GIS instruments and high resolution DTM to define risk flood areas

The Plan of Basin is the tool used by Italian Authority of Watershed to guarantee the hydraulic safety, the correct use of the water resource and the guardianship and management of Italian field. Particularly a detailed program for the flood defence contains the delineation of flooding risk areas and the actions to reduce the hazard to human life and the damages when a catastrophic flood event occurs. For these aim hydrodynamic studies has been carried out along the major rivers of Basilicata Region, in order to create flooded area maps. The present work shows GIS applications as instruments to support a more correct definition of flooding risk areas. The study area is Basento River in southern Italy and the software used for the hydrodynamic simulations are: Hec Ras (for mono dimensional studies) developed by the Hydrologic Engineering Centre; MIKE Flood developed from Danish Hydraulic Institute for bidimensional study in coastal plain. The river cross sections are obtained by grounded topographic relief in the first case, by laser scanned data in the second one. The GIS has been used either as input or as output of the hydraulic modelling. In the first case it has allowed to integrate the information about planimetric development of river and grounded cross sections through a detailed DTM (Digital Terrain Model). In the second one, the water surface elevation and top width achieved in riverbeds, for each hydrodynamic simulation, has been used with GIS software to draw the different flooded area maps. In particular differences between the results obtained using an automatic interpolation of cross sections with the HecRas tool and those obtained using river cross sections extracted by DEM are been evidenced. For the coastal plain, with the use of laser scanning techniques is possible apply bi-dimensional hydrodynamic model with accuracy data and more correct to describe the hydrodynamic motion on flat areas.