Rainfall induced debris flows in pyroclastic deposits, Campania (southern Italy)

• Published in: Engineering geology Vol. 75; no. 3; pp. 263 - 289
• Main Authors: Fiorillo, Francesco, Wilson, Raymond C.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.11.2004; Elsevier
• Subjects: Applied sciences; Buildings. Public works; Campania; Debris flow; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Exact sciences and technology; Geotechnics; Italy; Natural hazards: prediction, damages, etc; Rainfall; Soil mechanics. Rocks mechanics; Threshold pyroclastic; Water effect, drainage, ground water lowering, filtration; Campania; Italy; Europe; Rainfall; Italy; Debris flow; Campania; Threshold pyroclastic; Storm; Statistical analysis; Hydraulic model; Rock mechanics; Geology; Site analysis; Soil moisture; Pyroclastic rock; Mechanism analysis; Rainfall rate; Hydrology; Pore pressure; Rain water; Landslide; Debris; Geotechnics
• ISSN: 0013-7952; 1872-6917
• DOI: 10.1016/j.enggeo.2004.06.014

A combination of empirical and physically based hydrological models has been used to analyze historical data on rainfall and debris-flow occurrence in western Campania, to examine the correlation between rainfall and debris-flow events. Rainfall data from major storms recorded in recent decades in western Campania were compiled, including daily series from several rain gauges located inside landslide areas, supplemented by hourly rainfall data from some of the principal storms. A two-phase approach is proposed. During phase 1, soil moisture levels have been modelled as the hydrological balance between precipitation and evapotranspiration, on a daily scale, using the method of Thornthwaite [Geograph. Rev. 38 (1948) 55]. Phase 2 is related to the accumulation of surplus moisture from intense rainfall, leading to the development of positive pore pressures. These interactions take place on an hourly time scale by the “leaky barrel” (LB) model described by Wilson and Wiezoreck [Env. Eng. Geoscience, 1 (1995) 11]. In combination with hourly rainfall records, the LB model has been used to compare hydrological effects of different storms. The critical level of retained rain water has been fixed by the timing of debris-flow activity, related to recorded storm events. New rainfall intensity–duration thresholds for debris-flow initiation in western Campania are proposed. These thresholds are related to individual rain gauge and assume a previously satisfied field capacity condition. The new thresholds are somewhat higher than those plotted by previous authors, but are thought to be more accurate and thus need less conservatism.