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Revista de la Asociación Argentina de Sedimentología

versión impresa ISSN 1853-6360


MILANA, Juan Pablo. Predicción de caudales de ríos alimentados por deshielo mediante balances de energía: Aplicación en los Andes Centrales, Argentina. Rev. Asoc. Argent. Sedimentol. [online]. 1998, vol.5, n.2, pp.53-69. ISSN 1853-6360.

The prediction of fluvial discharges has two different interests, the first one is related to the forecast of the volume of water available for human consumption while the second is related to the geological importance of moving water: erosion, transport and deposition of sedimentary materials. With these interests in mind, the way the Arid Andes rivers compose their discharges is analyzed here. In times of maintained draughts, almost 80% of the fluvial discharges of these rivers could be supported by the few glaciers present. Thus the model was directed, in this first stage, to the estimation of the glacier water production by the employment of energy balance models. These models estimate the amounts of energy absorbed and reflected by the glacier surface. The absorbed energy is almost entirely used in melting ice, as the temperature of the surface cannot increase. The variable employed in the model are simple meteorological parameters, easy to measure in the field. This model was applied to the simulation of the discharge of the Río Colorado, tributary of the Los Patos river, during several days in March. To check out  the model, detailed measurements of the discharges were made at different points of this pilot basin. The "Glaciar" station was located almost at the glacier front (3900 m high), and besides discharge, hourly measurements of meteorological parameters were taken. Two other gauge stations were installed in intermediate and distal ports of the main drain of the basin, measuring simultaneously each hour during five days. A first sight of the data allowed to recognize that the discharge function is quite similar in shape to the energy balance function, although they are displaced in time Both theoretical and empirical methods were employed to simulate the discharge. In the theoretical method, the calculated energy was distributed by the area occupied by glaciers, taking into account an energy gradient with height, following gradients of temperature and pressure. Two different models were tried, by assuming different ways of absorbing the energy of the daily positive peaks. The second model, showed to be more realistic and although it cannot simulate the shape of the discharge curve, estimates quite well the amount of daily melt water produced by the glacier as measured at the glacier front. However, a underestimation occurs for the other stations, fact ascribed to the not inclusion in the model of 1) an algorithm simulating melting in debris covered ice bodies, and 2) an algorithm taking into account the orientation of the slopes. The good results suggest that this method has application to know the hydrologic contribution of a glacier, without the need of field measurements. The empirical model, based in composite regression analysis between energy and discharge, shows to be much better predictor of discharges, as it can simulate quite well the shape of the water wave generated daily by melting. Although the errors at the glacier front gauge average 25%, at the other gauges is between 3% and 4%, indicating that the method increases confidence when a group of glaciers is included in the simulation, even in flood conditions (discharge can duplicate during the day because the melt-water wave). These results suggest that energy-balance methods are useful tools to forecast fluvial discharges in these Andean rivers, for socio-economic purposes, as well as to use them as algorithms to simulate rates of erosion or sediment transport in different geological situations.

Palabras clave : Fluvial hydrology; Climate; Discharge.

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