High resolution mapping for the management of the fluvial dynamics in intensely urbanized areas

Category Sedimentology
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Morelli, Stefano; Segoni, Samuele; Kukavicic, Minja; Catani, Filippo
Holding Date 08 September 2008

Most of the areas contiguous to rivers are subjected to a constant hydraulic risk and show the presence of a number of elements having different vulnerability in relation to ordinary (normal evolution) or extraordinary (floods) events of fluvial dynamics. This is especially true for European rivers, where the human presence is widespread and strongly interconnected with the environment.
This contribution reports on an extensive high-resolution GPS mapping survey that has been carried out over the entire course of the Arno river within the Florence Province (spanning 62km on each river bank) using the RTK modality of measurement. This topographic survey was mainly performed to create a GIS database containing all the natural, urban, hydrological and morphological elements around the Arno to provide local public administrations with an helpful tool for managing hydrological risk, hydraulic policy and urban planning. The geodatabase includes artificial and natural elements such as railways, roads, buildings, assets, bridges, administrative boundaries, hydraulic works, drainage outlets, dikes, hydro-morphological elements (such as bars or eroding banks) and so on. All the mapped elements are georegistered and provided with alphanumerical attributes, including the present preservation condition for man-made objects, in order to plan ordinary and extraordinary maintenance works. The spatial location of the elements is very accurate (less than ±5cm error both as geographic coordinates and geoid height), with special attention to the accurate positioning for all the elements of flood containment, both natural (riverbank line) and artificial (dikes or walls).
Such a complete and accurate database contains all the elements connected with the fluvial dynamic and with the hydraulic risk and will provide very accurate topographic and geometric data to be used in hydrological models. Moreover, realistic assessments concerning hydraulic risk and flood inundation using numerical models cannot be obtained using a simple comparison between modelled heights and geometrical constraints (as currently happens in the Arno river), but should also include an evaluation of the geotechnical stability of the dykes, most of which have been built using heterogeneous materials in the first half of the last century. For this reason, the database has been integrated with geotechnical analyses and numerical modelling carried out on test sites along the river course in order to establish a preliminary assessment of the criteria to evaluate dikes stability at large scale. The proposed methodology can be easily and quickly extended to other rivers as well and could provide in the near future a first attempt at integrating geotechnical dikes stability schemes into hydrological models for the prediction of flood risk.