PERICOLOSITÀ CONNESSA A PROCESSI ALLUVIONALI IN AREE PEDEMONTANE: IL CASO DI CASTELLAMARE DI STABIA IN PENISOLA SORRENTINA

Abstract

A study of the geomorphological hazard due to alluvial processes in a sample area of Surrentine Peninsula was carried out. This was
done by the reconstruction of the short term geomorphological evolution analysis, by collection of historical data and by reconstruction of urban development.
Although the selected area is quite small, its geomorhological, topographical and urban features are very similar to those of other
zones of Campania region; in fact some portions of the urban area are built on holocenic alluvial fans systems. For these reasons, it
can be considered a representative ”sample area” in which the geomorphological hazard conditions due to alluvial processes in piedmont areas can be outlined.
The studied area is located in the piedmont area of Lattari mounts which is characterized by the presence of coalescent and entrenched alluvial fans systems. The oldest fans system are middle Pleistocene in age while the youngest are Holocene and have been active till historical times. This paper focuses its attention to the definition of hazard conditions of the youngest generation of fans.
The collection of historical data evidenced that several alluvial events have taken place in this sector of Surrentine Peninsula since the
end of 18th century. The reports are so detailed that it was possible to locate the damage for each event and in some cases to recognise the kind of damage; a “damage map” showing the zones affected by one or more alluvial events from 1764 to 1987 was thus produced. As the location of the damage of each alluvial event was based on historical topographic maps (1812, 1875, 1909, 1954 and
1990), the damage map also takes in account the urban development.
A morphometrical analysis of the hydrographic basins feeding the fans has been also carried out in order to define their concentration
time; basin area and media gradient, river length and media gradient, basin maximum , minor and media altitude have thus been calculated on a topographic map (1: 5.000 scale).
Although we do not have data on hourly precipitation, the minute description of historical reports allowed us to hypothesize that the studied alluvial events occurred in coincidence with isolated precipitation peaks concentrated in few hours.
The study thus evidences the high geomorhological hazard and risk conditions due to alluvial processes of the Castellammare urban
area. Unfortunately, the results obtained may concern many other urban areas of Surrentine Peninsula with similar geomorhological,
topographical and urban conditions. In these contexts the individuation of active fans together with a detailed historical research can
strongly contribute to a better definition of the areas of highest hazard and risk.