不同布置形态下刚性淹没植被对水流特性的影响

自然河道中植被呈现多种多样的分布状态,为探究不同布置形态下刚性淹没植被对水流特性的影响,利用室内水槽模拟含刚性淹没植被的明渠进行试验研究。结果表明:刚性淹没植被的布置形态对明渠流水流特性影响显著。在本文研究的植被布置形态下的水深、植被阻力系数与植被粗糙系数均增大,表现为交错型布置斑块型布置线性布置;流速与雷诺数均减小,表现为线性布置斑块型布置交错型布置;糙率n随着平均流速与水力半径之积VR的增大而减小。     

含植物河道曼宁阻力系数的研究

含植物河道的水流阻力不仅仅来源于边壁,传统的曼宁公式不能够直接用来计算这种河道的糙率。本文基于水流阻力等效原则,首次提出了一系列等效水力参数的概念,建立了等效综合曼宁糙率系数和等效植物附加曼宁系数的计算公式,并给出了能否使用水深代替水力半径的判别参数。使用刚性圆柱棒进行水槽试验,对植物在非淹没和淹没条件下的曼宁系数进行了计算和比较。试验结果验证了理论分析提出的关于判别参数的结论,并且表明使用水深计算的糙率在植物非淹没条件下可以用来表示植物引起的附加阻力。本文提出的等效综合曼宁糙率系数计算公式包含了植物的物理特性,因此具有普遍的应用价值,可以用来进行实际工程中糙率的计算。     

沉水植被群落状态对水流阻力的影响

沉水植被在水流作用下状态会发生改变,进而会对河流生态系统产生一定影响。通过室内水槽模型实验观测了均匀流下沉水植被群落内部各植株的状态,并分析了沉水植被群落状态以及内部植株相对间距对植被群落水流阻力的影响。研究结果表明:在沉水植被群落内部,各个植株的相对刚度各不相同,并且其状态随来流条件变化而改变,对于不同种群的沉水植被群落,在相同水流条件下也可能呈现出不同的状态,当沉水植被群落的植被处于非直立状态时,随着植被从弯曲状态向直立状态转换,水流阻力也在不断增大;植被处于完全刚性状态时,阻力系数则与植被相对刚度无关,仅与水流条件有关,随着流速的增大而减小;沉水植被群落内部植被相对间距不同,其阻水效果也不同,在相同植被状态下,植被相对间距越大,也就是植被带越长,植被阻力越大。     

HYDRAULIC RESISTANCE OF SUBMERGED VEGETATION RELATED TO EFFECTIVE HEIGHT

Submerged vegetation has a significant impact on water flow velocity. Current investigations include the impact through adding drag resistance and increasing bottom roughness coefficient, which cannot elucidate the characters of real submerged vegetation. To evaluate the effects of submerged vegetation on water currents at different velocities, a laboratory experiment was conducted using three kinds of vegetations. The effective heights of these vegetations on varying flow velocities were evaluated. An equation describing the relationship between the normalized resistance of the submerged plants and the Reynolds number based on the plant effective height was then established and used to calculate the hydraulic resistance parameters of submerged plants in different stages of growth.     

Characteristics of Flow Resistance in Open Channels With Non-Submerged Rigid Vegetation

The flow resistance factors of non-submerged rigid vegetation in open channels were analyzed. The formulas of drag coefficient CD and equivalent Manning＇s roughness coefficient na were derived by analyzing the force of the flow of non-submerged rigid vegetation in open channel. The flow characteristics and mechanism of non-submerged rigid vegetation in open channel were studied through flume experiments.     

河岸与河底相对粗糙度对河道平衡形态的影响研究

边界条件对河流地貌形态具有重要影响,基于河道边界阻力水力半径分割方法,利用变分方法研究河岸与河底相对粗糙度对冲积河流平衡河道形态的影响.结果表明,河岸与河底相对粗糙度对河流达到平衡时的最大输沙率有一定的影响,但对河道平衡形态的影响非常显著.在临界和平均水力几何形态关系式中,随着河岸与河底相对粗糙度的增大,河宽关系式的系...     

含淹没植物的水流阻力试验研究

河道中存在水生植物会改变水流阻力,在大多数情况下会导致水位抬高,降低河道的泄洪能力。然而,水生植物的存在对河道治理、边滩保护、水质净化等起积极作用。为了探索河道中水生植物对水流阻力的影响,在实验室水槽中进行了不同密度的流淹没刚性植物水流试验,观测了沿程的水位变化,计算了水面坡降,基于试验资料分析了雷诺数、植物密度对糙率系数的影响,并建立拖曳力同植物水流特征粗糙度对数关系表达式,丰富了植物条件下明渠流动的试验观测资料数据库。     

壅水条件下水流阻力试验研究

壅水条件下的水流阻力及输沙特性,在水利工程的应用中占有十分重要的位置。对壅水条件下河道开展概化水槽试验,采用声学多普勒测速仪ADV对水流流速进行了测量,并对壅水条件下水流阻力和床面切应力等进行了分析。结果表明壅水条件下,水流流速沿垂线分布较均匀流条件下更加均匀,当壅水程度越大时,水流流速沿垂线分布越均匀,且流速分布大致上仍服从对数率分布;壅水条件下,随着水深的增大,摩阻流速不断减小;壅水条件下河道水流阻力系数随着非均匀系数及水力半径的增大而增大;引入壅水程度指标,并拟合得到了床面切应力随壅水程度指标的变化关系式。成果可为壅水条件下水流结构特征及输沙规律的研究提供参考。     

植被对河道水流及岸滩形态演变影响研究进展

植被作为河流系统重要的阻力因素,在河道形态演变方面发挥着至关重要的作用。植被地表结构改变了河道水流阻力、河床切应力、流速分布及水流紊动特性,植被根系增强了岸滩土体强度和稳定性。从植被地表茎干结构对水流特性影响和植被地下根系加筋作用对岸滩稳固影响两个方面的研究进行了回顾和综述,并指出今后在植被水流研究方面,可进一步考虑植被枝、叶对水流特性的影响,加强对柔性植被变形、摆动引起的动边界问题的研究,以及全面考虑河道形态边界条件的影响,特别是含植被的分汊河道水流特性还需深入研究;在植被根系固土护岸方面,可同时考虑岸滩土体非均质性、河道水流对岸滩的侵蚀冲刷作用及水体渗流对岸滩土体力学特性的影响;在植被河道形态演变预测方面,可以综合考虑含植被河道的水动力学及土力学问题,以及两者间的互馈响应机制。     

Reach‐scale interactions between aquatic plants and physical habitat: River Frome,Dorset

Substrate and flow velocity are two key physical factors influencing the distribution of aquatic plants. These two controls are closely related and reflect interactions between flow regime, quantity and calibre of sediment supplied to and bounding river channels, and channel dimensions. Seasonal growth of aquatic plants has important impacts upon flow resistance, flow velocities and sediment dynamics. This paper focuses upon the reach scale and the aggregate impact of the seasonal growth of aquatic plants on the meso‐habitat characteristics of chalk rivers. It provides a contribution to the broader literature by illustrating how submerged and emergent macrophytes interact with one another at the reach scale to control flow patterns and the retention of fine sediment. The research was conducted within the River Frome, Dorset, UK. Four sets of observations from 2004 of the seasonal growth of aquatic plants, flow velocity behaviour and the storage of fine sediment are presented. Aggregate velocity behaviour over the four observation periods is classified using agglomerative, hierarchical cluster analysis. The spatial arrangement of patches exhibiting different aggregate velocity behaviour are explored and the degree to which velocity behaviour can be attributed to physical characteristics of patches and the growth of aquatic plants is discussed. Conclusions include: (i) patterns of aggregate velocity behaviour within reaches are strongly influenced by macrophyte growth; (ii) average fine sediment deposition is higher around emergents such as Sparganium erectum than submerged plants such as Ranunculus penicillatus subsp. pseudofluitans; (iii) complementary flow patterns evolve across the river channel as aquatic macrophytes grow and it appears that this allows marginal emergents to scavenge fine sediment from faster flow velocity threads that become diverted towards the channel edges. (iv) These processes are important for mesohabitat evolution and maintenance, and they also contribute to patterns of bank erosion and aggradation. Copyright © 2006 John Wiley & Sons, Ltd.     

淹没状态下河道植物偏斜高度与糙率的关系

利用室内变坡水槽,模拟了复式河道滩地3种植物对漫滩水流的干扰作用,并借助声学多普勒测速仪(ADV)施测了不同垂线、不同测点的瞬时流速,计算了不同条件下的河道糙率。基于水动力及植物柔性变形分析,建立了淹没状态下的植物河道糙率计算的基本关系,反映出糙率值不仅与水流动力条件有关,还与植物类型、淹没高度、布置及其自身力学性能有关,同时,利用试验资料及理论分析成果,进一步获取了植物河道的附加糙率值,借此分析与评价河道植物对水流阻力的影响程度。     

含植物河道水动力特性研究进展

水生植物群落是河流生态系统的重要组成部分,利用天然植被护坡固土、净化水质、改善河流生态环境已成为河流生态修复的重要措施。本文从水生植物影响下的河道水流阻力特性及水流结构两方面,总结了国内外对含植物河道水动力特性的研究进展,并对该领域的未来研究方向提出了展望。     

基于水动力的植被消长模型及河道植被演替模拟

针对植被斑块在河道中的演替规律,建立了概化河道下的植被斑块消长模型。该模型以二维浅水方程组为控制方程,采用有限体积法离散求解水动力参数,利用等效曼宁系数法概化植被影响,定义床面剪切力小于阈值区域为新植被生长区,大于阈值区域为植被消亡区。考虑植被阻力对水流的影响以及床面切力对植被消长的影响,建立了植被消长与水动力过程相耦合的数学模型,模拟了不同条件下的植被区演替过程,模拟过程中重点考虑了两个床面剪切力阈值和两个初始植被密度工况。计算结果表明：植被斑块在河道内的演变通常是由块状向条带状发展,较高的剪切力阈值将产生更大的最终植被面积;当剪切力阈值系数为0.5时,最终植被面积占河道总面积的比值为47%~49%;当剪切力阈值系数为0.7时,最终植被面积占比为58%~60%;不同的初始植被分布并不会对最终植被面积产生显著影响,但较大的初始植被密度会加快植被的初始生长速率,使植被面积更快达到基本稳定水平。     

Calibration, Validation and Sensitivity Analysis of the MIKE-SHE Model Using the Neuenkirchen Catchment as Case Study

Calibration and validation of the MIKE-SHE model was performed using the Neuenkirchen research catchment hydrologic characteristics and a two-year time series of stream flows at the outlet of the catchment. A reasonable match was obtained between the observed and simulated hydrograph at the catchment outlet with minor calibration effort. For the validation runs, the base flows were overestimated in the period of high rainfall intensity while the peak flows were reasonably matched. Sensitivity of the model to structural parameters such as grid size and time step, and to the functional parameters, including hydraulic resistance coefficient, surface and subsurface hydraulic properties, was investigated. The results indicated that the peak overland flow and the total overland flow were very sensitive to the flow resistance parameters and to the vertical hydraulic conductivity of the surface soil, while the peak aquifer discharge and the total aquifer discharge were sensitive to the horizontal hydraulic conductivity in the saturated zone. The model output variables considered were neither affected, to a significant extent, by the vegetation parameters nor by the specific storage coefficient.     

人工植被分布变化对坡面流阻力及局部水头损失系数的影响研究

基于室内坡面流实验,研究了人工植被分布变化对坡面流水动力学特性的影响。试验包括"细管整齐排列"、"细管1/2错开排列"、"细管1/4错开排列"、"粗管1/2错开排列"等植被分布方式。研究结果表明植被分布变化对坡面流扰动程度的影响显著,从而使得不同植被分布方式下的坡面流达西阻力系数、局部水头损失系数差异性很大。而随流量增大达西阻力系数、局部水头损失系数都呈现先减小后增大的趋势。     

含柔性植物明渠水流阻力特性试验研究

利用水槽试验研究了无草、淹没型、非淹没型柔性植物水流阻力特性的变化规律,分析了含植物明渠沿程水面比降和阻力系数的变化特性。得到各植物阻力系数变化与尼库拉兹曲线基本相似,紊流范围内同样可划分为紊流光滑区、紊流过渡区、紊流粗糙区;探讨了各植物明渠等效河床的问题,据此确定了各植物的粗糙度,对植物粗糙度、水流雷诺数和阻力系数之间的关系进行了分析,并通过对各植物水流阻力系数的分区回归计算,得到各植物水流阻力的分区经验表达式,该方法能较好地应用于含植物明渠水流阻力系数的推求。     

A STUDY OF DRAG COEFFICIENT RELATED WITH VEGETATION BASED ON THE FLUME EXPERIMENT

This study is focused on the effects of ecological factors (diameter and flexibility) and vegetation community composition on the drag coefficient related with vegetation. The single leafy shrub and three mixed communities (including shrub-grass, shrub-reed and reed-grass community) were studied. The flow velocity and water level were measured and used to calculate the drag coefficient based on the Bernoulli's equation, Darcy drag formula and the expression for the drag coefficient related with Darcy drag factor. The trend of the drag coefficient in the vertical direction was analyzed against flow depth, diameter, diameter Reynolds number, flow depth Reynolds number and relative roughness height in different discharges. The results show that beside the dense leafy shrubs community, the vertical trend of the drag coefficient among other cases against flow depth, diameter, diameter Reynolds number, flow depth Reynolds number and relative roughness height can be approximately expressed by power law functions under different flow discharges. Moreover, in a mixed community with two plants with distinctly different ecological factors, the one with the most distinct variations of ecological factors determines the vertical trend of the drag coefficient; the other one only affects the magnitude of the drag coefficient. Furthermore, if the ecological factors of the vegetation in the vertical direction are kept almost not changed, the drag coefficient can be approximately regarded as a constant.     

水利水电工程施工导截流模型试验中的阻力相似问题

施工导截流模型阻力不相似会导致试验成果与实际存在较大偏差。采用理论分析及水力计算方法,剖析了长导流隧洞壁面沿程阻力相似的影响因素,揭示了截流模型试验中阻力危机现象,提出了解决阻力不相似问题的途径。研究表明：对于隧洞导流模型受模型比尺制约,模型水流往往处于紊流过渡区,洞壁阻力系数是模型雷诺数的函数,如忽视模型阻力相似问题,会导致模型泄流能力试验值和洞内流态与原型存在较大偏差,可采取加大流量法或通过系统试验拟合阻力系数与模型雷诺数的关系,再对模型试验泄流能力成果予以修正。对于截流模型,块体抗冲稳定相似需满足推阻力系数相似,模型雷诺数Re_m只有在3×10⁴～2×10⁵时,绕流阻力系数C_d才为常数,可通过合理选择模型比尺使模型水流进入自模拟区,避免阻力危机。     

植被缓流效果试验研究

为深入研究植被减流减沙特征及对流域水土保持效益的影响,本文通过5个覆盖度,6个坡度和7个流量的组合条件下的室内放水试验,系统研究了植被对坡面水流的缓流特征。结果表明:随着植被覆盖度增加,植被对坡面水流的阻滞作用逐渐凸显,即缓流系数减小,缓流效果增强,当植被覆盖度大于4.650%时,缓流效果趋于稳定。在试验流量范围内,缓流系数随流量的增加呈现逐渐减少的趋势,而随坡度的增加略有增加。缓流系数随水深和雷诺数增加而减小,而与弗劳德数呈反C型分布。最后,建立了基于试验控制变量(植被覆盖度,流量和坡度)的缓流系数预测公式。     

POTENTIAL FOR VEGETATION‐BASED RIVER MANAGEMENT IN DRYLAND,SALINE CATCHMENTS

The approaches used to manage rivers have been developed and adapted to many different problems and settings. Because of their relatively low cost, vegetation‐based approaches implemented at the reach, landholder and catchment scales have become the foundation for river management in most landscapes. In many dryland agricultural catchments, secondary (anthropogenic) salinity caused by clearing native vegetation has resulted in rising saline groundwater, streamflow salinity values that exceed seawater and severe the degradation of riparian vegetation communities. The potential effectiveness of vegetation‐based strategies in these landscapes remains largely unknown, yet these strategies are still widely pursued. This study initially investigated the patterns of vegetation recovery and recolonization following a large flood in a saline river that disturbed the system. A conceptual model was developed to describe spatial patterns of where different vegetation types had regrown and recovered in relation to controls exerted by streamflow salinity, surface texture characteristics, topography and reach morphology. Using this model, vegetation‐based river management options for different reaches were developed, and their potential effectiveness in stabilizing reaches was investigated using a 1‐D hydraulic modelling approach. This study finds that in a dryland catchment with high stream salinity (20 000–93 000 mg L^?1), there is still a strong potential for successful vegetation‐based management, but only in selected reaches. Results showed that changes in stream power and channel velocity were not associated with the areas of most severe vegetation degradation. Rather, there is a complex interplay between channel morphology, channel slope and places of potential vegetation growth within a reach. This paper outlines an approach to evaluate the potential success of vegetation‐based river management in saline landscapes. It identifies the need to prioritize investment based on the following: an understanding of factors controlling revegetation potential, the likely impact of revegetation in mitigating adverse channel changes and the proximity of reaches to high‐value infrastructure and biodiversity assets. Copyright © 2011 John Wiley & Sons, Ltd.