The paper describes the geologic-hydraulic risk affecting the Quebrada de Humahuaca (Upper Valley of Rio Grande de Jujuy, in the Argentine Andes) elected World Heritage Site by UNESCO. The basin of Quebrada (6615 km2) extends in N-S direction, parallel to the main geological structures of the Cordillera Oriental. The difference in altitude is >4500 m; the riverbed, of braided type, is entrenched in a narrow valley with an average gradient of 19%. The tectonic lifting, still in progress, is the mean responsible for erosion and mass transport processes, favored by subarid climatic conditions (scarce rainfalls, concentrated in a few but intense events) and the outcrop of quaternary clastic rocks covering the precambrian-mesozoic metamorphic bedrock. These sediments, produced in periods wetter than present, are degradable and easily removable by fluvial erosion and debris flows triggering during intense meteoric events. Along the Quebrada, the Rio Huasamayo, flowing into Rio Grande, formed a large alluvial fan where the village of Tilcara was built. The final stretch of Huasamayo is an artificial channel, embanked by loose material got from the riverbed. The village is located at lower altitudes with respect to the hanging riverbed (still in aggradation), so affected by evident hydraulic risk. Recently, to solve the problem, the deviation of Huasamayo before the village was proposed, building an artificial channel working as drainage channel. The preservation of Tilcara, however, would not reduce the hydraulic risk, which would only be transferred downstream the Quebrada, towards the village of Maimarà. The alternative solution proposed here is to intervene at the origin of the problem: by applying the method proposed by Gavrilovic and using the CORINE Project data, the volume of material exiting from Huasamayo basin was estimated, identifying the main feeding areas where focused interventions for the control of solid transport could be realized. Another risk for Tilcara consists in the triggering of debris flows on the slopes of the Cordon de Alfarcito which often invade the village (the last event, here described, occurred in March 2017). Even here, it is proposed the building of defense works, to mitigate the debris flow risk in Tilcara.
Risk management in the Quebrada de Humahuaca (province of Jujuy, northwestern Argentina: Rio Huasamayo and Tilcara area
POGGETTI, EMILIOWriting – Original Draft Preparation
;PAGLIACCI, ALESSANDROMembro del Collaboration Group
;Cencetti C.
Writing – Original Draft Preparation
;De Rosa P.Writing – Original Draft Preparation
;Fredduzzi A.Writing – Original Draft Preparation
2018
Abstract
The paper describes the geologic-hydraulic risk affecting the Quebrada de Humahuaca (Upper Valley of Rio Grande de Jujuy, in the Argentine Andes) elected World Heritage Site by UNESCO. The basin of Quebrada (6615 km2) extends in N-S direction, parallel to the main geological structures of the Cordillera Oriental. The difference in altitude is >4500 m; the riverbed, of braided type, is entrenched in a narrow valley with an average gradient of 19%. The tectonic lifting, still in progress, is the mean responsible for erosion and mass transport processes, favored by subarid climatic conditions (scarce rainfalls, concentrated in a few but intense events) and the outcrop of quaternary clastic rocks covering the precambrian-mesozoic metamorphic bedrock. These sediments, produced in periods wetter than present, are degradable and easily removable by fluvial erosion and debris flows triggering during intense meteoric events. Along the Quebrada, the Rio Huasamayo, flowing into Rio Grande, formed a large alluvial fan where the village of Tilcara was built. The final stretch of Huasamayo is an artificial channel, embanked by loose material got from the riverbed. The village is located at lower altitudes with respect to the hanging riverbed (still in aggradation), so affected by evident hydraulic risk. Recently, to solve the problem, the deviation of Huasamayo before the village was proposed, building an artificial channel working as drainage channel. The preservation of Tilcara, however, would not reduce the hydraulic risk, which would only be transferred downstream the Quebrada, towards the village of Maimarà. The alternative solution proposed here is to intervene at the origin of the problem: by applying the method proposed by Gavrilovic and using the CORINE Project data, the volume of material exiting from Huasamayo basin was estimated, identifying the main feeding areas where focused interventions for the control of solid transport could be realized. Another risk for Tilcara consists in the triggering of debris flows on the slopes of the Cordon de Alfarcito which often invade the village (the last event, here described, occurred in March 2017). Even here, it is proposed the building of defense works, to mitigate the debris flow risk in Tilcara.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
