Flooding is the most common natural disaster throughout the world and requires efficient management. Therefore, the current investigation aimed to explore the impact of a composite defense system comprising dyke and vegetation on flow dynamics and velocity reduction. Experiments were conducted in an open channel setup with an adjustable bed slope and transparent sidewalls, and the vegetation model was replicated as real trees such as Eucalyptus trees. The study involved calculating several parameters, including flow velocity, reduction of fluid force index (RFI%), reduction in moment index (RMI%), and hydrostatic and hydrodynamic forces. These calculations were done by changing the channel bed slope and keeping the flow rate (discharge) constant while considering both subcritical and supercritical flow conditions. Moreover, regression analysis was performed for the prediction of RFI% and RMI% under various flow conditions. Also, statistical analyses were performed to assess the effectiveness of the defense system in reducing fluid force and moment indices. The result of the current investigation indicates that the highest values of RFI% and RMI% under subcritical flow conditions were 79% and 88%, while under supercritical flow conditions they were 94% and 78%, respectively. Moreover, a velocity reduction of 69% was observed under subcritical flow, while 84% was observed under supercritical flow conditions. Under subcritical flow conditions, RFI% and RMI% enhanced by enhancing Froude number (Fr) because of an increase in velocity reduction and hydraulic jump formation. Similar trends were observed under supercritical flow conditions, with effective mitigation of high-velocity flows by the composite system. The finding of current research helps in providing effective techniques for flood management.

Scour around river training structures is a critical concern in meandering channels, as excessive local erosion can threaten structural stability and alter channel morphology. The primary focus of previous studies has been the rectangular cross section and little, or no concentration has been given to trapezoidal section which is close to natural river cross sections. To address this gap, the present experimental study examines the effectiveness of curved spur dikes installed at different locations in trapezoidal meandering channels with sinuosity values of 1.35 and 1.50. Experiments were conducted using uniform sand ( d ₅₀ = 0.87 mm) under subcritical flow conditions with discharges of 0.015 and 0.020 m ³ s ⁻¹ . A spur dike of constant length (0.167 m) was installed with varying permeabilities (0%–75%) at five angular positions (0°, 30°, 60°, 90°, and 120°), designated as P ₁ through P ₅ . Results indicate that channel sinuosity, discharge, dike permeability, and installation angle significantly influence scour depth. The reduction if maximum scour depth was highest when a 50% permeable spur dike was installed at 90° from bend start achieving an efficiency of 54.3% (1.35 sinuosity and 0.015 m ³ s ⁻¹ discharge) and 42.4% (1.50 sinuosity and 0.020 m ³ s ⁻¹ discharge). This scour reduction is attributed to enhanced redistribution of secondary currents toward the channel centerline. Furthermore, the spur dike oriented towards downstream was found to be more effective in reducing scour compared to upstream-oriented orientation. In addition, a predictive equation was developed to estimate scour depth, demonstrating good performance with a coefficient of determination ( R ² = 0.854).

The meandering channels are result of sediment transport and secondary flow that arise due to curvatures. In the current paper, an experimental and numerical analysis of fluid hydrodynamics, turbulence behavior, and scour phenomena was conducted for curved permeable spur dikes on trapezoidal meandering channels. There were two sinuosity (1.35 and 1.50) and discharges (0.015 and 0.020 m³/s). Spur dikes were installed at five angles (0, 30, 60, 90, and 120 degrees) at P1, P2, P3, P4, and P5 inside the bend respectively. In this study, a Detached Eddy Simulation with Shear Stress Transport (DES-SST) k-ω approach has been adopted and validated through laboratory experiments on velocity measurement using a Pearson correlation coefficient (R) of 0.986 (coefficient of determination, R2 = 0.971; Nash–Sutcliffe Efficiency, NSE = 0.949). Results decide the orientation of the dikes as a primary determinant factor in effectiveness. A spur dike at 90 degrees (P4) gives the best efficiency in terms of minimizing the scour depth (45.6%) and bed shear stress (72%). About turbulence, it is evident that the slit acts as a concentrated jet having higher turbulent kinetic energy (TKE) levels and lower eddy viscosity, while having the highest specific dissipation rate (214 s⁻¹). From velocity helicity computations, curved dikes create secondary flows, characterized by counter rotating stable vortex pairs, minimizing chances of local scour formation. The correlation equation involving scour depth with Shields' stress, Froude number, relative flow depth, and sinuosity had an impressive agreement (R² ≈ 0.79)