Recent Changes in Floodplain Urban Development and in Intense Rainfall Patterns: Evidence and Effects for the Reclamation Network in North-Eastern Italy

Abstract:

Within the wide approach of watershed management, the crucial role of floodplains in hydrological processes and runoff generation, in particular during flood events, is well known. The recent changes in land use and/or intense rainfall patterns associated to climate changes, however, add complexity to the analysis of the hydrologic response. This study investigates and displays evidences and effects of land use changes and climatic changes in a small floodplain area in the north east of Italy. As in other countries in Europe, over the past half-century, intense urban and agricultural land uses changed the drainage networks, causing serious hydraulic dysfunctions. In this work we focused the research on the network drainage density and storage capacity, considering that they are the main requirements for hydraulic infrastructures and that the storage of water is crucial for any water management strategy. The effects of the changes in the network parameters have been then further investigated using the Network Saturation Index (NSI) that quantifies how fast an area is saturated by a design rainfall and can give an idea of the delay of the watershed response respect to the rainfall peak. Over the past half-century, the study site witnessed a drastic reduction of the storage volume, resulting in shorter times for saturation especially for storm events having a shorter return period and for events that were less critical in the past. For our case study, climatic evidence shows that the rainfall regime is highly irregular, with intense events taking an increasing role in determining the total precipitation over the past half-century. Considering this climatic trend that cannot be controlled, our study suggests to carefully plan the changes in the drainage networks, as these changes might seriously constrain the functionality of the reclamation system, especially for rather frequent rainfall events not necessarily associated with extreme meteorological conditions or with the worst case scenarios.

Sofia, G., Prosdocimi, M., Dalla Fontana, G., Tarolli, P. (2014). Evidences and effects of changes in the artificial drainage network during the past half-century: a case study in the Veneto floodplain (Italy), Anthropocene, doi:10.1016/j.ancene.2014.06.005.