Abstract
Abstract. For some decades, mass wasting processes such as landslides and debris floods have been threatening villages and transportation routes in the Rio Grande Valley, named Quebrada de Humauhuaca. One of the most significant examples is the urban area of Tilcara, built on a large alluvial fan. In recent years, debris flood phenomena have been triggered in the tributary valley of the Huasamayo Stream and reached the alluvial fan on a decadal basis. In view of proper development of the area, hazard and risk assessment together with risk mitigation strategies are of paramount importance. The need is urgent also because the Quebrada de Humahuaca was recently included in the UNESCO World Cultural Heritage. Therefore, the growing tourism industry may lead to uncontrolled exploitation and urbanization of the valley, with a consequent increase of the vulnerability of the elements exposed to risk. In this context, structural and non structural mitigation measures not only have to be based on the understanding of natural processes, but also have to consider environmental and sociological factors that could hinder the effectiveness of the countermeasure works. The hydrogeological processes are described with reference to present-day hazard and risk conditions. Considering the socio-economic context, some possible interventions are outlined, which encompass budget constraints and local practices. One viable solution would be to build a protecting dam upstream of the fan apex and an artificial channel, in order to divert the floodwaters in a gully that would then convey water and sediments into the Rio Grande, some kilometers downstream of Tilcara. The proposed remedial measures should employ easily available and relatively cheap technologies and local workers, incorporating low environmental and visual impacts issues, in order to ensure both the future conservation of the site and its safe exploitation for inhabitants and tourists.
Highlights
In the area of Tilcara village (23◦34 55 S, 65◦23 50 W) there is an urgent need of debris flood hazard assessment and mitigation
Debris flood phenomena have been triggered in the tributary valley of the Huasamayo Stream and reached the alluvial fan on a decadal basis
The Tilcara alluvial fan has been built by the Huasamayo Stream, under arid environmental conditions, in a compressive tectonic context (Sancho et al, 2008)
Summary
In the area of Tilcara village (23◦34 55 S, 65◦23 50 W) there is an urgent need of debris flood hazard assessment and mitigation. Besides Tilcara, almost 20 villages are located along the valley, but the population is significantly decreasing, as a secondary consequence of the high frequency of mass wasting phenomena that cause relevant damage to structures and infrastructures, halting traffic on transportation routes These mass movements threaten the farming activities, exploiting the terraces along the valley floor, with the effect of reducing the area of the land available for cultivation and the sustenance of the population. Landslides and debris floods are the main hazardous phenomena affecting the slopes and the valley floors, inducing serious consequences on the erosion and sedimentation activity of the Rio Grande (Chayle and Wayne, 1995; Cencetti et al, 2001; Cencetti, 2008) Most of these events occur on the Quaternary alluvial fans that are significant landforms within the Quebrada de Humahuaca landscape. The research activity includes geological and geomorphological investigations together with the analysis of social and economic aspects in order to assess the impact of mitigation measures on the urban environment
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