Mitigation measures preventing floods from landslide dams: analysis of pre- and post-hydrologic conditions upstream a seismic-induced landslide dam in Central Italy

The design of engineering measures during emergency phases is crucial in mitigating the river flow impacts on landslide dams, avoiding dam breaks and related downstream flooding. Man-made hydraulic facilities represent a possible mitigation strategy for reducing the occurrence of dam breaching by diverting river inflow. Semi-empirical equations published in the literature may help define the landslide dam evolution and design the discharge to be diverted into the hydraulic works assuring the dam's stability. These approaches need to be carefully validated with case studies, an important step in evaluating the accuracy of predictive models. The work presents and discusses the pre- and post-seismic hydrologic conditions along the Nera River gorge focusing on the role of the pre-existing anthropic works in mitigating the impact of river discharge on the Sasso Pizzuto landslide dam triggered by the October 30, 2016 earthquake (Central Italy). Considering historical data, the upper part of the river catchment has experienced the highest discharge values during the landslide dam lifetime. The discriminant analysis approach of the hydro-geomorphometric characteristics supported the definition of the critical peak flow, avoiding the dam's instability. Thanks to an upstream hydropower bypass, about 80% of the river discharge increase have been diverted into an underground pipeline built in 1928 to feed the Preci hydroelectric plant (located a few kilometers downstream of the landslide dam). The discriminant analysis model, developed in the literature on other landslides worldwide, had a good performance in managing the upstream river discharge of Sasso Pizzuto dam, expanding its validity on other landslide dams.