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1.
Changes in Geomorphic characteristics in the lower reaches of the Gongola River channel following construction of Kiri dam have been investigated. The study focused on changes in the channel bankfull width and of riverbed width after the control of the river flow, variation in discharge characteristics between pre- and post- dam periods and the impact of discharge variation on post- dam river channel. Results of the analysis revealed that the main effect of the impoundment of the Gongola channel is a drastic decrease in flood peaks below the reservoir by 11.5% (from 1,420 m3/sec to 1,256 m3/sec). The low flows have on the other hand increased by 268% (from 5.7 m3/sec to 21 m3/sec). The resultant effect of decrease in the discharge was reduction in the channel bankfull and riverbed widths by 38.3% and 72.2% respectively. Also, the post- dam channel became less sinuous and braided in some of the reaches downstream. Discharges of high peaks were found during the period of maximum precipitation (June to September) whereas low discharges were recorded during the period of minimum or no precipitation (December to May). Some of the observed implications of the flow control on the geometric variables were reduction in the overall channel width, concave bank erosion and emergence of vegetation in some of the reaches. 相似文献
2.
黄河上游内蒙古河段平滩流量对人类活动和气候变化的响应 总被引：1，自引：0，他引：1
冲积河流平滩流量既反映了河道尺度上的水文-地貌耦合关系,又与流域因素密切相关。从这一概念出发,以黄河上游内蒙古河段为例,研究了平滩流量的变化,并在流域层面与河道层面上对其成因进行了研究。结果表明：上游水库调节改变了出库流量过程,使汛期流量大幅度减小,泄流过程均匀化,因而平滩流量减小。在龙羊峡水库修建后洪水流量减小导致漫滩机遇降低的情形下,泥沙淤在主槽内,也是平滩流量减小的重要原因。泥沙冲淤对于平滩流量的影响存在着某种累积或滞后效应,巴彦高勒平滩流量Qbf,BY不仅与当年的冲淤量有关,还与以前冲淤量有关,前4 a平均淤积量对平滩流量的影响最大。建立了平滩流量与前4 a累计淤积量、年均流量、年最大日流量的多元回归方程,该方程表明平滩流量既与当年的流量特征相联系,也与一定时间尺度上河道冲淤造成的后果相联系,反映了某种水文地貌耦合关系。研究还表明,存在着以下因果关系链：龙羊峡水库修建→汛期来沙系数增大→河道淤积加强→平滩流量减小。因此,通过改变龙羊峡水库的运用方式,增大汛期下泄流量,可以减小河道淤积、增大平滩流量,从而增大下泄洪水的能力,降低凌汛期间的防洪压力。平滩流量的变化是流域因素变化的结果,所建立的多元回归方程表明,在50 a的时间尺度上,暖干化指标的增大、引水率的增大、水库总库容的增大和天然径流系数的减小,是黄河上游平滩流量减小的原因。 相似文献
3.
Bankfull discharge was identified in some 30 gravel-bed rivers representing in total c. 40 gauging stations. The catchment sizes cary from 4km2 to nearly 2700km2. Bankfull discharge value increases with basin size. In the case of gravel-bed rivers developed on an impermeable substratum, the following equation emerges: Qb=0·087 A1·044. Bankfull discharge recurrence interval was determined by fitting maximum annual floods (Ta) into Gumbel's distribution and then using the partial duration series (Tp) in this same distribution. Recurrence interval is below 0·7 years (Tp) for small pebble-bed rivers developed on an impermeable substratum; it reaches 1·1 to 1·5 years when the catchment size of these rivers exceeds 250km2. Rivers incised in the soft schists of the Famenne show larger channel capacity at bankfull stage, a small width/depth ratio and thus higher recurrence intervals (1·4–5·3 years with Ta and 1–4·4 years with Tp). Baseflow-dominated gravel-bed streams and sandy or silty rivers experience less frequent bankfull discharges, with a recurrence interval higher than 2 or even 3 years (Tp). © 1997 John Wiley & Sons, Ltd. 相似文献
4.
We consider the evolution of the hydraulic geometry of sand-bed meandering rivers. We study the difference between the timescale of longitudinal river profile adjustment and that of channel width and depth adjustment. We also study the effect of hydrological regime alteration on the evolution of bankfull channel geometry. To achieve this, a previously developed model for the spatiotemporal co-evolution of bankfull channel characteristics, including bankfull discharge, bankfull width, bankfull depth and down-channel bed slope, is used. In our modelling framework, flow variability is considered in terms of a specified flow duration curve. Taking advantage of this unique feature, we identify the flow range responsible for long-term bankfull channel change within the specified flow duration curve. That is, the relative importance of extremely high short-duration flows compared to moderately high longer duration flows is examined. The Minnesota River, MN, USA, an actively meandering sand-bed stream, is selected for a case study. The longitudinal profile of the study reach has been in adjustment toward equilibrium since the end of the last glaciation, while its bankfull cross-section is rapidly widening due to hydrological regime change in the last several decades. We use the model to demonstrate that the timescale for longitudinal channel profile adjustment is much greater than the timescale for cross-sectional profile adjustment due to a lateral channel shift. We also show that hydrological regime shift is responsible for the recent rapid widening of the Minnesota River. Our analysis suggests that increases in the 5–25% exceedance flows play a more significant role in recent bankfull channel enlargement of the Minnesota River than increase in either the 0.1% exceedance flow or the 90% exceedance flow. © 2020 John Wiley & Sons, Ltd. 相似文献
5.
In this study, we propose to identify morphological and hydraulic characteristics related to overbank flows in the water level time‐series available at many gauged stations. The results obtained at 13 river stations (the catchment sizes vary from 10 to 1700 km2 with contrasted geology, land use and rainfalls regime) show that overflow mechanisms at the river‐reach scale can be systematically identified in the water level frequency distribution estimated with the peaks‐over‐threshold (POT) method. A first level (Lts1) was in the range of the incipient flooding onto the floodplain. Even if the definition of this level is variable in terms of flooded area at the reach scale, this method can be useful in providing a first estimation of the bankfull level for many gauged stations, without complex and costly field surveys. A second level (Lts2) was systematically detected on average 38 cm above the topographic flat floodplain elevation. The Lts2 inflection in the water‐level frequency distribution is assumed to reflect a composite effect of catchment hydrology and local hydraulics and channel geometry, without possibility to make a clear distinction between both processes at the moment. The local or reach scale effect would probably play an essential role in the frequency distribution as flood attenuation at catchment scale may explain the inflection Lts2 at only three sites. In light of the knowledge acquired in laboratory flumes with compound channels, most of the time Lts2 level would correspond to the level of resumption of flow both in the main channel and the floodplain. Once this method is validated in various physiographic contexts, it should apply to many hydrometric stations for both synchronic (e.g. regional analysis) and diachronic analysis (e.g. evolution over time of the bankfull discharge) to evaluate anthropic impacts on river morphology. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
6.
Artur Radecki‐Pawlik 《地球表面变化过程与地形》2002,27(2):115-123
The results are presented of an investigation of bankfull discharge in two Polish Carpathian streams: Skawica and Krzyworzeka. Existing definitions of river bankfull were reviewed and applied in tests carried out on selected cross‐sections of the streams. The Woodyer method was given special attention, with a correspondingly detailed survey of plants characterizing river benches. Riley's bench index method and the methods of Williams, Wolman, Schumm and Brown, and Woloszyn were tested. The report concludes that bankfull discharge value for a mountain stream should not be reported as a single number, but rather as a range of discharges within which one could expect the bankfull value to lie. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
7.
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
8.
Extreme weather is an important noise factor in affecting dynamic access to river morphology information.The response characteristics of river channel on climate disturbances draw us to develop a method to investigate the dynamic evolution of bankfull channel geometries(including the hydraulic geometry variables and bankfull discharges)with stochastic differential equations in this study.Three different forms of random inputs,including single Gaussian white noise and compound Gaussian/Fractional white noise plus Poisson noise,are explored respectively on the basis of the classical deterministic models.The model parameters are consistently estimated by applying a composite nonparametric maximum likelihood estimation(MLE)method.Results of the model application in the Lower Yellow River reveal the potential responses of bankfull channel geometries to climate disturbances in a probabilistic way,and,the calculated average trends mainly run to synchronize with the measured values.Comparisons among the three models confirm the advantage of Fractional jump-diffusion model,and through further discussion,stream power based on such a model is concluded as a better systematic measure of river dynamics.The proposed method helps to offer an effective tool for analyzing fluvial relationships and improves the ability of crisis management of river system under varying environment conditions. 相似文献
9.
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
10.
黄河下游河床萎缩典型地表现为平滩水位下河床断面面积的趋势性减小,本文根据黄河下游实测断面和水沙资料采用相关分析方法研究了游荡段河床萎缩的主要影响因素。1960~1997年游荡段河床平滩水位下断面面积经历了1960~1964年和1974~1985年的扩张时期及1965~1973年和1986~1997年的萎缩时期,这种变化是多种因素共同作用的结果。在来水来沙中,年径流量是主要因素,洪峰流量和年平均含沙量是较次要的因素;本文所讨论的其它4个因素中,花园口以上引水量影响最大,降雨量影响次之,兰州以上水库的调节作用对河床断面面积的变化也有较明显的影响;三门峡水库三种不同的使用方式对下游河床有不同的影响,采取"蓄清排浊"方式后对下游河床的影响较小。 相似文献