Flood Risk Assessment of the Gleisdorf Region’s Flood Protection System

Recent flood experiences revealed the importance of assessing and managing possible flood scenarios in the vulnerable hinterland. This in particular applies when the flood protection system is designed for a magnitude that may be exceeded. The assessment of the remaining risks comprises 1. Possible flood and failure scenarios, 2. Consequences related to these scenarios, 3. Probability of these scenarios. The region of interest is the Gleisdorf area, located about 20 km in the west of Graz, at the confluence of the rivers Rabnitzbach and the Raab. Here, the flood protection system, constructed in the late 1990ies employs linear levees and a retention basin to withstand a 100-year event. Meanwhile, the River Raab’s former floodplains were utilized for industrial areas. Therefore, this investigation focuses in the assessment and combination of following system components: 1. Evaluation of possible load situations in terms of probabilities of peak discharges and flood durations and the related inundations 2. Assessment of the degree of protection in terms of possible failure events and probabilities within the flood protection system 3. Vulnerability assessment in the hinterland in terms of possible losses and monetary damages. From these interim results, risk is expressed as the probability of flood damages and the expected losses caused by events exceeding the design capacity. Uncertainties inherent in the evaluation of the design magnitudes, the reliability of the protection system and the estimation of the potential damage will be accounted for. Finally, these results are used to propose risk alleviation measures. Appropriate strategies cover measures to reduce the flood magnitude, the potential damage by object protection as well as prediction and warning.