediment concentration and discharge included many involutions. Suspended-sediment-concentration-discharge rating curves were different for rising and falling limbs of individual diurnal hydrographs and varied from day to day. Close-interval measurements of sediment concentration and discharge records allow interpretation of the nature of ice–water–sediment interactions at the bed of an Alpine glacier. At Gornergletscher, subglacial sediment is delivered to melt waters flowing in the smaller basal conduits, which often change course suddenly, entraining unworked sediment stored at the bed. During diurnal discharge maxima, sediment concentration in the Gornera is reduced because the rate of increase of water volume outstrips the rate of supply of sediment. The drainage of the ice-dammed lake Gornersee, producing exceptionally high flows, extended the drainage network over large areas of the glacier bed, and evacuated much sediment.

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