水利工程总溶解气体过饱和问题探讨

从对总溶解气体(TDG)过饱和概念的分析入手,阐述TDG过饱和的危害。通过对不同典型水体TDG饱和度的测量,表明泄流可以导致水体TDG含量增加甚至过饱和。在此基础上,采用试验研究的方法,探讨了TDG过饱和产生原因及其释放过程,表明水利工程泄流引起的TDG过饱和与泄流掺气、压力、紊动强度、水温等要素相关,并由此提出减缓水利工程TDG过饱和影响的建议。     

中国高坝工程过饱和总溶解气体研究进展

高坝泄洪会导致下游水体总溶解气体过饱和,鱼类长期处于这种环境容易患气泡病甚至死亡.为保护生态环境,找出切实可行的TDG饱和度消减措施,我国针对高坝泄洪导致的总溶解气体过饱和现象开展了大量研究.对高坝工程过饱和溶解气体的产生、释放过程、鱼类对过饱和溶解气体耐受性、TDG饱和度预测模型及TDG过饱和减缓措施的研究成果进行了总结,同时针对已有研究成果的不足提出了建议,旨在为进一步开展研究工作提供参考.     

大坝泄流下游过饱和TDG生成过程综述

研究发现大坝泄流引起的下游总溶解气体(total dissolved gas,TDG)过饱和问题会对鱼类等水生生物的生存、繁衍产生负面影响.解决这一问题的重要途径之一是从源头上阻碍过饱和TDG的生成,降低消力池中TDG浓度,因此了解过饱和TDG的生成机理将为制定TDG消减措施提供可靠的理论依据和参考价值.基于此,文章重...     

总溶解气体过饱和对鱼类影响研究进展

高坝下泄洪水导致大坝下游河道水体总溶解气体(TDG)过饱和,威胁着下游鱼类的生存。目前,高坝泄洪引起的TDG过饱和问题及其对鱼类的影响,已成为备受关注的生态环境问题之一。针对国内已有的研究,从气体过饱和引起的鱼类气泡病症状、耐受性、回避性等方面进行了总结。发现鱼类对TDG过饱和的耐受性阈值并未确定,TDG过饱和对鱼类影响的解决方案尚未明确。提出进一步开展野外原位观测试验,着手TDG与其他环境因子的耦合作用对鱼类的影响研究,以及利用多学科交叉的方法揭示TDG过饱和对鱼类影响的内在机制,有助于水库调度方案和鱼类保护措施的制定。     

风速对过饱和总溶解气体释放速率的影响

通过不同风速下的过饱和总溶解气体(TDG)室内释放试验,研究风速对过饱和TDG释放过程的影响,并根据已有释放模型对释放系数进行估算,建立了过饱和TDG释放系数与风速的定量关系式。结果表明在8.5~9.5℃条件下,风速较小时,水体中过饱和TDG释放相当缓慢,随着风速的增大,过饱和TDG的释放速率显著增大;在无风工况下,TDG释放系数为0.005 42 h-1;当风速为1.08~11.33 m/s时,TDG释放系数为0.007 09~0.066 68 h-1;相对释放系数为1~12.303,拟合的相对释放系数与风速的定量关系式计算偏差在-11.76%~10.21%之间。     

过饱和TDG释放系数与泥沙含量的关系研究

随着梯级电站的建成运行,总溶解气体(Total dissolved gas,TDG)过饱和对鱼类的不利影响受到更广泛关注。泄洪多发的夏季常伴随冲沙,泥沙含量的变化对过饱和TDG输移释放过程的影响。在自行设计的具有挡板结构的实验水槽中,开展了不同流量和泥沙含量条件下的过饱和TDG输移释放过程实验研究,并开展数值模拟计算,反算得到各条件下的释放系数。结果表明泥沙的存在增加了水中供溶解气体析出所需的介质,加快了过饱和TDG的释放过程,TDG的释放系数也随着泥沙含量的增大而增大。该研究为探讨加快过饱和TDG释放过程的工程措施和减缓TDG过饱和对鱼类不利影响的生态调度措施研究提供技术参考,具有一定应用价值。     

高坝泄水产生溶解气体过饱和水体对鱼类影响的模拟研究

采用高坝泄洪TDG生成预测模型,考虑泄洪水流的非恒定流特征及过饱和TDG水流在河道内的一维动力学释放,模拟某待建坝高289m的高坝工程以单泄洪洞分别持续泄洪不同时间,下游河段内TDG饱和度水体对鱼类影响。以已有鱼类研究成果为标准,研究得到,泄洪流量一定,泄洪持续时间延长,TDG过饱和水体对下河道内鱼类的影响区域从坝下逐渐向下游延长。当泄洪流量、泄洪时间一定,坝下游河道内TDG过饱和水流对鱼类的影响区域沿河流方向逐渐减小。     

紊动促进过饱和总溶解气体释放研究

总溶解气体(Total Dissolved Gas,简称“TDG”)过饱和可能直接导致鱼类和水中生物患有“气泡病”甚至死亡。文章为解决该问题开展研究。实验结果表明,在紊动的系列条件下,紊动能促进过饱和总溶解气体的释放,转速和温度对过饱和TDG释放起促进作用,而水深对其起抑制作用。研究还获得过饱和TDG释放系数(释放速率)分别与水深、转速和温度的关系表达式,以及紊动因素对过饱和TDG的影响大小为K_TDG,n>K_TDG,T>K_TDG,H。该研究成果是一种减缓过饱和TDG危害的方法,为探讨减缓过饱和TDG不利影响的措施提供科学指导和依据。     

高坝下游水中总溶解气体过饱和研究进展

随着水电工程的不断兴起,高坝建设引起的过饱和水体问题日渐突出。总结了近年来国内外的的研究成果,从鱼类的耐受性、鱼类对过饱和总溶解气体(TDG)的规避效应以及过饱和TDG对鱼类的致死机理3方面分析了过饱和TDG与下游水生生物之间的相互作用,并提出了一些研究思路和想法。此外,还重点论述了促进过饱和TDG释放速率方面取得的进展和不足之处,指出实际工况条件下过饱和TDG的释放易受河流形态等周边环境影响,而实验条件下无法准确反映实际工况,今后室内试验和原型观测需进一步加强。而如何在安全行洪的前提下实现快速高效的TDG释放是该领域下一步研究的重点。     

鱼类在TDG过饱和含沙水体中的耐受性

为探讨高坝泄洪引起的总溶解气体(TDG)过饱和含沙水体对鱼类的影响,以岩原鲤和鲢鱼为研究对象,开展TDG过饱和含沙水体对不同鱼类的急性暴露试验,根据鱼类受TDG过饱和含沙水体胁迫后的异常行为和死亡率、半致死时间等指标来分析不同鱼类受胁迫后的耐受性和差异性。试验结果表明:试验初期,试验用鱼出现较明显异常行为和气泡病症状,且岩原鲤早于鲢鱼;相同TDG饱和度下,随着含沙量的增加,试验用鱼半致死时间缩短,且岩原鲤半致死时间短于鲢鱼,表明鲢鱼比岩原鲤具有更强的适应能力和耐受能力;当TDG饱和度较高时,即使含沙量低,也会造成试验用鱼的大量死亡;过饱和TDG是导致试验用鱼死亡的主要原因,但不能忽略泥沙对试验用鱼死亡的促进作用。     

A laterally averaged two-dimensional simulation of unsteady supersaturated total dissolved gas in deep reservoir

Elevated levels of the Total Dissolved Gas (TDG) may be reached downstream of dams, leading to increased incidences of gas bubble diseases in fish. The supersaturated TDG dissipates and transports more slowly in reservoirs than in natural rivers because of the greater depth and the lower turbulence, which endangers the fish more seriously. With consideration of the topographical characteristics of a deep reservoir, a laterally averaged two-dimensional unsteady TDG model for deep reservoir is proposed. The dissipation process of the TDG inside the waterbody and the mass transfer through the free surface are separately modeled with different functions in the model. Hydrodynamics equations are solved coupling with those of water temperature and density. The TDG concentration is calculated based on the density current field. A good agreement is found in the simulation of the Dachaoshan Reservoir between the simulation results and the field data of the hydrodynamics parameters and the TDG distribution in the vertical direction and their unsteady evolution with time. The hydrodynamics parameters, the temperature and the TDG concentration are analyzed based on the simulation results. This study demonstrates that the model can be used to predict the evolutions of hydrodynamics parameters, the temperature and the TDG distribution in a deep reservoir with unsteady inflow and outflow. The results can be used in the study of the mitigation measures of the supersaturated TDG.     

水库泄水总溶解气体过饱和对鱼类的危害

水库建设促进了库区渔业养殖的发展，但高坝大库泄水导致的总溶解气体（Total Dissolved Gas, TDG）过饱和可能导致下游河道尤其下一梯级水库的鱼类患气泡病甚至死亡。为探究TDG过饱和对鱼类的胁迫效应，以金沙江梯级电站溪洛渡至向家坝江段为研究对象，构建立面二维TDG动态模型，推求库区控制断面的安全水深阈值，结合库区主要鱼类生活习性和网箱养殖深度，研究TDG过饱和对野生鱼类和网箱养殖鱼类的胁迫效应。结果表明:梯级电站库区的野生鱼类具有足够的垂向空间进行深度补偿以规避TDG过饱和的危害，其生活习性以及利用深度补偿的能力决定了受过饱和TDG胁迫的程度；但养殖鱼类受网箱限制难以自由下潜至安全水深，为保证养殖鱼类的安全，网箱深度至少应大于安全水深阈值，在TDG过饱和胁迫期，鱼类的游泳水深应持续限制在安全水深阈值以下。对于具有利用深度补偿能力的鱼类，梯级电站的库区比最后一个梯级的下游河道更安全，需要对最后一级电站实施比中间梯级更严格的坝下近区TDG饱和度限制标准。     

Microanalysis of supersaturated gas release based on wall-attached bubbles

Supersaturation of dissolved gases in natural water, due to spillage from high dams and other factors, may cause fish mortality. In previous experiments, the dissipation coefficient has been used to denote the degassing process of total dissolved gas(TDG) saturation. These experiments mainly analyzed supersaturated TDG dissipation from a macroscopic view. To precisely clarify the mechanism of supersaturated TDG release, this study investigated bubble adsorption at a wall surface from a microscopic view. The experiment was conducted in a Plexiglas-wall container filled with supersaturated TDG water. A model that calculates the adsorption flux of supersaturated TDG by a solid wall, and helps describe construction for a contact angle at a three-phase intersection, was developed according to Young's equation. This model was used to investigate the formation process of bubbles adsorbed on a solid polymethyl methacrylate(PMMA) surface in supersaturated TDG water. The adsorption effect of a solid wall on TDG release was analyzed based on the experimental data. The modeling results were compared with observations under different wall area conditions, and it was found that TDG release tended to increase with wall area. This study helps improve our understanding of the mechanisms of supersaturated TDG release and provides an important theoretical method for accurate calculation of the release process. The adsorption flux model of the solid wall provides mitigation measures to combat the adverse effects of TDG supersaturation,which will be beneficial to the protection of aquatic organisms in hydropower-regulated rivers.     

A parameter analysis of a two-phase flow model for supersaturated total dissolved gas downstream spillways

A high concentration of the total dissolved gas(TDG) in a flow downstream high dams may cause the gas bubble disease in fishes.To better understand the spatial distribution of a supersaturated TDG,a numerical simulation approach for determining the TDG concentration is shown to be effective and convenient; however,the determination of the model parameters relies to a great extent on the observed field data,which are scarce but are very sensitive to the accuracy of the simulation.In this regard,determining the source parameter in the TDG transport equation is the primary concern of this paper.Observed field data from six different spillways in China are used to calibrate the source parameter.A relationship between the source parameter and the hydrodynamic characteristics is established.The inclusion of this relationship in the predictive relationship will enable an accurate and rapid estimation of the source parameter and may help in developing mitigation measures for the TDG supersaturation downstream the spillways.     

SIMULATIONS OF THE THREE-DIMENSIONAL TOTAL DISSOLVED GAS SATURATION DOWNSTREAM OF SPILLWAYS UNDER UNSTEADY CONDITIONS

Dams are often operated in a way to discharge over the spillways, which would cause a high dissolved concentration of air and be harmful to fish. The bubble transfer and the water surface transfer play an important role in affecting the concentration of the Total Dissolved Gas (TDG). Based on recent numerical simulations of the total dissolved gas saturation, in this article, a two-phase TDG transport equation is adopted to develop an unsteady three-dimensional (3-D) two-phase flow Computational Fluid Dynamics (CFD) model, including a number of parameters such as water depth, pressure and air volume entrained. This model is used to predict the hydrodynamics and the TDG distribution under unsteady discharge conditions. Good agreement between measured and numerical results is obtained for a case study.     

过饱和总溶解气体释放过程预测

通过室内试验,研究泄流水体中过饱和总溶解气体的释放过程,分析了影响气体从水中释放的主要因素。利用原型观测资料对已有的过饱和总溶解气体释放的数学模型进行验证,同时对释放系数公式进行了修正。在此基础上预测了金沙江某电站下游河段过饱和总溶解气体的沿程释放规律。     

TDG过饱和对齐口裂腹鱼的影响及避难所营造研究

为探究山区河流TDG过饱和工况鱼类避难所营造的可行性,以半龄齐口裂腹鱼为研究对象,营造了TDG过饱和室内避难模型,定量开展了不同TDG饱和度工况下的室内实验,通过数理统计及显著性分析的方法对实验结果进行了比较。结果表明:齐口裂腹鱼的避难趋势随着水流TDG饱和度的升高逐渐增强,在主槽上游TDG饱和度小于等于130%时未出现明显的避难行为,140%时开始出现避难趋势,大于等于150%时的避难效应十分明显;实验结束时,TDG饱和度为150%及以下的各工况组中鱼苗的回避率存在显著差异,TDG饱和度为150%及以上各工况组的回避率极显著高于140%及以下的各工况组。     

三峡工程坝身泄流下游水体溶解氧浓度数值模拟

三峡工程坝身泄流与下游水体强烈碰撞,产生大量气泡,当气泡渗透进入水体一定深处时,气泡界面与水体之间的质量交换极易导致水体溶解气体浓度超饱和,可导致鱼类气泡病.该文应用气泡界面传质理论建立了掺气水流的溶解氧浓度对流扩散方程,与气液两相流混合模型相耦合,模拟计算了三峡大坝在库水位为139m情况下溶解氧浓度变化情况,成功地与现场观测数据进行了验证,完善了气泡界面传质系数公式.对关键因子进行敏感分析,表明气含率、紊动强度、下游水深是决定溶解氧浓度的关键因素.     

联合生态调度对超饱和气体影响的数值研究

在水利枢纽之间实现有效调度来减少总溶解气体对鱼类的危害是操作方便又经济的生态调度新方法。该文以哥伦比亚河上超饱和气体现象最严重的大古力坝下游鲁弗斯伍兹湖为研究对象,以现场观测资料为基础,采用二维两相流模型模拟电厂和泄洪孔之间流量转换下的鲁弗斯伍兹湖的超饱和气体浓度,对比分别利用改造泄洪建筑物结构和通过联合生态调度来降低其不利影响的效果,最终目的是通过合理水库调度方式,减轻或弥补对水生态环境的影响。     

Does swimming activity influence gas bubble trauma in fish?

Total dissolved gas (TDG) supersaturation from sources such as hydroelectric dams can cause harmful bubble growth in the tissues of aquatic animals, known as gas bubble trauma (GBT). Locomotion is known to exacerbate bubble growth in tissues during decompression under certain conditions (such as in diving animals), possibly because of increased bubble nucleation. As with decompression sickness, GBT is caused by the supersaturation of tissues with gas, and thus we hypothesize that locomotion promotes bubble nucleation in the tissues of fish exposed to TDG supersaturation. Many previous laboratory studies have tested the effects of TDG on fish exposed to low-velocity, non-directional flow, whereas fish in field conditions are exposed to higher-velocity flows and are likely more active. Therefore, it is important to understand the effects of locomotion on GBT to apply laboratory results to active fish in field conditions. We exposed rainbow trout (Oncorhynchus mykiss) to either control (100% TDG) or TDG supersaturation (123% TDG) in either static or flowing water conditions (1.8 Bl/s) and recorded time to 50% loss of equilibrium (LOE). We observed no statistically significant difference in time to 50% LOE between flow conditions. Given the lack of statistically significant difference between static and flowing water, our findings indicate that results from GBT experiments on rainbow trout in non-directional flow are applicable to more active individuals.