Author(s): Felix Bross; Isabella Schalko

Linked Author(s): Isabella Schalko

Keywords: Engineered logjams; Flow heterogeneity; Large-Scale PIV; Nature-based solutions; Wake dynamics

Abstract: Engineered logjams (ELJs) are widely used in river restoration to increase flow heterogeneity, yet quantitative field measurements that document their effects at full scale remain scarce. In this study, we used drone-based Large-Scale Particle Image Velocimetry (LSPIV) to characterize the surface flow field around a selected ELJ in a restored reach of the Emme River (Switzerland). The analysis focused on how ELJ geometry and discharge influence flow patterns. The ELJ generated distinct hydraulic signatures, including accelerated jets in the gaps between ELJ elements and pronounced wakes with reduced velocities downstream. Maximum gap velocities reached more than twice the upstream reference velocity, whereas wake regions exhibited strong deceleration and recirculation zones. Across three measurement days with moderate discharge variation, wake length and structure remained consistent, suggesting that ELJ-induced low-velocity zones are relatively robust under baseflow conditions. In contrast, gap velocities increased at lower discharges due to enhanced relative contraction. These results provide rare field-based evidence of ELJ hydraulics at full scale and support ongoing efforts to evaluate and design nature-based restoration measures.

DOI: https://doi.org/10.64697/iahr.proc.ise2026.abs.268

Year: 2026