Influence of submerged vegetation on flow structure and sediment deposition

doi:10.3785/j.issn.1008-973X.2021.01.009

Journal of ZheJiang University (Engineering Science)

2021, Vol. 55

Issue (1): 71-80 DOI: 10.3785/j.issn.1008-973X.2021.01.009

Influence of submerged vegetation on flow structure and sediment deposition

Zhi-lin SUN(

),Jia-yun ZHENG,Li-li ZHU,Lin CHONG,Jun LIU,Ju-yuan LUO

Ocean College, Zhejiang University, Hangzhou 310058, China

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Abstract

Thirty-three sets of flume experiments were conducted under turbid water and submerged vegetation with different arrangements in order to analyze the influence of vegetation on flow structure and sediment deposition. Results showed that the velocity profile was parabola below the canopy of short vegetation while that was logarithmic above it. A bi-Gaussian distribution formula for turbulence intensity in short vegetation zone was established considering plant spacing. The predicted values of velocity and turbulence intensity accorded well with the measured values. Velocity profile is C-type while the largest turbulence is near the canopy in tall vegetation zone. Average velocity below canopy in mixed vegetation with three kinds of plant spacing was 32.5%-72.3% of that without vegetation. The nonlinear relation of relative deposition increment with flow intensity and plant spacing in short vegetation zone was proposed under small Froude number (Fr≤0.18). The deposition in mixed vegetation zone was the largest with 7 times of that without vegetation under the same flow and plant spacing, followed by that in tall vegetation zone. Effects of tall and mixed vegetation on deposition increased with the decrease of plant spacing.

Key words： submerged vegetation velocity profile turbulence intensity sediment deposition

Received: 06 January 2020 Published: 05 January 2021

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Cite this article:

Zhi-lin SUN,Jia-yun ZHENG,Li-li ZHU,Lin CHONG,Jun LIU,Ju-yuan LUO. Influence of submerged vegetation on flow structure and sediment deposition. Journal of ZheJiang University (Engineering Science), 2021, 55(1): 71-80.

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http://www.zjujournals.com/eng/10.3785/j.issn.1008-973X.2021.01.009 OR http://www.zjujournals.com/eng/Y2021/V55/I1/71

沉水植物对水流结构与泥沙淤积的影响

为了研究水生植物对水流结构和泥沙淤积的影响，针对不同布置的沉水植物进行33组浑水水槽试验. 结果表明，矮株植物区流速冠顶下为二次多项式分布，以上为对数分布；考虑相对株距的影响，建立矮株植物区紊动强度的双高斯垂线分布公式，按该公式计算的流速和紊动强度与实测资料较吻合. 高株植物区流速呈“C”型分布，紊动强度以冠顶附近最大. 3种株距布置时，混合植物冠顶以下平均流速为无植物时的32.5%~72.3%. 提出小弗汝德数（Fr≤0.18）条件下矮株植物区相对淤积增量与水流强度和相对株距的非线性关系. 在相同水流和株距下，混合植物淤积量高达无植物时的7倍，高株植物次之，随着株距的减小促淤效果逐渐增强.

关键词： 沉水植物, 流速分布, 紊动强度, 泥沙淤积

Fig.1 Experimental flume with vegetation

Fig.2 Short vegetation A and tall vegetation B

Fig.3 Vegetation distribution under four different densities

Tab.1 Flume experiment conditions under turbid water

Fig.4 Velocity profile in short vegetation zone

Fig.5 Relation between undetermined coefficients in Eq.(1) and relative plant spacing

Fig.6 Comparison of flow velocities predicted and measured for short vegetation zone

Fig.7 Velocity profiles in tall and mixed vegetation zone

Fig.8 Vertical distribution of x-direction turbulence intensity in short vegetation zone

Fig.9 Relation between undetermined coefficients in Eq.（3）and relative plant spacing

Fig.10 Comparison of turbulence intensity predicted in x direction and measured for short vegetation zone

Fig.11 Vertical distribution of z-direction turbulence intensity in short vegetation zone

Fig.12 Relation between undetermined coefficients in Eq（5）and relative plant spacing

Fig.13 Comparison of turbulence intensity predicted in z direction and measured for short vegetation zone

Fig.14 Vertical distribution of turbulence intensity in tall vegetation zone with different densities

Fig.15 Vertical distribution of turbulence intensity in mixed vegetation zone with different densities

Fig.16 Deposition rate under different vegetation

Fig.17 Relation between relative deposition increment and Fr for short vegetation

Fig.18 Comparison of relative deposition increment predicted and measured for short vegetation zone


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