Modification of temperature behaviour through regulation of a British river system

The effects of flow regulation on temperature behaviour in the River Exe, Devon, U.K. have been studied, and attention is given to the local impact of impoundment and its downstream persistence. Temperature levels and seasonal thermal regime are considered as well as diel temperature fluctuations and temperatures during extreme weather conditions. Variations in temperature during individual reservoir releases have also been monitored. The impact of impoundment has been to make the stream environment immediately below the dam more homothermous so that temperatures rearely rise above 17·5°C or fall below 2·0°C, and monthyl average diel ranges are < 3 and < 1°C in summer and winter months respectively. In contrast to other reservoirs in Britain and abroad, this effect has been largely caused by increased groundwater flow downstream from the reservoir following impoundment. Regulation has also affected downstream temperature behaviour and has moderated the thermal regime of the Exe mainstream. This influence is generally restricted to a distance of up to 20 km from the dam, but in conditions of hot weather and low flows it may extend to almost 40 km from the impoundment.     

三峡坝址来水变化及水利工程对其影响分析

气候变化和人类活动导致长江流域水资源年际、年内均发生变化。利用不同趋势分析和突变分析法,选取1890—2020年三峡坝址来水资料分析来水变化趋势以及溪洛渡、向家坝、三峡水库建库前后三峡坝址处年均、消落期、汛期、蓄水期来水变化。结果表明：三峡坝址在年均、汛期、蓄水期来水减小趋势显著,消落期减小趋势不显著,三峡坝址来水变化趋势突变时间在1960年左右。溪洛渡和向家坝水库在枯水期向下游补水导致三峡坝址来水增加,造成溪洛渡、向家坝建库后三峡消落期来水比历史反向增大,说明巨型水库对长江上游及金沙江流域水资源时空分布影响较大。     

考虑蓄水期弃水风险的水库长期发电调度方法

短期径流的大幅波动使得以平均径流为基础制定的水库长期调度方案面临较大弃水风险,是影响水库长期调度决策合理性的重要因素。本文考虑日尺度径流波动影响,提出一种蓄水期弃水风险量化方法,并建立了耦合弃水风险的水库长期发电调度模型。利用长系列日径流资料,结合风险最小蓄水规则,以不蓄弃水流量为指标量化蓄水期各月弃水风险;采用Copula函数构建月均入流与弃水风险的联合分布和条件概率分布,明晰了特定入流条件的风险置信区间;最后,将弃水风险以弃电损失函数融入优化模型,以获得更符合实际的长期调度方案。以澜沧江流域小湾水库为工程背景进行调度模拟分析,结果表明本文方法能够有效降低水库长期优化调度方案的弃水风险,有利于提高优化结果的可操作性,与传统方法相比,能够使多年平均弃水减少约4.76亿m³、发电量增加约1.15亿kW·h。     

Toledo Bend reservoir and geomorphic response in the lower Sabine River

Downstream geomorphic responses of stream channels to dams are complex, variable, and difficult to predict, apparently because the effects of local geological, hydrological, and operational details confound and complicate efforts to apply models and generalizations to individual streams. This sort of complex geomorphic response characterizes the Sabine River, along the Texas and Louisiana border, downstream of the Toledo Bend dam and reservoir. Toledo Bend controls the flow of water and essentially prevents the flux of sediment from three‐quarters of the drainage basin to the lower Sabine River. Although the channel is scoured immediately downstream of the dam, further downstream there is little evidence of major changes in sediment transport or deposition, sand supply, or channel morphology attributable to the impoundment. Channels are actively shifting, banks are eroding, and sandbars are migrating, but not in any discernibly different way than before the dam was constructed. The Sabine River continues to transport sand downstream, and alluvial floodplains continue to accrete. The relatively small geomorphic response can be attributed to several factors. While dam releases are unnaturally flashy and abrupt on a day‐to‐day basis, the long‐term pattern of releases combined with some downstream smoothing creates a flow regime in the lower basin which mimics the pre‐dam regime, at least at monthly and annual time scales. Sediment production within the lower Sabine basin is sufficient to satisfy the river's sediment transport capacity and maintain pre‐dam alluvial sedimentation regimes. Toledo Bend reservoir has a capacity: annual inflow ratio of 1.2 and impounds 74% of the Sabine drainage basin, yet there has been minimal geomorphic response in the lower river, which may seem counterintuitive. However, the complex linked geomorphic processes of discharge, sediment transport and loads, tributary inputs, and channel erosion include interactions which might increase as well as decrease sediment loads. Furthermore, if a stream is transport‐limited before impoundment, the reduced sediment supply after damming may have limited impact. Copyright © 2003 John Wiley & Sons, Ltd.     

Effects of an upland impoundment on structural and functional properties of a small stream in a basaltic plateau (golan heights,Israel)

The aim of the study was to evaluate the impact of an upland storage reservoir, typical of the series of reservoirs in the Golan Heights basaltic plateau, on structural and functional properties of the downstream ecosystem, in the vicinity of the reservoir, shortly after damming. The effect of impoundment on water quality conditions may be divided into winter-spring, and summer periods. In the former, the impoundment seems to lengthen the period of flow of runoff quality water. This is evident by the elevated winter and spring turbidities and the higher concentrations of suspended solids below the reservoir. In summer, water quality below the reservoir is controlled by the consequences of stratification in the reservoir. The hypolimnial release results in depression of the maximal temperature and narrowing of the daily and seasonal temperature variations. It supplies water enriched in nutrients and low in oxygen, suspended solids and turbidity. The macroinvertebrate community responds to impoundment in density changes and shifting of dominance. We hypothesize that the thermal effect of hypolimnial release from warm monomictic reservoirs on the invertebrate community of warm streams will differ from an equivalent thermal change caused by cold dimictic reservoirs in cold, temperate zone, streams. The effect of impoundment on functional properties of the ecosystem are most pronounced. The rate of production of benthic algae biomass below the reservoir increased by more than two orders of magnitude, but the effect diminished downstream. The rate of processing of plant material below the reservoir was lower than above the reservoir. Further investigation is needed to clarify this effect. Changes in reservoir operation are recommended to diminish the effects of impoundment.     

水温分层水库中大规模高浓度泥沙侵入及长期浊水放流问题的对策

用数值模型描述了水温分层水库中大规模高浓度泥沙流入时的水动力学现象,定量研究并讨论了如何改善这种情况下水库形成的长期浊水化现象。在大流量、高浓度时,洪水水流沿着水库底部向下游高速流动,撞击大坝后造成的回流形成洪水的混浊水体与水库内周围环境水体的混合,导致水库长时间浑浊,形成长期浊水放流。该机理提示了减少洪水后库内混浊水体积的可能性。数值实验表明,如果合理采用选择性取水设备,或通过下层泄洪口可以成功地减少混浊水和清洁水体的混合,将洪水后库内残余混浊水的量减少88％。进一步的计算表明,如果可以改变温度跃层的位置或泄洪口的高程,则可以控制洪水时泥水在水库中的流动,以改善洪水后浊水放流的状况。     

溪洛渡-向家坝-三峡梯级水库水温分布特性

梯级水库蓄水运行后,改变了河流的天然水流情势和水体的年内热量分配,水库内的水温分布特性随之变化。为了解溪洛渡-向家坝-三峡梯级水库蓄水运行后河道水温分布特征,对梯级水库沿程19个断面水温进行了观测,并根据观测资料系统地分析了梯级水库进出库水温和沿程水温分布,以及垂向温度分布变化情况。研究结果表明:溪洛渡、向家坝、三峡梯级水库的下泄水温在降温季节略有增加,在升温季节略有下降,形成了"高温不高,低温不低"的平坦化现象;溪洛渡和向家坝水库坝前区域在垂向上均出现明显的温度分层,而三峡水库近坝区的温度分层现象在梯级水库运行后明显减弱,近几年表层和底层水温相差最大值仅为2.5℃。研究结果可为梯级水库联合调度、水生态研究、水库水温数学模型验证等提供参考。     

The potential role of tributaries as seed sources to an impoundment in Northern Sweden: a field experiment with seed mimics

Fragmentation and flow regulation of rivers by large dams are known to obstruct the longitudinal dispersal of waterborne plant propagules between impoundments, and to affect plant community composition. However, even several decades after a dam has been built, impoundments may still have a relatively species‐rich riparian flora. We hypothesized that free‐flowing tributaries act as the major gene pools for such impoundments, thus alleviating the fragmenting effect large dams have on the main channel. The importance of tributaries as seed sources was tested by releasing wooden seed mimics in three different‐sized (0.22–6.93 m³ s^?1) tributaries of an impoundment in the Ume River in Northern Sweden. In each tributary seed mimics were released, during the spring flood peak, from three points approximately 1, 2 and 3 km upstream the outlet in the impoundment. The importance of a tributary as a seed source increased with tributary size. Of the 9000 released seed mimics 1.5% reached the impoundment; 1.2% of the 9000 originated from the largest tributary and 0.3% from the middle‐sized one. The smallest tributary retained all its mimics. Copyright © 2007 John Wiley & Sons, Ltd.     

WATER QUALITY DURING TWO HIGH‐FLOW YEARS ON THE LOWER MISSOURI RIVER: THE EFFECTS OF RESERVOIR AND TRIBUTARY CONTRIBUTIONS

Complex socioeconomic and ecological issues, ranging from impaired streams to Gulf of Mexico hypoxia, have made nutrient management an increasingly important issue across the USA. High flows during 2010 and 2011 provided a unique opportunity to investigate trends in discharge, total nitrogen, nitrate/nitrite, total phosphorus, ortho‐phosphorus, suspended sediment and total suspended solids during two distinct high‐flow years on the Missouri River. We compared collections taken during 2010 and 2011 at 12 lower Missouri River locations (river kilometers 1212 to 71) and 22 Missouri River tributary locations. During 2011, average concentrations for all sampled parameters were significantly lower, despite significantly higher total discharge, than 2010 concentrations. Differences in water chemistry between years are likely attributed to the primary source of water. Tributary inflow created high flows during 2010, whereas record releases from Gavins Point Dam created high flows during 2011. Analysis of flow estimated the contribution of these releases at each site and revealed strong positive relationships between the percentage of estimated tributary flow at each site and the concentrations of total nitrogen, total phosphorus and total suspended solids. These monitoring efforts underline the contrasting impacts that tributary streams and reservoir releases have on nutrient export of the Missouri River during high‐flow events and reveal a larger trend of increased nutrient concentrations as the proportion of Missouri River tributary flow increased. Published 2013. This article is a U.S. Government work and is in the public domain in the USA. River Research and Applications published by John Wiley & Sons, Ltd.     

The downstream impacts of the burgomillodo reservoir,Spain

The Burgomillodo Dam, located in the middle Rio Duraton (north Spain, Duero Basin), has created a small eutrophic reservoir with a capacity of 15 × 10⁶ m ³ and a maximum depth of 40m. Burgomillodo Reservoir is solely used for producing hydroelectric power. The regulated flow pattern of hypolimnial waters is characterized by higher daytime flows than those by night, with low flows at weekends all the year round. The environmental impact generated by this hydropower scheme on the river downstream was assessed by comparing physiochemical characteristics and aquatic communities of an upstream site (reference station) with those of three downstream stations, which were located 0–2, 2–5, and 7–6 km below the dam. Water temperature, pH and dissolved oxygen were significantly lower downstream from the reservoir. Hardness, alkalinity, suspended inorganic matter, and conductivity had reduced annual variability below the dam. Photosynthetic activity was directly involved in the recovery of dissolved oxygen and pH values. Species richness and abundance of macrophytes increased just below the dam. Macrobenthic and fish communities were composed of higher numbers of potamic species. Number of taxa, density, biomass, and diversity were higher at the reference site, recovering their values as the distance below the reservoir increased. Macrobenthic trophic structure was changed by an increase in predators and filter feeders and a decrease in shredders. Environmental impact values for the macrobenthic community living just below the dam were higher than those for the fish community. It is concluded that the main physiochemical factors involved in environmental impacts were dissolved oxygen deficit and short-term flow fluctuations for the macrobenthic community, and oxygen deficit for the fish fauna. Benthic macroinvertebrates appear to be the best aquatic organisms for detecting changes and for reflecting the spatial recovery of environmental conditions.     

川西高原某水库坝址区渗流场模拟及渗漏量计算

为定量评价某水库坝址坝肩渗漏量,以期为大坝防渗处理提供依据。运用Visual MODFLOW三维渗流软件,模拟坝址区在水库蓄水前后的三维渗流场,同时计算坝址断面处水库蓄水前的渗流量和水库蓄水后的渗漏量。模拟结果表明由于大坝的修建,坝址上游的地表水位抬升,使得地下水流动方向发生逆转,坝址断面处的渗漏量也有较大增长,工程对区域地下水环境造成了较为明显的影响。故从工程安全角度考虑,需要对坝基、坝肩进行防渗处理。     

Impact Assessment of Mtera and Kidatu Reservoirs on the Annual Maximum Floods at Stiegler's Gorge of the Rufiji River in Tanzania

Abstract

The impoundment of any river causes changes in the downstream flow regime. The effect of a dam on flow regime depends on both the storage capacity of the reservoir relative to the volume of river flow and the way the dam is operated. The most common attribute of flow regulation is a decrease in the magnitude of the flood peaks and an increase in low flows. This paper reports the findings of a study to assess the cumulative impact of two dams on the Great Ruaha River in Tanzania (the Mtera and Kidatu Reservoir System) on flood flows. The method used was to compare the observed annual maximum flows at downstream locations after the construction of the dams with mathematically modeled estimates of the annual maximum flows at the same locations, assuming that the dams were not built (i.e. generating naturalized flows). Contrary to expectations, the study found that annual maximum peaks were supposed to be less than those actually observed. For instance, in 1989, annual maximum peak flow of 1,400 m³/s was recorded at Kidatu, but the estimated uncontrolled peak flow should have been 800 m³/s, signifying an artificially-induced flood wave. Although, there was a significant impact on the peak flows at Kidatu awing to the dams, the impact was found to be minimal on the flow peaks at Steigler's Gorge.     

Suspended solids transport in the regulated River Blithe,Staffordshire, U.K.

Suspended solids concentrations and turbidity were monitored on the regulated River Blithe at two sites downstream of the reservoir for a period of 18 months. Changes in the suspended solids loads transported and the nature of the material in suspension are related to dam overspill and tributary flood events. A hysteretic relationship between suspended solids concentrations and discharge is characteristic of both sites, sediment supply being limited within the regulated river. Downstream of the dam, rapid bank erosion occurred on meander bends but the suspended solids loads transported by the regulated river relate more to the resuspension and transport of tributary injected sediments and scouring of a dense periphyton. Close to the dam, fine biogenic matter dominated the seston, which scanning electron microscopy revealed to contain algal fragments and inorganic diatom frustules, but downstream, tributary-derived minerogenic particles were dominant.     

Immediate downstream effects of the Petit-Saut dam on young neotropical fish in a large tributary of the Sinnamary River (French Guiana,South America)

The effects of artificially low runoffs in the Sinnamary River, French Guiana, South America, on flow patterns and on richness and abundance of young fish in Venus Creek, one of its main downstream tributaries were examined. After Petit-Saut dam's gates were closed, the areas adjacent to this tributary were never once flooded for the entire duration of the rainy season. The daily maximal averages of water speed at the tributary's mouth were found to be significantly increased. Young fish sampled using light-traps were less abundant and less diverse after dam closure. Young Characiformes appeared to be the most affected by these flow disturbances. These findings enabled us to develop a conceptual model of the consequences of impoundment on young fish assemblages through the modifications of tributaries and associated floodplains hydrology. Because of flow reduction in the river during the first year of impoundment, young fish that previously had a tendency of being trapped in tributaries and flooded areas were then at risk of being flushed away. The pattern of flow release by dam operations is known to be very different from natural flow variations. The consequences for downstream tributaries will be similar to those of channelization: lack of adjacent flooding areas and higher rates of downstream water transfer. How the recovery of downstream fish assemblages will occur is discussed. © 1998 John Wiley & Sons, Ltd.     

三峡水库支流库湾低流速条件下测流方法探讨及应用

三峡蓄水成库后,库区部分支流受长江干流回水顶托,形成了支流库湾,水体流态由典型的河流形态变为类湖泊形态,受上游来流和水库调度等因素综合影响,库湾水动力条件变得极其复杂.在野外长期现场观测的基础上,针对支流库湾水体复杂的水动力条件,提出了一种独特的流速监测方法.运用该方法在香溪河库湾测流,获得了较好的测流结果,能较好地表...     

Short‐term effects in a reduced flow stretch: The case of the Antas River in South Brazil

The building of adduction channels (penstocks) that conduct water from reservoirs to turbines, which are located kilometres from the dam, is becoming common, optimizing the electricity generation in small dams. This design creates a river stretch with reduced discharge between the dam and the powerhouse. This study evaluates the short‐term impacts of the below‐dam decrease in river flow on fish assemblages. Samples were collected in the reduced flow stretch of the Castro Alves Hydropower Plant (Antas River, Rio Grande do Sul, Brazil) before the reservoir started operating (January 2008; mean discharge of 103.7 m³/s) and immediately after operation began (March 2008; mean discharge of 12.4 m³/s). Sampling was conducted in distinct habitats of the reduced flow stretch (slow waters—gillnets, sand beaches—seining nets, structured littoral—electrofishing, and fast waters—cast nets) with a strongly standardized effort. The attributes of the fish assemblages were not negatively affected by the flow reduction in any habitat sampled. However, distinct changes in the spatial structure were observed considering the different types of habitat predominantly used by the species, which represents an entire reorganization of the fish assemblages in the short term. It is fundamental that these short‐term aspects be considered in the licensing of hydropower plants in addition to the long‐term changes.     

葛洲坝电站运行对中华鲟产卵场水流条件的影响

葛洲坝修建后,中华鲟被迫于每年10~11月在葛洲坝下游产卵繁殖。但三峡水库蓄水后,中华鲟产卵期,葛洲坝来水量减小,使中华鲟产卵场水流条件发生变化,从而对其自然繁殖产生不利影响。通过建立中华鲟产卵场二维水动力模型,在探讨中华鲟产卵场适宜水流速、流量和葛洲坝机组增容的基础上,提出2种葛洲坝水电站生态优化调度方案。结果表明:改变发电流量泄流位置将一定程度改善中华鲟产卵场水流条件,但增加机组额定发电流量对改善产卵场水流条件作用有限。     

乌江梯级开发对东风水库水温分布影响分析

为探讨梯级电站联合运行对下游水库水温影响,以乌江梯级开发电站中的东风水库为研究对象,根据东风水库2002年及2006年实测水温数据,分析了东风上游水库建成前后东风水库水温的变化过程,同时运用EFDC模型计算了东风水库上游引子渡和洪家渡水电站下泄低温水对东风库区表层水温及坝前垂向水温的影响。结果表明:梯级水库运行对天然河道水温的累积性影响程度跟主要支流水体温度及流量均有关,入库流量越大,东风库区相同位置库表水温越低,与天然水温的温差越大;下泄低温水温度越低,相同位置库表水温越低,与天然水温的温差越大;入库流量越大、入流温度与天然水温温差越大,低温水影响越大,上游下泄低温水对库区累积性作用越明显。     

2016年秋长江中下游枯水分析及对水库调度的启示

2016年7月长江中下游发生了区域性大洪水,上中游水库群联合调度,发挥了重要的防洪作用。洪水过后涝旱急转,长江中下游干流及“两湖”（洞庭湖、鄱阳湖）水位持续走低,9月份出现了历史同期严重枯水。为了探究此次枯水成因,总结经验规律,采用水量平衡法和水位流量关系曲线方法还原了2016年秋季枯水过程。对比分析发现,天然来水偏少和水库群拦蓄是导致长江中下游干流及两湖水位严重偏低的主要原因。此外,针对2020水平年投入运行的水库群规模将进一步扩大,汛末水库群蓄水对长江中下游来水的影响可能将持续加大且呈现常态化的现象,指出加强中长期水文预报技术与水库群联合蓄水研究是下一步的重点研究方向。     

基于原型监测的黏土心墙堆石坝渗流分析

某黏土心墙坝在蓄水期间,出现渗流量较大、坝体渗流、绕坝渗流增大等现象。为了寻找原因,通过对某黏土心墙坝的环境量、坝体渗流、绕坝渗流、渗流量等原型监测数据进行分析,得到渗流量、坝体坝基渗压、绕坝渗流等监测成果。为进一步分析渗流来源,对渗流量进行模型分析。结果表明各监测成果互为印证,受库水位影响显著;库水位是影响渗流量大小及变化的主要因素,降雨量是次要因素,其中,库水位对渗流量的影响主要是通过两岸绕坝渗流,其次是通过坝体坝基渗流。库水位对渗流量的影响既是即时的又是持续的。