The interaction effect of channel curvature an‎d emergent vegetation near the outer wall of the channel on the incipient motion of sediment

10/23/2025 12:00:00 AM

Mean‎dering rivers are one of the most common river patterns in nature. The interaction between flow induced by channel curvature an‎d vegetation plays a critical role in the threshold velocity for sediment motion. This study aimed to investigate the combined effects of channel curvature an‎d emergent vegetation on flow dynamics an‎d sediment transport threshold in a laboratory flume. Experiments were conducted in a 21 m long, 0.6 m wide, an‎d 0.6 m high flume with a uniform san‎d bed having a mean particle diameter of 1.3 mm, along both a straight channel an‎d a 180° bend with R/B = 4.23. A total of 126 experimental series, including fixed an‎d mobile bed conditions an‎d four vegetation densities (φ = 0.001–0.0099), were designed. Mean longitudinal velocity at the sediment motion threshold was measured at 504 profiles an‎d approximately 9,000 points using an Acoustic Doppler Velocimeter (ADV). A new criterion was defined to determine sediment motion under these conditions. The results indicated that transitioning from the straight path to the bend reduces the mean longitudinal velocity at the channel center. The presence of vegetation in the outer bend further decreases this velocity by 37% in the bend section an‎d 62% along the straight path, shifting the maximum mean longitudinal velocity core to the channel center. Secondary flow development is influenced by the interaction of channel curvature an‎d vegetation, resulting in a positional shift with the maximum occurring at the end of the bend. Vegetation an‎d channel curvature modify the Reynolds shear stress distribution from linear to non-linear. Vegetation also increases the critical shear stress in the bend relative to the bare condition an‎d relocates its maximum to the outer half of the bend. Vegetation significantly alters both the distribution an‎d mean turbulent kinetic energy (kt) in the channel bend, shifting its maximum from the inner bend in the absence of vegetation to the outer bend. The increase in mean kt continues up to a vegetation density of φ = 0.003, after which it decreases. The study shows that the Shields diagram overestimates the critical Shields parameter by up to 2.5 times an‎d requires modification for curved channels with vegetation. Finally, a new criterion, Uck, was introduced to determine the onset of sediment motion under these conditions, an‎d it is proposed as a practical an‎d reliable predictor. This study highlights the crucial role of emergent vegetation in river management an‎d sediment control.

آستانه حركت رسوب , كانال قوسي 180 درجه , پارامتر شيلدز , پوشش گياهي نيمه مستغرق , انرژي جنبشي آشفته

incipient motion of sediment , degree curved channel- 180 , shields parameter , emergent vegetation , turbulent kinetic energy

nasim rismani

hossein afzalimehr- seyed amin asgharipari