PSI - Issue 84

Stefano Pagliara et al. / Procedia Structural Integrity 84 (2026) 1270–1277

1276

Fig. 6. Variation of C D / C L with h u / H D for Db01–Db03.

4. Conclusions This study examined hydrodynamic forces on debris accumulations under low Froude number flow. Drag and lift forces increased with h bw and  H . Impervious debris generated higher forces than permeable debris due to increased flow obstruction. Normalized water level rise and head loss showed consistent behaviors across all debris types. We found that existing backwater equations significantly underestimated backwater for complex debris geometries. Overall, experimental evidence confirmed that C D / C L decreases with relative debris submergence. Differences between debris configurations become negligible under unbounded flow conditions. The results suggest the necessity of additional analyses to improve existing design approaches. Future works should also include unsteady flows and floating debris to replicate real world scenarios more accurately. References Ballio, F., Viscardi, S., Pallavicini, P., Malavasi, S., 2024. Drag coefficients of debris accumulations. Journal of Hydraulic Engineering 150(6), 06024003. https://doi.org/10.1061/JHEND8.HYENG-13865 Eames, I., Robinson, T., 2024. Free-surface channel flow around a square cylinder. Journal of Fluid Mechanics 980, A16. https://doi.org/10.1017/jfm.2023.964 Follett, E., Schalko, I., Nepf, H., 2020. Momentum and energy predict the backwater rise generated by a large wood jam. Geophysical Research Letters 47, e2020GL089346. https://doi.org/10.1029/2020GL089346 Kabir, S.M.I., Ahmari, H., Dean, M., 2023. Contribution of debris and substructures to hydrodynamic forces on bridges. Engineering Structures 283, 115878. https://doi.org/10.1016/j.engstruct.2023.115878 Malavasi, S., Guadagnini, A., 2007. Interactions between a rectangular cylinder and a free-surface flow. Journal of Fluids and Structures 23(8), 1137–1148. https://doi.org/10.1016/j.jfluidstructs.2007.04.002 Naudascher, E., Medlarz, H.-J., 1983. Hydrodynamic loading and backwater effect of partially submerged bridges. Journal of Hydraulic Research 21, 213–232. https://doi.org/10.1080/00221688309499416 Pagliara, S., Kumar, A., Palermo, M., 2026. Hydrodynamic loadings on debris accumulations at low Froude numbers in straight channel. Water, 18(2), 220. https://doi.org/10.3390/w18020220. Pagliara, S., Kumar, A., Wei, H., Palermo, M., 2025. Hydrodynamic impacts on bridge decks: A comprehensive literature review, in Proceedings of the 41st IAHR World Congress. IAHR, Singapore, pp. 190–198. https://doi.org/10.64697/978-90-835589-7-4_41WC-P1636-cd Palermo, M., Kumar, A., Wei, H., Pagliara, S., 2025. Hydrodynamic loads on rectangular bridge decks at very low proximity in fixed and movable beds. Water 17(5), 617. https://doi.org/10.3390/w17050617 Panici, D., De Almeida, G.A.M., 2018. Formation, growth, and failure of debris jams at bridge piers. Water Resources Research 54, 6226–6241. https://doi.org/10.1029/2017WR022177 Parola, A.C., Apelt, C.J., Jempson, M.A., 2000. Debris Forces on Highway Bridges. National Cooperative Highway Research Program Report 445, Transportation Research Board, Washington, DC, USA. Picek, T., Havlik, A., Mattas, D., Mares, K., 2007. Hydraulic calculation of bridges at high water stages. Journal of Hydraulic Research 45, 400– 406. https://doi.org/10.1080/00221686.2007.9521773