Investigating the morphological changes of scour hole around gabion spur dikes

River banks protection is one of the most significant challenges due to the impact of flowing ‎water and the erosion caused. The accurate estimation of morphological changes due to the generated scour around environmentally friendly spurs, such as gabion spurs is crucial for sustainable and safe hydraulic design. This study aims to analyze the effect of different grades of median gravel size (d_mg = 15, 27, and 45 mm, for grade 1, 2, and 3 respectively) of rectangular gabion spurs on the scour hole characteristics under clear water condition by experimental investigation. The experiments were conducted in horizontal laboratory flume with non-cohesive sand (d₅₀ = 0.72 mm) for varied ranges of flow intensity (0.5 ≤ V/Vc ≤ 0.998) and flow depth (7 and 10 cm). For tested gabion spurs, when the size of median gravels diameter decreases, it was found that the scour hole dimensions increase ‎as intensity of flow increases. According to the experiments results, the maximum relative scour (d_s/y) equals to 1.886, 1.786, and 1.657 for grade1, 2 and 3 respectively. Furthermore, a comparisons have been characterized for the effect of the influence parameters such a flow intensity, and Fraud's number on the morphological scour hole around modelled gabions spurs. According to the extracted results of the present study and based on dimensional analysis ‎technique and statistical indicators, new validated empirical formula has been presented to estimate the scour depth near gabion ‎spurs utilizing multiple nonlinear regression. Finally, findings underscore that gabion spurs with finer gravel require careful design to mitigate excessive scour, while the formula provides a practical tool for optimizing erosion control in river engineering.