Aquatic vegetation commonly grows in patches at early succession periods, playing a critical role in mediating hydrodynamics, geomorphodynamics and surface water ecosystem. The structures of mean flow and wake around a vegetation patch have been extensively explored experimentally and numerically. However, the adjustment of these flow structures due to the streamwise extension of the patch remains poorly understood, which hampers effective management of the surface water system utilizing aquatic vegetation. This study employs a depth-averaged large eddy simulation (DA-LES) model to investigate the effect of patch length on the flow structure around a rectangular vegetation patch located at the channel center. The observed longitudinal profiles of mean flow velocity along the center axis of the patch are used for model validation. Our results demonstrate that the DA-LES model can effectively capture the interior flow adjustment within the patch and the downstream wake structure as the patch grows in length. Notably, our modeling accurately visualizes the vortex evolution from the along-edge Kelvin-Helmholtz (K-H) vortices to after-patch Karman vortices. Furthermore, our finding indicates that increasing patch length can trigger the formation of wake Karman vortices despite lower patch density if cumulative vegetation resistance exceeds a certain threshold required for triggering such vortices. Additionally, DA-LES modeling provides valuable insights into interactions between different types of vortices around elongated patches and enhances understanding of the mean flow behavior of the wake. The results from the present study and future further research are useful for predicting contaminant dispersion and sediment dynamics within the wake region of a vegetation patch with variable lengths.

自三峡工程以及上游大型梯级水库的建成运用后,长江河道水流特性发生了一定的变化,本文基于新情势下长江典型河道演变的航道效应与水沙调控进行研究,采用多种手段定量提出了航道条件改善的三峡水库水沙调控关键参数和实施时机,研究表明,通过控制坝前水位消落速度并结合上游流量预报,可达到较好的库尾减淤效果,库尾减淤调度实践证明变动回水区减淤效果明显,有力保障了变动回水区的航道水深条件.研究成果已在长江上游朝天门至涪陵河段长寿水道航道整治工程、长江中游芦家河河段航道维护性疏浚工程等航道治理工程中得到应用,产生了显著的经济与社会效益,也为新情势下其他长江典型碍航浅段的治理提供支撑.

河流滨岸带在净化水体、截留污染、景观休闲等方面起着极为重要的作用.为了分析鄱阳湖五河不同河段滨岸带的生态水利功能,从自然功能和社会功能两大方面构建了滨岸带功能分类体系,综合运用遥感、GIS等空间信息技术,对鄱阳湖五河典型河段的滨岸带进行了地表覆盖解译和功能分区,进一步分析鄱阳湖五河典型河段滨岸带现状及横纵向的空间差异.基于典型河段滨岸带现状分析,探讨了滨岸带生态水利功能在河流纵、横向上的空间分区,最终结合不同河流不同河段的特点给出针对性的生态水利治理建议,为实施流域生态保护与生态建设的分区管理、区域产业布局、生态防灾减灾、环境保护与建设规划等提供科学依据.

Understanding hydro‐morphological characteristics in mountain river confluences is significant in flood disaster mitigation and mountain river restoration, which is still poorly explored. This study employed a 2D hydro‐morphological model based on the finite element method to simulate the major bed morphological features in a mountainous‐type flume confluence and evaluate the effects of main controlling factors on these features. The modelling results show that the dominant bed morphological features in mountain river confluences can be well produced by the 2D model. Five controlling factors including downstream water level ( H ), branch discharge ratio ( Qr ), main channel sediment supply ratio ( ψ ), tributary slope ( St ) and confluence angle ( α ) reflecting different flow‐sediment‐geometry scenarios were adopted into a sensitive study. The upstream reach of the main channel is controlled by H and ψ and their decreases lead to bed degradation. The increase in Qr, St, and α mainly results in bed aggradation and steepening in the tributary, attaining a higher sediment transport rate. This contrasts the existing experimental results, due to the difference in sediment feeding. The size of the bank‐attached bar is promoted by the increase in Qr, St, and α and the decrease in H and ψ . A quantitative analysis shows that the water surface slope well correlates with various dimensions of the scour hole and bar morphology (correlation = 0.58–0.8). Meanwhile, the bank‐attached bar displays a strong self‐similarity (correlation = 0.84–0.98) regarding its geometric dimensions. This study provides new insights into the existing knowledge of the hydro‐sediment‐morphodynamics of mountain river confluences obtained from laboratory studies and field investigations.

Mid-river bars are important agents that impact the flow and sediment dynamics of rivers and are commonly used for the development of human society. This study focused on the geomorphologic change (riverbed and bar morphology) around a large-scale river bar system in the lower Yangtze River (namely, Heishazhou) that was possibly impacted by the Three Gorges Dam (TGD) and other river engineering works. Relevant data sources including field surveys, hydrological station records, satellite images and historical practice reports were gathered for the investigation. The Heishazhou bar system previously consisted of two major subbars and recently merged as an entirety. Rapid bar growth occurred after the construction and operation of the TGD, leading to the closure of the Middle Channel and the South Channel dominating water conveyance at the reach. With the examination of another three bar systems in the lower Yangtze River, the lower-reach bar systems generally grew due to sediment deposition around bars, which differred from those in the middle reach that generally shrunk. The underlying cause may be that the middle-reach riverbed still supplies sediment to the lower reach. The riverbed at the Heishazhou reach, however, experienced apparent erosion after the construction of the TGD. Combining historical investigations and satellite images, a conceptual description was created to understand the geomorphologic cycle of river bar systems at a meandering reach and found that the formation of an inner-bank bar shall be a major force driving the geomorphologic cycle. Sediment deficits caused by the TGD and human activities such as dikes, bank revetments and riverbed dredging are highly likely to cause a slow-down of the geomorphologic cycle of these river bar systems with distinct mechanisms.

鄱阳湖流域是长江生态系统的关键支点,在长江经济带发展中占有重要地位.面向鄱阳湖五河及湖区分布广泛的岸坡及滨水带区域,辨析了滨水带纵横向上的空间差异与存在的主要问题,提出生态防洪堤岸、生态水利血防、生态岸坡净化等单项关键技术的思路.通过分析单项技术的功能属性及其适用范围,明确了不同区域相协调的关键技术总体布局,初步构建了包括对象层、功能层、技术层、效果层和应用层的河湖生态岸坡及滨水带综合治理关键技术体系,为在鄱阳湖五河及湖区典型区域开展技术应用试验打下了基础.研究成果对其他类似河湖水系综合治理具有参考价值.

In 2018, a flash flood occurred in the Zhongdu river, which lies in Yibin, Sichuan province of China. The flood caused many casualties and significant damage to people living nearby. Due to the difficulty in predicting where and when flash floods will happen, it is nearly impossible to set up monitors in advance to detect the floods in detail. Field investigations are usually carried out to study the flood propagation and disaster-causing mechanism after the flood’s happening. The field studies take the relic left by the flash flood to deduce the peak level, peak discharge, bed erosion, etc. and further revel the mechanism between water and sediment transport during the flash flood This kind of relic-based study will generate bigger errors in regions with great bed deformation. In this study, we come up with numerical simulations to investigate the flash flood that happened in the Zhongdu river. The simulations are based on two-dimensional shallow water models coupled with sediment transport and bed deformation models. Based on the real water level and discharge profile measured by a hydrometric station nearby, the numerical simulation reproduced the flash flood in the valley. The results show the flood coverage, water level variation, and velocity distribution during the flood. The simulation offers great help in studying the damage-causing process. Furthermore, simulations without considering sediment transport are also carried out to study the impact of bed erosion and sedimentation. The study proved that, without considering bed deformation, the flood may be greatly underestimated, and the sediment lying in the valley has great impact on flood power.

五河入湖水沙通量及河道形态变化对五河尾闾演变、湖区低枯水位、江湖关系等研究有重要意义.以1956—2018年实测资料为基础,利用Mann-Kendall检验法和河道特征对五河入湖水沙通量、典型断面形态变化特性及其影响因素进行了研究.结果表明:①五河入湖径流量总体呈小幅度减小态势,2003—2018年五河入湖平均径流量较1956—2002年减小5.3％;②除饶河外,入湖泥沙通量均有不同幅度的减小,其中赣江和信江大幅度减小,2003年后分别减少约72.3％和52.6％;③五河典型断面形态2014年前变化较大,断面多呈锯齿状;随后逐渐恢复正常;④水利枢纽工程、水土保持工程和人工采砂是影响五河入湖泥沙通量和河道形态的主要人为因素.

Since the establishment of the world-class Three Gorges Dam (TGD) across the Yangtze River, China, the downstream reach has experienced a long-term adjustment with regard to the river morphology and hydrodynamics, imposing a profound impact on the environmental conditions of human living and aquatic ecosystem. This study presents an investigation on the river channel morphological characteristics and hydrodynamic environment of a large bifurcation-confluence complex downstream of the TGD through detailed field survey and numerical modeling. Results show that the main stem, before being bifurcated into two sub-channels (the North Channel and the South Channel), experiences a meander, leading to the severe bed scouring near the outer bank (pools) resulted from a high flow mass flux and bed shear stress. Because of being bifurcated, the river width with largely growing may result in the reduction of flow velocity and sediment deposition (riffles), and thereby two plugbars are formed near the entrance of two sub-channels. In the meantime, the velocity-reversal phenomenon (flow velocity and friction velocity) is identified when low flows are transited into high flows. The flow mass flux, however, is always larger in pool regions, which is highly related to water depth. As a result, the topographic steering of flows by riffles, bars and floodplains may have more impact on flow path under low flow conditions, while the bankline shape would become more important under high flows. Furthermore, the topographic steering could play a key role in the pattern of flow separations near the confluence. More interestingly, the confluence flow separation only occurs under low flow conditions and its occurring location shifts upwards the tributary (the North Channel), which differs from observations in previous studies. The visualized numerical results of friction velocity distribution indicate that sediment is more likely to deposit in the North Channel (entrance) with lower friction velocity, implying the potential closure of the sub-channel.

近十几年来随着水沙情势的显著变化,长江中下游干流崩岸险情频发,加强崩岸治理和岸线保护是沿江防洪安全和经济发展的重要保障.在梳理三峡水库蓄水以来坝下游水沙情势变化、河道冲刷和崩岸情况的基础上,以2017年11月江苏省扬中市江堤崩岸为例,分析崩岸段近期河道演变特征和地勘资料,认为河槽持续冲刷下切贴岸及二元土质结构河岸是崩塌的主要原因,而2016～2017年连续大洪水加了快崩岸的发生.崩岸发生后立即实施了窝塘抢护并修筑临时挡水子堤,随后实施完成干堤复建和窝塘上下游岸线守护工程,实现了2018年成功度汛.此次崩岸的特点和原因在长江中下游较为典型,对崩岸治理与岸线保护具有启示作用.

With the operations of the Three Gorges Dam and its upstream cascade reservoirs, sediment load in the middle and lower reaches of the Changjiang River has decreased sharply, and the long-term and long-distance riverbed erosion has been extending towards the Estuary. Understanding the controlling factors of morphological processes and future evolution trend of the Changjiang Estuary is a major question for estuarine evolution and regulation. Using GIS techniques, morphological evolution of the Changjiang Estuary (Xuliujing to Hengsha) since 1997 were quantitatively analyzed, and the evolution trends till 2030 and 2050 were predicted by a well calibrated and validated numerical model (Delft3D). The results indicated that the study area shows overall erosion with significant local changes in 1997—2015. The erosion gradually increases as the sediment discharge decreases sharply, and the net erosion volume in 2010—2015 is as high as 75 million m3. Erosion mainly occurs at deep channel lower than 10 m, while the shallow shoals are dominated by accretion. Model predictions indicated that the study area would maintain strong erosion in 2015—2030 under present sediment supply condition (125 million t/a) and the erosion may decrease in 2030—2050 due to the increased resistance of river bed erosion. However, strong erosion still occurs under extremely low sediment supply (100 million t/a) with conversion from accretion to erosion at shallow shoals. Under the combined natural and human impacts, estuarine evolution processes are complex, and the evolution trend could be an important guidance to the integrated regulation of the Changjiang Estuary.

A movable-bed physical model is presented to investigate characteristics of hydrodynamic and sediment transport (ST) in a planned excavating channel downstream the Fuhe River (FHR) and the Qinglan Lake (QLL), Jiangxi Province, China. The model is validated by the observed water level and velocity data during the low water period in May 13 and high water period in June 21 2014, respectively, which shows well agreements between simulated and observed data. With repeating 6-years cycle of the runoff discharge and suspended sediment concentration condition from the Lijiadu hydrological station downstream the FHR during 2006 and 2008 similar to 2012, experiments are conducted to predict bed evolution process in the excavated channel and QLL after the implement. The hydrodynamic results indicate that the cross-section averaged velocity generally increases both in the QLL and upstream of the excavated channel during a 20-year return period flood. The ST results show that erosion develops mainly in the left side of the channel and deposition occurs slightly upstream of the QLL after 30 years. Some deposition becomes visible in the center of the QLL after 90 years, and a relatively stable balance between deposition and erosion is observed in the whole QLL after 150 years.

全面推行河长制是我国管水治水工作模式的创新,有助于打破部门壁垒,构建共治体系.信江是鄱阳湖水系五大河流之一,生态文化资源丰富,产业特色鲜明.为研究河长制下的信江流域保护与治理对策,从流域层面梳理了水生态环境的现状及存在的主要问题.结果表明:信江水质总体良好,但少数断面水质差,城市黑臭水体、河流生态功能及水生态监测等方面问题较突出.在此基础上,结合流域及江西省实际情况,提出推进信江流域保护与治理的重点对策和措施,并建议从加强关键技术支撑、制度建设、统一规划管理和鼓励民众参与等4个方面深入推进和落实河长制,促进其在信江流域保护与治理中形成长效机制.

Under the combined impacts of climate change and human activities, water resources, environment and ecological problems of China’s rivers and lakes interweave and overlap. As the largest freshwater lake in China, the Poyang Lake region and its five major tributaries are facing serious problems, including the reduction of water quantity, soil erosion, shoreline shrinkage and deterioration of aquatic habitat, whereas the current research level and key technologies cannot meet the requirements of ecological priority and green high-quality development. How to integrate resources, ecology, environment and other constraints into water conservancy project planning, construction and operation, clarify the impact of water conservancy projects on the ecological environment of rivers and lakes and the evolution trend of ecosystems under this influence, put forward technical measures to mitigate their effects, and meet the needs of human society and health to water ecosystem, are the forefront and hot issues of current ecological water conservancy theory system research and key technology research and development, but also the inevitable requirements of promoting the construction of national ecological civilization and the implementation of the Yangtze River protection. Aiming at the above problems, the characteristic factors of ecological water conservancy in the Poyang Lake region and its five major tributaries and its response mechanism to the development and utilization were distinguished and analyzed; the technical system of integrated ecological water conservancy for the land, bank and water was studied and developed; the integrated management technology and planning design scheme of ecological water conservancy were put forward and engineering demonstration was carried out, and the construction mode and monitoring and evaluation system of river and lake ecological water conservancy were constructed. Through the research of multi-disciplinary intersection, point combination, theory and practice, the interreaction mechanism of the characteristic factors of ecological water conservancy in rivers and lakes was revealed, and the monitoring and evaluation index system of coupling engineering, resources, environment and ecology was put forward to realize the theoretical innovation; a series of key technologies for agricultural water-saving pollution control and soil protection in red soil hilly and dry slopes and key technologies for hydraulic engineering assisted repair of damaged aquatic habitats were developed to realize technological innovation; solutions for comprehensive controlling system of river and lake ecological water conservancy were proposed, including planning guidelines, design guidelines, governance techniques, monitoring indicators, evaluation methods and construction models, to achieve integrated innovation.

River-communicating lakes in the middle and lower reaches of the Yangtze River connect with river through culverts and sluices except Poyang Lake and Dongting Lake. Its water quality is poorer due to the lack of natural exchange of water, especially in dry season. Taking Huayang Lake group as an example, the feasibility of ecological operation and the specific plan during non-flood period were studied by data analysis, field investigation and numerical simulation. Data analysis result presents the concentration of TN and TP decreases with the increase of water level, but the tendency slows down when the water level exceeds a certain value. In addition, based on the current sluice gate dispatching mode, relationship between river and lakes, flood control security, improvement of water environment and the simulated results, the ecological operation plan was obtained, that is, using Yangwan and Huayang sluices to control the water level in the lake from October to December at 13 m, January to February at 12.5 m and March to April at 11.8 m.

Abstract Morphological evolution of estuaries and deltas at the decadal timescale is becoming a global issue in recent decades due to their economic and environmental significances. Present study explores the decadal morphological evolution under high river discharge and decreasing river sediment. Quantitative analysis of bathymetric data indicates that frequent river floods in the 1990s enhanced erosion of the inner estuary superimposed with river sediment decline. A process-based modeling approach (Delft3D) is applied to investigate the physical mechanisms of river flooding on morphological change. Hydrodynamic simulations indicate that the water level gradient and residual transport in the inner estuary increase with river discharge. High water level gradient occurs simultaneously with peak ebb flow, and this status can last for about 5-6 hours. This hydrodynamic condition with sufficient long period facilitates channel erosion and sandbar incision. Morphological simulations indicate that erosion along the main channels is enhanced under higher river discharge, especially in the upstream part. The enhanced erosion can be offset by the increase in sediment load. River flooding superimposed with further decreased sediment supply in the future may induce more significant modifications of channel-shoal systems within the inner Yangtze Estuary than the present.

基于1958-2015年间多个年份实测地形资料,定量分析了长江口口内河段的冲淤演变过程,结果表明:该河段经历了剧烈的河势调整,深槽冲刷、浅滩淤积为主要特征,其中20世纪80年代尤为显著,之后整体河势趋于相对稳定.冲淤量从净淤积向净冲刷转换,与河流来沙量的变化趋势一致,5—15m水深范围内对来沙量的变化最敏感.洪水事件和特枯水文年对河槽冲淤量的影响同样显著,包括20世纪90年代的连续洪水年、2010年大洪水及2006年特枯水年.

This paper presents a model to simulate the growth of cohesive sediment flocs in 3-D space, which takes into account: Brownian motion contribution, gravity contribution, flow contribution, flow shear stress, floc breakage, and non-uniform initial sediment size distribution. Results of validation tests indicate the model is feasible to simulate the growth of cohesive sediment floc under different contributions. Floc structure in different water depths and the influence of initial sediment size distribution were tested using the new model, taking fractal dimension as an index. The simulated results show that, the sediment floc at the lower region possesses a larger fractal dimension than that of the upper region. It is mainly due to the reproduction of new stronger, denser flocs from the breakage and reform under the higher flow shear stress in the lower region. Additionally, on the assumption condition that the initial sediment size distribution follows normal distribution, an increase in the standard deviation results in the fractal dimension presents a trend from increasing to decreasing.

The deceleration flow,called backwater in engineering,is a pattern of non-uniform flow.Research of bed sediment's incipient motion under deceleration flow condition is of great application value in water conservancy pro-ject.In line with generalized flume experiment and field measured natural flow data,four classic formulae for incipi-ent flow velocity are verified and compared.Results suggest that all the four classic formulae are suitable for decel-eration flow condition in flume experiment,yet difference still exists in the selection of particle size.Representative particle size d95 is of good accuracy.Moreover,the incipient motion of sediment under deceleration flow meets the Shields curve in general.According to verification of power incipient motion formula,the dimensionless incipient power is 0.0191 ,which can be used as the criterion of bed sediment initiation.