| The Apuan Alps region is one of the rainiest areas in Italy (more than 3000 mm/year), in which frequently heavy and concentrated rainfall occurs. This
is particularly due to its geographical position and conformation: the Apuan
chain is located along the northern Tuscan coast, close to the Ligurian Sea,
and the main peaks reach almost 2000 m. In several cases, the storms that
hit the area have triggered many shallow landslides (soil slip-debris flows),
which exposed the population to serious risks (during the 19 June 1996
rainstorm about 1000 landslides were triggered and 14 people died). The
assessment of the rainfall thresholds is very important in order to prepare
efficient alarm systems in a region particularly dedicated to tourism and
marble activities.
With the aim of contributing to the landslide hazard evaluation of the
southern Apuan Alps territory (upper Versilia area), a detailed analysis of
the main pluviometric events was carried out. The data recorded at the main
rain gauge of the area from 1975 to 2002 were analysed and compared with the
occurrence of soil slips, in order to examine the relationship between soil
slip initiation and rainfall. The most important rainstorms which triggered
shallow landslides occurred in 1984, 1992, 1994, 1996, 1998 and 2000.
Many attempts were made to obtain a possible correlation between rainfall
parameters and the occurrence of soil slip phenomena and to identify the
local rainfall threshold for triggering shallow landslides. A threshold for
soil slip activity in terms of mean intensity, duration and mean annual
precipitation (MAP) was defined for the study area. The thresholds obtained
for the southern Apuan Alps were also compared with those proposed by other
authors for several regions in the world. This emphasized the high value of
the rain threshold for shallow landslide activity in the Apuan area. The
high threshold is probably also linked to the high mean annual precipitation
and to the high frequency of rainstorms. |