Abstract
This paper describes the hydrogeological hazard in a reach of Quebrada de Humahuaca, (Upper Valley of Rio Grande de Jujuy, in the Argentine Andes), elected a World Heritage Site by UNESCO in 2003. Along the Quebrada, the Rio Huasamayo, flowing into the Rio Grande, formed a large alluvial fan where the village of Tilcara was built. The final reach of Rio Huasamayo is an artificial channel, embanked by unconsolidated material removed from the riverbed. The village is located in an area at a lower elevation with respect to the riverbed, still in aggradation; so it is affected by an evident hydrogeological hazard. The main cause of the riverbed aggradation is the enormous sediment supply from the slopes of the Rio Huasamayo basin. The aim of the paper is to estimate the soil loss on the slopes and the consequent sediment supply to the main stream, identifying the areas of the basin mostly affected by erosion processes that cause the aggradation of the Rio Huasamayo riverbed. In this case, due to the lack of hydrometeorological stations (monitoring rainfalls, temperature, flow rates, etc.), soil loss and sediment supply to the main stream cannot be estimated through the application of commonly used models in the literature (e.g., USLE, RUSLE, USPED). Here the Gavrilovic method (EPM) was applied in combination with the data of the CORINE Project, allowing the estimation of the volume of material exiting from the catchment. So the main supplying areas (sub-basins of the Rio Huasamayo) can be identified where focused interventions for the control of solid transport could be realized, to mitigate the process of riverbed aggradation.
Highlights
The study of the sediment yield/supply from the slopes is very important because it has implications for flood hazard—if the volume of sediment exceeds the stream power, the aggradation of the riverbed and the raising of the free surface of the water occur
Project [27], the volume of material produced by the Rio Huasamayo basin was estimated and the main areas that constitute the source of this material were identified, that is, characterized by greater erosion
The Soil Erosion Index (SEI) was determined taking into consideration the geological map “Ciudad de Libertador General San Martin, 2366-IV”, in scale 1:250,000 and the respective explanatory notes [72], as well as the observations made in the field and from aerial photos by the authors
Summary
The study of the sediment yield/supply from the slopes is very important because it has implications for flood hazard—if the volume of sediment exceeds the stream power, the aggradation of the riverbed and the raising of the free surface of the water occur. The correlation between morphological changes in riverbeds, processes of aggradation or degradation and consequent changes in water levels is widely debated and demonstrated, for events with a high return period [3,4,5]. A detailed knowledge of sediment production (both in terms of supplying areas and in quantitative terms) is important to correctly define the conditions of hydrogeological hazard and risk in mountain environments
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