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设置挡水隔板的鱼类友好型涵洞水力特性试验研究
Experimental Study on Hydraulic Characteristics of Fish-friendly Culverts with Baffles
涵洞是沟通河系、连接生物生境的重要通道,在其中布置小型挡水结构可有效减小局部流速,增加弱游泳能力鱼类上溯成功率,提高涵洞的生态效益。为明确设置三角形挡水隔板涵洞内水力特性,在水槽单侧布置多个三角形挡水隔板模拟涵洞中的小型挡水建筑物开展水槽试验研究,利用SonTek声学多普勒流速仪(ADV)采集三维流速数据,分析挡水隔板后流速分布、湍流特性、动量输运模式等,论证增设三角形挡水隔板系统对促进弱游泳能力鱼类(小鳈)上溯行为的可行性。研究结果表明:增设三角形挡水隔板,主流区流速仍能维持为25~30 cm/s,对主流区流速影响较小;在隔板边壁产生稳定的低速区(LVZs),其流速为-4~15 cm/s,相较光滑侧壁水槽低速区的面积占比由5%~10%增加为14.80%~18.07%;挡水隔板下游低速区水流湍动能和雷诺应力明显大于无挡水隔板侧的高速区,但未超过相应的鱼类游泳偏好阈值;水流动量交换以喷射和扫掠形态为主,该瞬时形态可提供更适宜弱游泳能力鱼类游动的流动环境。
[Objectives] Traditional culvert designs often result in excessively high flow velocities within the channel, impeding the upstream movement of weak-swimming fish species. Installing small triangular baffles inside culverts has the potential to provide upstream passage for small fish while maintaining discharge capacity. This study aims to clarify the hydraulic effects of triangular baffles by arranging multiple small baffles along one side of a flume to simulate internal culvert structures and verify the hydraulic effects through flume experiments. [Methods] Three-dimensional velocity data were collected using an Acoustic Doppler Velocimeter (ADV) to analyze the distribution patterns of turbulent kinetic energy and Reynolds stress. The quadrant analysis method was employed to quantitatively assess the impact of the baffle system on flow velocity distribution, turbulence characteristics, and momentum transport modes. [Results] The results showed that the triangular baffles created stable low velocity zones (LVZs) along the sidewall, with longitudinal velocities ranging from -4 to 15 cm/s, and velocities at the outer edge of the baffles around 25 cm/s, below the critical swimming speed of small fish such as Rhinogobius giurinus. In the mainstream zone, the lateral profiles of longitudinal velocity were nearly identical, ranging from 25 to 30 cm/s, indicating that the small triangular baffles had minimal impact on mainstream flow and thus preserved discharge capacity, achieving synergistic optimization of hydraulic efficiency and ecological function. The proportion of the low velocity zone area remained relatively consistent along the flow path, accounting for 14.80%-18.07% of the total cross-sectional area, demonstrating the feasibility of using triangular baffles to stably expand LVZs. The baffles significantly enhanced turbulence intensity in the region near the baffle-side sidewall, generating clockwise vortices and positive horizontal Reynolds stress that play an important role in maintaining swimming stability. Although the turbulent kinetic energy and Reynolds stress in downstream LVZs were higher than those in high-speed regions without baffles, they remained below the threshold of fish swimming preferences. This moderate turbulence enhancement not only provided energy for swimming but also avoided excessive turbulence that could impair the sense of direction or balance. Momentum exchange was dominated by jetting (Q2) and sweeping (Q4) events, whose dominance increased with higher threshold parameter H0 (with a contribution rate of about 60% at H0=4). The transient vortices formed had planes parallel to the fish’s spine and body axis, reducing energy loss during upstream movement and improving swimming efficiency through vortex energy transfer. This provided a more favorable flow environment for weak-swimming fish species. [Conclusions] This study identifies the distribution patterns of mean flow and turbulence characteristics and introduces quadrant analysis into the study of culvert turbulence-fish behavior interactions. It reveals the promoting effect of small baffle structures in fish upstream migration and addresses the lack of detailed flow field and turbulence structure analyses in previous research. The findings offer a feasible hydraulic optimization paradigm and model reference for the design of eco-friendly culverts.
culverts / flume experiment / baffles / low velocity zones / momentum exchange
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作为现代水利工程建设中河流修复的一种特有手段,涵洞的基本功能除了作为路桥系统的输水通道之外,还要为工程所在流域水生动物能顺利通过障碍提供一条通道。但国内关于涵洞式过鱼通道水力设计方面的文献较少,我国涵洞式鱼道在修建过程中可供参考的理论依据非常有限。在分析国外涵洞式鱼道相关试验数据的基础上,对偏移式(OB)、槽堰式(SWB)和堰式(WB)3种典型挡板的水力特性及流场分布特征进行了归纳,得到了无量纲流量、水深、坡度与流速的关系表达式,比较并分析了3种挡板的工作性能。研究成果将为国内涵洞式鱼道的内部改造和水力设计提供理论依据与参考。
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As a special means of river restoration in hydraulic engineering construction, culvert mainly functions as a water channel for road and bridge system, and for local aquatic animals to passing through barriers. Since the hydraulic design of culvert fishway is rarely reported in China, theoretical basis for the construction of culvert fishway is insufficient. By analyzing some experiment data of culvert fishway abroad, we summarized the hydraulic characteristics and flow fields of classical baffle systems of culvert fishways,including offset bafe(OB),slotted-weir bafe(SWB) and weir bafe(WB).We obtained the expressions of dimensionless flow rate, water depth, slope against velocity, and compared the working performance of the three baffles.The research achievements would provide theoretical basis and reference for the internal transformation and hydraulic design of culvert fishway in China.
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Low-level river crossings can have negative impacts on freshwater ecosystems, including blocking upstream fish passage. In order to restore upstream fish passage in culverts, we developed physically-based design methods to yield cost-effective culvert structures in order to maintain or restore waterway connectivity for a range of small-bodied fish species. New guidelines are proposed for fish-friendly multi-cell box culvert designs based upon two basic concepts: (1) the culvert design is optimised for fish passage for small to medium water discharges, and for flood capacity for larger discharges, and (2) low-velocity zones in the culvert barrel are defined in terms of a percentage of the wetted flow area where the local longitudinal velocity component is less than a characteristic fish speed linked to swimming performances of targeted fish species. This approach is novel and relies upon an accurate physically-based knowledge of the entire velocity field in the barrel, specifically the longitudinal velocity map, because fish tend to target low-velocity zone (LVZ) boundaries. The influence of the relative discharge threshold Q/Q, characteristic fish swimming speed U, and percentage of flow area on the size of box culvert structures was assessed. The results showed that the increase in culvert size and cost might become significant for a smooth culvert barrel with U< 0.3 m/s and Q/Q> 0.3, when providing 15% flow area with 0 < V< U. Similar trends were seen for culvert barrel with recessed cell(s).
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在工程设计和施工时，为减少截流对鱼类生态环境影响，需要考虑特有鱼类洄游通道的要求而设置专门的鱼道。通过对国内外涵洞式鱼道相关资料的收集整理和分析，针对国内外的发展现状，较详细地介绍了涵洞式鱼道的发展过程、鱼道隔板类型和水力特性及其优缺点，分析了涵洞式鱼道的设计方法和要点，包括收集信息、选址、隔板类型和水力计算等，并对国内外鱼道的建设和发展进行了展望。特别是国外在涵洞式鱼道领域的研究方法和成功经验，可为我国在该领域的后续工作提供良好的借鉴。
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Special fish migration channels should be set up to reduce the impact on fish eco-environment in engineering design and construction. The authors presented the development, baffle types and hydraulic characteristics of culvert fishway, and described the main points in designing a culvert fishway, including the collection of information, site selection, baffle types and hydraulic calculations, and also prospected the construction and development of fishway in China and abroad. The research methods and successful experiences in foreign countries could provide good reference for our country in the subsequent work.
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Turbulence characteristics in fishway are important for fish migration towards the upstream reach. In this article, we made a review on the research progresses of turbulence parameters including turbulence velocity, turbulent kinetic energy, turbulence intensity, Reynolds shear stress, and vortex in Danilian fishway, vertical slot fishway, composite fishway and culvert fishway. We also analyzed the rules and characteristics of turbulence distribution in different types of fishway, and pointed out that turbulence intensity and turbulent kinetic energy have great impact on habitat selection and fish passage. Finally we recommend conducting in-depth research on the turbulence characteristics of vortexes in fishway, which has received few research attentions, to improve the hydraulic condition in fishway and ensure an efficient operation.
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