PSI - Issue 84

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

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obstruction. Here, h bw and  H are influenced by the flow resistance due to the submerged debris.

Fig.2. Pictures of (a,d) Db01, (b,e) Db02, and (c,f) Db03 for h * <1.

Fig.3. Pictures of (a,d) Db01, (b,e) Db02, and (c,f) Db03 for h *  1.

3. Results and discussions The experimental results are presented in terms of debris-induced hydrodynamic forces, water-level response, and energy losses under both partially and fully submerged conditions. Fig. 4 shows variation of F D and F L - B with  H and h bw for Db01–Db03. Both forces monotonically increase with  H and h bw . An increase in  H corresponds to higher energy loss and a stronger pressure gradient acting on the debris (Palermo et al. 2025). This results in higher F D and F L values. Similarly, Schalko et al. (2019) showed that h bw increases as LWD reduces the effective flow cross-section. This rise in upstream water level is directly linked to enhanced flow resistance caused by the obstruction, resulting in amplified hydrodynamic forces under subcritical and choked free surface channel flows (Wüthrich et al. 2020; Eames and Robinson 2024). In Fig. 4, we can observe that debris type Db03 consistently produces larger forces because n = 0. This agrees with Wüthrich et al. (2020) who showed that impervious bodies generate higher hydrodynamic forces than porous ones under steady free-surface flow, forcing the flow to pass around and beneath the obstruction, thus enhancing momentum exchange, pressure accumulation, and flow separation. This results in increase in both F D and F L . In contrast, the permeable debris configurations (Db01 and Db02) allow partial flow transmission, resulting in lower and overlapping force magnitudes.