Building resilience to extremity and climatic changes investigating the phenomena of Compound Events: case study: Odense, Denmark

This report investigates the phenomenon of compound flooding. The combined effect of river flow with tide and surge, and the frequencies of which such events occur, resulting with extreme water levels in tidal rivers and estuaries, increasing potential risk to society. To investigate this phenomenon the location of Odense has been selected as a case study. Due to the EU Floods Directive (Directive 2007/60/EF) call for all EU member states to be prepared for extreme flood risk, a reaction to events in Central Europe during the period of 1998-2002, the Danish State selected Odense Fjord as one of ten areas at risk of extreme flooding conditions (2011). A quality check of observational data at the locality took place and conditions of the variables investigated. Statistical methods and numerical modelling techniques using software created by DHI are then utilized to define and simulate the relationships between the hydrological variables. Initially an extreme value analysis takes place using the DHI’s EVA tool feature, to investigate the extremity and return frequency of singular extremes, and then furthered by a joint probability analysis. Where the dependence between the variables is explored and potential return frequencies of extremity in different return combinations calculated. A coupled MIKE-11-MIKE-SHE numerical model is then investigated, with calibration of the Manning Number taking place to simulate peak flow conditions. Scaled events based from the EVA return analysis are then produced and simulated, to assess variable dynamics and illustrate risk of flooding from hypothetical flood events. An alternative numerical coupling of a MIKE-11-MIKE-21-MIKE-FLOOD has also taken place. The Aim of this is to display alternative numerical options, while helping to emphasise uncertainty within modelling, techniques and relationships of variables. A climatic factor has also been emulated to highlight the relevant climatic change consequences and significance.