Grundlagenuntersuchungen und Methodikentwicklung zur Bewertung des Wasserkraft-Schwalls bei unterschiedlichen Flusstypen

Due to the disparate characteristics of Austria’s rivers, streams and surrounding riparian areas, similar anthropogenic impacts on our water systems can spark varying reactions. This is also true in the case of those waters affected by hydropeaking. In this context, the specific geometry of the river in question and the potential for “natural development” should be considered the basis for the river’s use as a habitat. These river-type-specific traits and their interplay with hydropeaking processes are at the core of this work, which summarizes the key findings of the SCHWALL_2012 research project. The results show that a river-type-specific and also river-reach-specific assessment of the influence of base and peak flows is essential to effective future river management, as different habitat changes can arise, depending on the respective river morphology and seasonal flow variations. Furthermore, detailed sedimentological studies show that on the one hand the base flow to peak flow ratio does not influence the accumulation of fine sediment in the constantly wetted areas of riverbeds, and that on the other the coarsening of gravel bars can have a major influence on the stranding risk for juvenile fish. With regard to this stranding risk, the findings also show that shallow-water areas display good hydraulic characteristics at both base and peak flow, though, given the habitat they provide for benthic organisms, naturally formed shallow-water areas (e.g. downstream from gravel bars) offer certain advantages over artificially created groin fields. In order to restore rivers and streams affected by hydropeaking, it will be necessary to improve both (a) the hydrological conditions (e.g. ramping velocity) and (b) the morphological situation on the rivers in question (e.g. through restructuring).     

Effects of cold and warm thermopeaking on drift and stranding of juvenile European grayling (Thymallus thymallus)

Intermittent water releases from hydropower plants, called hydropeaking, negatively affect river biota. The impacts mainly depend on hydrological alterations, but changes in physical habitat conditions are suspected to be co-responsible. For example, hydropeaking accompanied by a sudden change of water temperature in the downstream river—called thermopeaking—is also presumed to impair aquatic ecosystems. Still, knowledge about these thermopeaking impacts on aquatic species and life-stages is limited. We performed flume experiments under semi-natural conditions to fill this knowledge gap, simulating single hydropeaking events with a change in water temperature. As response parameters, we quantified the drift and stranding of early life-stages of European grayling (Thymallus thymallus L.), a key fish species of Alpine hydropeaking rivers. Hydropeaking events with a decrease in water temperature (“cold thermopeaking”) led to significantly higher downstream drift (mean = 51%) than events with increasing water temperature (“warm thermopeaking”, mean = 27%). Moreover, during cold thermopeaking, a comparably high fish drift was recorded up to 45 min after the start of peak flows. In contrast, drift rates quickly decreased after 15 min during warm thermopeaking. Remarkably, the spatial distribution of downstream drift along gravel bars during cold thermopeaking showed the opposite pattern compared to those triggered by warm thermopeaking events indicating different behavioral responses. Furthermore, the stranding rates of the cold thermopeaking trials were twice as high (mean = 31%) as those of the warm thermopeaking experiments (mean = 14%). The outcomes present vital information for improving mitigation measures and adapting environmental guidelines.     

Dynamic flow modelling of riverine amphibian habitat with application to regulated flow management

In regulated rivers, relicensing of hydropower projects can provide an opportunity to change flow regimes and reduce negative effects on sensitive aquatic biota. The volume of flow, timing and ramping rate of spring spills, and magnitude of aseasonal pulsed flows have potentially negative effects on the early life stages of amphibians, such as the Foothill yellow‐legged frog (Rana boylii). Two‐dimensional hydrodynamic modeling is one method to evaluate potential effects of flow variation on frog egg masses and tadpoles. We explored the usefulness of this technique by modeling habitat suitability under several pulsed flow scenarios in two river reaches in northern California, USA. We conducted analyses beyond simple weighted usable area calculations, such as quantifying the risk of scour or stranding, in order to quantify potential loss under different flow scenarios. The modeling results provided information on potential susceptibility to flow fluctuations as well as the influence of channel morphology on habitat suitability. Under each flow scenario, low percentages of suitable habitat remained suitable or were ‘buffered’ from the pulse, creating high potential for scour of egg masses or tadpoles. However, due to differences in channel morphologies, the wide, shallow study site provided 2‐3 times the buffering capacity of the entrenched study site. Additional analyses suggested that limited buffering capacity and lack of connectivity between suitable egg mass and tadpole habitats may explain why some hydraulically suitable habitats are unoccupied. This type of model‐based analysis would be useful for managing foothill yellow‐legged frogs or similar aquatic species in regulated river systems. Copyright © 2010 John Wiley & Sons, Ltd.     

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.     

Classification of hydropeaking impacts on Atlantic salmon populations in regulated rivers

This article proposes and demonstrates a new classification system of fish population level effects of hydropeaking operations in rivers. The classification of impacts is developed along two axes; first, the hydromorphological effect axis assesses the ecohydraulic alterations in rivers introduced by rapid and frequent variations in flow and water level, second the vulnerability axis assesses the site-specific vulnerability of the fish population. Finally, the population level impact is classified into four classes from small to very large by combining the two axes. The system was tested in four rivers in Norway exposed to hydropeaking, and they displayed a range of outcomes from small to very large impacts on the salmon populations. The river with a relatively high base flow and ramping restrictions scored better than rivers with the lower base flow or limited ramping restrictions, indicating that hydropeaking effects can be mitigated while maintaining high hydropower flexibility. Most effect factors could easily be calculated from timeseries of discharge and water level, whereas the use of hydraulic models to estimate potential stranding areas may require more work. The vulnerability factors are mainly qualitative and depend more heavily on expert judgments and are thus more uncertain. The system was deemed suitable for the purpose of supporting management decisions for rivers exposed to hydropeaking operations. It evaluates the severity of the additional pressures due to hydropeaking operations and proved useful to identify mitigating measures. While the system was developed for Atlantic salmon river systems, it could be adapted to other species or systems.     

Response of Fish Communities to Hydrological and Morphological Alterations in Hydropeaking Rivers of Austria

Climate change asks for the reduction in the consumption of fossil‐based fuels and an increased share of non‐regulated renewable energy sources, such as solar and wind power. In order to back up a larger share of these intermittent sources, ‘battery services’ are needed, currently provided only in large scale by hydropower, leading to more rapid and frequent changes in flows (hydropeaking) in the downstream rivers. Increased knowledge about the ecosystem response to such operations and design of cost‐effective measures is needed. We analysed the response of fish communities to hydropeaking (frequency, magnitude, ramping rate and timing) and the interaction with the habitat conditions in Austrian rivers. An index of biotic integrity (Fish Index Austria) was used to compare river sections with varying degrees of flow fluctuations under near‐natural and channelized habitat conditions. The results showed that habitat conditions, peak frequency (number of peaks per year), ramping rate (water level variation) and interaction between habitat and ramping rate explained most of the variation of the Fish Index Austria. In addition, peaking during the night seems to harm fish more than peaking during the day. Fish communities in hyporhithral and epipotamal types of rivers are more affected by hydropeaking than those in metarhithral type of rivers. The results support the findings of other studies that fish stranding caused by ramping rates >15 cm h^?1 are likely to be the main cause of fish community degradation when occurring more often than 20 times a year. While the ecological status degrades with increasing ramping rate in nature‐like rivers, fish communities are heavily degraded in channelized rivers regardless of the ramping rate. The mitigation of hydropeaking, therefore, requires an integrative approach considering the combined effects of hydrological and morphological alterations on fish. © 2014 The Authors. River Research and Applications published by John Wiley & Sons, Ltd.     

Der Einfluss der Ufervegetation auf die Wassertemperatur unter gewässertypspezifischer Berücksichtigung von Fischen und benthischen Evertebraten am Beispiel von Lafnitz und Pinka

This study is based on the results of the transdisciplinary research project BIO_CLIC. The aim of this study was (1) to synthesize and reflect the scientific knowledge, (2) to understand the potential of riparian vegetation on water temperature and (3) to ameliorate the impacts on the aquatic habitats of benthic invertebrates and fish at the rivers Lafnitz and Pinka. These objectives had been achieved by detailed field investigations, the assessment of abiotic environmental parameters (water temperature, riparian vegetation, shading and morphology), the comparison of effects of dynamic processes (incl. water temperature, riparian vegetation, change of river morphology) and biotic habitat use of benthic invertebrates and fish assemblages. The results provide an environmental and biological overview of potential local impacts on water temperature during heat wave periods and additionally taking into account diverse climate scenarios. Three hotspots at each river were selected to characterize specific river types with respect to river morphology, riparian vegetation, thermal regime, as well as the biocoenosis of fish and benthic invertebrates. The temperature regime influences all life stages of fish species and benthic invertebrates. They prefer different temperature regimes along a river continuum that correspond with typical species assemblages. Our evaluation of water temperatures for longitudinal biozenotic zones showed significant differences for shaded and unshaded river reaches. The river type specific mean water temperature for trout and grayling zone in summer is between 11 °C and 16 °C and for barbel and nase above 16 °C. Temperature changes of 2 °C lead to a shift of species composition preferring ?warm-water“ species. River reaches with functioning riparian vegetation are able to mitigate these effects of extreme water temperature increase.     

Evaluating the risk of fish stranding due to hydropeaking in a large continental river

With the continuous development of hydropower on a global scale, stranding of freshwater fishes is of growing concern, and an understanding of the mechanisms and variables affecting fish stranding in hydropeaking rivers is urgently needed. In particular, a methodology is required to identify the magnitude and timing at which fish stranding occurs in relation to environmental conditions. Here, we studied fish stranding in three reaches downstream of a hydropeaking generation station in the Saskatchewan River, Saskatchewan, Canada, using an innovative remote photography approach with 45 trail cameras and traditional transect monitoring, conducting 323 transects. We observed that juvenile sport and commercial fish species are stranding at a higher proportion than small bodied fish species. The remote photography approach provided more precise fish stranding timing and associated the environmental and physical conditions with a given stranding event, but captured fewer fish and only rarely allowed species identification. The comparison of the two methodologies resulted in similar stranded fish densities, but the remote photography allowed for continuous observations whereas the transect monitoring was limited by the observer availability in the field. Remote photography allowed for additional information on the scavenging of stranded fish, with scavenging occurring on average within 240 minutes of the fish being stranded. The probability of fish stranding increased significantly with increasing water temperature and substrate particle size resulted in greater stranding on finer substrates. Our findings have important implications for hydroelectric flow management by introducing an innovative, standardized method to study the effects of hydropeaking events on fish stranding that can be applied to increase our understanding of the impacts of hydropeaking on fish communities.     

Growth,Condition and Survival of Three Forage Fish Species Exposed to Two Different Experimental Hydropeaking Regimes in a Regulated River

Hydroelectric dam operation can alter discharge and temperature patterns, impacting fish populations downstream. Previous investigations into the effects of river regulation on fish have focused on a single species within a river, yet different results among studies suggest the potential for species‐specific impacts. Here, we compare the impacts of two different hydropeaking regimes relative to a naturally flowing river on three ecologically important members of the forage fish community: longnose dace (Rhinichthys cataractae), slimy sculpin (Cottus cognatus) and trout‐perch (Percopsis omiscomaycus). Annual growth, estimated from otolith back‐calculations, was higher for each of the species in the regulated river relative to the naturally flowing river but did not differ between hydropeaking regimes. Condition was assessed using weight–length relationships and differed between rivers for each species, and between hydropeaking regimes for longnose dace and slimy sculpin. Survival of longnose dace and slimy sculpin was lower in the regulated river relative to the naturally flowing river, but comparable between rivers for trout‐perch. Annual growth was significantly related to mean summer discharge in the regulated river and to mean summer water temperature in the naturally flowing river for each species, and significantly different slopes among species indicate species‐specific responses to discharge and temperature alterations. This study demonstrates different biological responses among fish species within rivers to regulation in general, as well as to specific hydropeaking regimes. Future studies should focus on multiple species and multiple indicators of fish health to more fully characterize the impacts of river regulation on downstream fish communities. Copyright © 2016 John Wiley & Sons, Ltd.     

水电开发对鱼类资源的影响及其保护措施

水电开发造成了河流环境结构和水文情势的改变,对河流水生生态系统形成了破坏。水电开发对鱼类资源的影响主要表现为阻隔了鱼类洄游通道以及对鱼类多样性、鱼类栖息地、下泄水水温、气体过饱和的影响。针对这些影响,提出采用修建过鱼设施、建设鱼类增殖站、建立鱼类种质资源保护区、下泄生态流量、分层取水等保护措施,以维持鱼类资源的多样性。水电开发应采取综合措施解决水生生态问题,特别是流域梯级开发更应注重对整个流域生态系统结构进行统筹规划,保护河流生态系统的完整性。     

By-pass valves in hydropower plants: An ecologically important measure to mitigate stranding in rivers due to emergency turbine flow shutdown

Hydropeaking operations or accidental shutdown in hydropower (HP) plants lead to rapid reduction in river flows downstream HP outlets and cause severe stranding of biota. Stranding of fish in dewatered riverbeds is a major consequence of hydropeaking. To mitigate the direct negative impacts of accidental powerplant shutdown implementation of automated by-pass valves (BPVs) is suggested as an efficient measure. Proper configuration and operation of the BPV is crucial. At present, more than 110 Norwegian HP plants have BPVs as a license requirement. We found that the function of the BPVs in small-scale HP plants (HPPs <10 MW) were found to be inadequate. Re-configuration to better mitigate the ecological impacts were required to minimize stranding risk for juvenile salmonids. The valves were found to come into operation too late, did not open automatically, or were found to reduce the flow too rapidly. Hence, the function of the valves did not meet best practice. This is alarming seen both from a governance perspective as well as from an ecological standpoint. Our second objective was to develop a generic cost-efficient formula for BPVs configuration to dampen severe flow dewatering in case of HP fallout. Our configuration formula is adjustable to meet down-ramping flow rules, and hence may helps to mitigate stranding of key species in rivers. For most of the large-scale HPPs (>10 MW), the BPVs seems to operate as expected, namely to secure base-flow until the HP turbine is re-started and hence mitigate the most severe dewatering events. Potentially more than 650 HPPs in Norway, and hence several thousand of river km downstream HPP outlets may need well-operated BPVs to mitigate accidental stranding of riverine biota worldwide.     

Factors affecting stranding of juvenile salmonids by wakes from ship passage in the Lower Columbia River

The effects of deep‐draft vessel traffic in confined riverine channels on shorelines and fish are of widespread concern. In the Pacific Northwest of the United States, wakes and subsequent beach run‐up from ships transiting the Lower Columbia River have been observed to strand juvenile salmon and other fish. As part of a before‐and‐after study to assess stranding effects that may be associated with channel deepening, we measured 19 variables from observations of 126 vessel passages at three low‐slope beaches and used multiple logistic regression to discern the significant factors influencing the frequency of stranding. Subyearling Chinook salmon were 82% of the fish stranded over all sites and seasons. Given a low‐slope beach, stranding frequencies for juvenile salmon were significantly related to river location, salmon density in the shallows, a proxy for ship kinetic energy, tidal height and two interactions. The beach types selected for our study do not include all the beach types along the Lower Columbia River so that the stranding probabilities described here cannot be extrapolated river‐wide. A more sophisticated modelling effort, informed by additional field data, is needed to assess salmon losses by stranding for the entire lower river. Such modelling needs to include river‐scale factors such as beach type, berms, proximity to navigation channel, and perhaps, proximity to tributaries that act as sources of outmigrating juvenile salmon. At both river and beach scales, no one factor produces stranding; rather interactions among several conditions produce a stranding event and give stranding its episodic nature. Published in 2010 by John Wiley & Sons, Ltd.     

Why do fish strand? An analysis of ten years of flow reduction monitoring data from the Columbia and Kootenay rivers,Canada

Stranding of fish due to flow reductions has been documented in the near shore of the Columbia and Kootenay Rivers, Canada, and can result in sub‐lethal or lethal effects on fish. Ten years (1999–2009) of monitoring data have been collected at sites below two hydro‐electric dams (Hugh‐L‐Keenleyside and Brilliant Dam) following flow reductions. A generalized linear mixed effects model analysed the probability of a stranding event in relation to environmental and operational variables including the rate of change in the water levels, the duration of shoreline inundation prior to a reduction (wetted history), the river stage, the magnitude of the reduction, distance downstream from the dam, time of day, day of year (season) and whether a site had been physically altered to mitigate stranding. The results demonstrated statistically significant effects on stranding risk from minimum river stage, day of the year and whether a site had been physically re‐contoured. The combination of investigated factors giving the highest probability of stranding was a large magnitude reduction completed in the afternoon in midsummer, at low water levels when the near shore had been inundated for a long period. This research is significant in its approach to assessing years of ecosystem scale monitoring data and using the modelling results to determine ways for these findings to be applied in regulated river management to minimize fish stranding. It also highlighted data gaps that require addressing and provides ecosystem scale results to compare with stranding studies carried out in mesocosms. © 2014 The Authors. River Research and Applications published by John Wiley & Sons Ltd.     

二维水流数学模型在多分汊河道鱼类栖息地设计中的应用

多分汊河道汇合或分流口水流流态复杂,常常存在河口滩及深槽,复杂多样的水文水力条件为鱼类提供了良好的进食及休憩场所。针对多分汊河道边界复杂的特点,建立了基于一般曲线坐标系下的平面二维水流数学模型。将所建立的数学模型应用于大渡河乐山段安谷水电站左岸生态河网建设和鱼类栖息地设计,对工程投运前后河段的水深、流速、流场、分流比进行模拟和对比分析,设置生态工程措施,使得鱼类产卵场河段水流特性仍满足鱼类栖息地要求。从安谷水电站运行效果看,设计的生态措施对河道鱼类栖息改善取得了较好的实践效果。     

Integrating two-dimensional water temperature simulations into a fish habitat model to improve hydro- and thermopeaking impact assessment

Storage hydropower plants, which are an important component of energy production in Switzerland, can lead to hydro- and thermopeaking, affecting river habitats and organisms. In this study, we developed an approach for integrating water temperature simulations into a habitat model to assess the impact of both hydro- and thermopeaking on the availability of suitable fish habitats. We focused on the habitat requirements of juvenile brown trout (Salmo trutta) in a semi-natural braided floodplain along the Moesa River (Southern Switzerland) in early summer. First, we defined different scenarios (with and without hydropeaking) based on the local hydrological and meteorological conditions. Second, we used a two-dimensional depth-averaged hydro- and thermodynamic model to simulate the spatial distributions of water depth, flow velocity, and water temperature. Third, we applied generalized preference curves for juvenile brown trout to identify hydraulically suitable habitats, and developed a new index to assess the availability of thermally suitable habitats. Finally, we quantified the extent to which hydraulically and thermally suitable habitats overlap in space and time. During both base and peak flow phases, most of the hydraulically and thermally suitable habitats are located in the side channels. High flow conditions combined with strong cold-thermopeaking lead to a higher thermal heterogeneity. However, disconnected habitats originate in the dewatering zone, increasing the risk of stranding as well as thermal stress. By helping to better understand the effects of thermopeaking on the availability of fish habitats, our approach could contribute to the design and evaluation of ecological restoration in hydropeaking rivers.     

A probability-based model to quantify the impact of hydropeaking on habitat suitability in rivers

A negative effect of hydropower on river environment includes rapid changes in flow and habitat conditions. Any sudden flow change could force fish to move towards a refuge area in a short period of time, causing serious disturbances in the life cycle of the fish. A probability-based model was developed to quantify the impact of hydropeaking on habitat suitability for two fish species, brown trout (Salamo trutta) and Grayling (Thymallus thymallus). The model used habitat preference curves, river velocity and depth to develop the suitability maps. The suitability maps reveal that habitat suitability deteriorates as flow increases in the studied part of the river. The probability model showed that, on average, suitability indices are higher for adult grayling than juvenile trout in hydropeaking events in this part of the river. The method developed shows the potential to be used in river management and the evaluation of hydropeaking impacts in river systems affected by hydropower.     

Determination of hydraulic parameters for instream flow assessments

Determination of the hydraulic parameters of a stream is the first stage in the instream flow incremental method (IFIM). Two different modellings have been applied to simulate the hydraulic conditions (i.e. depth and velocity) of the Orne river at Rabodanges in order to assess the changes in fish habitat with the flow. One process consists of representing the reach examined by a few sections (the pilot sections), the other is a conventional flow model. The accuracy of both types of model has been calculated by comparison with depth and velocity data available for four different rates of flow. As regards the flow model, the accuracy of depth calculations is average (16 per cent) but decreases for low rates of flow. Velocity values are less accurate (24 per cent). Concerning the pilot sections method, the degree of accuracy of velocities should be improved (80 per cent) but the accuracy of depths is interesting (7 per cent). The representation of the flow conditions the accuracy of per cent usable area (PUA). For brown trout juveniles and fry the accuracy on PUA is of the same order of magnitude as the degree of accuracy of depth. The inaccuracy on velocities due to the method is not totally reflected in the PUA values, the probability-of-use curves of the species considered can act as a filter for errors linked to the method followed for assessing hydraulic parameters.     

水事活动对洪湖鱼类资源的生态影响

长江中游两岸绝大多数湖泊自20世纪50年代以来因水利工程建设，先后失去与长江的天然联系而产生一系列的生态问题。以洪湖为例开展江湖阻隔对单个湖泊鱼类资源所产生的生态影响进行研究，结果表明：江湖阻隔导致湖泊渔业生产经营方式改变，野生渔业的产量和在渔业经济结构中的比重不断降低；阻隔后湖泊鱼类品种由20世纪50年代的不下100种下降到现在的49种，其中，天然捕捞渔获物中洄游性和流水型鱼类比重由20世纪50年代初的60％降到现在几近为0，大型经济鱼类减少，鱼类多样性指数下降。因此，江湖阻隔对湖泊渔业具有明显影响。     

An experimental study of stranding of juvenile salmonids on gravel bars and in sidechannels during rapid flow decreases

Juvenile salmonids can become stranded over gravel bars or trapped in off-channel habitat during rapid flow decreases that often occur in regulated rivers. In a stream channel experiment that simulated stranding over a gravel bar, more juvenile chinook salmon (Oncorhynchus tshwytscha) were stranded when the water was 6°C compared with 12°C. The rate of flow decrease was not a significant factor in the incidence of stranding. In contrast, the number of chinook and coho (O. kisutch) salmon juveniles that became trapped in side channels built in the stream channel increased with increasing rate of dewatering, and for coho salmon, more fish were trapped at night compared with the day. Even at the slowest rate of flow decrease some fish remained in the side channels after the channels became disconnected from the main flow. My results suggest that mortality as a result of trapping in side channels or pot-holes will be decreased, but may not be eliminated, by flow ramping, although this result needs to be corroborated with field studies. © 1997 John Wiley & Sons, Ltd.