Abstract
Local scour is a major cause of instability and structural degradation in hydraulic systems, driven by high-energy flows and sediment entrainment. Developing sustainable countermeasures remains an essential task in hydraulic engineering. This study investigates the effectiveness of xanthan gum in mitigating scour downstream of a rostral drop. The experiments were conducted in a fully turbulent flow regime (48,686 < Re < 110,160) with discharges between 5 and 8.33 L/s. The mobile-bed section was 1.0 m long with a 12-cm sediment layer in a 5-m-long, 0.33-m-wide rectangular flume. A drop structure with a 120° vertex angle and 15-cm height was installed 1.0 m upstream of the bed. Four xanthan concentrations (0.05%, 0.1%, 0.3%, 0.5% by weight) were tested together with a constant 10% clay content. A total of 160 experiments were categorized into four scenarios. The results indicated that clay alone provided moderate reductions in scour dimensions, while increasing xanthan concentrations produced progressively stronger improvements. The combined xanthan–clay mixture yielded the most significant enhancement, reducing maximum scour depth by more than 93%, demonstrating its strong potential as an eco-friendly scour-mitigation treatment. These scenarios were designed to isolate the role of natural clay in improving baseline cohesion and to assess how increasing xanthan dosage enhances mechanical resistance. This structure enabled a systematic evaluation of how progressive sediment modification influences downstream scour development.