In the Carrara Marble Basin (CMB, Apuan Alps) quarrying has accumulated widespread and thick quarry waste, lying on steep slopes and invading or blocking valley bottoms. The Apuan Alps area is one of the rainiest in Italy and intense rainfall events often cause flood and landslides (mainly soil slips and debris flows): on September 2003 a heavy 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 and complexity. 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 the characteristics of rainfall inducing debris flows, may be effective in assessing landslide hazard and planning warning systems. Therefore, a detailed analysis of the main rainfall events from 1950 to 2005 was carried out, comparing their characteristics (cumulative rainfall, rainfall duration and intensity) with the occurrence of debris flows, obtained by several sources: technical and scientific reports, archives of local Municipal Administrations, Civil Protection Service of the Massa-Carrara Province and fire brigades, newspapers, and information provided by residents and quarry workers. Rainfall data were collected by three rain gauges: Carrara (90 m a.s.l.), Fossacava (670 m a.s.l.), and Rifugio Belvedere (1261 m a.s.l.). The rainfall events investigated were subdivided into two groups: events that induced debris flows, and events that did not. This dataset was fitted using a generalization of the widely used method of logistic regression for binary outcomes. This method allows at defining a set of empirical thresholds, corresponding to a different probability of occurrence of failure; consequently, different warning levels may be defined. The rainfall thresholds were defined in terms of mean intensity I, rainfall duration D, and normalized using the mean annual precipitation. The thresholds obtained in this work were compared with those proposed for some areas of north-western Tuscany and Eastern Liguria, finding that the rainfall thresholds for quarry waste may often be lower than those obtained for natural slopes. These thresholds were also compared with global curves proposed by various authors. Finally, the rainfall thresholds obtained for the CMB were validated using rainfall events occurred between 2010 and 2011, obtaining promising results.
Probabilistic rainfall thresholds for triggering debris flows in the Carrara Marble Basin (Tuscany)
GIANNECCHINI, ROBERTO;GALANTI, YURI;D'AMATO AVANZI, GIACOMO ALFREDO;BARSANTI, MICHELE
2013-01-01
Abstract
In the Carrara Marble Basin (CMB, Apuan Alps) quarrying has accumulated widespread and thick quarry waste, lying on steep slopes and invading or blocking valley bottoms. The Apuan Alps area is one of the rainiest in Italy and intense rainfall events often cause flood and landslides (mainly soil slips and debris flows): on September 2003 a heavy 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 and complexity. 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 the characteristics of rainfall inducing debris flows, may be effective in assessing landslide hazard and planning warning systems. Therefore, a detailed analysis of the main rainfall events from 1950 to 2005 was carried out, comparing their characteristics (cumulative rainfall, rainfall duration and intensity) with the occurrence of debris flows, obtained by several sources: technical and scientific reports, archives of local Municipal Administrations, Civil Protection Service of the Massa-Carrara Province and fire brigades, newspapers, and information provided by residents and quarry workers. Rainfall data were collected by three rain gauges: Carrara (90 m a.s.l.), Fossacava (670 m a.s.l.), and Rifugio Belvedere (1261 m a.s.l.). The rainfall events investigated were subdivided into two groups: events that induced debris flows, and events that did not. This dataset was fitted using a generalization of the widely used method of logistic regression for binary outcomes. This method allows at defining a set of empirical thresholds, corresponding to a different probability of occurrence of failure; consequently, different warning levels may be defined. The rainfall thresholds were defined in terms of mean intensity I, rainfall duration D, and normalized using the mean annual precipitation. The thresholds obtained in this work were compared with those proposed for some areas of north-western Tuscany and Eastern Liguria, finding that the rainfall thresholds for quarry waste may often be lower than those obtained for natural slopes. These thresholds were also compared with global curves proposed by various authors. Finally, the rainfall thresholds obtained for the CMB were validated using rainfall events occurred between 2010 and 2011, obtaining promising results.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
