Discussion of "Abbas, F. M., & Tanaka, N. (2022). Investigation of flow structure with moat acting as a water cushion at the toe of an overflowing levee. Environmental Fluid Mechanics, 22(4), 865–889.".

The authors of the discussed paper presented an interesting study in which a moat is introduced just downstream of an overflowing levee for reducing the energy of the overflowing water. The authors investigated the effect of the geometric parameter of the moat downstream of the overflowing levee on its hydraulic characteristics and energy reduction. The Reynolds-Averaged Navier-Stokes and Volume of Fluid methods were implemented to simulate and measure water depths and flow structures in order to optimize the geometric parameters of the moat, including dimensionless depths and lengths, and then to explore the effect of downstream slope, upstream slope, levee crest length, and levee height on energy reduction. Following the turbulence model validation and mesh convergence analysis were both satisfactory, an enormous amount of numerical simulations for overflowing levees with a moat under various hydraulic circumstances were conducted. The present discussion paper shows that when the dimensionless overflow depth is less than 0.81, the ideal dimensionless length of the moat is 1.50 and the optimal dimensionless depth is 0.35, which may fulfill energy dissipation requirements while saving construction costs. Moreover, when the dimensionless overflow depth is larger, it can be beneficial to reduce downstream energy by improving the overflow levee structure, which primarily involves steepening the upstream slope, reducing the downstream slope, increasing the levee crest length, and decreasing the levee height. However, when the dimensionless overflow depth decreases, the effect of these factors diminishes gradually. [ABSTRACT FROM AUTHOR]