黄河尾闾段一维耦合水沙数学模型研究及其应用

小浪底水库于1999年运用以后,该河道经历了长时间持续冲刷过程.为掌握小浪底水库运用后黄河尾闾段洪水演进特点及河床冲淤规律,采用一维水沙数学模型研究是一条重要的途径.本研究首先采用浑水控制方程,建立了一维耦合水沙数学模型,并利用2003年利津-西河口段汛期实测水沙及汛前断面地形资料对该模型进行率定,计算的流量、水位及含沙量等过程与实测值吻合较好;然后采用2015年利津—汊3段汛期实测资料对该模型进行验证,结果显示水位与冲淤量计算值与实测值较为符合;最后基于2015年实测洪水过程,计算了若干组不同断面间距下的洪水演进及冲淤过程,分析了不同断面间距对沿程水位及河段冲淤量等计算结果的影响,结果表明:采用不同断面间距对水位计算结果影响较小,而对冲淤量计算结果会产生一定影响;在河段水沙及冲淤特性复杂的情况下,采用一维数学水沙模型计算时应考虑断面间距的选择.     

长江中游沙质河段床沙级配调整过程计算

三峡工程运用后,长江中游荆江河段持续冲刷,床沙与推移质、悬移质泥沙不断交换,从而造成该河段床沙发生不同程度的调整,对长江中下游河床演变及非平衡输沙机理的研究具有重要影响.在新水沙条件下,总结分析了沙波运动特性及床沙交换方式,引入Markov三态转移概率及非均匀沙隐暴系数,得到基于状态转移概率的沙质河段床沙级配调整的计算模型.研究结果表明:(1)20092014年,沙市站年内床沙中值粒径有先增大后减小的趋势,而监利站年内床沙中值粒径则先减小后增大,且荆江河段年际床沙中值粒径总体呈上升趋势,粗化程度约为6.9%~9.3%;(2)20092014年,沙市站床沙组成中粒径d<0.062 mm的泥沙所占比重不变,0.062 mm≤d<0.25 mm的泥沙所占比重逐年减少(累计减少11.4%),d≥0.25 mm的泥沙所占比重逐年增加(累计增加11.4%),而监利站床沙组成均存在波动性变化;(3)荆江河段床沙转换为推移质的概率随着泥沙粒径的增大而增大,床沙转换为悬移质的概率随着泥沙粒径的增大而减小,而推移质和悬移质转换为床沙的概率均随着泥沙粒径的增大而增大,河床发生冲刷粗化时泥沙输移的主要形式为悬移质(概率为81%~87%),而淤积细化时床沙补给主要来源于推移质(概率为8%~12%).通过验证,本文概率模型的计算结果与实测资料符合较好,能够应用于长江中游沙质河段年际床沙粗化及年内床沙级配调整过程预报,为进一步开展三峡工程下游非均匀悬移质泥沙沿程恢复机理的研究提供理论基础.     

三峡工程运用后长江中下游河道冲刷特征及其影响

三峡及其上游干支流梯级水库建成运用后,大坝下游“清水下泄”引起了长江中下游河道发生长时间、长距离的冲刷。2001—2021年期间宜昌至长江口已累计冲刷了50.3亿m³,需厘清河道冲刷对河势、防洪、航运等方面产生影响。分析表明:三峡工程运用后,长江中下游河势总体稳定,弯道段出现切滩撇弯、汊道段出现塞支强干等现象;河道槽蓄量的持续增加,进一步增大了河道调蓄和行洪能力,但水流顶冲点的变化和近岸河床的冲刷下切,使得河道崩岸频发,并影响河势稳定和防洪安全;在河道冲刷、河势控制与航道工程综合作用下,长江中下游航道条件总体得到改善,但河道不均衡冲刷使得坝下游砂卵石河段出现“坡陡流急”,沙质河段出现洲滩散乱、航槽移位等现象,影响航道条件;同流量下枯水位呈下降态势,逢极枯年份影响长江中下游用水安全;江湖关系发生新变化,“三口”分流道由原淤积转为冲刷,两湖湖区水位不同程度的降低,枯水位出现时间有所提前,不利于湖区水资源和生态环境的安全与可持续发展;三峡工程实施枯水期补水调度和“压咸潮”调度以及长江口北支淤积减缓,对于遏制长江口咸潮入侵有利,入海泥沙显著减少引起长江口近岸河床冲刷,影响...     

三峡工程运用后荆江河段崩岸时空分布及其对河床调整的影响

三峡工程运用后长江中游荆江河段河床持续冲刷,局部河段崩岸频发,影响河道内悬沙输移与河床形态调整.本研究采用实测长程河道地形及固定断面地形资料,确定了2002-2018年荆江河段的主要崩岸区域,估算了崩岸土体的泥沙总量,进而定量分析了河岸崩退对河床调整的影响.计算结果表明:荆江段累计河岸崩退体积约为2.0亿m3,约占该河...     

Two-dimensional modeling of channel evolution under the influence of large-scale river regulation works

In the middle and lower reaches of alluvial rivers, various kinds of river regulation projects affecting natural channel evolution often are distributed due to the requirements of flood control, navigation,and channel stability. However, the influence of large-scale river regulation works on fluvial processes is not fully known. Therefore, a two-dimensional(2D) morphodynamic model has been improved to address this problem. The new detailed procedure is presented in this paper:(i) First, each nod...     

Sensitivity of simulated flow fields and bathymetries in meandering channels to the choice of a morphodynamic model

Morphodynamic models are used by river practitioners and scientists to simulate geomorphic change in natural and artificial river channels. It has long been recognized that these models are sensitive to the choice of parameter values, and proper calibration is now common practice. This paper investigates the less recognized impact of the choice of the model itself. All morphodynamic models purport to simulate the same flow and sediment dynamics, often relying on the same governing equations. Yet in solving these equations, the models have different underlying assumptions, for example regarding spatial discretization, turbulence, sediment inflow, lateral friction, and bed load transport. These differences are not always considered by the average model user, who might expect similar predictions from calibrated models. Here, a series of numerical simulations in meandering channels was undertaken to test whether six morphodynamic codes (BASEMENT, CCHE‐2D, NAYS, SSIIM‐1, TELEMAC‐2D and TELEMAC‐3D) would yield significantly different equilibrium bathymetries if subjected to identical, initial flow conditions. We found that, despite producing moderately similar velocity patterns on a fixed‐flat bed (regression coefficient r of 0.77 ± 0.20), the codes disagree substantially with respect to simulated bathymetries (r = 0.49 ± 0.31). We relate these discrepancies to differences in the codes' assumptions. Results were configuration specific, i.e. codes that perform well for a given channel configuration do not necessarily perform well with higher or lower sinuosity configurations. Finally, limited correlation is found between accuracy and code complexity; the inclusion of algorithms that explicitly account for the effects of local bed slope and channel curvature effects on transport magnitude and direction does not guarantee accuracy. The range of solutions obtained from the evaluated codes emphasizes the need for carefully considering the choice of code. We recommend the creation of a central repository providing universal validation cases and documentation of recognized fluvial codes in commonly studied fluvial settings. Copyright © 2016 John Wiley & Sons, Ltd.     

Empirical and conceptual modelling of the suspended sediment dynamics in a large tropical African river: the Upper Niger river basin

A 7-year sediment transport monitoring on the Upper Niger rivers was used to study the relationship between suspended sediment concentration and river discharge. During annual floods, these relationships show positive hysteresis. This paper presents the results of two models that estimate the time evolution of suspended sediment concentration using water discharge data only. The first model is based on a statistical approach using two relationships, one for the rising stage period of the flood and one for the recession period of the annual flood; the second model is a lumped conceptual one; it supposes that the sediment flux observed in the river comes from two different sources of sediment and that these two sources may be regarded as two different reservoirs. The erosion of the first reservoir represents hillslope erosion observed during the runoff season. Sediment supply from this ‘reservoir’ is limited in time because depletion occurs during the runoff season. The second reservoir is unlimited in time and quantity and its erosion represents contributions coming from bank erosion and mobilisation of deposits in the channel network.

Both of the models are compared with a simple rating curve based model. The model results show that the conceptual model has the highest efficiency to reproduce from weekly discharge only the time evolution of weekly suspended sediment concentrations, the time evolution of weekly sediment fluxes, and the global annual sediment yields.     

Implications of climate change in the twenty‐first century for simulated magnitude and frequency of bed‐material transport in tributaries of the Saint‐Lawrence River

More frequent extreme flood events are likely to occur in many areas in the twenty‐first century due to climate change. The impacts of these changes on sediment transport are examined at the event scale using a 1D morphodynamic model (SEDROUT4‐M) for three tributaries of the Saint‐Lawrence River (Québec, Canada) using daily discharge series generated with a hydrological model (HSAMI) from three global climate models (GCMs). For all tributaries, larger flood events occur in all future scenarios, leading to increases in bed‐material transport rates, number of transport events and number of days in the year where sediment transport occurs. The effective and half‐load discharges increase under all GCM simulations. Differences in flood timing within the tributaries, with a shift of peak annual discharge from the spring towards the winter, compared to the hydrograph of the Saint‐Lawrence River, generate higher sediment transport rates because of increased water surface slope and stream power. Previous research had shown that channel erosion is expected under all GCMs' discharge scenarios. This study shows that, despite lower bed elevations, flood risk is likely to increase as a result of higher flood magnitude, even with falling base level in the Saint‐Lawrence River. Copyright © 2010 John Wiley & Sons, Ltd.     

Land use changes,torrent control works and sediment mining: effects on channel morphology and sediment flux,case study of the Reno River (Northern Italy)

As with most Italian rivers, the Reno River has a long history of human modification, related also to morphological changes of the lower Po River since Roman times, but in the last decades, significant land use changes in the headwaters, dam construction, torrent control works and extensive bed material mining have caused important channel morphology and sediment budget changes. In this paper, two main types of channel adjustment, riverbed incision and channel narrowing, are analysed. Riverbed degradation is discussed by comparing four different longitudinal profiles surveyed in 1928, 1951, 1970 and 1998 in the 120 km long reach upstream of the outlet. The analysis of channel narrowing is carried out by comparing a number of cross‐sections surveyed in different years across the same downstream reach. Field sediment transport measurements of seven major floods that occurred between 2003 and 2006 are compared with the bedload transport rates predicted by the most renowned equations. The current low bedload yield is discussed in terms of sediment supply limited conditions due to land use changes, erosion‐control works and extensive and out of control bed material mining that have affected the Reno during the last decades. Copyright © 2011 John Wiley & Sons, Ltd.     

The distribution and residence time of suspended sediment stored within the channel margins of a gravel‐bed bedrock river

Previously undocumented deposits are described that store suspended sediment in gravel‐bedded rivers, termed ‘fine‐grained channel margin’ (FGCM) deposits. FGCM deposits consist of sand, silt, clay, and organic matter that accumulate behind large woody debris (LWD) along the margins of the wetted perimeter of the single‐thread, gravel‐bed South River in Virginia. These deposits store a total mass equivalent to 17% to 43% of the annual suspended sediment load. Radiocarbon, ²¹⁰Pb and ¹³⁷C dating indicate that sediment in FGCM deposits ranges in age from 1 to more than 60 years. Reservoir theory suggests an average turnover time of 1·75 years and an annual exchange with the water column of a mass of sediment equivalent to 10% to 25% of the annual sediment load. The distribution of ages in the deposits can be fitted by a power function, suggesting that sediment stored in the deposits has a wide variety of transit times. Most sediment in storage is reworked quickly, but a small portion may remain in place for many decades. The presence of FGCM deposits indicates that suspended sediment is not simply transported downstream in gravel‐bed rivers in agricultural watersheds: significant storage can occur over decadal timescales. South River has a history of mercury contamination and identifying sediment sources and sinks is critical for documenting the extent of contamination and for developing remediation plans. FGCM deposits should be considered in future sediment budget and sediment transport modeling studies of gravel‐bed rivers in agricultural watersheds. Copyright © 2010 John Wiley & Sons, Ltd.     

长江中下游地区铜矿体综合找矿模型

本文在收集研究长江中下游地区主要铜矿床的发现和勘查过程、矿床地质特征、物化探异常特征、勘查方法等大量资料的基础上,对矿体特征进行了归纳,提出了将长江中下游主要铜矿体划分为二型四式的矿体类型划分方案。分别建立了四种类型铜矿体的找矿模型,并建立了铜矿体综合找矿模型。     

Gravel excavation and geomorphic evolution of the mining affected river in the upstream reach of the Yangtze River,China

As economic development upstream in the Yangtze River basin has progressed in recent decades,the demand for sediment has rapidly increased and contributed to an expansion in sediment excavation that may affect the river’s stability and navigation safety.In the current study,the distribution of gravel mining in the upstream reach of the Yangtze River was investigated using field measurements obtained from2008 to 2017.An experimental investigation was then done to analyze the bed load behavior in ...