Extreme coastal events require careful prediction of wave forces. Recent tsunamis have resulted in extensive damage of coastal structures. Such scenarios are the result of the action of long waves on structures. In th...Extreme coastal events require careful prediction of wave forces. Recent tsunamis have resulted in extensive damage of coastal structures. Such scenarios are the result of the action of long waves on structures. In this paper, the efficiency of vegetation as a buffer system in attenuating the incident ocean waves was studied through a well controlled experimental program. The study focused on the measurement of forces resulting from cnoidal waves on a model building mounted over a slope in the presence and absence of vegetation. The vegetative parameters, along with the width of the green belt, its position from the reference line, the diameter of the individual stems as well as the spacing between them, and their rigidity are varied so as to obtain a holistic view of the wave-vegetation interaction problem. The effect of vegetation on variations of dimensional forces with a Keulegan-Carpenter number （KC） was discussed in this paper. It has been shown that when vegetal patches are present in front of structure, the forces could be limited to within F＊≤I, by a percentile of 92%, 90%, 55%, and 96%, respectively for gap ratios of 0.0, 0.5, 1.0, and 1.5. The force is at its maximum for the gap ratio of 1.0 and beyond which the forces start to diminish.展开更多
Vegetation plays a critical role in influencing runoff processes and soil loss during gully bed erosion.However,it is still unclear how the stem coverage affects gully bed erosion processes by altering the runoff hydr...Vegetation plays a critical role in influencing runoff processes and soil loss during gully bed erosion.However,it is still unclear how the stem coverage affects gully bed erosion processes by altering the runoff hydraulics and soil sedimentation.A series of in situ scouring experiments were conducted to investigate the influence of shrub stem coverage on the concentrated flow pathway characteristics,hydrodynamic parameters,and sediment concentration during gully bed erosion processes.The Flow pathway characteristics expressed by the Number of flow pathways(FN),total Flow path Width(FW),Tortuosity Ratio(TR),and Fractal Dimension(FD)were quantified by analyzing photographs of the gully bed surface taken during experimental periods.Structural equation model was used to analyze the comprehensive effect of stem coverage on hydraulic erosion of gully beds.The results showed that FN,FW,and TR increased linearly,and FD increased exponentially as stem coverage increased.Compared with the bare gully bed,the flow velocity and shear stress of gully beds with shrub stem covers decreased by 17.47%-25.19%and 4.75%-11.42%,respectively,while the Darcy-Weisbach friction factor increased by 35.94%-68.71%.The sediment concentration of stem-covered gully beds decreased by 11.82%-26.93%.The increasing stem coverage promoted concentrated flow branching and significantly increased FW,which in turn altered hydraulic parameters,particularly reducing flow velocity,and ultimately reducing sediment concentrations indirectly.These results contribute to partially explaining the differences in flow hydraulics and soil loss of vegetated gully beds in previous studies that failed to account for changes in flow pathways.展开更多
文摘Extreme coastal events require careful prediction of wave forces. Recent tsunamis have resulted in extensive damage of coastal structures. Such scenarios are the result of the action of long waves on structures. In this paper, the efficiency of vegetation as a buffer system in attenuating the incident ocean waves was studied through a well controlled experimental program. The study focused on the measurement of forces resulting from cnoidal waves on a model building mounted over a slope in the presence and absence of vegetation. The vegetative parameters, along with the width of the green belt, its position from the reference line, the diameter of the individual stems as well as the spacing between them, and their rigidity are varied so as to obtain a holistic view of the wave-vegetation interaction problem. The effect of vegetation on variations of dimensional forces with a Keulegan-Carpenter number （KC） was discussed in this paper. It has been shown that when vegetal patches are present in front of structure, the forces could be limited to within F＊≤I, by a percentile of 92%, 90%, 55%, and 96%, respectively for gap ratios of 0.0, 0.5, 1.0, and 1.5. The force is at its maximum for the gap ratio of 1.0 and beyond which the forces start to diminish.
基金financially supported by the National Natural Science Foundation of China(42277358)the Science and Technology Research Program of Institute of Mountain Hazards and Environment,Chinese Academy of Sciences(IMHE-GJHZ-03)the National Natural Science Foundation of China(42107377).
文摘Vegetation plays a critical role in influencing runoff processes and soil loss during gully bed erosion.However,it is still unclear how the stem coverage affects gully bed erosion processes by altering the runoff hydraulics and soil sedimentation.A series of in situ scouring experiments were conducted to investigate the influence of shrub stem coverage on the concentrated flow pathway characteristics,hydrodynamic parameters,and sediment concentration during gully bed erosion processes.The Flow pathway characteristics expressed by the Number of flow pathways(FN),total Flow path Width(FW),Tortuosity Ratio(TR),and Fractal Dimension(FD)were quantified by analyzing photographs of the gully bed surface taken during experimental periods.Structural equation model was used to analyze the comprehensive effect of stem coverage on hydraulic erosion of gully beds.The results showed that FN,FW,and TR increased linearly,and FD increased exponentially as stem coverage increased.Compared with the bare gully bed,the flow velocity and shear stress of gully beds with shrub stem covers decreased by 17.47%-25.19%and 4.75%-11.42%,respectively,while the Darcy-Weisbach friction factor increased by 35.94%-68.71%.The sediment concentration of stem-covered gully beds decreased by 11.82%-26.93%.The increasing stem coverage promoted concentrated flow branching and significantly increased FW,which in turn altered hydraulic parameters,particularly reducing flow velocity,and ultimately reducing sediment concentrations indirectly.These results contribute to partially explaining the differences in flow hydraulics and soil loss of vegetated gully beds in previous studies that failed to account for changes in flow pathways.
