Laboratory Investigation of Hydrodynamic and Sand Dune Morphology Changes Under Wave Overwash

Since the field measurement of wave overwash is difficult to obtain during severe storms, a laboratory experiment is conducted to measure the time and space evolution of the overwash and beach profile over the sand dune continuously using high-speed video image analysis for different wave conditions of irregular waves and solitary waves. Characteristics of the cross-shore sediment transport and morphology change are discussed from the laboratory experiment data. The inflection point, which marks the shifting turn in dune crest movement during overwash, is determined by analyzing feature points in the variation of dune geometry. It is confirmed that the overwash water volume rate reaches a maximum value when the inflection point occurs. Additionally, the overwash water volume is found to be linearly related to the deposited sediment volume, and the dune erosion volume is proportional to wave energy flux during the overwash process. The presence of secondary dunes is found to significantly alleviate coast erosion during overwash and reduce shoreline retreat by more than 40%, regardless of the height of the secondary dune crest. Furthermore, the advances and limitations in overwash hydrodynamics are discussed. It is recommended that this continuous morphological change monitoring data be combined with a wave resolution model for detailed hydrodynamic simulations to further understand the overwash process.

Automated summary

A laboratory experiment using high-speed video image analysis was conducted to continuously measure the time and space evolution of overwash and beach profile under different wave conditions. The presence of an inflection point in dune geometry indicates a shifting turn in dune crest movement during overwash, with the overwash water volume reaching its maximum at this point. The study also found a linear relationship between overwash water volume and deposited sediment volume, and dune erosion volume proportional to wave energy flux. Secondary dunes were found to significantly alleviate coast erosion and reduce shoreline retreat, regardless of their height.