The effects of flow reduction rates on fish stranding in British Columbia,Canada

Juvenile fish can strand in pools or in interstitial spaces when the water elevation drops in regulated rivers due to flow reductions. Three years of summer and winter experiments on the Columbia and Kootenay Rivers (Canada) assessed the effect of the rate of change in water level (ramping rate) on the probability of pool and interstitial stranding for juvenile (<100 mm) fish. The factors of wetted history of the site, time of day, natural fish density and the occurrence of a conditioning reduction prior to the operational reduction were also examined for their effect on stranding. Experimental net pens were constructed to test these factors in situ in the varial zones of the two rivers. Linear models with plausible additive combinations of the potential explanatory factors and a null model were fitted to the logistically transformed data and ranked using the second‐order Akaike Information Criterion (AIC_c). The null model was the top ranked model for the interstitial stranding analyses, highlighting that none of the factors tested were significant variables in predicting the probability of stranding. Natural fish density, wetted history of the site, ramping rate and the presence of a conditioning reduction were variables included in the top three ranking models for the pool stranding analyses. Probability of pool stranding in summer was reduced by the occurrence of a conditioning reduction prior to the operational reduction. Higher natural fish density, longer periods of wetted history and higher ramping rates all led to higher probabilities of pool stranding. Copyright © 2008 John Wiley & Sons, Ltd.     

Effects of large woody debris on surface structure and aquatic habitat in forested streams,southern interior British Columbia,Canada

It is well known that large woody debris (LWD) plays an important functional role in aquatic organisms' life. However, the influence of LWD on channel morphology and aquatic environments at watershed levels is still unclear. The relationships between wood and surface structure and aquatic habitat in 35 first through fifth order streams of southern interior British Columbia were investigated. Study streams in the channel networks of the study watersheds were classified into four size categories based on stream order and bankfull width: Stream size I: bankfull width was less than 3 m, Stream size II: 3–5 m, Stream size III: 5–7 m, Stream size IV: larger than 7 m. We found the number of functional pieces increased with stream size and wood surface area in stream sizes I, II and III (24, 28 and 25 m²/100 m², respectively) was significantly higher than that in stream size IV (12 m²/100 m²). The contribution of wood pieces to pool formation was 75% and 85% in stream sizes II and III, respectively, which was significantly higher than those in stream size I (50%) and size IV (25%). Between 21% and 25% of wood pieces were associated with storing sediment, and between 20% and 29% of pieces were involved in channel bank stability in all study streams. Due to long‐term interactions, LWD in the intermediate sized streams (Size II and III) exhibited much effect on channel surface structure and aquatic habitats in the studied watersheds. Copyright © 2008 John Wiley & Sons, Ltd.     

Wind-driven Summertime Upwelling in a Fjord-type Lake and its Impact on Downstream River Conditions: Quesnel Lake and River,British Columbia,Canada

Observations and modeling results are presented to explore the response of a multi-basin, fjord-type lake to episodic wind forcing. Field observations show that abrupt cooling and warming events (magnitude greater than 5°C d-1) lasting 3–6 days in a large, salmon-bearing river (Quesnel River) are due to upwelling in its upstream lake (Quesnel Lake) during the summer, stratified season. Within the lake, vertical displacement of isotherms in the vicinity of the river mouth associated with this upwelling is shown to be forced by wind events longer than one quarter of the fundamental seiche period and of sufficient magnitude that the Wedderburn number approaches one. Upwelling occurs nearly-simultaneously throughout a smaller basin adjacent to the outflow (West Basin) that is separated from the Main Basin of Quesnel Lake by a sill and contraction. Wind-driven water fluxes across the sill are estimated using a conceptual model based on volume and heat budgets. These estimates provide an upper bound for flow across the sill and suggest that exchange flow may at times be internally hydraulically controlled, with epilimnetic velocities of up to ∼25 cm/s. Computed fluxes suggest the West Basin hypolimnion has a residence time of 6-8 weeks during the summer stratified period with each upwelling episode irreversibly exchanging 25–30% of the hypolimnetic volume with the rest of the lake. Implications of such events are profound for salmon bearing rivers wherein the thermal habitat is critical to migration success.     

Flow and water temperature simulation for habitat restoration in the Shasta River,California

Low instream flows and high water temperatures are two factors limiting survival of native salmon in California's Shasta River. This study examines the potential to improve fish habitat conditions by better managing water quantity and quality using flow and water temperature simulation to evaluate potential restoration alternatives. This analysis provides a reasonable estimate of current and potential flows and temperatures for a representative dry year (2001) in the Shasta River, California. Results suggest restoring and protecting cool spring‐fed sources provides the most benefit for native salmon species from a broad range of restoration alternatives. Implementing a combination of restoration alternatives further improves instream habitat. Results also indicate that substituting higher quality water can sometimes benefit native species without increasing environmental water allocations. This study shows the importance of focusing on the limitations of specific river systems, rather than systematically increasing instream flow as a one size fits all restoration approach. Copyright © 2009 John Wiley & Sons, Ltd.     

热参数对冻土温度场的影响及敏感性分析

为评估热参数取值对冻土温度场的影响,将导热系数、比热、潜热作为冻土温度场的影响因素进行试验设计。通过室内试验测定了饱和粉质粘土在不同负温下的导热系数、比热及潜热值,并基于Johansen法提出了考虑冻土未冻水含量的热参数修正算法,按照变参数和常参数形式代入数值分析软件ABAQUS,获取了不同的温度场计算值。将不同负温下的热参数和某负温阶段的平均热参数代入数值分析软件,分析热参数变化对冻土温度场的影响。依据冻结试验获取了冻结150 h的模型箱温度场实测值,并将计算值与实测值进行了比较。结果表明:不同的热参数对冻结初期影响较大,随着冻结的深入各计算值间的差值逐渐缩小。采用一定负温阶段的平均热参数作为恒定热参数进行数值计算,从微观上不能满足精度要求。潜热是影响冻结温度场计算精度的主要因素,考虑不同负温土体导热系数、比热、潜热的计算更接近于实测值。研究成果为寒区水利工程设计和施工提供参考。     

温排水对长江安徽段水温的影响模拟

为研究温排水对长江安徽段水温的影响,建立长江干流安庆至芜湖段三维水动力温度输运模型,根据水文实测数据对模型参数进行率定及验证,分别在纵、横断面上预测分析了不利条件下两种排放工况(减排前、减排后)对周边水域温度的影响范围及程度.结果表明:在两种排放工况下,保护目标水温均未受影响;水体温升分布有显著垂向差异,随着水深增加,...     

温排水模型试验中变态率对流场和 温度场的影响

通过设计一系列温排水模型试验,研究不同模型几何变态率对典型环境流条件下流场和温度场的影响。结果表明：变态率ε的增大（ε≤3）对典型流场的纵向流速以及水流特征点分布均有所影响,但都没有改变原有工况（ε=1）的流态特征和分布结构。随着变态率ε增大（ε≤3）,温排水向上游发生偏转,表面温度场温升包络面积逐渐变大,主流区垂向温度分布规律基本没有发生变化,但垂向温度梯度加大,热水层厚度趋向变薄。     

分层型水库取水水温量纲分析及其影响因素研究

水温分层作为影响库区水生生态系统的重要因素逐渐成为研究热点。影响下泄水温的主要因素包括:坝前水温梯度、取水水头、取水流量、取水口宽度、温跃层厚度、重力加速度等。通过量纲分析法,基于π定理尝试建立了溢流式分层取水下泄水温估算模型。采用SAS 9.3统计软件对实验数据进行了回归分析,提出了下泄水温估算方程,相关系数达到95.6%。研究结果表明,水温梯度项为下泄水温估算的最主要因素,其次为取水水头项,最后为流量项;随着坝前水温温跃层强度增大,下泄水温升高,且强度越大,对下泄水温的影响越显著;下泄水温随取水水头的增加而降低,下泄水温降低幅度明显小于取水水头变幅;当取水流量逐渐增大时,下泄水温逐渐升高,但取水流量大于临界值时,下泄水温转而表现出缓慢下降趋势;在本文研究范围内,估算方程可以用于较好地预测下泄水温,预测结果与实验数据的相关系数为99.4%。     

Modelling spatial and temporal variability of water temperature across six rivers in Western Canada

Increasing river water temperature in response to the warming climate is concerning for water quality and ecosystem health of rivers. This study provides an assessment of the spatio-temporal variability of the ongoing and potential future river water temperature (T_w) change in western Canada. We use the air2stream model to reconstruct historical T_w dataset for 17 stations across six rivers, and employ the reconstructed T_w to analyze hydro-climatic controls, trends, and sensitivities in relation to air temperature (T_a) and discharge. Results provide insights on the contrasting summer (July and August) T_w responses. While T_w is primarily T_a controlled for the northern rivers, discharge exerts increasing influence that approaches T_a control for the southern rivers. Trends in T_w are increasing and spatially varied, with significant increases and occurrences above the critical 18 and 20°C thresholds for the southern Fraser and Similkameen Rivers. A sensitivity analysis indicated 0.5–1.5°C T_w increases for a 2.0°C T_a increase, and 0.2–0.6°C T_w increases for a 20% summer discharge decline. Overall, the results provide critical information for understanding the river ecosystem health, such as cold-water species habitat.     

围岩温度对输水洞衬砌混凝土温度与温度应力的影响研究

为了研究围岩温度对隧洞衬砌混凝土温度应力的影响规律,确保长距离输水隧洞的安全运行,以某水电站无压输水洞为研究对象,采用三维有限元温度场与徐变应力场仿真计算平台,对20、40、60、80℃围岩温度情况下的输水洞施工期及运行期进行仿真模拟.分析围岩温度对输水洞衬砌混凝土温度场和徐变应力场的影响,并研究了浇筑温度对高围岩温度...     

基于全局灵敏度分析的大坝温度场影响因子探讨

运行期大坝温度场与渗流场耦合数学模型包含诸多参数,采用灵敏度分析方法能确定大坝温度场的主要影响因子,从而减小模型校正的工作量,为相关研究提供借鉴。基于大坝热-流耦合稳态模型,对大坝温度场分别做了局部灵敏度分析和全局灵敏度分析。分析结果表明,大坝温度场对上游水库库底温度和下游坝面温度较灵敏,其余参数的灵敏度顺序依次为水力梯度、渗透率、岩石热导系数、孔隙率和介质比热。实例分析结果也证实全局灵敏度分析能用来定量研究参数间共同作用对数值模型的影响。     

Atlantic salmon (Salmo salar) in the regulated River Alta: effects of altered water temperature on parr growth

The chief objective of this study was to analyse the effects of altered water temperature, due to the hydropower regulation of the River Alta, on growth of Atlantic salmon parr. The river was developed for hydroelectric purposes in 1987. A 110 m high concrete dam was built in the main river 49 km upstream from the outlet to the sea. The outlet of the power station is located 2.5 km downstream from the dam. The annual regime of water temperature has been altered downstream from the power station because of the regulation. It has decreased 1–2° C during June, July and the first half of August, while it has increased up to 3° C during late summer. During winter, water temperature has increased from 0° C to about 0.3–0.4° C. Atlantic salmon is the predominant fish species in the river. They can penetrate 46 km from the sea, up to the outlet of the power station. In this paper I have studied the relationship between growth of juvenile Atlantic salmon and water temperature in the upper part of the river. At similar temperatures, the growth rate of salmon parr in the River Alta is higher in early summer than later in the growing season. In early summer the salmon grew faster than the maximum rate predicted by a recently published model. Therefore, I adjusted the model to describe growth rates of salmon in early summer (ice break to mid‐August), using data derived prior to the hydropower development (1981–1986). The new model proved effective at describing growth rates of fish in early summer following the hydropower development (1987–1996). After development, growth rates decreased during early summer, but increased correspondingly later in the season. There was close agreement between these growth changes and the altered annual regime of river temperature. Overall, only minor changes in annual growth rates have been observed after the hydropower development. Copyright © 2003 John Wiley & Sons, Ltd.     

分汊河道水沙运动特性及其对河道演变的影响

以实测资料为依据,从理论上分析得出了稳定分汊河段的水面纵比降大于单一河段;分析了分汊河道进口段的水沙运动及输沙特性以及对汊道演变的影响;基于平衡输沙原理,分析得出了分流分沙变化对分汊河道冲淤影响的关系式,即分汊河道的冲淤演变与上游来沙量、主支汊分流分沙比及其变化等因素有关。     

径向温度梯度对β平面上斜压波热力结构影响的实验研究

本文用转环实验模拟方法研究了径向温度梯度对β平面上斜压波热力结构的影响。结果表明在转速相同的条件下，三波态流动对应的径向温度梯度比四波态流动的大；在三波态下，冷流闭势力强，急流向暖区推进，无量纲温度值跃变化深厚，流动表现为静力稳定；而在四波态下，冷流团势力减弱，急流向冷区收缩，无量纲温度值跃变化被抬升，低层表现为多小尺度运动。     

热分层环境下船模尾流温度分布与扩展规律的试验研究

通过对船模在水槽中稳定热分层环境下运动后留下的尾流中的温度测量及红外摄像，试验研究了双螺旋桨船模在二种速度运动下，螺旋桨相对向内旋转、向外旋转及螺旋桨不工作时，船模尾流中的温度分布与与扩展规律。     

Fishway passage and post‐passage mortality of up‐river migrating sockeye salmon in the Seton River,British Columbia

Adult sockeye salmon (Oncorhynchus nerka) were studied to assess the consequences of a dam and vertical‐slot fishway on mortality during their spawning migration in the Seton–Anderson watershed, British Columbia, Canada. Since previous research suggests fishway passage may be difficult, our main hypothesis was that the dam and fishway have post‐passage consequences that affect subsequent behaviour and survival. Eighty‐seven sockeye were caught at the top of the fishway, implanted with an acoustic telemetry transmitter, non‐lethally biopsied to obtain a small blood sample and released either upstream or downstream of the dam. Indices of physiological stress (i.e. plasma cortisol, glucose, lactate and ions) indicated that fish were not stressed or exhausted after capture from the fishway, and were not unduly stressed by transportation to release sites or net‐pen holding. Of 59 fish released downstream of the dam, 14% did not reach the dam tailrace. Overall passage efficiency at the fishway was 80%. Mortality in two lakes upstream of the dam was greater in fish released downstream of the dam (27%) compared to fish released upstream of the dam (7%; p = 0.04) suggesting that dam passage has consequences that reduce subsequent survival. Cumulative mortality of fish released downstream of the dam (n = 55) resulted in only 49% survival to spawning areas, compared to 93% of fish released upstream of the dam (n = 28). Survival was significantly lower for females (40%) than for males (71%; p = 0.03), a finding that has implications for conservation because spawning success of sockeye salmon populations is governed primarily by females. Copyright © 2010 John Wiley & Sons, Ltd.     

大型分层型水库下泄水温对取水高程敏感性分析研究

为分析下泄水温随取水高程变化规律,探讨分层型水库下泄水温的敏感性,结合丰满水电站,建立了全三维水动力-水温耦合数学模型,并同时开展了物理模型实验,计算结果与实验结果进行了相互验证。对取水水头16.0~25.0 m下取水水温进行预测研究,结果表明:大型分层型水库下泄水温不仅与上游取水高程有关,还取决于坝前库区取水层水温垂向分布;随着取水水头的降低,下泄水温逐渐升高,而增幅表现出逐渐减小,且该变化规律与坝前取水层水温垂向梯度无关;当老坝缺口拆除高程大于240.0 m时,下泄水温受老坝缺口拆除高程影响有限;大型分层型水库取水水头建议取16.0~18.0 m,但该结论仅根据单一工程研究得出,其通用性尚需要根据其他工程进一步研究验证。     

Hydrology and aquatic habitat characteristics of a riverine swamp: I. Influence of flow on water temperature and chemistry

We monitored water temperature, air temperature, hydrologic characteristics, and chemical variables for 25 months in a 254‐km² portion of the Atchafalaya Basin, Louisiana, USA, a distributary swamp of the Mississippi River. We related observed trends in thermal and chemical variables to characteristics of the flood pulse, available channel types, and paths of water flow within the study area. Dissolved oxygen (range 0.05–13.05 mg L⁻¹), percent oxygen saturation (range 0.6–142.4%), and pH (range 6.31–8.52) increased as river stages decreased, and water temperatures (range 4.75–32.25°C), specific conductance (range 207.8–931.5 μmhos), and the top–bottom difference in dissolved oxygen (−7.5–12.05 mg L⁻¹) increased as air temperatures rose. The maximum variance observed for all chemical and thermal habitat characteristics occurred during periods when air temperatures exceeded, and river stages were less than, their respective medians observed during the study. At any point in time, thermal and chemical variables varied most among stations in water courses with no visible water turbulence (low‐energy channels), and these channels consistently had lower dissolved oxygen, percent oxygen saturation, and pH than turbulent water courses (high‐energy channels) or lakes contained. Water was directed from the river into one region of the study area from two opposing directions, thereby impeding water flow through the region. Low‐energy channels in this region consistently exhibited lower dissolved oxygen concentrations, percent oxygen saturation, and pH than was observed in low‐energy channels of regions where water flow was unimpeded. The quantity and quality of aquatic habitat characteristics in riverine swamps can be manipulated by controlling the timing and magnitude of the flood pulse, relative availability of different water courses, and internal paths of water flow through the swamp. Copyright © 1999 John Wiley & Sons, Ltd.     

某水电站溢洪道闸室施工期温度场和温度应力有限元分析

为了闸室的安全施工,对某水电站溢洪道闸室施工期进行了三维有限元仿真计算,获得了该闸室混凝土结构温度场和应力场的分布及其随时间的变化规律,并分析了该闸室混凝土裂缝可能产生的原因,为施工过程提供参考依据.     

特高拱坝温度应力仿真与温度控制的几个问题探讨

特高拱坝由于底宽大、岸坡陡,故采用通仓浇筑时施工期的温度控制难度大。特高拱坝的温度场和温度应力有如下几个特点:(1)约束面长且约束强,在二期水冷时约束区会存在上下两个约束面;(2)最低温度出现在封拱灌浆水冷终了时,此时也是拉应力最大的时刻,因此二次水冷是温度控制的关键时刻;(3)陡坡坝段应力大,温控难度大。结合如上特点,以小湾、溪洛渡两座拱坝为例,通过仿真分析结果,讨论施工期温度场、应力场仿真分析的基本要求,及温度控制中需注意的几个关键问题。结论认为:(1)除强约束区很容易出现裂缝要特别注意外,非约束区同样要严格进行温度控制;(2)二期冷却前或过冬前要进行一次大范围中期冷却,以降低二期水冷的降温幅度,同时要严格控制降温速率;(3)冷却区高度要大于2个灌区高度或0.3~0.4L;(4)应以精细仿真分析的结果作为特高拱坝温度控制的依据,如有条件应进行全坝仿真,无条件时则须以3个以上坝段为对象进行仿真分析。