Wood‐induced backwater effects in lowland streams

Placement of wood in streams has become a common method to increase ecological value in river and stream restoration and is widely used in natural environments. Water managers, however, are often hesitant to introduce wood in channels that drain agricultural and urban areas because of backwater effect concerns. This study aims to better understand the dependence of wood‐induced backwater effects on cross‐sectional area reduction and on discharge variation. A newly developed, one‐dimensional stationary model demonstrates how a reduction in water level over the wood patch significantly increases directly after wood insertion. The water level drop is found to increase with discharge, up to a maximum level. If the discharge increases beyond this maximum, the water level drop reduces to a value that may represent the situation without wood. This reduction predominately depends on the obstruction ratio, calculated as the area covered by wood in the channel cross section divided by the total cross‐sectional area. The model was calibrated with data from a field study in four lowland streams in the Netherlands. The field study showed that morphologic adjustments in the stream and reorientation of the woody material reduced the water level reduction over the patches in time. The backwater effects can thus be reduced by optimizing the location where wood patches are placed and by manipulating the obstruction ratio. The model can function as a generic tool to achieve a stream design with wood that optimizes the hydrological and ecological potential of streams.     

BENDING OF SUBMERGED WOODY RIPARIAN VEGETATION AS A FUNCTION OF HYDRAULIC FLOW CONDITIONS

Woody riparian vegetation provides numerous ecological benefits such as stabilizing streambanks, storing and cycling nutrients, shading streams and providing habitat for wildlife. However, vegetation also increases hydraulic roughness and reduces the effective flow area, resulting in an increased water surface elevation for a given streamflow. Balancing the desire to preserve woody vegetation in stream corridors with the need to manage flood risks requires accurate techniques for predicting the influence of vegetation on stream hydraulics. However, this is a challenging problem because woody vegetation responds to the flow field itself by bending and streamlining in response to hydraulic forces. The goal of this study was to predict the bending behaviour of woody riparian vegetation as a function of hydraulic flow conditions. Field tests were performed to elucidate tree biomechanical properties for select riparian taxa of the southwestern USA. Biomechanical results served as input parameters for a numerical algorithm designed to predict tree bending for water velocities likely to be encountered during flood events. Bending simulations revealed appreciable variability in bent tree heights. Variability was likely a manifestation of the extensive variance in plant characteristics and properties inherent in biological specimens. However, no trees were expected to bend to a height lower than approximately 42% of their original height, even in water moving at 2.5 m·s^‐1. The results of this work provide an important first step in an effort to predict a dynamic hydraulic roughness for vegetated channels and floodplains under flood conditions. Copyright © 2011 John Wiley & Sons, Ltd.     

基于生态修复理论在河流整治中的研究

介绍了河流治理要以生态水工学的理念进行生态整治,通过表述了遭到破坏的河流生态系统所面临的问题,即进行生态修复首先要治污、要满足河流的最低生态需水量、尽量恢复河流的自然状态,进一步从不同角度介绍生态修复的各种措施即从点、线、面、体各方位考虑生态修复。     

明渠流动S-K模型在具有垂直壁面的复式断面下的数值模拟

在具有垂直壁面的复式断面S-K模型数值计算中一般都是采用斜坡近似法,但该方法在滩槽交界面处的流速计算值与S-K模型解析解差别较大,为解决该问题,提出了结合解析解求解时拟定的边界条件的耦合迭代方法,该方法大大改善了斜坡近似法的不足,其数值模拟结果与S-K模型解析结果吻合良好,能够更为精确地计算棱柱体河槽深度平均流速分布和壁面切应力分布,可有效解决直立壁面边界速度突变的问题,对数值计算中类似问题的解决具有参考价值,也为S-K模型在实际工程中的广泛应用提供新的途径.     

黄登水电站截流水力学计算分析

该文采用水量和能量平衡原理建立计算模型,对黄登水电站截流进行了水力学分析,计算结果与试验成果基本吻合。类似方法亦可在单个泄流建筑物水力计算分析中采用。     

弱环境流速水域内陆核电厂液态流出物排放设计优化研究

理论和实践经验均表明,内陆核电厂采用多孔扩散器有利于加快近排放口区域液态流出物的掺混稀释。基于美国环保署推荐的近区模拟工具——CORMIX专家系统,对低环境流速水文条件下的内陆核电厂的多孔扩散器开展了研究。分析表明:对于近岸布置的多孔扩散器,在低环境流速、相对较强射流以及水深较深条件下,(1)扩散器主管长度Ln与排放口下游断面的最小相对稀释比例H呈正相关,喷口直径D与H呈负相关,喷口水深HD与H呈正相关;在排热量相同的情况下,流量Q与H呈正相关。(2)对于排放口下游1 000 m断面处的最小相对稀释比例H1 000 m,各几何参数灵敏度由高到低排序为,喷口直径D、喷口数量n、主管长度Ln。研究结论可供内陆核电厂液态流出物排放工程的设计及优化参考。     

基于微分进化算法的污染物源项识别反问题研究

利用微分进化算法研究了污染物源项识别反问题,包括单点固定源和多点固定源的位置和强度的反演.该方法把源项识别反问题转化为非线性优化问题,通过第i个个体和三个随机选取的父代共同产生子个体,新产生的一个子个体只有当它比种群中的个体优良时才替换种群中的个体.多个算例的计算结果表明,采用该算法对含点源的二维环境水力学反问题能够给出精度较高的反演结果.     

折板消能竖井中的折板功能分析

折板是折板消能竖井的关键结构。本文以模型试验为依托,测试了折板消能竖井的水力特性,分析了不同典型位置折板的功能及布置准则,结果显示:首层折板的主要功能为承接和调节水流,使其平顺地跌向次层折板,首层折板与竖井入流口的间距是影响首层折板功能发挥的主要因素,该值过大易引起水流不能跌至首层折板或水流直接冲击中隔板等不利现象;中间层折板的主要功能为消能,折板间距是影响其功能发挥的主要因素,折板间距过大会影响消能效率,过小会影响过流能力;水下折板的主要功能为消能和除气,根据试验资料,当水下折板至少设置2~3层时,即可良好地满足其功能需求。     

长距离明渠调水工程蓄量动态调节控制算法研究

本文阐明了明渠渠池蓄量与节制闸闸前水位之间的单值对应关系,在此基础上提出一套通过动态调节渠池蓄量,实现闸前常水位运行的控制算法。该算法基于流量平衡和蓄量平衡关系推导,前馈控制与反馈控制相结合。前馈控制根据分水口计划主动调节各渠池蓄量,起粗调作用;反馈控制针对前馈控制过程出现的水位偏差,通过动态调节各渠池蓄量实时校正,起细调作用。该算法具有原理简单,参数率定简便,控制规则灵活,实用性强等特点。算法在南水北调东线工程胶东段渠道进行了仿真测试,模拟环境包含水位死区和闸门运动死区。结果表明,所提算法能够有效克服长距离明渠水力滞后的影响,及时有效消除各渠池闸前水位偏差,将水位波动限定在安全范围内。     

临界水深计算方法的研究

总结了渠道临界水深常见的计算方法,分析了过水断面比能曲线的特性,根据渠道临界水深的定义,利用计算机软件编程技术可以解决大量繁琐计算的特点,求解了明渠临界水深,并且分析与总结了用定义法解决工程计算的意义。