Evaluation of debris flow hazard to Chalala village, Quebrada de Humahuaca UNESCO World Heritage Site, Jujuy Province, Argentina

摘要

Chalala village is situated on the alluvial fan of Quebrada Chalala that is periodically affected by extensive debris flows. Servicio Geologico Minero Argentino (SEGEMAR) sought to establish the magnitude and frequency of debris flows from unmonitored Chalala basin. Analysis of historical records, oral accounts, and investigations of debris flow deposits and surveys of two debris flows in 2007 assigned Chalala and adjacent Coquena fans to high frequency and large magnitude ratings in semi-quantitative hazard rating schemes. Two methods were used to estimate the volume of the maximum likely debris flow for the purposes of debris-flow-defence design and hazard evaluation. Method one extrapolated known peak discharge/total volume relationships using a power relationship for debris (mud) flows displaying similar rheology. Method 2 involved extrapolation of known extreme sediment yield values. The methods yielded comparable results for the two basins. The method 2 estimate of 4.6×10{sup}5m{sup}3 is consistent with geomorphic and stratigraphic investigations and eyewitness accounts of events over the past 62 years. An additional uncertainty coefficient of 1.2 is recommended.