Quantification of Modelling Uncertainties in Bridge Scour Risk Assessment under Multiple Flood Events

Abstract

Local scour is a dynamic process evolving during the lifetime of bridges as a result of the changes in hydrologic and hydraulic conditions. Current approaches for scour risk assessment are generally based on the evaluation of the equilibrium scour depth for a flood event with a prefixed return period. The temporal evolution of the bridge-pier scour process is usually disregarded, by assuming that equilibrium conditions are always attained, regardless of the flood properties. However, recent studies have highlighted the importance of accounting for the contribution of multiple flood events and their exact hydrograph shape. This study aims at quantifying the epistemic uncertainty related to the modelling of the temporal evolution of scour under multiple consecutive flood events in clear-water conditions. A simple numerical case study is considered, using a Markovian framework to describe probabilistically the progression of scour. Well-known time-dependent scour models are used to estimate the temporal evolution of the scour-depth under each flood hydrograph, and the scour estimates are compared with those obtained using widely employed equilibrium scour formulas. Results show that the expected scour depth is influenced by the parameters used to describe the flood hydrograph and that the probability distribution of the scour depth is highly sensitive to the choice of the time-dependent scour model. The uncertainty in the scour estimation stemming from the formula adopted in this study for describing the temporal evolution of the scour depth can be higher than those related to the formula adopted for equilibrium scour.

The Science behind Scour at Bridge Foundations: A Review

“…Figure 4 compares the results of the application of some of the equilibrium scour formulae listed in Table 2 (figure adapted from Pizarro and Tubaldi [92]). The input variables considered for the comparison were taken from the numerical case study considered in Pizarro and Tubaldi [92], i.e., (see, e.g., Liang et al [86], Gaudio et al [87], Park et al [88], Sheppard et al [84], Qi et al [89], Wang et al [90], Qi et al [91], and Sheppard et al [83]). Despite experimental-based scour modelling having been performed under different ranges of hydraulic and sediment material, the range corresponding to standard field scales is frequently unexplored.…”

“…Naturally, this hampers the comparison and uniformity of experimental data, derived equations, and trends on bridge scour. Figure 4 compares the results of the application of some of the equilibrium scour formulae listed in Table 2 (figure adapted from Pizarro and Tubaldi [92]). The input variables considered for the comparison were taken from the numerical case study considered in Pizarro and Tubaldi [92], i.e., d50 = 2.0 (mm), D = 1.5 (m), river width B = 22.0 (m), channel slope S = 0.0001 (m/m), and Manning's roughness coefficient nGMS = 0.017 (s/m 1/3 ).…”

“…Results confirmed that assuming both independence of scour events and always attained equilibrium scour depths, they may lead to unrealistic estimates of scour. On these findings, Pizarro and Tubaldi [92] assessed the epistemic uncertainty related to the temporal evaluations of clear-water scour under multiple flood events. They included more realistic flood shapes into the Markovian framework, identifying the most influencing hydraulic parameters in the computation of scour depths.…”

Electromagnetic Sensors for Underwater Scour Monitoring

“…This is mainly because they are based on laboratory tests under controlled conditions that are not representative of real ones (see e.g., [4]). Thus, the information from scour monitoring at bridge foundations could be very useful to reduce the bias and improve scour estimation models [50].…”

Multi-Hazard Assessment of Bridges in Case of Hazard Chain: State of Play and Application to Vehicle-Pier Collision Followed by Fire

“…Multi-hazard analysis and design methods for bridges have been studied under different perspectives and focusing on different aspects: risk analysis (Decò and Frangopol, 2011;Andriae and Lu, 2016), influence of aging parameters (Padgett et al, 2010;Zhong et al, 2012;Capacci and Biondini, 2020), bridge design (Lee, 2010), bridge pier structural stability (Fioklou and Alipour, 2019), and intervention strategies (Nikellis and Sett, 2020). Research includes aspects focusing on the concatenated actions of surge and wave (Ataei et al, 2010); earthquake and hurricane (Kameshwar and Padgett, 2014); earthquakes and extreme wind (Martin et al, 2019); earthquake and scouring (Wang et al, 2014); earthquake and flood (Gehl and D'Ayala, 2016;Yilmaz et al, 2018); earthquake, tsunami, and corrosion (Akiyama et al, 2020); and earthquake and scouring (Prasad and Banerjee, 2013;Markogiannaki, 2019;Pizarro and Tubaldi, 2019), also in a infrastructural resilience perspective (Argyroudis et al, 2020), scouring and impact (Kameshwar and Padgett, 2018) and earthquake and blast (Fujikura and Bruneau, 2012). Table 1 provides a snapshot and a timeline of principal research, including the hazards they address, the principal methods used, and the indication (last column) of which key issue they contributed to address referring to the list provided in the introduction of this paper.…”