S Pagliara

Department of Civil Engineering, University of Pisa, Pisa, Italy

Abstract. Aim of the work is to present examples of flood risk management and mitigation in central Italy. Many studies have been conducted in this region in order to cope with flood risk. Different aspects are still open, particularly, for rivers and tributaries that pass through highly urbanized areas where the risk management and its mitigation could be complex. The work analyses interesting case studies of complex river basins in which the hazard maps are derived from many assumptions and in which a temporal evolution of the flood is connected with the presence of civil protection plans.

The case of the Camaiore River and its tributaries will be analyzed together with the case of the area enclosed between the Arno and the Bisenzio rivers. The last part of the paper will deal with the mitigation measures that can be foreseen in order to diminish the risk.

Keywords: Flood risk, mitigation, flood defense, flood management 1. Introduction

Flooding of urban areas is a frequent disaster (Yen, 1995). In Italy, a large amount of work has been done in order to cope with floods in the last 20 years. With the national law n.183/1989 the concept of river security at a basin level has been introduced. Further, the flood disasters in Tuscany with the Versilia River (1996), in Campania with the Sarno River (1998) and in Calabria at Soverato in the year 2000 have focussed attention on the necessity for developing specific master plans regarding the hydraulic risk for the whole nation. In this sense, many River Basin Authorities have approved a master plan of the structural and non-structural measures to reduce the hydraulic risk and the Hydro-geological Asset Plan (P.A.I.).

The P.A.I. today represents the synthesis of the knowledge sharing among all the stakeholders involved in the government and in land manage -ment issues. Actually, in Italy the acceptable risk level corresponds to a flood with a return period Tr = 200 years and the P.A.I. must contain the flood risk maps for different return period up to 500 years.

* To whom correspondence should be addressed. e-mail: [email protected]

In Tuscany, all the River Authorities, both regional and national, have approved the P.A.I. with major consequences for urban planning and the urbanization process. In fact, the norms connected with the P.A.I. foresee considerable limitations of the urbanization process depending on the specific risk level of the area.

1.1. ZONING OF THE HYDRAULIC HAZARD

The hazard maps are different according to the different river basin authorities. In mapping the hydraulic hazard the Arno River Authority distinguishes between four levels:

(a) Very high hydraulic hazard (PI4): covering areas flooded with return period Tr < 30 years with water depths h > 30 cm

(b) High hydraulic hazard (PI3) covering areas flooded with return period Tr < 30 years with water depths h <30 cm and areas flooded with return period 30 < Tr < 100 years with water depths h > 30 cm

(c) Medium hydraulic hazard (PI2) covering areas flooded with return period 30 < Tr < 100 years with water depths h <30 cm and areas with flooded for 100 < Tr < 200 years

(d) Low hydraulic hazard (PI1) covering areas flooded with events that have a return period of 200 < Tr < 500 years

Regional river basin Authorities have chosen a different hazard classification, dividing the flood prone territory into three zones:

(a) Areas with very high hydraulic hazard level (PIME): corresponding to areas flooded by the flood with a return period of 30 years

(b) Areas with high hydraulic hazard level (PIE): corresponding to areas flooded by the flood with a return period of 200 years

(c) Areas with low hydraulic hazard level

The mapping of hazardous areas is the main output of the work and it is important because it involves laws and regulations that deeply interact with the life of the territory. In fact, each of the areas involved in the PAI is subjected to building restrictions and rules for flood protection.

The aim of the present work is to analyze selected cases of flood prone areas and mitigation measures in river basins located in the Tuscany region.

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