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1.
Hydropeaking leads to artificial fluctuations in discharge and corresponding water levels with pronounced dewatering areas between base and peak flow along gravel bars and channel banks. In the present study, 16 hydropeaking reaches in Austria were investigated to assess possible differences in the estimated stranding risk for young of the year brown trout according to different gravel bar types and differences in microtopography roughness. Based on hydrodynamic‐numerical modelling, a predictive habitat modelling approach was implemented in the study design. Accompanied by grain size sampling along the various channel bars, a conceptual stranding risk model (SRM) was developed. The results showed that a high variability in estimated stranding risk exists for the tested sites considering discharge ratios of 1:3, 1:5 and 1:10. With respect to the discussion of establishing legal thresholds for ramping ratios in discharge, it was documented that, exemplarily, a discharge ratio base flow/peak flow of 1:5 (winter base flow conditions) could cause minor differences in the spatial extent of dewatering areas and the related estimated stranding risk for juvenile brown trout compared to a ratio of 1:2 for summer base flow conditions. Microtopographic roughness was addressed due to sampling and analysis of grain size distributions. Statistical testing of grain size distributions revealed significant differences between the surface material compositions of the investigated gravel bars. Those differences are evident, particularly for the coarser fraction (d90), which is important as cover for young of the year brown trout. These aspects of grain size in habitat use and hydraulics have been addressed in the conceptual SRM. The results showed that point bar morphology, in particular, was less sensitive to the risk of stranding compared to, for example, alternating gravel bars. Considering the multiple pressures for alpine rivers, the improvement of structural features due to bar formation and related self‐forming processes is discussed as a possible alternative for future mitigation measures to reduce the negative impacts of hydropeaking. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

2.
Severe bank erosion at lowland rivers in Bangladesh devours vast tract of lands and renders thousands of people homeless at high flood; also,rapid deposition changes bed topographies and seriously redu...  相似文献   

3.
We adopt a multidisciplinary approach toward the quantitative assessment of juvenile fish habitats in Alpine rivers using analytical modeling. The study focuses on braided and single-thread channel configurations together with their associated hydrodynamic patterns. A distinct difference between flows in these channels is the number and spatial arrangement of recirculation zones. These are due to the separation of flow from the river banks and result in a higher retention of flow in braided channels. Braided channels were also shown to provide more favourable shelter and nursing conditions for fish larvae and juveniles by mitigating high velocities during floods, by maintaining relatively shallow areas of flow, and by significant adjustments in the thermal regime. A historical analysis revealed a significant reduction of braided reaches along Alpine rivers that have most likely led to a significant degradation of the fish fauna.  相似文献   

4.
The overpresence of fine sediment and fine sediment infiltration (FSI) in the aquatic environment of rivers are of increasing importance due to their limiting effects on habitat quality and use. The habitats of both macroinvertebrates and fish, especially spawning sites, can be negatively affected. More recently, hydropeaking has been mentioned as a driving factor in fine sediment dynamics and FSI in gravel-bed rivers. The primary aim of the present study was to quantify FSI in the vertical stratigraphy of alpine rivers with hydropeaking flow regimes in order to identify possible differences in FSI between the permanently wetted area (during base and peak flows) and the so-called dewatering areas, which are only inundated during peak flows. Moreover, we assessed whether the discharge ratio between base and peak flow is able to explain the magnitude of FSI. To address these aims, freeze-core samples were taken in eight different alpine river catchments. The results showed significant differences in the vertical stratification of FSI between the permanently wetted area during base flow and the dewatering sites. Surface clogging occurred only in the dewatering areas, with decreasing percentages of fine sediments associated with increasing core depths. In contrast, permanently wetted areas contained little or no fine sediment concentrations on the surface of the river bed. Furthermore, no statistical relationship was observed between the magnitude of hydropeaking and the sampled FSI rate. A repeated survey of FSI in the gravel matrix revealed the importance of de-clogging caused by flooding and the importance of FSI in the aquatic environment, especially in the initial stages of riparian vegetation establishment. © 2018 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

5.
A mobile-bed, undistorted physical model （1：40） has been used to investigate different sediment supply strategies to the Old Rhine through bank protection removal and modifications of groyne dimensions and configuration, which cause bank erosion. This trained channel was previously the main bed of the upper Rhine downstream of Basel （Switzerland）, but it has an artificially low flow regime since the construction of the Grand Canal d＇Alsace, a navigation canal, and a flow control dam at Kembs （France）. Training works and subsequent channel incision have also greatly reduced sediment transport rates and created a heavily armoured bed. The modelled pilot site has a groyne field on the left bank. Results show that the currently existing groynes at the site are not effective in creating high bank-side velocities conducive to bank erosion, even for flow rates significantly higher than the mean annual flow rate. The river bank has also proved to be more resistant than previously thought, allowing long stretches of bank protection to be safely removed. The physical model testing process has produced a new configuration for the groyne field, where two higher, larger island groynes are placed further apart than the three existing attached groynes. This innovative approach has proved effective, causing bank erosion for flow rates below the mean annual flow rate, with consistent erosion being observed. It has also been found that such a configuration does not pose a hazard for the Grand Canal d＇Alsace, which is situated next to the Old Rhine, through excessive bank erosion during high flow events.  相似文献   

6.
Channelization of the severely polluted Odra and Vistula Rivers in Poland induced intensive accumulation of fine‐grained deposits rich in organic matter and heavy metals. These sediments have been identified in vertical profiles in a narrow zone along river banks both in groyne‐created basins and on the floodplain. Grain size, organic matter, zinc (Zn), lead (Pb), copper (Cu) content and cesium‐137 (137Cs) was used for sediment dating and, stratigraphy and chemistry have been diagnostic features for these deposits, named industrial alluvium. In the most polluted river reaches stabilized by bank reinforcements and groynes, 2‐m‐thick slack water groyne deposits are composed of uniform strata of polluted silts with organic matter content over 10%, Zn content over 1000 mg/kg and average Cu and Pb over 100 mg/kg. The average rate of sediment accretion in groynes is higher than on the floodplain and reaches 5 cm/yr. Stratification which appears at higher levels in the groyne fields and on the levees reflects a change from in‐channel to overbank deposition and is typified by dark layers separated by bright, sandy, and less polluted strata. Stratified, 4‐m‐thick, sediment sequences have been found in groyne fields of incised river reaches. The average rate of sediment accretion in these reaches is of the order of 5 cm/yr. In stable and relatively less polluted river reaches, vertical‐accretion organic deposits are finely laminated and the average rate of deposition amounts to a few millimeters per year. Investigations indicate that groyne construction favors conditions for long‐term storage of sediments at channel banks. For this reason, groynes should be considered as structures that efficiently limit sudden release of sediment‐associated heavy metals stored in channels and in floodplains of the historically polluted rivers. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

7.
This paper examines a variety of recirculation flow patterns that develop in the groyne fields on rivers. A comprehensive data set was obtained from flume experiments at Delft University of Technology and field measurements performed on the Elbe River in Germany. The analysis focuses on patterns of velocity, scour and deposition, and corresponding change of riverbed morphology. The results show that velocity patterns in the groyne fields depend mainly on the aspect ratio between groyne length and length of groyne field. When the aspect ratio is greater than 0·5, a one‐gyre pattern of recirculation develops, while at groyne fields with aspect ratios less than 0·5 a two‐gyre recirculation pattern emerges. The spatial distribution of fine‐sediment deposition between the groynes coincides with the locations of gyres. Moreover, the thickness of the fine‐sediment layer decreases toward the gyre margins where recirculation velocities are greatest. Although the total concentration of suspended sediment in the river does not change considerably as the flow moves through the groyne field, the biological and gravimetrical composition of the suspended material changes substantially within the groyne field. These changes are due to preferential deposition of coarse mineral particles and the replacement of those minerals with finer organic material. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

8.
The importance of long‐term storage of heavy metals in groyne fields, functioning over 150 years, is investigated for the River Odra (Oder), western Poland. Construction of groynes along the Odra preceded rapid development of heavy industrialization in the largest coal mine districts in Poland and the Czech Republic that resulted in persistent riverine pollution. The 187 km long Middle Odra reach was repeatedly channelized from the first half of the eighteenth century to the turn of the twentieth century, during which time partially filled groyne fields were dissected by new bank lines and groyne systems, with older groyne fields partially keyed into the floodplain. Consequently, concentrations of zinc, lead, cadmium, and copper within historically deposited groyne field sediments exceed local geochemical background levels by more than 60, 40, 15 and 10 times, respectively. Sediments contaminated with heavy metals occur within three distinctive geomorphic zones: zone I is up to 250 m wide and furthest from the present channel, comprising decimeter‐thick polluted sediments, overlying eighteenth century sand and gravel bars; zone II represents the former nineteenth century groyne fields, with widths between 10 and 100 m, filled with as much as 3 m of polluted sediments; zone III represents the twentieth century groyne fields, which are several to a dozen metres wide and filled with polluted sediments averaging depths of more than 2 m. This investigation indicates that large and extensive sediment quantities of moderately polluted sediments are stored immediately along the banks of the River Odra. These sediments could be a significant secondary pollution source and therefore careful maintenance of contemporary bank protection structures is required. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

9.
Many of the unionoid mussel species are threatened, and to be able to develop strategies for effective conservation, one of the needs is to distinguish host fish species from non-host fish species using reliable methods. Margaritifera margaritifera lives as a parasite on brown trout (Salmo trutta) and/or Atlantic salmon (Salmo salar). The aim was to compare the reliability of two methods measuring the host specificity of M. margaritifera in two rivers that flow out into Skagerrak in the Atlantic Ocean. A second aim was to compare the time- and cost-efficiency of the two methods. The methods were (1) natural encystment abundances on fish in their native streams using electrofishing, and (2) encystment abundances from controlled artificial infestation in aquaria, on fish that were sacrificed. In both rivers, young-of-the-year (YOY), but not older brown trout, were naturally infested with relatively low loads of glochidia larvae, while the Atlantic salmon was not infested at all. When using artificial infestation, both YOY and older brown had encysted glochidia larvae on their gills, while glochidia larvae were not able to develop in Atlantic salmon at all. Here, the encystment was higher on the brown trout from the Lärje River, and older brown trout from the Lärje River did not seem to have as strong immunity response compared to older brown trout from the Brattefors River. In summary, brown trout is the only host fish for M. margaritifera in these rivers. Both methods can be used to discriminate between host fish species, but the method measuring natural encystment seems most time- and cost-efficient. In addition, natural encystment can be measured using a non-destructive photo-method, and is therefore suggested to be used when discriminating between host fish species for M. margaritifera.  相似文献   

10.
Rivers are worldwide highly fragmented due to human impacts. This fragmentation has a negative effect on fish movement and dispersal. Many artificial barriers such as river bed sills and small weirs are nowadays replaced by block ramps in order to reestablish longitudinal connectivity for fish in rivers and streams. We studied the upstream passage of several fish species on different types of block ramps with slopes between 3.6 and 13.4 %. We conducted translocation experiments in the field based on mark-recapture and on the use of PIT-tags. Temporal movement patterns were observed by an instream antenna. Hydraulic and morphological characteristics of block ramps were measured and compared with fish passage efficiency. Our results clearly showed that upstream passage efficiency differs between fish species, size classes and block ramps. We observed that brown trout (Salmo trutta fario) performed better than bullhead (Cottus gobio) and several cyprinid species on the same block ramps. Passage efficiency of brown trout and chub (Leuciscus cephalus) was size-selective, with small-sized individuals being less successful. For brown trout, size-selectivity became more relevant with increasing slope of ramp. We conclude that block ramps with slopes of >5 % are ineffective for the small-sized cyprinid species and that vertical drops within step-pool ramps can hinder successful upstream passage of bullhead.  相似文献   

11.
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12.
Unionoid mussels are obligate parasites on one or more fish species. The objective was to compare growth and survival of encysted mussel larvae of the freshwater pearl mussel (Margaritifera margaritifera) on young-of-the-year (YOY) versus one-year old brown trout (Salmo trutta). YOY and one-year old trout from the Brattefors and Lärje Rivers, Sweden, were infested with mussel larvae from their home river. The mass-normalized encystment abundance was higher on YOY trout than on one-year old trout. The proportional decrease in mass-normalized encystment abundance was larger on YOY brown trout from the Brattefors River than on YOY brown trout from the Lärje River. Encystment per individual fish was higher on YOY trout than on one-year old trout from the Brattefors River, whereas this relationship was reversed for trout from the Lärje River. Larval growth was higher on YOY trout than on one-year old trout. There was a larger difference in larval growth between YOY trout and one-year old trout from the Brattefors River than on the brown trout from the Lärje River. The ability to use both YOY and older fish, such as in the Lärje River, may increase the reproduction potential of mussel populations, compared to a reduced ability to use more than one year class, such as in the Brattefors River. This may also affect the dispersal of mussels, as older brown trout often move and migrate to a higher degree within and between rivers. The dispersal potential of mussels may therefore be relatively high in the Lärje River, but low in the Brattefors River. In rivers where the mussels have to rely on YOY brown trout, it could be worth facilitating passage through migration obstacles for YOY brown trout. Infested YOY brown trout could be artificially re-distributed within rivers, to places with former mussel distributions. It could also be worth testing the suitability of brown trout of different age classes when starting breeding programs.  相似文献   

13.
River restoration works often include measures to promote morphological diversity and enhance habitat suitability. One of these measures is the creation of macro‐roughness elements, such as lateral cavities and embayments, in the banks of channelized rivers. However, in flows that are heavily charged with fine sediments in suspension, such as glacier‐fed streams and very low‐gradient reaches of large catchment rivers, these lateral cavities may trap these sediments. Consequently, the morphological changes may be affected, and the functionality of the restoration interventions may be compromised. Herein, we analyse the influence of these macro‐roughness elements on the transport of fine sediments in the main channel. Laboratory tests with uniform flow charged with sediments in a channel with banks equipped with large‐scale rectangular roughness elements were carried out. The laboratory experiments covered a wide range of rectangular cavity geometrical configurations and shallowness ratios. The influence of key parameters such as flow shallowness, geometric ratios of the cavities and initial sediment concentration was tested. Surface particle image velocimetry, sediment samples and temporal turbidity records were collected during the experiments. The amount of sediments captured by the cavities, the temporal evolution of the concentration of sediments in suspension and the flow hydrodynamics are cross‐analysed and discussed. It is shown that the trapping efficiency of the macro‐roughness elements is a clear function of the channel geometry and the shallowness of the flow. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

14.
The development of alternate bars in channelized rivers can be explained theoretically as an instability of the riverbed when the active channel width to depth ratio exceeds a threshold. However, the development of a vegetation cover on the alternate bars of some channelized rivers and its interactions with bar morphology have not been investigated in detail. Our study focused on the co‐evolution of alternate bars and vegetation along a 33 km reach of the Isère River, France. We analysed historical information to investigate the development of alternate bars and their colonization by vegetation within a straightened, embanked river subject to flow regulation, sediment mining, and vegetation management. Over an 80 year period, bar density decreased, bar length increased, and bar mobility slowed. Vegetation encroachment across bar surfaces accompanied these temporal changes and, once established, vegetation cover persisted, shifting the overall system from an unvegetated to a vegetated dynamic equilibrium state. The unvegetated morphodynamics of the impressively regular sequence of alternate bars that developed in the Isère following channelization is consistent with previous theoretical morphodynamic work. However, the apparent triggering dynamics of vegetation colonization needs to be investigated, based on complex biophysical instability processes. If instability related to vegetation colonization is confirmed, further work needs to focus on the relevance of initial conditions for this instability, and on related feedback effects such as how the morphodynamics of bare‐sediment alternate bars may have affected vegetation development and, in turn, how vegetation has created a new dynamic equilibrium state. Copyright © 2018 John Wiley & Sons, Ltd.  相似文献   

15.
River channelization and the construction of high-head storage schemes have been the basis of agricultural and socio-economic development in many alpine regions. One example is the Upper-Rhone River in Switzerland. The Upper-Rhone’s morphology changed considerably between 1863 and 1960 as a result of two major channelizations and, from 1950 on, the construction of a large number of high-head storage hydropower schemes in the catchment. These modifications have brought large benefits to the local population, at the cost, however, of substantial disturbances in aquatic and terrestrial ecosystems in and along the river. A primary factor behind these disturbances is the alteration of the natural flow regime, namely hydropeaking due to the operation of the high-head storage hydropower plants. For sustainable river-restoration projects on regulated rivers, scientists and engineers now widely accept the necessity of integrated management of the river. Different aspects such as river morphology, sediment management, water quality, temperature, and the naturally variable flow regime should be considered simultaneously. Mitigation of non-natural, sub-daily flow fluctuations due to hydropeaking is a crucial step in restoring natural flow regimes, but is especially challenging due to the economic constraints such mitigation places upon hydropower plants. With the goal of addressing this challenge, this paper proposes three indicators to describe the flow regime of rivers in alpine catchments with and without high-head storage hydropower plants. The indicators quantify: (1) the seasonal distribution and transfer of water, (2) sub-daily flow fluctuations, and (3) the intensity and frequency of flow changes. Indicators are evaluated in a case study of the Upper-Rhone River for pre- and post-impact situations, and the benefit of a multipurpose project reducing hydropeaking on hydrologic conditions is quantified. Furthermore, the paper explores the possibility of using these indicators to link aquatic and terrestrial ecosystem well being to their hydrology.  相似文献   

16.
Knowledge of locomotion of fish near river confluences is important for prediction of fish distribution in a river network.The flow separation zone near the confluence of a river network is a favorite habitat and feeding place for silver carp,which is one of the four major species of Chinese carp and usually provides positive rheotaxis to water flow.In the current study,a series of laboratory experiments were done to determine the behavioral responses of juvenile silver carp to the hydrodynamic ...  相似文献   

17.
针对我国室内地震应急避难场所极度缺乏、无法推进的现状,本文介绍了国内外室内避难场所的建设经验及我国现行避难场所抗震设防标准现状,提出依据《中华人民共和国标准化法》,整合现行避难场所强制性标准、完善避难场所推荐性标准的建议。并分析、探讨影响避难建筑设防标准的因素,结合我国中小学校抗震设防及建筑规模,给出基于“平灾结合”原则推进室内应急避难场所建设的建议。  相似文献   

18.
Floods can destroy fish habitat. During a flood a fish has to seek shelters (refuges) to survive. It is necessary to know the maximum discharge that the fish can sustain against the strong current. Ecological and hydraulic engineers can simulate the flow condition of high flow for designing the refuge when restoring and enhancing the rivers are needed. Based on the average ratio of the mean and maximum velocities invariant with time, discharge and water level, this paper tries to introduce the concept of ecological high flow. The mean‐maximum velocity ratio can be used to estimate the mean velocity of the river. If the maximum velocity of the cross section is replaced by the maximum sustained swimming speeds of fish, the mean velocity of ecological high flow can be calculated with the constant ratio. The cross‐sectional area can be estimated by the gage height. Then the ecological high flow can be estimated as the product of mean velocity of ecological high flow multiplied by the cross‐sectional area. The available data of the upstream of the Dacha River where is the habitat of the Formosan landlocked salmon were used to illustrate the estimation of the ecological high flow. Any restoration project at Sonmou that try to improve the stream habitat can use the ecological high flow to design the hydraulic structure at suitable location to offer refuges for the Formosan landlocked salmon that is an endangered species in Taiwan Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

19.
We assessed the effectiveness of pulse flows in facilitating the upstream migration of an imperiled summer-run Chinook salmon (Oncorhynchus tshawytscha) stock in the Puntledge River, BC, Canada. During July and August, over 3 years, we tracked radio-tagged fish (n = 100) in a reach of the Puntledge River where water is diverted for power generation, resulting in stable low flows that are believed to impede migration. Over the course of  13 pulse flows, we measured migration rate, passage rate at natural barriers that are difficult to pass during low flows, movement away from the turbine outlet pool that creates distracting flows, and locomotor activity. Mean river flow during the peak of the pulses varied from 12.1 to 42.5 m3 s?1 and was at least 6.1 m3 s?1 above residual base flows. Typically, the pulse flows lasted 48 h. Migration rate was higher during some pulse flows, but results varied among pulses. Passage at natural barriers was only higher during an abnormal pulse where flows reached twice that of the prescribed flow (i.e., 24+ m3 s?1). Some fish moved away from the turbine outlet pool during pulse flows. Pulse flows did not affect fish activity levels, as measured by electromyogram telemetry. Although the effect of pulsed flows on the migration of the Puntledge River summer-run Chinook salmon was unclear, no negative impacts, such as hyperactivity or downstream displacement were observed. The use of pulse flows as a management tool still requires further research.  相似文献   

20.
On 11 March 2011, a moment magnitude M w = 9.0 earthquake occurred off the Japan Tohoku coast causing catastrophic damage and loss of human lives. In the immediate aftermath of the earthquake, we conducted the reconnaissance survey in the city of Rikuzentakata, Japan. In comparison with three previous historical tsunamis impacting the same region, the 2011 event presented the largest values with respect to the tsunami height, the inundation area and the inundation distance. A representative tsunami height of 15 m was recorded in Rikuzentakata, with increased heights of 20 m around rocky headlands. In terms of the inundation area, the 2011 Tohoku tsunami exceeded by almost 2.6 times the area flooded by the 1960 Chilean tsunami, which ranks second among the four events compared. The maximum tsunami inundation distance was 8.1 km along the Kesen River, exceeding the 1933 Showa and 1960 Chilean tsunami inundations by factors of 6.2 and 2.7, respectively. The overland tsunami inundation distance was less than 2 km. The tsunami inundation height linearly decreased along the Kesen River at a rate of approximately 1 m/km. Nevertheless, the measured inland tsunami heights exhibit significant variations on local and regional scales. A designated “tsunami control forest” planted with a cross-shore width of about 200 m along a 2 km stretch of Rikuzentakata coastline was completely overrun and failed to protect the local community during this extreme event. Similarly, many designated tsunami shelters were too low and were overwashed by tsunami waves, thereby failing to provide shelter for evacuees—a risk that had been underestimated.  相似文献   

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