From theoretical fixed return period events to real flooding impacts: a new approach to set flooding scenarios, thresholds and alerts Paola Parravicini1, Matteo Cislaghi1, Leonardo Condemi1 (1) ARPA della Lombardia, [email protected] MOTIVATION AND 2. EVENT BASED ANALYSIS FOR THRESHOLDS IDENTIFICATION 3. APPLICATIONS PURPOSES A range of discharges is associated with each scenario, considering their flood impact; the Civil protection emergency planning and threshold is set as the discharge corresponding to the transition between two scenarios. ARPA Lombardia is the Environmental river monitoring values of return period can A wide range of event-based information is used to estimate the thresholds, together with Protection Agency of Lombardy, a wide show the areas characterized by higher risk ARPA Lombardia gauging network data. region in the North of Italy. ARPA is in Finally, return period is computed from discharge values. Lambro River, red scenario (major flood) charge of river monitoring either for Civil Protection or water balance Floods Directive purposes. It cooperates with the Civil Flooded areas maps Studies about flood hazard (2007/60/EC) maps and flood risk Protection Agency of Lombardy in Rural mountainous area flood forecasting and early warning. Return period: 50y The early warning system is based on rainfall and discharge thresholds: when a threshold exceeding is expected, RL-PC disseminates an alert from yellow to red. The conventional threshold evaluation Flat urbanized area is based on events at a fixed return Return period: 4y period. Anyway, the impacts of events with the same return period may be Reference: Po River Basin Authority (AdBPo) different along the river course due to http://www.geoportale.regione.lombardia.it/ http://www.geoportale.regione.lombardia.it/ the specific characteristics of the News from websites and newspapers Flat agricultural area affected areas. A new approach is Return period: 160y proposed. It defines different Data from river gauging network scenarios, corresponding to different flood impacts. A discharge threshold is then associated to each scenario and Evaluation of the compliance of the the return period of the scenario is Seveso River during november 2014 event monitoring network with early warning 3,00 computed backwards. Seveso River - Milano Niguarda Seveso River - Palazzolo requirements further development of the 2,50 network itself 2,00 1,50 h (m) Mella River, new gauging station 1. FLOOD SCENARIOS DEFINITION 1,00 0,50 Flood scenario definition is based on the description of flood impact, 0,00 12/11/2014 00:00 12/11/2014 06:00 12/11/2014 12:00 12/11/2014 18:00 13/11/2014 00:00 13/11/2014 06:00 13/11/2014 12:00 13/11/2014 18:00 14/11/2014 00:00 instead of starting from a fixed return period. idro.arpalombardia.it Expected flood Scenario description impact Local Civil Protection No relevant effects On site measurements Emergency Plans River Chiese at Mezzane Existing station gauging station, 06/11/2014 (since 2003) Measured Q: 217,3 mc/s New station (2017) Major floods City of Lodi ‘‘Piano di Emergenza Comunale edizione 2011 Piano Stralcio del Rischio Reference: National Idraulico’’ Civil Protection http://www.protezionecivile.gov.it/jcms/it/view_prov.wp?facetNode_1=f4_4_2&prevPag guidelines e=provvedimenti&toptab=1&catcode=f4_4_2&contentId=LEG56184#top-content.