Abstract: A wavebreak forest combing rigid and flexible vegetation is founded out through experimental tests on the water attenuation property of different wavebreak forests in this study. This combination is specific to rivers with significant seasonal variation in water level, and it seems to ensure a better wave breaking performance of ecological revetment projects. We conduct wave breaking tests on four combined types of rigid and flexible vegetation under eight different water levels, considering the height of existing wavebreak forests and the measured water levels in the Laolongkou reach. Results show that in different inflow conditions, a large disparity in the wave-breaking effect of a wavebreak forest of the single vegetation type is observed, while the combined vegetation types produce an improved, stable effect. The transmission coefficients of rigid-flexible combined wavebreak forests are smaller than 58%. Different type of vegetation has its own superiority in water attenuation under different water levels, and such an advantage can be utilized and integrated by a combined type adequately. Therefore, a combined type can achieve better, stable effect in water attenuation, making it more cost-efficient and reasonable to construct rigid-flexible wavebreak forests within rivers featured with a wide range of fluctuations in water level. The results would help the design of ecological revetment projects on rivers similar to the Laolongkou reach.

Key words: wave hydraulics, wave attenuation, physical model test, rigid-flexible combined wavebreak forests, Laolongkou reach