Developing management tools for hydrogelogic risks: from historic analysis to emergency plans

The IRPI-National Research Council of Turin and Regione Lombardia of Milan, since 1998, have carried out some studies for the identification of flood-prone areas along river courses with the final aim to reassess the town plannings of the municipalities located on the valley bottoms. In these studies many municipal territories were examined in the Valle Staffora, Valsassina, Valseriana, Val Camonica and also along the Lombardy shore of Lago Maggiore: in this last case the study has been preparatory to develop a hydrogeological risk management system. The critical flood-prone areas were identified using historical investigation and morphological analysis. Initially a detailed historical investigation was performed to produce a chart of the most frequently damaged sites. This was achieved by visiting various flood sites, State technical office archives (Ministry of Public Works, Hydrographical Offices of the Po River, Civil Engineers, Record Office), public libraries, local and national newspapers and municipal archives. Thousands of historical documents on past floods were collected, selected and validated to map the most vulnerable sites. A geomorphological analysis was successively carried out: multi-temporal aerial photographs were analysed and field survey conducted to verify the reliability of the historical data, the survey planform changes of the rivers and to identify the critical hydraulic conditions on the valley bottoms. From the results of the historical and morphological analyses a floodprone area map was obtained and two strips with different hazard along the rivers were identified. The third step was a review of the town plans. Aerophotogrammetric and cadastral maps were used to verify and update the urban planning of the municipalities studied. Eight categories of land-use destinations formed the mosaic map of the urban plans. These were divided into four classes based on vulnerability exposure values, measured using the following parameters: a) presence or concentration of people in the 24 hours or in particular hours of the day; b) presence of machineries or properties; c) presence of social-recreational activities and/or loss of profit due to damage to the agricultural zones; d) presence of environmentally attractive areas. On a matrix, the four classes were matched to flood hazard sites of the two strips: the resulting "criticality map" singles out five classes of different critical levels. 80 Based on these results, emergency plans for each municipality located along Lombardy shore of Lago Maggiore were drafted and a risk scenario, related to the alert thresholds, was hypothesized. An intervention model was therefore designed, which details emergency procedures for the crisis units of the local Civil Protection, under the coordination of the Mayors of the affected municipalities.