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Bridge failures due to scour occur more frequently than expected, although bridge design considers conservative scenarios, evidencing a stochastic scour behaviour and the need for improvements in current design procedures. In this paper, a new method for determination of design local scour depth at bridge piers is proposed. The results show that peaks-over-threshold series are better suited than annual-maximum series of maximum scour depths for frequency analysis. Extreme scour depths follow the heavy-tailed Cauchy distribution. Scour depths with a 100-year return period resulted in 22 to 202% of the equilibrium scour depth currently used in design, evidencing the need for a different criterion to select the design scour depth. The proposed method computes the design local scour depth based on its probability of occurrence, introducing a novel probabilistic approach in bridge design for enhanced infrastructure risk management compatible with multi-hazard analysis. [ABSTRACT FROM AUTHOR]

The relations between preparedness and psycho-social attributes of people and communities exposed to river floods in a nearly pristine socio-hydrological system were investigated, applying a hydrological-hydraulic analysis of flood risk in combination with results from a survey, social cartography, semi-structured non-participant observation, and semi-structured interviews. Results show that preparedness in nearly pristine systems is noticeably different to that reported for altered systems. People adopt innovative and simple but efficient measures against floods, conditioned by (1) damage suffered during past floods, (2) perceived exposure to floods, and (3) the number of dependent people in the household. The studied system proved to be well adapted to floods but not resilient. Studying attributes that explain preparedness as part of flood risk management plans would contribute towards uncertainty reduction in risk calculations and increase the safety of goods and people from floods. [ABSTRACT FROM AUTHOR]

The pier scour caused by flood waves is analyzed, introducing the dimensionless effective work by the flow on the sediment bed around the pier, W*. The three-parameter exponential function is adopted to relate the normalized scour depth Z* with W*. A novel experimental installation able to reproduce any hydrograph with high precision in the laboratory flume is described and used to carry out four series of scour experiments in order to calibrate and validate the proposed relation. The first series consists of experiments with constant discharge until advanced stages of scour. The second and third series of experiments use single flood waves of different shapes and durations, respectively. The fourth series consists of scour experiments caused by more realistic flow hydrographs with multiple peaks. Results show that the relation between W* and Z* is unique and thus W* represents a reliable concept for the prediction of the flood wave scour because it appropriately integrates the effects of the hydrograph properties, duration, peak discharge, and shape, on scour. The proposed relation allows a straightforward prediction of maximum scour depth after a flood wave with high precision. A good agreement between measured and computed scour was observed in all cases. [ABSTRACT FROM AUTHOR]

The new toolbox ScourApp is presented and applied for analysis of the complex interactions between local scour and sediment deposition at bridges during floods and to determine the relative importance of the controlling parameters on scour depth. ScourApp represents the time-dependent sediment transport processes through modern empirical formulations to compute the evolution of scour depth at a bridge pier. Results show that the mathematical model reproduces observed scour depths with high accuracy and confirm that ScourApp is a suitable tool for scour analysis. The model parameters controlling the time dependent scour depth were the equilibrium scour depth, and two constants representing the effects of pier geometry, flow and sediment. Sensitivity analysis showed that all three scour model parameters exhibited a nearly linear relation with the final scour depth. Moreover, results considering sediment deposition obtained for the Rapel Bridge showed that scour depths are highly sensitive to the sediment supply rate. ScourApp is recommended in scour assessment for bridge planning, design, management, and forensic analysis, as well as for engineering education. • The open-source toolbox ScourApp for scour analysis is developed. • Complex interactions of time-dependent scour and scour hole refilling are analysed for several laboratory and real-life cases. • The relative importance of controlling parameters on scour is analysed. [ABSTRACT FROM AUTHOR]

Native forest deforestation has been identified as one of the main land cover changes affecting flood risk specially during small and moderate storm events. In this regard, forest protection and reforestation are considered a nature-based solution (NbS) for flood regulation. However, there is a lack of knowledge about the effects of different deforestation spatial patterns over floods. Effects of land cover changes on floods in a humid tropical basin within the Ecuadorian Amazon are assessed distinguishing forest location and forest fragmentation. The hydrological distributed model TETIS was applied to simulate the hydrological response of a basin to extreme storms having return periods of 1, 10 and 100 years, considering five land cover scenarios. The model was calibrated and validated using nine storm samples collected at a gauge station during the years 2018 and 2020. The simulated overland flow in hillslopes and stormflows within the river channel were analyzed to i) assess the statistical differences among all land use scenarios with the Kruskal-Wallis test; ii) assess the statistical differences among pairs of both location and fragmentation scenarios through the post-hoc evaluation Dunn test; iii) assess the statistical differences in relation to the baseline. Obtained results indicate that stormflow is less sensitive than overland flow to land cover changes. Forest location have more influence than forest fragmentation over both, overland flow and storm flows. Deforestation of the upper basin represents the worst scenario for flood regulation, thus protection of existing forest, as well as reforestation of deforested areas located in the upper watersheds is a priority for flood risk mitigation and forest conservation. The results enhance our understanding of ecosystem services provided by tropical Andean foothills forests. [Display omitted] • Forest location is more important than forest fragmentation for flood regulation. • Deforestation in the upper basin is the worst land cover change scenario regarding floods. • Overland flow is more sensitive than stormflow to land cover changes. • As storm intensity increases the influence of land cover change over floods decreases. [ABSTRACT FROM AUTHOR]