In recent years severe floods have occurred in several parts of Europe and particularly in Italy, both as localised flash floods and basin-wide floods on major river systems.

 

By their nature, floods are generated by the random coincidence of several meteorological factors but man’s use of river catchment, also, has an impact upon the severity and consequences of the event: practically, when the runoff exceeds the capacity of the drainage channels – rivers, creeks (in rural environment) and storm water channel (in the urban environment). Floods frequently cause loss of life, property damage and destruction, disruption of communication, transportation, electric and community services.

Their catastrophic effects are significantly increased with the rapid population growth which includes on hand a large urbanization and, on the other hand, the land misuses (e.g. deforestation and overgrazing). One of the output goals of flood damage reduction is to reduce environmental degradation caused by physical forces such as erosion. Erosion causes landslides, particularly in the upper part of the catchment river basin (e.g. rockfalls, landslides and avalanches, linear erosion channels, etc.) which occur, generally, in recent unconsolidated material with a shallow water table.

In the last decades, the Friuli Venezia Giulia region has experienced many floods (1965-1966, 1979, 1983, 1990, 1995, 1996, 2000 and 2003) due to heavy rainfall (e.g. 50 – 60 mmph); most of these cases occur where the hill slope (with very poor geological and geotechnical characteristics) is very steep. At the base of the hill slopes, the landslides material often accumulates in the form of talus slopes which may pose an additional risk in presence, for example, of torrent bed. It is obvious that in cases of heavy rainfall or rainstorm, the sudden flash flood can trigger phenomena such as debris and mud flows (15.000 – 20.000 m3/sqkm).

These may affect the hydraulic and hydrologic system and, consequently, the landscape, the infrastructures and the human activities. To deal with these phenomena and their effects, the management rural territory and irrigation Service of the Friuli Venezia Giulia Region for many years, with its own specialized staff, has developed soil bioengeineering techniques. The aim of reducing solid transport (about 30%) and, indirectly, the time of concentration (20 – 25%) of the catchment basin which is the basic factor influencing the floods. With the techniques mentioned above, the Service can take part in the consolidation of the slopes (with sodding, fascine bundle, fascine drain, wattle works, wattle system-honey-combed configuration, log cribwall with branch layers, etc.) and in the stabilization of the river beds (with longitudinal sills, longitudinal training walls, check dams, brush-rock works, etc.), reducing in such a way the flood risk, making use of natural elements such as vegetation, trees, stones, etc.

Prof. Sebastiano SANNA