Soil sealing and flood risks in the plains of Emilia-Romagna, Italy

Abstract

The plains of Emilia Romagna, Italy. Urban expansion is among the main causes of increase in flood frequency and intensity in small rural catchments in Europe, and our study region is paradigmatic in this respect. We present here a regional screening-level assessment of soil sealing impacts in terms of increased flood peak discharges and flooding volumes on the secondary drainage network of the plains. We estimate flood peak discharges and flooding volumes through a simple kinematic model with runoff coefficients for the land use of 2008 and 1976. Additionally, we calculate an equivalent compensatory flood detention volume that would enable preserving flood peak discharges as prior to soil sealing (principle of “hydraulic invariance”). The proposed approach is simple and readily applicable to any region facing similar issues, for screening-level assessment of flood hazards over an extended stream network. The analysis highlights a significant increase in flood hazards throughout the secondary stream network. The impact. Widespread and relatively uniform, is more apparent in smaller catchments and in the case of more permeable soils. This demands retrofitting of the majority of the drainage network and/or significantly higher costs from flooding damages. The analysis suggests that costs of additional flooding after soil sealing may be higher than those of soil sealing impacts compensation through flood detention (hydraulic invariance).