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Assessment of the flow regime alterations in the middle reach of the Yangtze River associated with dam construction: potential ecological implications 
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下载免费PDF全文 Hydrological regimes strongly influence the biotic diversity of river ecosystems by structuring physical habitat within river channels and on floodplains. Modification of hydrological regimes by dam construction can have important consequences for river ecosystems. This study examines the impacts of the construction of two dams, the Gezhouba Dam and the Three Gorges Dam, on the hydrological regime of the Yangtze River in China. Analysis of hydrological change before and after dam construction is investigated by evaluating changes in the medians and ranges of variability of 33 hydrological parameters. Results show that the hydrological impact of the Gezhouba Dam is relatively small, affecting mainly the medians and variability of low flows, the rate of rise, and the number of hydrological reversals. The closure of the Three Gorges Dam has substantially altered the downstream flow regime, affecting the seasonal distribution of flows, the variability of flows, the magnitude of minimum flows, low‐flow pulses, the rate of rise, and hydrological reversals. These changes in flow regime have greatly influenced the aquatic biodiversity and fish community structure within the Yangtze River. In particular, populations of migratory fish have been negatively impacted. The results help to identify the magnitudes of hydrological alteration associated with the construction of dams on this important large river and also provide useful information to guide strategies aimed at restoration of the river's ecosystems. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
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Near‐bed shear stress,turbulence production and dissipation in a shallow and narrow tidal channel 下载免费PDF全文
下载免费PDF全文 Near‐bed, highly resolved velocity profiles were measured in the lower 0.03 m of the water column using acoustic Doppler profiling velocimeters in narrow tidal channels in a salt marsh. The bed shear stress was estimated from the velocity profiles using three methods: the log‐law, Reynolds stress, and shear stress derived from the turbulent kinetic energy (TKE). Bed shear stresses were largest during ebbing tide, while near‐bed velocities were larger during flooding tide. The Reynolds stress and TKE method gave similar results, while the log‐law method resulted in smaller bed shear stress values during ebbing tide. Shear stresses and turbulent kinetic energy followed a similar trend with the largest peaks during ebbing tide. The maximum turbulent kinetic energy was on the order of 1 × 10? 2 m2/s2. The fluid shear stress during flooding tide was approximately 30% of the fluid shear stress during ebbing tide. The maximum TKE‐derived shear stress was 0.7 N/m2 and 2.7 N/m2 during flooding and ebbing tide, respectively, and occurred around 0.02 m above the bed. Turbulence dissipation was estimated using the frequency spectrum and structure function methods. Turbulence dissipation estimates from both methods were maximum near the bed (~0.01 m). Both the structure function and the frequency spectrum methods resulted in maximum dissipation estimates on the order of 4 × 10? 3 m2/s3. Turbulence production exceeded turbulence dissipation at every phase of the tide, suggesting that advection and vertical diffusion are not negligible. However, turbulence production and dissipation were within a factor of 2 for 77% of the estimates. The turbulence production and dissipation decreased quickly away from the bed, suggesting that measurements higher in the water column cannot be translated directly to turbulence production and dissipation estimates near the bed. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
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Sabrina M. Parra Ismael Mariño-Tapia Cecilia Enriquez Arnoldo Valle-Levinson 《Ocean Dynamics》2014,64(11):1601-1614
The influence of sea level variations due to tides and wave setup on turbulent kinetic energy (TKE) was observed at a point source submarine groundwater discharge in a fringing coral reef lagoon. Tidal and wave setup variations modulated speed, TKE, TKE dissipation, and water temperature and salinity at the buoyant jet. The primary driver of jet TKE and speed variations was tides, while wave setup was a minor contributor. An inverse relationship between surface elevation and TKE was explained with an exponential equation based on sea level variations. During low tides, peak jet speeds (up to 0.3 m s?1) and TKE per unit mass (up to 0.4 m2 s?2) were observed. As high tide approached, the jet produced minimum TKE of ~0.003 m2 s?2 and TKE dissipation ranged from 2 to 8×10?4 m2 s?3. This demonstrated the sensitivity of the jet discharge to tides despite the small tidal range (<20 cm). Jet temperatures and salinities displayed semidiurnal oscillations with minimum salinity and temperature values during maximum discharge. Jet salinities increased throughout low tides while temperatures decreased. This pattern suggested the jet conduit was connected to a stratified cavity within the aquifer containing cool fresh water over cool salty water. As low tides progressed, jet outflow increased in salinity because of the mixing within the conduit, while lower jet temperatures suggested water coming from further or deeper in the aquifer. The presence of such a cavity has been recently confirmed by divers. 相似文献
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Timothy P. Hanrahan 《水文研究》2008,22(1):127-141
The flow magnitude and timing from hydroelectric dams in the Snake River Basin of the Pacific north‐western US is managed in part for the benefit of salmon. The objective of this research was to evaluate the effects of Hells Canyon Dam discharge operations on hydrologic exchange flows between the river and riverbed in Snake River fall Chinook salmon spawning areas. Interactions between river water and pore water within the upper 1 m of the riverbed were quantified through the use of self‐contained temperature and water level data loggers suspended inside of piezometers. The data were recorded at 20 min intervals over a period of 200 days when the mean daily discharge was 218–605 m3 s?1, with hourly stage changes as large as 1·9 m. Differences in head pressure between the river and riverbed were small, often within ± 2 cm. Measured temperature gradients in the riverbed indicated significant interactions between the surface and subsurface water. At the majority of sites, neither hydraulic nor temperature gradients were significantly affected by either short‐ or long‐term changes in discharge operations from Hells Canyon Dam. Only 2 of 14 study sites exhibited acute flux reversals between the river and riverbed resulting from short‐term, large magnitude changes in discharge. The findings suggest that local scale measurements may not be wholly explanatory of the hydrological exchange between the river and riverbed. The processes controlling surface water exchange at the study sites are likely to be bedform‐induced advective pumping, turbulence at the riverbed surface, and large‐scale hydraulic gradients along the longitudinal profile of the riverbed. By incorporating the knowledge of hydrological exchange processes into water management planning, regional agencies will be better prepared to manage the limited water resources among competing priorities that include salmon recovery, flood control, irrigation supply, hydropower production, and recreation. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
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Groundwaters feeding travertine‐depositing rivers of the northeastern segment of the Barkly karst (NW Queensland, Australia) are of comparable chemical composition, allowing a detailed investigation of how the rate of downstream chemical evolution varies from river to river. The discharge, pH, temperature, conductivity and major‐ion concentrations of five rivers were determined by standard field and laboratory techniques. The results show that each river experiences similar patterns of downstream chemical evolution, with CO2 outgassing driving the waters to high levels of calcite supersaturation, which in turn leads to widespread calcium carbonate deposition. However, the rate at which the waters evolve, measured as the loss of CaCO3 per kilometre, varies from river to river, and depends primarily upon discharge at the time of sampling and stream gradient. For example, Louie Creek (Q = 0·11 m3 s?1) and Carl Creek (Q = 0·50 m3 s?1) have identical stream gradients, but the loss of CaCO3 per kilometre for Louie Creek is twice that of Carl Creek. The Gregory River (Q = 3·07 m3 s?1), O'Shanassy River (Q = 0·57 m3 s?1) and Lawn Hill Creek (Q = 0·72 m3 s?1) have very similar gradients, but the rate of hydrochemical evolution of the Gregory River is significantly less than either of the other two systems. The results have major implications for travertine deposition: the stream reach required for waters to evolve to critical levels of calcite supersaturation will, all others things being equal, increase with increasing discharge, and the length of reach over which travertine is deposited will also increase with increasing discharge. This implies that fossil travertine deposits preserved well downstream of modern deposition limits are likely to have been formed under higher discharge regimes. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
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This paper describes and analyses a hillslope–channel slope failure event that occurred at Wet Swine Gill, Lake District, northern England. This comprised a hillslope slide (180 m3, c. 203 ± 36 t), which coupled with the adjacent stream, resulting in a channelized debris flow and fluvial flood. The timing of the event is constrained between January and March 2002. The hillslope failure occurred in response to a rainfall/snowmelt trigger, on ground recently disturbed by a heather moorland fire and modified by artificial drainage. Slide and flow dynamics are estimated using reconstructed velocity and discharge values along the sediment transfer path. There is a rapid downstream reduction in both maximum velocity, from 9·8 to 1·3 m s?1; and maximum discharge, ranging from 33·5 to 2·4 m3 s?1. A volumetric sediment budget quantified a high degree of coupling between the hillslope and immediate channel (～92%: 167 m3), but virtually all of the sediment was retained in the first‐order tributary channel. Approximately 44% (81 m3) of the slide volume was retained in the run‐up deposit, and termination of the debris flow prior to the main river meant that the remainder did not discharge into the fluvial system downstream. These results suggest poor transmission of sediment to the main river at the time of the event, but importantly an increase in available material for post‐event sediment transfer processes within the small upland tributary. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
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Abstract The Colorado River is one of the most highly regulated and extensively utilized rivers in the world. Total reservoir storage is approximately four times the mean annual runoff of ?17 × 109 m3 year?1. Reservoir storage and regulation have decreased annual peak discharges and hydroelectric power generation has increased daily flow variability. In recent years, the incidental impacts of this development have become apparent especially along the Colorado River through Grand Canyon National Park downstream from Glen Canyon Dam and caused widespread concern. Since the completion of Glen Canyon Dam, the number and size of sand bars, which are used by recreational river runners and form the habitat for native fishes, have decreased substantially. Following an extensive hydrological and geomorphic investigation, an experimental flood release from the Glen Canyon Dam was proposed to determine whether sand bars would be rebuilt by a relatively brief period of flow substantially greater than the normal operating regime. This proposed release, however, was constrained by the Law of the River, the body of law developed over 70 years to control and distribute Colorado River water, the needs of hydropower users and those dependent upon hydropower revenues, and the physical constraints of the dam itself. A compromise was reached following often difficult negotiations and an experimental flood to rebuild sand bars was released in 1996. This flood, and the process by which it came about, gives hope to resolving the difficult and pervasive problem of allocation of water resources among competing interests. 相似文献
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Large wood distribution,mobility, and recruitment in an inter‐dam river reach: A comparison with geomorphic process on the Garrison Reach of the Missouri River pre and post the historical 2011 flood 下载免费PDF全文
下载免费PDF全文 Edward R. Schenk Adam J. Benthem Mark D. Dixon Melissa Mittelman Katherine J. Skalak Cliff R. Hupp Joel M. Galloway Rochelle A. Nustad 《地球表面变化过程与地形》2018,43(8):1677-1688
This study assessed the effect of the largest flood since dam regulation on geomorphic and large wood (LW) trends using LW distributions at three time periods on the 150 km long Garrison Reach of the Missouri River. In 2011, a flood exceeded 4390 m3/s for a two‐week period (705% above mean flow; 500 year flood). LW was measured using high resolution satellite imagery in summer 2010 and 2012. Ancillary data including forest character, vegetation cover, lateral bank retreat, and channel capacity. Lateral bank erosion removed approximately 7400 standing trees during the flood. Other mechanisms, that could account for the other two‐thirds of the measured in‐channel LW, include overland flow through floodplains and islands. LW transport was commonly near or over 100 km as indicated by longitudinal forest and bank loss and post‐flood LW distribution. LW concentrations shift at several locations along the river, both pre‐ and post‐flood, and correspond to geomorphic river regions created by the interaction of the Garrison Dam upstream and the Oahe Dam downstream. Areas near the upstream dam experienced proportionally higher rates of bank erosion and forest loss but in‐channel LW decreased, likely due to scouring. A large amount of LW moved during this flood, the chief anchoring mechanism was not bridges or narrow channel reaches but the channel complexity of the river delta created by the downstream reservoir. Areas near the downstream dam experienced bank accretion and large amounts of LW deposition. This study confirms the results of similar work in the Reach: despite a historic flood longitudinal LW and channel trends remain the same. Dam regulation has created a geomorphic and LW pattern that is largely uninterrupted by an unprecedented dam regulation era flood. River managers may require other tools than infrequent high intensity floods to restore geomorphic and LW patterns. Copyright © 2018 John Wiley & Sons, Ltd. 相似文献
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A field‐based project was initiated in order to characterize velocities and sediment entrainment in a forced‐pool and riffle sequence. Three‐dimensional velocities and turbulence intensities were measured with an acoustic Doppler velocimeter at 222 different points at three similar flows that averaged approximately 4·35 m3 s−1 within a large pool–riffle unit on North Saint Vrain Creek, Colorado. Sediment‐sorting patterns were observed with the introduction of 500 tracer particles painted according to initial seeding location. Tracer particles moved sporadically during a 113 day period in response to the annual snowmelt peak flow, which reached a maximum level of 14·8 m3 s−1. Velocity data indicate high instantaneous velocities and turbulence levels in the centre of pools. Patterns of sediment deposition support the notion that stream competence is higher in the pool than the downstream riffle. Flow convergence around a large channel constriction appears to play a major role in multiple processes that include helical flow development and sediment routing, and backwater development with low velocities and turbulence levels above the constriction that may locally limit sediment supply. Jet flow, flow separation, vortex scour and turbulence generation enhance scour in the centre of pools. Ultimately, multiple processes appear to play some role in maintenance of this forced pool and the associated riffle. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
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The Tongariro Power Development Scheme (TPDS) is used to regulate flow in the headwaters of the largest catchment on the North Island of New Zealand (the Waikato). Two small dams, the Rangipo Dam and the Poutu Intake Dam, were constructed in 1973 and 1983. The flow regime of the river is managed to divert freshes into the power scheme, but allows flows larger than 100 m3 s?1 to be released, to rework and transport sediment through the catchment. Analysis of aerial photos and maps spanning 1928 to 2007, alongside field measurements, show that there have been few hydrogeomorphic adjustments since dam construction. This includes limited changes to channel geometry, channel planform and bed material organization immediately downstream of the dams. In addition, offsite effects are minimal, both 500 m downstream of each dam, and in the more sensitive, less confined reaches in the lower catchment (11 km downstream of the Poutu Intake dam). The limited changes can be attributed to the locations of the dams within reaches characterised by bedrock gorges and confined within terraces. These locations act to flush sediments and impose margins that allow minimal adjustment of the channel. Bed material within this reach is characterised by the presence of a boulder lag. This is sourced from long-term incision into lahar deposits, and acts to limit the rate of incision, creating a steep and stable base upon which active fractions are transported. Just as importantly, significant storage in the low-relief volcanic plateau located in the upper catchment acts to disconnect and store the high sediment yields generated by active volcanic cones in the western sub-catchment upstream of the dams. This limits the rate of sediment supply to regulated reaches. Findings from this study show that analysis of reach-scale controls is essential in framing dam site locations in relation to the distribution of reaches and landscape units across the catchment. In this instance, tributary inputs downstream of the dams do not replenish the sediment and flow removed at the dam locations, as has been observed in other regulated systems. Rather, the river itself is resilient to change and flow variability is well managed allowing geomorphically effective floods to occur. Landscape setting is a key consideration in determining the hydrogeomorphic impact of flow regulation. 相似文献
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Quantifying River‐Groundwater Interactions of New Zealand's Gravel‐Bed Rivers: The Wairau Plain 下载免费PDF全文
下载免费PDF全文 New Zealand's gravel‐bed rivers have deposited coarse, highly conductive gravel aquifers that are predominantly fed by river water. Managing their groundwater resources is challenging because the recharge mechanisms in these rivers are poorly understood and recharge rates are difficult to predict, particularly under a more variable future climate. To understand the river‐groundwater exchange processes in gravel‐bed rivers, we investigate the Wairau Plain Aquifer using a three‐dimensional groundwater flow model which was calibrated using targeted field observations, “soft” information from experts of the local water authority, parameter regularization techniques, and the model‐independent parameter estimation software PEST. The uncertainty of simulated river‐aquifer exchange flows, groundwater heads, spring flows, and mean transit times were evaluated using Null‐space Monte‐Carlo methods. Our analysis suggests that the river is hydraulically perched (losing) above the regional water table in its upper reaches and is gaining downstream where marine sediments overlay unconfined gravels. River recharge rates are on average 7.3 m3/s, but are highly dynamic in time and variable in space. Although the river discharge regularly hits 1000 m3/s, the net exchange flow rarely exceeds 12 m3/s and seems to be limited by the physical constraints of unit‐gradient flux under disconnected rivers. An important finding for the management of the aquifer is that changes in aquifer storage are mainly affected by the frequency and duration of low‐flow periods in the river. We hypothesize that the new insights into the river‐groundwater exchange mechanisms of the presented case study are transferable to other rivers with similar characteristics. 相似文献
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The influence of flow discharge variations on the morphodynamics of a diffluence–confluence unit on a large river 下载免费PDF全文
下载免费PDF全文 Christopher R. Hackney Stephen E. Darby Daniel R. Parsons Julian Leyland Rolf Aalto Andrew P. Nicholas James L. Best 《地球表面变化过程与地形》2018,43(2):349-362
Bifurcations are key geomorphological nodes in anabranching and braided fluvial channels, controlling local bed morphology, the routing of sediment and water, and ultimately defining the stability of their associated diffluence–confluence unit. Recently, numerical modelling of bifurcations has focused on the relationship between flow conditions and the partitioning of sediment between the bifurcate channels. Herein, we report on field observations spanning September 2013 to July 2014 of the three‐dimensional flow structure, bed morphological change and partitioning of both flow discharge and suspended sediment through a large diffluence–confluence unit on the Mekong River, Cambodia, across a range of flow stages (from 13 500 to 27 000 m3 s?1). Analysis of discharge and sediment load throughout the diffluence–confluence unit reveals that during the highest flows (Q = 27 000 m3 s?1), the downstream island complex is a net sink of sediment (losing 2600 ± 2000 kg s?1 between the diffluence and confluence), whereas during the rising limb (Q = 19 500 m3 s?1) and falling limb flows (Q = 13 500 m3 s?1) the sediment balance is in quasi‐equilibrium. We show that the discharge asymmetry of the bifurcation varies with discharge and highlight that the influence of upstream curvature‐induced water surface slope and bed morphological change may be first‐order controls on bifurcation configuration. Comparison of our field data to existing bifurcation stability diagrams reveals that during lower (rising and falling limb) flow the bifurcation may be classified as unstable, yet transitions to a stable condition at high flows. However, over the long term (1959–2013) aerial imagery reveals the diffluence–confluence unit to be fairly stable. We propose, therefore, that the long‐term stability of the bifurcation, as well as the larger channel planform and morphology of the diffluence–confluence unit, may be controlled by the dominant sediment transport regime of the system. © 2017 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd. 相似文献
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Natural tracers (alkalinity and silica) were used to infer groundwater–surface‐water exchanges in the main braided reach of the River Feshie, Cairngorms, Scotland. Stream‐water samples were collected upstream and downstream of the braided section at fortnightly intervals throughout the 2001–2002 hydrological year and subsequently at finer resolution over two rainfall events. The braided reach was found to exert a significant downstream buffering effect on the alkalinity of these waters, particularly at moderate flows (4–8 m3 s?1/?Q30–70). Extensive hydrochemical surveys were undertaken to characterize the different source waters feeding the braids. Shallow groundwater flow systems at the edge of the braided floodplain, recharged by effluent streams and hillslope drainage, appeared to be of particular significance. Deeper groundwater was identified closer to the main channel, upwelling through the hyporheic zone. Both sources contributed to the significant groundwater–surface‐water interactions that promote the buffering effect observed through the braided reach. Their impact was less significant at higher flows (>15 m3 s?1/>Q10) when acidic storm runoff from the peat‐covered catchment headwaters dominated, as well as under baseflow conditions (<4 m3 s?1/<Q70), when upstream alkalinity was already buffered owing to headwater groundwater sources assuming dominance. The significant temporally and spatially dynamic influence of these groundwater–surface‐water interactions was therefore seen to have important implications for both catchment functioning and instream ecology. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
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长江的生物多样性危机——水利工程是祸首,酷渔乱捕是帮凶 总被引：6，自引：3，他引：3
长江是我国第一大河流,全长达6300 km.长江是一条生命之河,它的活力来自于干流、支流、湖泊和湿地的血脉沟通形成的独特生命系统.长江流域是世界生物多样性的热点区域,分布有鱼类400余种,其中纯淡水鱼类350种左右,特有鱼类多达156种.长江中下游是东亚季风气候下形成的洪泛平原区域,湖泊星罗棋布,并与江河相连,生活有珍稀水生哺乳动物——白鱀豚和江豚.1980s初中下游湖泊面积约有23123 km~2.1950—1970年间,沿江大建闸节制,除鄱阳湖(2933 km~2)和洞庭湖(2625 km~2)等外,绝大多数湖泊失去了与长江的自然联系,江湖阻隔使支撑长江鱼类的有效湖泊面积减少了76%.1981年,长江上建成了第一个大坝——葛洲坝;2003年,三峡大坝开始蓄水.长江干流的渔业捕捞量从1954年的43万t下降到1980s的20万t,最后到2011年的8万t(降幅为81%).与此完全不同的是,1950s以来,洞庭湖和鄱阳湖的渔产量分别在2~4万t之间徘徊.长江干流的饵料生物丰度不足两湖的1/7,因此干流对物种的承载力十分有限,以鱼为生的白鱀豚和江豚种群的衰退属于情理之中,加上酷捕误杀,白鱀豚已经灭绝,江豚也危在旦夕.葛洲坝的建设阻挡了鲟鱼和胭脂鱼等的生殖洄游通道,中华鲟和白鲟的灭绝已近在咫尺.长江上游建有1万多座水坝,大部分鱼类的生存受到威胁.根据对长江生物多样性危机成因的粗略估算,节制闸和水电站等水利工程"贡献"了70%,酷渔乱捕等其它因素"贡献"了30%.所谓的生态调度、鱼道或人工放流等也难以拯救膏肓之疾,即使在长江干流十年禁渔也难有根本改观.如果鄱阳湖和洞庭湖相继建闸,将使长江中下游的渔业资源量进一步衰退,江豚的灭绝在所难免,其它物种的灭绝将难以预料.长江在哭泣,众多的物种需要生态文明的呵护! 相似文献
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葛洲坝下中华鲟(Acipenser sinensis)性腺退化严重吗？ 总被引：2，自引：2，他引：0
葛洲坝对中华鲟(Acipenser sinensis)性腺发育的影响,是一个存在争议的问题,其影响程度直接关系到中华鲟的种群生存.利用中华鲟洄游动力学模型和性腺发育模型,我们揭示了中华鲟在长江的种群结构特点、时空分布和性腺发育过程以及葛洲坝的影响.通过对相关文献的分析和评价,我们认为,在葛洲坝救鱼过程中,长江水产研究所柯福恩等(1985)对葛洲坝下中华鲟性腺退化的研究工作是扎实的,他们关于中华鲟性腺退化十分严重,产卵规模相当有限,若干年后资源要下降的结论是可靠的,也得到了1990s以来中华鲟持续衰退事实的证明.作为葛洲坝救鱼的重要专业机构,中国科学院水生生物研究所的相关成果否认中华鲟性腺退化的方法和材料,是不充分和不可靠的.利用新理论重新分析历史调查数据,我们给出中华鲟性腺发育严重退化的其他证据.研究表明,葛洲坝的阻隔效应导致中华鲟性腺退化率为75%左右;该问题被长期忽视或轻视,对中华鲟保护产生了严重影响. 相似文献
17.
Sue White Jos M. García-Ruiz Carlos Martí Blas Valero M. Paz Errea Amelia Gmez-Villar 《水文研究》1997,11(14):1797-1812
On the evening of the 7 August 1996 an intense storm occurred over the Arás catchment near Biescas in the central Pyrenees. Eighty-seven people were killed as a result of the subsequent flood, which hit a campsite located on the alluvial fan at the outlet of the 18·8 km2 catchment. This paper presents the main results of a hydromorphological study of the event. The Betés subcatchment received the most intense rainfall, estimated at somewhat in excess of 250 mm, which resulted in a peak flow from this tributary of 300 m3 s−1. Just downstream from the Betés river junction, flow in the main channel reached 400 m3 s−1, increasing to around 500 m3 s−1 further downstream. Rainfall in the larger Aso tributary was less intense, and in the head reaches flow remained within-bank, representing a one in two-year return period event. Flow from this tributary did not exceed 100 m3 s−1, indicating that the Betés subcatchment supplied some 75% of the flow from just 28·7% of the catchment area. The extreme flows caused the collapse of a series of sediment trap dams in the Arás channel downstream of the Betés junction. This resulted in the addition of 68 000 m3 of sediment to an already disastrous event. Data from other rain gauges in the area showed both the extremely local nature of the event, and the problems of return period analysis for such storms, whose peaks are rarely observed at gauges. Together with the high geomorphological risks of the zone, this leads to the conclusion that a new method of spatial and temporal risk analysis is required for infrastructure planning. © 1997 John Wiley & Sons, Ltd. 相似文献
18.
Quantitative measures of the relationships between channel morphology and the habitat use of Chinese sturgeon(Acipenser sinensis) can help management and regulatory agencies to quantify potential spawning habitats and develop recovery goals in view of the decreasing area of sturgeon spawning habitat.This study determined the specific bedform types at the pool-riffle scale and evaluated the slopes,aspects and bed load gradation composition of Chinese sturgeon spawning areas in the Yangtze River,China.A bedform differencing technique was used to objectively quantify the longitudinal riverbed profile into four distinct pool-riffle units that were independent of discharge.The vertical location of thalweg points within these units was quantified with a riffle proximity index.Chinese sturgeon spawning areas were mapped and correlated with the pool-riffle units,slopes and aspects.The results indicate that Chinese sturgeon spawning areas occur primarily in riffles.The majority of Chinese sturgeon spawning occurred at elevations greater than 75%of the difference in elevation between the nearest riffle crest and the pool bottom.The slope of spawning sites was distributed between 0.05 and 6.36,and the average aspects were 219.92 and 207.63,respectively.The bed load is mainly composted of gravel and pebble,sediment diameter concentrated on 50-500mm.These analyses of bedform morphology will assist regional fish managers in quantifying existing and potential Chinese sturgeon spawning habitats and will provide a quantitative framework for evaluating general ecological implications of channel morphology in the Yangtze River. 相似文献
19.
Employing long‐range correlation, complexity features and clustering, this study investigated the influence of dam and lake‐river systems on the Yangtze River flow. The impact of the Gezhouba Dam and the lake systems on streamflow was evaluated by analysing daily streamflow records at the Cuntan, the Yichang and the Datong station. Results indicated no evident influence of the Gezhouba Dam on streamflow changes. Distinct differences in scaling behaviour, long‐range correlation and clustering of streamflow at the Datong station when compared with those at the Cuntan and Yichang stations undoubtedly showed the influence of water storage and the buffering effect of the lake systems between the Datong station and other two hydrological stations on streamflow in the lower Yangtze River basin. Decreased regularity, enhanced long‐range correlation and increased clustering of streamflow in the lower Yangtze River basin due to the effect of water storage of the lake systems were corroborated. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
20.
三峡水库调度运行改变了库区江段的水文情势,影响漂流性卵苗在库区江段内的时空分布特征。在水库低水位运行时,具有流水生境特征的库中和库尾江段是产漂流性卵鱼类在整个三峡库区内重要的产卵江段。了解三峡库中和库尾江段产漂流性卵鱼类的早期资源状况及其对水文和水温特征的响应关系,对于采取适宜的保护措施促进鱼类早期资源的恢复具有重要的意义。本文通过2017—2020年5—7月在库中涪陵断面进行的逐日早期资源监测,了解三峡库中和库尾江段产漂流性卵鱼类早期资源的种类组成、产卵规模、产卵场分布及其年际变动特征,并采用随机森林(RF)模型,分析鱼类逐日产卵规模变动与水文、水温格局及其过程的关系,辨识影响不同种类产卵规模变动的关键水文及水温要素。结果表明:2017—2020年共采集到漂流性鱼卵21种,包括长江上游特有鱼类鱼卵3种;以圆筒吻鮈Rhinagobio cylindricus、蒙古鲌Chanodichthys mongolicus、贝氏(?)Hemiculter bleekeri等6种鱼类的鱼卵为主,占总采集鱼卵数的88.76%;各年的鱼卵规模分别为83.04×108、14.29×... 相似文献