A vegetation roughness model to evaluate flood risk along Secchia River.

Dario Bernardi, Leonardo Schippa

Thursday 2 july 2015

16:45 - 17:00h at Europe 2 (level 0)

Themes: (T) Flood risk management and adaptation, (ST) Adaptation measures

Parallel session: 13K. Floodrisk - Adaptation

In January 2014, a serious flooding event occurred in the towns of Bastiglia and Bomporto, located in the Modena Province (Italy) along Secchia River. After 3 days of intense precipitation on the river basin (120 mm total), a breach opened in the early morning January 19th on the right levee, close to the village of Albareto. More than 36 Mm3 of water flew through the breach, with a peak discharge of 500 m3/s, leading to damage worth more than 400 M€. Since then, concerns have increased about the role of vegetation during big floods in this confined reach. A detailed characterization of riparian vegetation features has then been carried out by the Po River Interregional Agency (AIPo) - responsible for the river management - to point out critical issues about current vegetation pattern along Secchia river banks and possibly plan a maintenance - remediation strategy. The aim of the Agency is to go beyond the usual emergency-driven, ineffective countermeasure consisting in indiscriminate cutting and removal of every species, to approach solutions at reach scale accounting for the different hydrodynamic conditions during floods. This characterization work constitutes a good basis for hydrodynamic modelling; a 1D finite-volume model with mobile bed, accounting for the influence of different vegetation patterns and densities on flow resistance has been applied to a 60 km long stretch of Secchia river, to support management choices and possibly check the effectiveness of a proposed vegetation plan in reducing flood risk. The model has been validated, indeed the agreement of the simulation results (for a real flood event) with gauged values is satisfactory.