In the Carrara Marble Basin (CMB, Apuan Alps, Italy) quarrying has accumulated widespread and thick quarry waste, lying on steep slopes and invading or damming valley bottoms. The Apuan Alps area is one of the rainiest in Italy and rainstorms often cause floods, landslides and debris flows: on September 2003 a rainstorm hit the CMB, inducing more than 500 slope failures and causing damage and casualties. The stability conditions of quarry waste are difficult to assess, owing to its textural, geotechnical and hydrogeological variability. The waste mainly includes boulders and cobbles, together with a matrix formed of a mixture of sand, silt and clay. Therefore, an empirical approach, basing on properties of rainfall able to trigger debris flows, may be effective in assessing landslide hazard and planning warning systems. Aiming at defining the critical rainfall thresholds in the CMB, a detailed analysis of the main rainstorms was carried out. The hourly rainfall recorded by three rain gauges from 1950 to 2005 was analysed and compared with the occurrence of debris flows. Critical threshold curves were defined in terms of duration, intensity, cumulative rainfall and normalized by the mean annual precipitation. The curves were obtained applying statistical techniques (logistic regression) in order to separate rainfall events which trigger debris flows from events that do not. The curves obtained for the CMB were compared with the threshold curves proposed for surrounding areas, finding that the rainfall thresholds for quarry waste can often be lower than those obtained for natural slopes. These curves were also compared with global curves proposed by various authors. Finally, the rainfall thresholds obtained for the CMB were validated using rainfall events occurred in 2010 and 2011, obtaining encouraging results.
Critical rainfall thresholds for triggering debris flows in a human-modified landscape: the case of Carrara Marble Basin (Italy)
GIANNECCHINI, ROBERTO;GALANTI, YURI;D'AMATO AVANZI, GIACOMO ALFREDO;BARSANTI, MICHELE
2013-01-01
Abstract
In the Carrara Marble Basin (CMB, Apuan Alps, Italy) quarrying has accumulated widespread and thick quarry waste, lying on steep slopes and invading or damming valley bottoms. The Apuan Alps area is one of the rainiest in Italy and rainstorms often cause floods, landslides and debris flows: on September 2003 a rainstorm hit the CMB, inducing more than 500 slope failures and causing damage and casualties. The stability conditions of quarry waste are difficult to assess, owing to its textural, geotechnical and hydrogeological variability. The waste mainly includes boulders and cobbles, together with a matrix formed of a mixture of sand, silt and clay. Therefore, an empirical approach, basing on properties of rainfall able to trigger debris flows, may be effective in assessing landslide hazard and planning warning systems. Aiming at defining the critical rainfall thresholds in the CMB, a detailed analysis of the main rainstorms was carried out. The hourly rainfall recorded by three rain gauges from 1950 to 2005 was analysed and compared with the occurrence of debris flows. Critical threshold curves were defined in terms of duration, intensity, cumulative rainfall and normalized by the mean annual precipitation. The curves were obtained applying statistical techniques (logistic regression) in order to separate rainfall events which trigger debris flows from events that do not. The curves obtained for the CMB were compared with the threshold curves proposed for surrounding areas, finding that the rainfall thresholds for quarry waste can often be lower than those obtained for natural slopes. These curves were also compared with global curves proposed by various authors. Finally, the rainfall thresholds obtained for the CMB were validated using rainfall events occurred in 2010 and 2011, obtaining encouraging results.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
