An integrated approach for investigating the correlation between floods and river morphology: A case study of the Saalach River, Germany

Man-made structures in the Saalach River have changed the hydromorphological characteristics of the river regime. In some river reaches, the Saalach has lost the high morphological versatility and high variation in sediment transport characteristic of a mountain river. Among the negative effects, an extreme flow discharge in combination with riverbed variation could be one of the possible causes of flood disasters along the river. For example, the heavy and long lasting rainfall in June 2013 led to a peak discharge of 1100 m³/s, which was slightly above the 100-year flood return period, inundating a nearby city. However, the influence of the man-made structures on this flood event in this reach is unclear. In this study an integrative hydromorphological model is applied to evaluate this impact by a comparison with a standard clear water model with fixed bed. Moreover, a comparative analysis of a three-and two-dimensional flow model is performed to assess the models suitability representing the flow in this river stretch. The integrative model concept is based on the software TELEMAC-MASCARET, in an enhanced version for better representing graded sediment transport in rivers. In contrast to our integrative model, the standard clear water model with fixed bed overestimates the water elevations as it cannot take the significant changes in morphology into account. Results demonstrate that our proposed model more accurately represents the inundation in the floodplain and could thus be used to provide more reliable predictions to decision-makers for improved flood protection strategy.