Towards a robust assessment of bridge clogging processes in flood risk management

• Published in: Geomorphology (Amsterdam, Netherlands) Netherlands), 2017-02, Vol.279, p.128-140
• Main Authors: Gschnitzer, T., Gems, B., Mazzorana, B., Aufleger, M.
• Format: Article
• Language: English
• Subjects: Bridge clogging; Bridges (structures); Computational fluid dynamics; Flood protection; Floods; Fluid flow; Freshwater; Hydraulic scale model; Hydraulics; Hydrodynamic numerical modeling; Large wood (LW); Logistic regression; Mathematical models; Plugging; Rivers
• ISSN: 0169-555X; 1872-695X
• DOI: 10.1016/j.geomorph.2016.11.002

River managers are aware that wood-clogging mechanisms frequently trigger damage-causing processes like structural damages at bridges, sudden channel outbursts, and occasionally, major displacements of the water course. To successfully mitigate flood risks related to the transport of large wood (LW), river managers need a guideline for an accurate and reliable risk assessment procedure and the design of river sections and bridges that are endangered of LW clogging. In recent years, comprehensive research dealing with the triggers of wood-clogging mechanisms at bridges and the corresponding impacts on flood risk was accomplished at the University of Innsbruck. A large set of laboratory experiments in a rectangular flume was conducted. In this paper we provide an overall view of these tests and present our findings. By applying a logistic regression analysis, the available knowledge on the influence of geometrical, hydraulic, and wood-related parameters on LW clogging probabilities is processed in a generalized form. Based on the experimental modeling results a practice-oriented guideline that supports the assessment of flood risk induced by LW clogging, is presented. In this context, two specific local structural protection measures at the bridge, aiming for a significant decrease of the entrapment probabilities, are illustrated: (i) a deflecting baffle installed on the upstream face of the bridge and (ii) a channel constriction leading to a change in flow state and a corresponding increase of the flow velocities and the freeboard at the bridge cross section. The presented guideline is based on a three-step approach: estimation of LW potential, entrainment, and transport; clogging scenario at the bridge; and the impact on channel and floodplain hydraulics. For a specific bridge susceptible to potential clogging caused by LW entrapment, it allows for a qualitative evaluation of potential LW entrainment in the upstream river segments, its transport toward the hydraulic bottleneck, and for a quantification of expected entrapment probabilities. Depending on the amount and characteristics of the impacting LW, consequences of bridge clogging can be determined and LW bridge-clogging scenarios can be considered within hydrodynamic numerical modeling. •The large wood clogging phenomenon at bridges was addressed.•We refined the quantitative understanding of entrapment behavior at bridges.•We present approaches to make experimental results accessible to inundation mod