河道植被对水流运动影响研究之现状

研究植被与河道水流的相互作用,对于防洪和生态环境治理具有实际意义.总结了沉水植被和挺水植被对水流的阻力的研究进展情况.针对单一类型植被对水流的阻力已经开展了物理模型试验研究,但试验中忽略了植被的生态特征变化对水流运动的影响.已有的植被对水流阻力的数值模型,是通过调整河床糙率来考虑沉水植被对水流的阻力,采用圆柱绕流的阻力公式计算挺水植被引起的水流阻力.今后在分析植被对水流运动影响的研究时,需要进一步考虑植被的多样性和生态特征.     

非淹没刚性植被流动阻力研究

水生植物环境中,水流受植被的阻碍作用,流动阻力增加。为了定量研究植被对水流的阻力,本文采用应力计对非淹没刚性植被的流动阻力进行了实验室测量。能量方程计算的拖曳力与应力计实测的拖曳力进行了对比,两者的一致性证明了拖曳力测力装置的有效性。对不同水深条件下的植被拖曳力的测量表明,非淹没刚性植被的流动阻力与速度的平方成正比,拖曳力系数受雷诺数和能量底坡的影响较大。     

非淹没刚性植被流动阻力研究

摘要：水生植物环境中,水流受植被的阻碍作用,流动阻力增加。为了定量研究植被对水流的阻力,本文采用应力计对非淹没刚性植被的流动阻力进行了实验室测量。能量方程计算的拖曳力与应力计实测的拖曳力进行了对比,两者的一致性证明了拖曳力测力装置的有效性。对不同水深条件下的植被拖曳力的测量表明,非淹没刚性植被的流动阻力与速度的平方成正比,拖曳力系数受雷诺数和能量底坡的影响较大。     

植被覆盖下坡面流的水流特性实验研究

为研究柔性植被和刚性植被覆盖下坡面流的水流特性,用水槽模拟坡面,PVC塑料薄膜模拟植被,通过调节水槽的坡度和柔性、刚性植被覆盖度对坡面流的水流流态、流速、水流深度进行了研究。经过多组实验得出了大量植被覆盖下的坡面流水力特性数据,并通过数据分析,总结了在不同植被覆盖、不同坡度条件下坡面流流速的变化规律。最后得出,通过减小坡面流流速、增加水流水深、控制水流流态、选择刚性植被覆盖坡面,可减少对坡面土壤的水力侵蚀。实验结果对控制流域非点源污染和选择水土流失防治措施有参考作用。     

山区宽窄相间河道平面二维水流数值模拟

针对山区河道受地质条件及河床演化的影响,其平面形态常呈现宽窄相间的渐变形态特征,采用贴体坐标法剖分正交贴体曲线网格求解域,用有限体积法离散控制方程,以SIMPLER计算程式求解耦合方程,建立山区宽窄相间河道平面二维水流数学模型。将模型计算值与宽窄相间水槽水流试验实测值及水动力学SMS软件计算结果进行比较,结果表明:该模型能够较好地模拟宽窄相间河道平面二维水流运动特性,宽窄相间河道河宽渐变将引起水深和流速的变化,在河道最窄处水深降到最低,流速最大;在河道最宽处水深达到峰值,流速最小。     

非棱柱形河道恒定非均匀流水面线的一种数值计算方法

利用水力学的连续方程和运动方程并采用适合非棱柱形河道的定步长法求解偏微分方程,可计算出河道沿程的水深和流速分布情况。据此确定河道堤防断面和布置水工建筑物,以满足工程安全和投资经济的要求。     

平面水流运动方程式和在明渠均匀流中的解

本文从雷诺方程出发,忽略方程中的粘滞项和假定压力服从静压分布,并考虑到近壁边界条件后,对方程沿垂线积分,求得平面水流方程式。在式中包含水深沿断面的改变对侧向切应力项的影响。对上述平面水流方程,求得在矩形明渠稳定、均匀流条件的分析解,从而导出垂线平均流速沿河宽的分布公式。该式计算结果与实测资料比较获得较为满意的验证。     

有限植被群水流尾流场特征的数值模拟研究

绕植物群流动通常被简化为绕柱群流动问题,而多孔介质模型可用于概化植被对水流的影响。该文基于自主开发的自由表面水流计算模型HydroFlow?,建立了多孔介质水流模型。该模型采用坐标变换捕捉自由表面,湍流模型选用SST k-ω两方程模型。开展了不同植被密度(Φ=0.03, 0.1, 0.22, 0.38)及植被相对水深高度(hv/H=0.25, 0.5, 0.75, 1)条件下的数值模拟研究。通过对比已有的物理模型实验测量数据,验证了数值模型的模拟精度和可靠性。基于设计工况的计算结果分析,提炼得到综合考虑了植被相对水深高度和植被密度影响的特征变量(hv/H)/CDaD。研究结果表明,植物群落后的溢出流速Ue和尾流区剪切层发展长度L1均与该特征量满足对数增长规律。分析尾流场的流动特征,在植被尾流流动的自由恢复阶段,横断面内流速分布均具有相似性,满足平面尾流方程,且该相似性与植被密度和植被淹没深度相关性较弱。     

植被群落之间水流紊动强度垂向分布规律探讨

以生态特征参数不同的植被群落为研究对象,在室内水槽中种植灌木、芦苇和灌木-草本植被混合群落,利用多普勒流速仪沿程测量各测点瞬时流速,基于河流动力学和紊流力学理论,将水流紊动强度表达为植被直径、水流绕流阻力因数、植被直径梯度和水流绕流阻力因数梯度的函数,比较不同类型植被群落之间水流紊动强度垂向分布规律的差异。结果表明,灌木完全淹没时,紊动强度在垂向上最大值位于灌木冠层顶端区域,极小值位于茎杆向冠层过渡区域。植被群落水流紊动强度垂向分布曲线上存在三个拐点,即茎杆向冠层过渡处、植被偏转点和植被冠层顶端。     

地表-土壤水动力学耦合模型在 复杂沟灌条件下的应用

反映地表水流运动和土壤水分运动的数学模型大多都是非线性偏微分方程,通常采用数值计算方法来求解较为复杂的地表水流运动模型和土壤水分运动方程。本文以辽宁某灌区玉米覆盖垄为例,利用零惯量模型和土壤水分运动方程(Richards方程)来描述沟灌灌水时水分的运动特征,构建沟灌地表-土壤水动力学的耦合模型,通过迭代法实现有效耦合,借助Matlab软件进行数值模拟与计算,将模拟结果与实测结果相对比,模拟结果符合实际情况,能够满足实际工作要求。     

浅尾水深水平底板上表面射流水力特性的数值模拟研究

采用VOF(volume of fluid)方法追踪自由液面,辅以Realizable(可实现化)湍流模型封闭两相流时均方程,对浅尾水深水平底板上的表面射流水力特性进行了数值模拟。微分方程的离散采用有限体积法,速度与压力耦合求解使用了压力隐式算子分裂PISO(Pressure-Implicit with Splitting of Operators)算法。研究并分析了入射速度、尾水深和进口宽度等对流场流线分布、速度场及横断面最大流速沿程衰减规律等水力特性的影响。研究发现:流场内存在一个大的漩涡,入射流速越大,漩涡长度越长;横断面上水平流速和纵向流速在漩涡区和明渠流区分布规律不同;横断面最大流速沿程衰减主要受进口流速大小的影响。     

基于元胞自动机和大伙房模型的洪水演进研究

为了快速、准确地模拟洪水演进过程,将元胞自动机和二维圣维南方程相结合,构建了基于元胞自动机的洪水演进模型,实现了元胞间的局部水量交换,以及全流域洪水模拟过程的全局转换。接着,创新性地构建了基于DEM的单元栅格大伙房产流模型并将其作为元胞产流输入,将直接径流、地面壤中流和邻域元胞入流共同作为水深增量,充分考虑到了降雨对河道滩地洪水演进模拟带来的影响。以浑河沈阳城区河段物理模型试验数据为基础,选取了不同设计频率洪水进行实例验证与分析。分析结果表明:水深的模拟具有较高的精度;流速总体上满足模拟需求;淹没范围具有相同的变化趋势,具有合理性和有效性。研究结果可为洪水演进模拟提供一种新方法,同时对其他相似地区洪水演进模拟工作也具有借鉴意义。     

基于生态水力半径法的武江流域生态流量研究

采用综合反映水生生物需求和河道断面信息的生态水力半径法,对武江河上北江特有珍稀鱼类省级自然保护区内的生态流量和生态水位进行估算。结果表明:生态水力半径法计算的生态流量过程线上存在明显的低流量、高流量和流量脉冲等水文要素,符合鱼类的自然需求;天然径流量下生态水力半径法估算的生态需水均可得到满足,但武江上梯级开发较多,需进行生态水位开展闸坝联合调度来保障河道的生态需水,确保犁市(二)站断面处各月份水深不小于平均生态水深。     

Modeling the Infiltration Capacity of Permeable Stormwater Channels with a Check Dam System

The use of permeable stormwater channels has introduced concerns over the effects of infiltration on the hydraulic behavior of their flow and the effects of flow hydraulic conditions (e.g., the water level, channel section, flow velocity, and vegetation) on the channel infiltration capacity. A check dam system provides backwater ponding, which increases the flow water depth along a channel. In this study, a channel model was used to investigate the variation in the infiltration capacity of permeable stormwater channels under different flow hydraulic conditions. Increasing the downstream check dam height and using a grass cover increased the infiltration rate and cumulative infiltration because of the decreased velocity and increased flow depth. The presence of subsurface water did not affect the hydraulic characteristics of the channel flow but decreased the cumulative infiltration because of the fast saturation of the soil. An empirical equation was developed for predicting the infiltration capacity of grassed channels in which four hydraulic parameters (i.e., the water depth, base width, side slope, and velocity) are introduced to the modified Kostiakov model. The developed model was used to calculate the runoff reduction due to infiltration along a grassed channel with and without a check dam system. The percentage of infiltrated water increased from 8 to 14% with the check dam system. The developed model can be used to predict the infiltration capacity of permeable channels for improved stormwater management and provides a valuable decision support tool for permeable channel design.

     

An Approximately Semi-Analytical Model for Describing Surface Runoff of Rainwater Over Sloped Land

Accurate prediction of surface runoff is critical to watershed management. In this research a semi-analytical model was adopted to solve the kinematic wave equation based on the assumption that the rate of overland-flow depth change is proportional to the rainfall excess. Simulations were compared with the results from laboratory experiments at various rain intensities. Parameters of infiltration rate and Manning’s roughness coefficient were determined. The accuracy of the semi-analytical model was evaluated by numerical simulations. The predicted outflow rates from the numerical simulations agreed well with the observed data. Further, our study indicated that the ratio (c) of the overland-flow depth change to the rainfall excess was a power function of the rain intensity. The depth and velocity of water flow at any time and distance could be calculated with the semi-analytical model. Hydraulic parameters including Reynolds number, Froude number, hydraulic shear stress, stream power and Darcy-Weisbach friction factor characterizing the dynamic features of overland flow of rainwater were calculated based on calculated overland-flow depth and velocity. The proposed analytical method can provide a new way to predict infiltration and runoff over sloped land.     

单边突扩浅水回流水流结构研究

试验资料表明,回流段流速及底部切应力横向分布沿流向呈自相似性。根据相似原理,水深平均方程可化为常微分方程,经求解获得了无量纲速度剖面公式。验证表阴,速度剖面公式不仅适用于垂线平均流速剖面,而且也适用于沿水深各流层速度剖面。利用速度剖面公式计算的垂线平均流速场与实测值符合较好。拟合了无量纲切应力剖面公式,探讨了主回流区阻力分布规律。 此外,还分析了影响回流长度的因素,建立了回流长度经验公式。     

基于降雨空间变异的潜水运动随机模拟方法Ⅰ——非条件模拟

将降雨视为随机场，考虑降雨入渗补给量与地下水埋深的关系，采用二维稳定-非稳定潜水运动的KLPC模型，分析了降雨的空间变异性对水头均值、方差和协方差的影响，利用变异系数描述了水头、流速和水动力弥散系数的变异程度。结果表明，KLPC算法的随机模型具有优越的计算效率；水头方差随降雨场方差和相关长度的增大而增大；在降雨空间变异的条件下，水头随机场呈现出明显的非平稳特性且具有各向异性结构；在非稳定流中，水头协方差表现出“扩散”和“平移”的特性；水头的变异程度较小，在随机模拟中可以不考虑降雨空间变异对地下水流动的影响；但水头的变异导致了流速和水动力弥散系数强烈的变异性，在溶质运移的随机分析中需要予以充分重视。     

盐龙湖表面流人工湿地底泥氧化层对污染物释放的影响

为了解盐城市盐龙湖表面流人工湿地底泥氧化层理化性质,探讨其对底泥氮、磷及有机物释放过程的影响,在测定底泥理化性质的基础上进行了室内静态柱状试验。结果表明:盐龙湖表面流人工湿地长期运行后在底泥表层形成了厚度为1 cm、呈棕黄色、无明显臭味、含水率低、TP含量高、TOC和TN含量低的氧化层;氧化层对于底泥中污染物的释放特征影响显著(P0.05),对内源污染的控制具有一定的正面作用;无氧化层试验组上覆水中TN、NH_3-N和COD的平均质量浓度分别比有氧化层试验组高9.5%、30.8%和3.5%;在湿地的实际管理中,不宜对湿地进行疏浚,如疏浚则疏浚深度应达到健康层。     

Hydrological Evolution of Wetland in Naoli River Basin and its Driving Mechanism

Naoli river basin(NRB), with an area of 24,863 km², is the largest basin and also the largest marsh distribution area in Sanjiang Plain, Heilongjiang, China. The hydrological evolution process of wetland in NRB has made a marked ecological responses for anthropic activities, also reflects the drying trend of the Sanjiang Plain, Northeast China. Global climate warming also contributes to the hydrological evolution process. The following key research results are obtained: (1) The monthly average water level of Naoli river at Caizuizi hydrological station in different ages showed a marked decline tendency, the annual mean water level dropped from 96.63 m during 1960–1969 to 95.59 m during 2000–2005, the water level drawdown is 1.04 m; (2) The annual runoff flowing into wetlands in NRB decreased. Duration of Naoli river and its tributaries being thoroughly frozen from riverbed to river-water-surface showed an prolonged trend, and the water level drawdown in frozen seasons increased. The water storage capacities of wetlands in NRB declined. (3) The interactions between ground water and surface water in wetland areas are close. The ground water level variation span is bigger than that of surface water level in wetland areas of NRB. The drawdown of ground water level promotes the surface water level to decline, correspondingly. In recent 20 years, the cultivated area extension of rice field in upstream NRB has made an adverse influence on the hydrological processes of wetlands. (4) The wetland area decrease and farmland area increase significantly contribute to the runoff depth decrease of wetlands in NRB. The runoff depth variability has been mostly posed by anthropic activities. (5) Reservoirs, ditches and dykes in NRB have greatly changed the runoff generation processes. Thickness of the seasonal frozen soil layer becoming thinner and the evaporation potential becoming bigger also contribute to the runoff depth reduction and the water level drawdown of rivers. The present study results will provide a scientific basic for developing an integrated watershed management program for NRB, especially, restoring the wetland hydrological processes, maintaining or improving the wetland structure and enhancing the wetland service functions.     

面流消能近底紊动流速特性的研究(面流消能试验研究之一)

本文主要论述了面流消能五种典型流态近底紊动流速特性,总结出了近底时均流速和紊动强度沿程变化规律,提出了近底紊动流速可能出现的最大瞬时值及相应位置的计算公式。面流消能工程的下游防冲设计中考虑的主要水力参数之一是,消能段近底流速紊动可能出现的最大瞬时值及其相应的部位,但目前国内外研究成果较少。笔者通过水工模型试验重点研究了面流消能各典型流态近底流速及其紊动纵向分量沿程的变化规律,并提出了计算公式,为优化面流设计提供科学依据。