Modification of artificial drainage networks during the past half-century: evidence and effects in a reclamation area in the Veneto floodplain (Italy)

Abstract One of the most important human-landscape interactions in the Anthropocene is the creation of reclamation landscapes. However, over the past half-century, reclamation networks have changed due to more intense urban and agricultural land use. These transformations imply a number of serious hydraulic dysfunctions, underlined by the recent floods affecting the floodplains in Europe. This study investigates the evidence and effects of these changes in a small area in Veneto (Italy). We analysed 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 network transformations were investigated using the Network Saturation Index (NSI) that quantifies how fast an area is saturated by a design rainfall. 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.