Wave dissipation and erosion reduction under the combined effect of gravel and Cynodon dactylon cover
Wave erosion is one of the main ecological and environmental problems in the water-level fluctuation zone of the Three Gorges Reservoir area.As single factors,the presence of plants and gravel can effectively control wave erosion.However,it is unknown how the combination of these control measures affects wave erosion.Therefore,wave experiments were conducted under three levels of Cynodon dactylon cover(20%-30%,40%-50%,60%-70% )and nine different gravel conditions(three thicknesses of gravel cover,20,40 and 60 mm;and three gravel particle sizes,5-10,10-15,and 15-20 mm).The bare slope without gravel and plant cover served as the control check(CK).The effects of plant cover and gravel as single and combined factors on wave erosion were explored by measuring the wave pressure and wave erosion rate in each treatment.The results indicated that gravel decreased the wave pressure by 26.49%-86.52% and the wave erosion rate by 8.70%-73.91%,compared with values for the CK.The wave pressure and wave erosion rate decreased as the gravel particle size decreased and as the gravel cover increased.The presence of C.dactylon decreased the wave pressure by 4.10%-46.36% and the wave erosion rate by 19.56%-77.17%,compared with values for the CK.The wave pressure and wave erosion rate decreased with increasing cover of C.dactylon.The wave pressure and wave erosion rate decreased by 28.95%-94.74% and 28.20%-80.43%,respectively,under the combined effects of gravel and C.dactylon.Also,under the combined effects,the wave pressure and wave erosion rate increased with increasing gravel particle size,and decreased with increasing gravel thickness and cover of C.dactylon.Compared with the single effect,further reductions of wave pressure and wave erosion rate under the combined effects were attributed to the synergistic effects of plant and gravel cover.The largest reductions in wave pressure and wave erosion rate were obtained with a gravel particle size of 5-10 mm,gravel cover thickness of 60 mm,and C.dactylon cover of 60%-70% .Multivariate analysis of variance showed that the combined effect of gravel and C.dactylon cover synergistically reduced the wave pressure and wave erosion rate.The factors were ranked,from highest degree of influence on wave pressure to lowest,as follows:gravel cover thickness>gravel particle size>plant cover;and from highest degree of influence on wave erosion rate to lowest,as follows:plant cover>gravel cover thickness>gravel particle size.Our results show that gravel and vegetation work synergistically to reduce wave energy and erosion,and can be used as a sustainable and ecologically friendly treatment to control wave erosion on sloping banks.These findings provide guidance and reference data for the ecological management and ecological reconstruction of the water-level fluctuation zone in water reservoirs.
gravelCynodon dactylonwave pressurewave erosion ratewater-level fluctuation zone
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