共查询到20条相似文献，搜索用时 31 毫秒
1.
lCOMPOSITIONOFTHE"92.8"FLOODThreerainstormsoccurredfrom7ththrough13,,,August,1992inShaanxiProvince,diStributingfromnorthtosouthinsequence.Therainfallareacoveredtheregionsofintensivesoilerosion,'wheretheaveragerateoferosionis10,000-15',000ton/kmZ'year.Fig.IshowsisohyetsofrainfallintensityinthecatchmentoftheMiddleYellowRiVerdepictingthedistributionoftherainstormsfrom7thto13,,,August,1992(thehydrologicalBureauYRCC,1992).ThecenterofthefirstrainstormwaslocatedattheYikezhaomengPrefec… 相似文献
2.
The adjustment of the bankfull channel area in the Lower Yellow River has been dramatically affected by altered flow regimes caused by human activities. This paper presents a study on the effects of altered discharge and suspended sediment load on the bankfull area at Gaocun, a representative hydrometric station in the Lower Yellow River. The analysis demonstrates the cumulative effect of previous years' flow and sediment conditions on channel adjustment, a phenomenon commonly occurring in geomorphic systems due to the delayed channel response to flow and sediment conditions. A methodology for the prediction of bankfull area was developed based on the general concept that the rate of adjustment is proportional to the difference between the bankfull area and its equilibrium value. The proposed methodology is not only applicable for the prediction of the bankfull area in response to the changes in flow and sediment conditions in the Lower Yellow River, but can also be extended to other studies where the response times have a key role to play in the assessment of channel adjustment to external changes. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
3.
This paper presents a study on the characteristics of multiple time scales of bankfull discharge and its delayed response to changes of flow conditions using continuous wavelet analysis for data from selected hydrological stations in the Yellow River basin. Results showed that bankfull discharge series had one or two dominant time scales. For example, the Huayuankou station in the lower reach of the Yellow River had two dominant time scales of 19-20 years and 545 years. The dominant time scales of the bankfull discharge series were generally consistent with the dominant time scales of water discharge and sediment concentration series, indicating that the channel morphology inherits the characteristics of the hydrological system in terms of multiple time scales. In addition, the wavelet coefficients of the bankfull discharge series had a phase difference in relation to those of the sediment concentration series, with a delay time that varied from 3 to 16 years at different sites. This delay time or relaxation time is a result of the delayed response of bankfull discharge to flow conditions, which was significant for channel adjustments in response to changes of flow conditions. The findings of the multiple time scales and the delayed response are of importance for further study of channel morphology of fluvial systems. 相似文献
4.
Sedimentation of overbank floods in the confined complex channel–floodplain system of the Lower Yellow River,China 
下载免费PDF全文
下载免费PDF全文 The channel boundary conditions along the Lower Yellow River (LYR) have been altered significantly since the 1950s with the continual reinforcement and construction of both main and secondary dykes and river training works. To evaluate how the confined complex channel–floodplain system of the LYR responds to floods, this study presents a detailed investigation of the relationship between the tempo‐spatial distribution of sedimentation/erosion and overbank floods occurred in the LYR. For large overbank floods, we found that when the sediment transport coefficient (ratio of sediment concentration of flow to flow discharge) is less than 0.034, the bankfull channel is subject to significant erosion, whereas the main and secondary floodplains both accumulate sediment. The amount of sediment deposited on the main and secondary floodplains is closely related to the ratio of peak discharge to bankfull discharge, volume of water flowing over the floodplains, and sediment concentration of overbank flow, whereas the degree of erosion in the bankfull channel is related to the amount of sediment deposited on the main and secondary floodplains, water volume, and sediment load in flood season. The significant increase in erosion in the bankfull channel is due to the construction of the main and secondary dykes and river training works, which are largely in a wide and narrow alternated pattern along the LYR such that the water flowing over wider floodplains returns to the channel downstream after it drops sediment. For small overbank floods, the bankfull channel is subject to erosion when the sediment transport coefficient is less than 0.028, whereas the amount of sediment deposited on the secondary floodplain is associated closely with the sediment concentration of flow. Over the entire length of the LYR, the situation of erosion in the bankfull channel and sediment deposition on the main and secondary floodplains occurred mainly in the upper reach of the LYR, in which a channel wandering in planform has been well developed. 相似文献
5.
Along the lower reaches of the Waipaoa River, New Zealand, cross‐section survey data indicate there was a 23 per cent decrease in bankfull width and a 22 per cent reduction in channel cross‐section area between 1948 and 2000, as the channel responded to increased inputs of fine (suspended) sediment following deforestation of the headwaters in late C19 and early C20. We determined the bankfull discharge within a ～39 km long reach by routing known discharges through the one‐dimensional MIKE 11 flow model. The model runs suggest that the bankfull discharge varies between ～800 and ～2300 m3 s?1 and that the average recurrence interval is 4 ± 2 years on the annual maximum series; by contrast, the effective flow (360 m3 s?1) is equaled or exceeded three times a year. The variability in bankfull discharge arises because the banks tend to be lower in places where flood flows are constricted than in reaches where overbank flow is dispersed over a wide area, and because scour has counteracted aggradation in some locations. There is no downstream variation in Shields stress, or in relative shear stress, within the study reach. Bankfull shear stress is, on average, five times greater than the shear stress required to initiate motion. At the effective discharge it is more than twice the threshold value. The effective discharge probably has more relevance than the bankfull discharge to the overall picture of sediment movement in the lower reaches of the Waipaoa River but, because width is constrained by the stability and resistance of the bank material to erosion during high flows that also scour the bed, the overall channel geometry is likely determined by discharges at or near bankfull. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
6.
《国际泥沙研究》2020,35(6):651-658
Scientific evaluation of the sediment allocation effects in the Yellow River plays an important role in the comprehensive harnessing of the Yellow River. A new evaluation index system for sediment allocation has been established using the Analytic Hierarchy Process, and six main evaluation indexes have been selected for this study. The calculation methods and evaluation criteria of each evaluation index are proposed. The evaluation criterion of bankfull discharge in the upper reach is 2,000 m3/s, that of Tongguan elevation in the middle reach is 325.7 m, and that of bankfull discharge in the lower reach is 4,000 m3/s. The evaluation criteria of water volume and sediment volume into the Yellow River are 25 billion m3/a and 300 million t/a, respectively, and that of sediment volume into the sea to maintain stability of the estuary is 130–260 million t/a. The comprehensive evaluation method and grade index are proposed, and the effect of sediment allocation in the Yellow River from 1960 to 2015 is evaluated. The comprehensive evaluation grades in different periods are determined. The evaluation results objectively reflect the situation of sediment allocation in the Yellow River, and the new comprehensive evaluation method can be applied to evaluate the sediment allocation scheme of the Yellow River in the future. 相似文献
7.
Bankfull discharge is a key parameter in the context of river engineering and geomorphology, as an indicator of flood discharge capacity in alluvial rivers, and varying in response to the incoming flow and sediment regimes. Bankfull channel dimensions have significantly adjusted along the Lower Yellow River (LYR) due to recent channel degradation, caused by the operation of the Xiaolangdi Reservoir, which has led to longitudinal variability in cross‐sectional bankfull discharges. Therefore, it is more representative to describe the flood discharge capacity of the LYR, using the concept of reach‐averaged bankfull discharge. Previous simple mean methods to estimate reach‐scale bankfull discharge cannot meet the condition of flow continuity or account for the effect of different spacing between two sections. In this study, a general method to calculate cross‐sectional bankfull discharge using the simulated stage‐discharge relation is outlined briefly, and an integrated method is then proposed for estimating reach‐scale bankfull discharge. The proposed method integrates a geometric mean based on the log‐transformation with a weighted average based on the spacing between two consecutive sections, which avoids the shortcomings of previous methods. The post‐flood reach‐scale bankfull discharges in three different channel‐pattern reaches of the LYR were estimated annually during the period from 1999 to 2010 using the proposed method, based on surveyed post‐flood profiles at 91 sedimentation sections and the measured hydrological data at seven hydrometric sections. The calculated results indicate that: (i) the estimated reach‐scale bankfull discharges can effectively represent the flood discharge capacity of different reaches, with their ranges of variation being less than those of typical cross‐sectional bankfull discharges; and (ii) the magnitude of the reach‐scale bankfull discharge in each reach can respond well to the accumulative effect of incoming flow and sediment conditions. Finally, empirical relationships for different reaches in the LYR were developed between the reach‐scale bankfull discharge and the previous four‐year average discharge and incoming sediment coefficient during flood seasons, with relatively high correlation coefficients between them being obtained, and the reach‐scale bankfull discharges in different reaches predicted by the delayed response model were also presented for a comparison. These relations for the prediction of reach‐scale bankfull discharges were validated using the cross‐sectional profiles and hydrological data measured in 2011. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
8.
Delayed response means that channels cannot achieve a new equilibrium state immediately following disruption;the channel requires a response time or relaxation time to reach equilibrium.It follows that the morphological state of fluvial system represents the cumulative effects of all previous disturbances and environmental conditions.A unique feature of the delayed response model for bankfull discharge is that the model is capable of representing the cumulative effects of all previous flow conditions when applied to predict the path/trajectories of bankfull discharge in response to altered flow regimes.In this paper,the delayed response model was modified by readjusting the weight for the initial boundary conditions and introducing a variableβwith respect to time.The modified model was then applied to the bankfull discharge calculations for three selected river reaches of the Yellow River,with each reach having different geomorphic settings and constraints. Results indicated that the modified model can predict accurately the bankfull discharge variation in response to changes in flow discharge and sediment load conditions that have been dramatically altered in the past.Results also demonstrated the strong dependence of current bankfull discharge on the previous years’ flow conditions,with the relaxation time varied from 2 to 14 years,meaning that the bankfull discharge was not only affected by the flow discharge and sediment load in the current year,but also by those in previous 1 to 13 years.Furthermore,the relaxation time of bankfull discharge adjustment was inversely proportional to the long-term average suspended sediment concentrations,and this may be explained by fact that high sediment concentrations may have a high potential to perform geomorphic work and there is more sediment readily available to shape the channel boundary and geometry. 相似文献
9.
Abstract The objectives of this work are: (a) to statistically test and quantify the decreasing trends of streamflow and sediment discharge of the Yellow River in China during 1950–2005, (b) to identify change points or transition years of the decreasing trends, and (c) to diagnose whether the decreasing trends were caused by precipitation changes or human intervention, or both. The results show that significant decreasing trends in annual streamflow and sediment discharge have existed since the late 1950s at three stations located in the upper, middle, and lower reaches of the Yellow River (P?=?0.01). Change-point analyses further revealed that transition years existed and that rapid decline in streamflow and sediment discharge began in 1985 in most parts of the basin (P?=?0.05). Adoption of conservation measures in the 1980s and 1990s corroborates the identified transition years. Double-mass curves of precipitation vs streamflow (sediment) for the periods before and after the transition years show remarkable decreases in proportionality of streamflow (sediment) generation. All percentiles of streamflow and sediment discharge after the transition years showed rapid reduction. In the absence of significantly decreasing precipitation trends, it is concluded that the decreasing trends were very likely caused by human intervention. Relative to the period before the transition, human intervention during 1985–2005 reduced cumulative streamflow by 13.5, 14.3 and 24.6% and cumulative sediment discharge by 29.0, 24.8 and 26.5%, at Toudaoguai, Huayuankou and Lijin, respectively, showing the quantitative conservation effect in the basin. Citation Gao, P., Zhang, X.-C., Mu, X.-M., Wang, F., Li, R. & Zhang, X. (2010) Trend and change-point analyses of streamflow and sediment discharge in the Yellow River during 1950–2005. Hydrol. Sci. J. 55(2), 275–285. 相似文献
10.
This paper analyses the processes and mechanisms of a three‐stage channel adjustment over a cycle of the Yellow River mouth channel extension based on data comprising hydrologic measurements and channel geometric surveys. Rapid siltation in the mouth channel takes place in the young stage when the channel is being built by deposits and in the old stage when the channel cannot further adjust itself to keep sediment transport in equilibrium. It is disclosed that the bankfull width–depth ratio, bed material size and slope decrease in the young and mature stages but do not change in the old stage. The reduction of bankfull width–depth ratio and bed material size during the young and mature stages is found to be able to offset the effect of the slope reduction on sediment transport due to continuous mouth progradation. They reach their limits in old stage, and a constant slope is kept by unceasing sediment accumulation. The grain size composition of incoming sediment and the fining mechanism are responsible for the occurrence of lower limit of bed material size. The reason for the existence of a limit of bankfull cross‐sectional shape is that the large flows can fully transport the sediment load they are carrying, and siltation in the channel in the old stage takes place mainly in the low flows. It is suggested that the bankfull discharge plays an important role in shaping the channel but that the entire channel form is the product of both the large and low flows plus the effects of interaction between them. Channel pattern change shows a process from a braided pattern in the young stage to a straight pattern in the mature and old stages, and the straight channel becomes gradually sinuous. The occurrence and transformation of the channel patterns are supported by two planform predictors, but are also facilitated by some other conditions. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
11.
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
12.
Micha Klein 《地球表面变化过程与地形》1985,10(5):525-531
The annual discharge of the Lower Jordan River has decreased from about 1250 × 106 m3 y?1 to about 300 × 106 m3 y?1 due to water exploitation. The decrease in water discharge was not followed by a similar decrease in the suspended sediment. Evidence from air photographs and maps from 1920s to early 1970s show that the river is adjusting itself by shortening its course. The shortening is not distributed uniformly along the valley length. Local effects obscure the effect of decreasing discharge. Since the early 1970s the channel is becoming longer again due to a change in the dominant flow. 相似文献
13.
Retrogressive erosion, a widespread phenomenon of sediment transport in reservoirs, often impacts on both the reservoir capacity and the sedimentation in the downstream river channel. Based on field data from the Sanmenxia Reservoir and the Lower Yellow River over the past decades, three courses of ret-rogressive erosion with distinctive features were analyzed. The results indicate that retrogressive erosion, especially caused by rapid reduction in the water level till the reservoir is empty, often results in the serious siltation of the lower Yellow River and threatens the safety of the flood control in the Lower Yellow River. Unreasonable operation of the reservoir and incoming hyperconcentrated floods accom-panied by retrogressive erosion also aggravate the siltation of the main channel of the river. However, a reasonable operation mode of the reservoir so named"storing the clear (low sediment concentration) water in the non–flood season, and sluicing the muddy(high sediment concentration) water in the flood season" was found, which might mitigate the deposition in both the reservoir and the Lower Yellow River. This operation mode provides important experience for the design and operation of large reser-voirs in other large rivers carrying huge amounts of sediment. 相似文献
14.
Jan Pietroń Jeffrey A. Nittrouer Sergey R. Chalov Tian Y. Dong Nikolay Kasimov Galina Shinkareva Jerker Jarsjö 《水文研究》2018,32(2):278-292
The Selenga River delta (Russia) is a large (>600 km2) fluvially dominated fresh water system that transfers water and sediment from an undammed drainage basin into Lake Baikal, a United Nations Educational, Scientific, and Cultural Organization World Heritage Site. Through sedimentation processes, the delta and its wetlands provide important environmental services, such as storage of sediment‐bound pollutants (e.g., metals), thereby reducing their input to Lake Baikal. However, in the Selenga River delta and many other deltas of the world, there is a lack of knowledge regarding impacts of potential shifts in the flow regime (e.g., due to climate change and other anthropogenic impacts) on sedimentation processes, including sediment exchanges between deltaic channels and adjacent wetlands. This study uses field measurements of water velocities and sediment characteristics in the Selenga River delta, investigating conditions of moderate discharge, which have become more frequent over the past decades (at the expense of peak flows, Q > 1,350 m3 s?1). The aims are to determine if the river system under moderate flow conditions is capable of supporting sediment export from the main distributary channels of the delta to the adjacent wetlands. The results show that most of the deposited sediment outside of the deltaic channels is characterized by a large proportion of silt and clay material (i.e., <63 μm). For example, floodplain lakes function as sinks of very fine sediment (e.g., 97% of sediment by weight < 63 μm). Additionally, bed material sediment is found to be transported outside of the channel margins during conditions of moderate and high water discharge conditions (Q ≥ 1,000 m3 s?1). Submerged banks and marshlands located in the backwater zone of the delta accumulate sediment during such discharges, supporting wetland development. Thus, these regions likely sequester various metals bound to Selenga River sediment. 相似文献
15.
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
16.
Yunzhen Chen Irina Overeem Albert J. Kettner Shu Gao James P. M. Syvitski Yuanjian Wang 《地球表面变化过程与地形》2019,44(2):581-594
The lower Yellow River channel was maintained by artificial levees between 1580 and 1849. During this period, 280 levee breaches occurred. To estimate sediment storage on the floodplains outside the levees, a regression model with a decadal time step was developed to calculate the outflow ratio for the years when levee breaching occurred. Uncertainty analysis was used to identify the likely outflow ratio. Key variables of the model include annual water discharge, a proxy for levee conditions, and potential bankfull discharge of the channel before flood season. Uncertainty analysis reveals an outflow ratio of 0.35–0.56. We estimate that during this period, 18.8–30.1% of the total ~312 Gt of sediment load was deposited on the floodplains outside the levees. Human-accelerated erosion in the Loess Plateau caused a 4-fold increase in sediment delivery to the lower Yellow River, which could not be accommodated by channel morphodynamic changes. As a result, 21.2–27.5% of the total sediment load was deposited within the levees, creating a super-elevated channel bed that facilitated an uncommonly high breach outflow ratio. Hence, the factor of a large super-elevation relative to the mean main channel depth should be considered when designing diversions to restore floodplains. © 2018 John Wiley & Sons, Ltd. 相似文献
17.
Discharge characteristics in six adjacent mountainous watersheds in northern New Mexico, U.S.A., vary substantially between basins underlain by different lithologies. Relatively resistant gneisses and granites underlie two basins (drainage areas: 43 and 94 km2) that have high unit discharge (0·010 to 0·14 m3s?1 km?2), high bankfull discharge, and sustained high discharge. Less resistant sandstones and shales underlie four basins (drainage areas: 96 to 215 km2) that have relatively low unit discharge (0·001 to 0·005 m3s?1 km?2), relatively low bankfull discharge, and peak discharges that are not sustained as long as those in the crystalline terrane. Analysis of snowmelt-runoff water budgets suggests that three factors control hydrologic conditions in the basins. First, area-elevation distributions appear to control the timing and amounts of water input. These distributions probably reflect the erosional resistance of the different lithologies. Second, lithology appears to control runoff production in areas having minor amounts of storage. Third, glacial deposits in headwater regions control discharge duration and timing via storage and return flow releases. The amount of return flow released by glacial deposits, however, is probably controlled by the permeability of underlying bedrock. Therefore it appears that the duration, timing, and magnitude of discharge events in the study area are controlled both directly and indirectly by lithology. Stream power and shear stress estimates derived from bankfull discharge and bed-material size data suggest that higher bedload transport rates and larger bedload particle sizes exist in streams draining crystalline rocks than in streams draining sedimentary terrane. It appears that source-area lithology, by controlling discharge production, also influences stream power, bedload transport capabilities, and therefore total amounts of bedload transport. 相似文献
18.
Geomorphic evidence along bedrock-confined reaches of the Salt River in east-central Arizona provides a record of the river's largest flood events. Fine-grained flood slackwater deposits accumulated at channel margin irregularities several metres above the low-flow channel. Discharges associated with flow events responsible for the deposits were estimated by computer flow modelling. These estimates document flood magnitudes in excess of gauged historic streamflows. Relative and radiocarbon dating suggest that a flood record in excess of 600 y is preserved in the slackwater sequences. A prominent flood scar cut into grussy hillslope soils allows the extension of the prehistoric flood record to several thousand years. A maximum discharge estimate of 4600 m3s?1 affixed to the flood scar represents the largest flood event in the record, and is given a minimum recurrence interval of 1000–2000 y. The 1952 flood is the largest historic flow event experienced along the study reach and is estimated at 2900 m3s?1. Two palaeoflood events preserved in the slackwater stratigraphy exceed the 1952 event, and are given recurrence intervals of 300 and 600 y. The latter flood event had an estimated discharge of 3200 m3s?1. It is apparent that discharge estimates affixed to these infrequent, large-magnitude flood events approach a maximum with decreased probabilities (large recurrence intervals). This suggests that a physical limit on discharge may exist within the Salt River drainage basin and is perhaps directly related to drainage basin size. 相似文献
19.
Dynamic Changes of Sediment Discharge and the Influencing Factors in the Yellow River,China, for the Recent 90 Years 总被引：3，自引：0，他引：3
The dynamic changes in the sediment discharge over 90 years from 1919 to 2008 in the Yellow River in China were assessed on the basis of annual rainfall series and annual sediment series in Shan County hydrological station. The key factors affecting sediment discharge, such as rainfall, and human activities were studied. Anomaly accumulation method and double mass curve were employed to test the stage changes of sediment discharge, and to determine the main factors of sediment decline. Results showed that the annual average sediment discharge under natural conditions was about 16 × 108 t, but the measured annual average sediment during 1919–2008 was 12.71 × 108 t. The highest annual average during the study period was 39.10 × 108 t in 1933 while the lowest was 1.77 × 108 t in 2008. Sediment discharge in the Yellow River experienced two low sediment stages (1924–1931 and 1979–2008) and a high sediment stage (1932–1971), respectively. Since 1979, there was a significant decreasing trend in the sediment discharge, and the main influencing factor was fierce human activities. Annual average sediment discharge in the post‐development period (1979–2008) was 69.7% lower than that in the pre‐development period (1919–1978), with average reduction of 81 and 19% caused by human activities and rainfall, respectively. These results provide important evidence for making protecting policy for water resources quality and environmental safety of the Yellow River. 相似文献
20.
三峡工程运行后,坝下游河道发生持续冲刷。本文研究了长江中游(955 km)不同河段沿程演变差异及其原因。总体而言,河床形态调整幅度自上而下减弱,这是因为在河床持续冲刷过程中,水流含沙量沿程恢复,故越往下游冲刷相对缓慢。平面形态方面,长江中游岸线崩退及洲滩变形的强度均呈沿程减弱趋势,且在荆江河段最为显著。断面形态方面,河床冲深幅度在宜枝下段>荆江河段>宜枝上段>城汉河段>汉湖河段。理论上距离三峡工程最近的河段冲刷应最为剧烈,但由于宜枝上段床沙粗化显著,限制了冲刷的进一步发展。过流能力方面,宜枝河段由于距洞庭湖较远,并未受到入汇顶托作用,故其平滩流量的调整基本由进口水沙条件控制,并随着河床冲深下切而增大;对于荆江、城汉和汉湖河段,河床冲刷虽显著,但支流或湖泊的入汇顶托对平滩流量产生的影响大于前者,故平滩流量总体随上下游水位差同步波动。 相似文献