Wave Dissipation Characteristics of Floodplain Vegetation on Levee Cross-section

To establish a comprehensive and multifunctional coastal shelterbelt system for disaster prevention, it is crucial to deepen the understanding of the wave dissipation mechanisms by floodplain vegetation and accurately quantify the contributions of the vegetation. Existing methods for calculating wave height reduction by vegetation are typically based on the single vegetation condition, such as the normative method considering wave height at the end of the vegetation area and the along-track method considering wave height reduction along the belt. To verify the applicability of the wave height calculation method proposed under a condition without the levee in the specific condition where a levee exists, this paper conducts experiments on horizontal and gentle slope floodplains with sloped and composite levee cross-sections, and analyzes the problem through along-track method, normative method and simplified normative method. The results show that the reflection from the levee impairs the wave dissipation by floodplain vegetation, proving an overestimation of the wave dissipation effect by existing theoretical calculation methods. The measured wave height behind the vegetation area is 1 to 2 times the calculated value. In conditions where vegetation effectively dissipates waves, the wave height reduction results obtained from the above three methods are similar; the normative method and the along-track method results are closer to the measured values when the vegetation area is relatively narrow or the vegetation is submerged. In practical applications, different methods can be selected to calculate the wave height reduction effect by vegetation, with a safety factor considered. The results can provide scientific support for the planning and design of floodplain vegetation for ecological levees and the design of levee cross-sections.