Hydrodynamic Characteristics And Evolution Law Of Roll Waves In Overland Flow

The frequent occurrence of roll waves in overland flow can increase the water depth and accelerate sheet erosion. To investigate the variation laws and hydrodynamic characteristics of roll waves, indoor artificial experiments with five roughness types, seventeen flow discharges, and five slope gradients were conducted in a hydraulic flume. The results showed that the evolution process of roll waves is divided into three phases: monochromatic, quasi-sine, and mature wave regions. In addition, the parameter roll-wave velocity increased in terms of its power function with the unit discharges, while the slopes showed that a positive line was related to this increase. An empirical formula of the wave velocity was obtained by conducting a regression analysis after synthesizing the influencing factors. The wavelength varied at a single peak with increasing unit discharges, showing a negative linear correlation with the test slope. Additionally, an empirical formula of the wavelength was derived using regression methods. The correction coefficients in the laminar flow instability zone varied from 0.27 to 0.39, while the Reynolds number was approximately 100. The critical average Freud number Fr and the Onsager value Z were 0.6 and 3.33 x 10(-3), respectively. In addition, the correction coefficients in the turbulent flow instability zone varied within 0.412-0.730, while the Reynolds number fluctuated between 900 and 3300. The range of the critical Fr value was 1.59-2.20, and the critical average Z was 1.88 x 10(-3). These results are vital for understanding the hydrodynamic characteristics and evolution laws of roll waves in overland flow.