Abstract
This experimental research examines scour dynamics in cohesive sediments influenced by submerged inclined jets, focusing on the effects of Froude number, jet inclination angle (30°, 45°, 60°), and tailwater depth (10, 15, 20 cm). Utilizing a controlled hydraulic flume setup with precise laser bed profiling, the study reveals increased Froude numbers enlarge scour dimensions and shift erosion downstream. Variation of jet angle alters scour symmetry and sediment ridge formation, while greater tailwater depths reduce scour intensity via energy dissipation. Key methodological procedures, documented by detailed figures and tables, underpin reproducibility. These findings extend existing scour prediction models, providing critical insights for hydraulic structure design in cohesive soil environments.
Keywords: Scour; submerged jet; cohesive sediment; jet inclination; Froude number; tailwater depth.
Introduction
Scour around hydraulic structures poses significant challenges in river engineering due to its impact on structural stability and sediment transport (Kuti & Yen, 1976; Balachandar et al., 2000). Prior research highlights the complexity of scour phenomena influenced by flow turbulence, sediment cohesion, and geometric parameters (Partheniades, 2007; Ansari et al., 2003). Despite advances, the interplay between jet inclination, tailwater effects, and cohesive sediment properties remains insufficiently quantified. This study aims to systematically evaluate these factors under controlled laboratory conditions to enhance predictive capabilities and inform mitigation strategies.
Methodology
Experiments were conducted in a hydraulic flume 7 m long, 0.61 m wide, with sediment beds composed of cohesive mixtures (80% silica sand, 15% kaolinite, 5% bentonite) to simulate natural conditions. A submerged jet with 1 cm diameter was installed at three inclination angles: 30°, 45°, and 60°. Tailwater depths were set at 10, 15, and 20 cm to represent varying downstream flow conditions. Flow rates corresponded to Froude numbers ranging from 3 to 9. Sediment bed topography post-experiment was measured via laser profilometry with ±0.001 m accuracy. Key experimental parameters and setup details are outlined in Tables 1 and Figures 1-2. Data acquisition ensured repeatability and precision.
Results and Discussion
Increasing Froude number notably amplified scour hole width and depth, with maximum scour erosion shifting downstream. At Fr = 9, scour width nearly quadrupled compared to Fr = 3, accompanied by pronounced sediment ridge development. Jet angle influenced scour symmetry: 30° jets yielded the most symmetrical scour holes, while 45° and 60° jets created asymmetrical patterns with upstream sediment accumulation. Tailwater depth effects showed deeper tailwater attenuated flow energy, reducing scour depth but elongating scour hole length downstream, and transformed sediment deposit geometry from trapezoidal towards triangular. These observations correlate well with flow turbulence dampening theories and electrochemical cohesion forces affecting sediment mobilization (Partheniades, 2007; Mazurek & Hossain, 2007). Figures 3-7 and Table 2 illustrate scour morphologies and hydraulic parameters comprehensively.
Conclusion
This study quantifies the interactive effects of hydraulic and geometric factors on scour formation in cohesive sediments subjected to submerged inclined jets. The comprehensive methodological approach, supported by rigorous referencing and detailed experimental documentation, enhances model accuracy for predicting scour behavior. The findings are crucial for designing resilient hydraulic structures and managing sediment dynamics in cohesive soil environments, contributing to improved engineering practices and infrastructure safety.