Investigating the Hydromorphological changes due to the construction of bridges on the mountainous Jalayer River, Central Iran

Bridges, as anthropogenic structures on river channels, exert significant influences from hydrological, morphological, morphometric, and sedimentological perspectives. Research aimed to investigate the effects of bridge structures on the Jalayer River, located in the mountainous region of Markazi Province, Iran. The research methodology integrates morphometric and morphological analyses, hydrological modeling using HEC-RAS, UAV photogrammetry, and sediment grain-size assessment. Utilizing a high-resolution digital elevation model (16 cm), specified cross-sections with predetermined intervals were obtained both upstream and downstream of the bridge. Key findings reveal substantial variations in morphometric and hydrological parameters, including channel slope, cross-sectional area, wetted perimeter, width-to-depth ratio, flow velocity, stream power, and Froude number, between upstream and downstream sections of both bridges. Sediment texture transitions from coarse sand to fine pebble along the flow direction. HEC-RAS simulations indicate a risk of destructive flow overtopping during 100-year return period events. Variability coefficient analysis highlights the maximum fluctuations in slope, stream power, and shear stress parameters upstream/downstream of Bridge A2, particularly within 10-m cross-sections. In contrast, Bridge A22 exhibits minimal variability in cross-sectional area, flow velocity/depth, maximum flow depth, Froude number, and stream power. Results underscore the spatially heterogeneous impacts of bridge structures on fluvial system parameters across diverse geographical settings.