1.福州大学 土木工程学院,福建 福州 350116
2.福建省水利水电勘测设计研究院有限公司,福建 福州 350000
3.福建省水工程水动力研究中心,福建 福州 350001
4.福建省水利水电科学研究院,福建 福州 350001
蒋北寒(1988-),女,副教授. 研究方向:水力学及河流动力学. E-mail:jiangbeihan@fzu.edu.cn
蔡枫,讲师,E-mail:caifeng@fzu.edu.cn
收稿:2025-09-17,
修回:2025-10-26,
网络出版:2025-10-29,
移动端阅览
蒋北寒,蔡靖铭,蔡枫等.不同特性植被群对河床形态的影响[J].工程科学与技术,
JIANG Beihan,CAI Jingming,CAI Feng,et al.Effects of Vegetation Patches with Different Characteristics on Riverbed Morphology[J].Advanced Engineering Sciences,
蒋北寒,蔡靖铭,蔡枫等.不同特性植被群对河床形态的影响[J].工程科学与技术, DOI:10.12454/j.jsuese.202500721.
JIANG Beihan,CAI Jingming,CAI Feng,et al.Effects of Vegetation Patches with Different Characteristics on Riverbed Morphology[J].Advanced Engineering Sciences, DOI:10.12454/j.jsuese.202500721.XXXX,XX(XX):1‒11.
植被群广泛分布于天然河道中,是河流动力与生态系统的重要组成部分,通过调控水流结构与泥沙输运,影响河床形态的演变。本文基于室内动床水槽试验,采用圆柱体木棍模拟相邻植被群,研究不同植被群密度、间距及来流流速对河床形态的影响规律。试验结果表明:植被群密度通过增强阻水与绕流作用,改变局部流速分布,进而调节冲淤过程。随着无量纲密度
aD
(
a
为单位体积内植被总迎水面积,
D
为植被群直径)的增大,植被群周围的冲刷范围扩大。当
aD
<
4时,泥沙在植被群后方低速带沉积,形成主沉积区。当
aD
≥4时,尾流融合作用促使下游形成新沉积区,即次沉积区;随着密度的进一步增大,主、次沉积区在纵向上合并,沉积范围向下游延展。植被群间距调控尾流融合程度与沉积区形态,在小间距
Δ
/
D
<
0.4(
Δ
为植被群间距)时,植被群后方的沉积区连通,形成主沉积连接型床面;在间距适中时(0.4≤
Δ
/
D
≤1.3),尾流相互作用增强,次沉积区在下游发育并向外扩展,形成扩张发散型床面;在大间距下(
Δ
/
D
>
1.3),尾流分离,沉积区趋于独立,地形变化范围缩小,形成分离收缩型床面。来流流速
U
0
通过调节泥沙起动程度,控制床面冲淤的空间分布。床面冲淤过程表现出阶段性特征,局部起动阶段(
U
0
/
U
c
<
1.3,
U
c
为泥沙临界起动流速):仅有少量泥沙起动,沉积集中于尾流区,床面变化有限;沙波形成阶段(1.3≤
U
0
/
U
c
≤1.6):舌状沙波形成,冲淤范围拓展;冲淤分离阶段(
U
0
/
U
c
>
1.6):泥沙远距离输移,床面呈现中间淤积、两侧冲刷的平面形态,冲刷与淤积区域界限分明。进一步分析表明:密度与来流流速对最大淤积高度
D
max
的影响较大,间距次之;最大冲刷深度
S
max
主要受来流流速影响,密度为次要影响因素,间距作用最弱。研究结果可为河道生态修复工程中植被的优化配置提供数据支撑与技术参考。
Objective
2
Vegetation patches
which are widely distributed in natural channels
are fundamental elements of both river hydraulics and ecosystems. Vegetation patches influence the evolution of riverbed morphology primarily by altering flow structures and sediment transport. Previous studies have predominantly centered on isolated factors or localized flow fields
with scant attention paid to the integrated effects of vegetation patch density
patch separation
and incoming flow velocity on riverbed morphology. In this study
a systematic experimental investigation was conducted to quantify the impact of adjacent vegetation patches with distinct characteristics on bedform evolution.
Methods
2
The experiments were conducted in a recirculating flume (55 m × 1 m × 1.5 m) with a movable bed
where circular
emergent vegetation patches with a diameter of 0.1 m were constructed from rigid wooden cylinders (5 mm diameter
0.3 m height). The movable bed was composed of uniform sediment with a grain size of 0.15 mm
and a constant water depth of 0.16 m was maintained throughout the experiments. A series of tests was designed to isolate the effects of three dimensionless parameters: (1) patch density
represented by the dimensionless parameter
aD
where
a
is the frontal area per unit volume and
D
is the patch diameter
ranging from 1 to 8; (2) patch separation
expressed by the dimensionless parameter
Δ/D
where
Δ
is the gap width between patches
ranging from 0.2 to 1.5; and (3) incoming flow velocity
U
0
normalized by the cr
itical flow velocity for sediment incipient motion
U
c
i.e.
U
0
/U
c
ranging from 0.9 to 1.8. Bed topography data were acquired through close-range digital photogrammetry for the subsequent construction of digital elevation models (DEM).Results and Discussions The results indicated that an expansion of the horseshoe-shaped scour zones around the vegetation patches was observed with increasing density. For
aD
<
4
a primary deposition zone was observed in the low-velocity region of the wake. For
aD
≥ 4
a new deposition area downstream
namely a secondary deposition zone
was formed due to wake interactions. At higher densities
the primary and secondary zones were merged longitudinally
resulting in an enlarged
elongated depositional zone
which consequently enhanced the complexity of the bed morphology. The maximum scour depth (
Sₘₐₓ
) exhibited a continuous increase with
aD
. In contrast
the maximum deposition height (
Dₘₐₓ
) remained stable prior to a threshold of
aD
<
4
beyond which a pronounced growth occurred. Patch separation (
Δ/D
) proved to be a secondary factor for scour intensity
as the extent of scouring around the patches remaining consistent across different separations. At small patch separations (
Δ/D
<
0.4)
a single
large wake structure formed downstream
leading to a continuous and concentrated sediment deposition
which was classified as a primary-deposition-connected bed type. At intermediate separations (0.4 ≤
Δ/D
≤ 1.3)
enhanced wake interactions promoted the expansion of the depositional area both downstream and laterally
leading to an expansion-diverging bedform characterized by coexisting primary and secondary depositions. At large separations (
Δ/D
>
1.3)
the wake structures were observed to be largely detached
and the bed morphology was char
acterized by independent scour-and-deposition pattern
which is defined as a separated-contracting pattern. Accordingly
S
max
was found to be insensitive to separation variations
whereas
D
max
demonstrated a tri-phasic response (decrease-increase-decrease) with increasing
Δ/D
peaking at intermediate separation. Three stages were identified with increasing
U
0
/U
c
. The localized incipient-motion stage (
U
0
/U
c
<
1.3) was marked by limited sediment movement
where deposition remained confined to the wake region. At the sand-wave formation stage (1.3 ≤
U
0
/U
c
≤ 1.6)
with enhanced sediment transport
regular and continuous sand waves were formed
accompanied by a significant expansion in the scope of scour and deposition. At the scour-deposition separation stage (
U
0
/U
c
>
1.6)
with extensive sediment transport
a clearly differentiated bed morphology was formed
comprising a central depositional area flanked by lateral scour zones. As a result
S
max
showed an accelerating increase with flow velocity
whereas
D
max
exhibited a non-monotonic response
first increasing then decreasing with increasing
U
0
/U
c
. Comprehensive parametric analysis identified density and flow velocity as the most significant factors for
D
max
and separation as less influential. For
S
max
flow velocity was the dominant parameter
followed by density and then separation.
Conclusions
2
The key mechanisms influencing bed morphology evolution by vegetation patches with differing characteristics were identified in this study. The patch density was found to significantly influence scour intensity around patches and the extent of downstream depositional zones by enhancing flow blockage and lateral deflection. The spatial distribution of depositional areas is mainly governed by patch separation
which regulates wake merging or separation. Furthermore
the intensity of scour and deposition
as well as their spatial separation
are dominated by flow velocity through its control over sediment incipient motion and transport capacity. A systematic classification of bedforms was developed
and the influence of each factor on scour and deposition processes was quantified. This study provides an experimental basis for predicting the evolution of vegetated channels
thereby directly guiding the optimization of vegetation layout and hydraulic design in ecological restoration.
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