Assessment of the Recent Hydromorphological Features of Nokoue Lake and Its Channels (South-East Benin)

Based on 2022 and 2023 hydrometric data and satellite images (Sentinel 2022, SPOT 2010), this study aims to present the Nokoué Lake and its channels’ re-cent hydromorphological characteristics. Integrating flow, tributary morphology, and topography data determined specific power values along the axes studied. The values obtained range from 2.69 to 12.92 W/m2 for Ouémé River and 2.46 to 10.99 W/m2 for Sô River. The resulting water erosion on banks and bottoms is of linear, areolar, or gully and claw types. Lake bathymetry varies from -0.5 to -2.6 m (low flow period) and -1 to -4 m;in the Ouémé, Sô, and Totchè rivers, it varies from -5 m to -7 m, reaching -10 m at the Cotonou channel entrance (flood period). Bathymetric profiles reveal varied “U”, “V” and “Intermediate” bottom morphologies, influenced by erosion/sedimentation processes and human activities. The flow facies identified are lentic in the northern tributaries and lotic in the Cotonou and Totchè canals. Spatial analysis identified nine (09) thematic classes. In 2022, the surface area of the water body has increased from 274 km2 at low water to 280 km2 at high water, whereas in 2010 (a recent year of exceptional flooding), the surface area was 270 km2 at low water and 277 km2 at high water. Significant changes in land use are observed between 2010 and 2022. The floodplain area decreased slightly, from 421 km2 in 2010 (year of exceptional flooding) to 419 km2 in 2022. The evolution of land use shows a progressive expansion of the urban environment to the detriment of the natural environment. In the medium to long term, this trend could threaten the hydromorphological balance and even the existence of this important lagoon ecosystem.

River channel flood forecasting method of coupling wavelet neural network with autoregressive model

Based on analyzing the limitations of the commonly used back-propagation neural network （BPNN）, a wavelet neural network （WNN） is adopted as the nonlinear river channel flood forecasting method replacing the BPNN. The WNN has the characteristics of fast convergence and improved capability of nonlinear approximation. For the purpose of adapting the timevarying characteristics of flood routing, the WNN is coupled with an AR real-time correction model. The AR model is utilized to calculate the forecast error. The coefficients of the AR real-time correction model are dynamically updated by an adaptive fading factor recursive least square（RLS） method. The application of the flood forecasting method in the cross section of Xijiang River at Gaoyao shows its effectiveness.

Channel changes of the Makou-Tianjiazhen reach in the middle Yangtze River during the past 40 years

Quantitative analysis was performed on the filling-scouring process for the river reach within Makou and Tianjiazhen, the middle Yangtze River with the help of GIS and DEM techniques. The research results indicate that the river reach between Makou and Tianjiaz- hen was dominated by the scouring process, and the magnitude of scouring is increasing over time. The intensity of scouring process is more in the deep and narrower river reach than shallower and wider ones. The river reach in the Makou and Tianjiazhen river knot is in frequent scouring and filling process, however the river reach upper to the Makou and lower to the Tianjiazhen river knot is in moderate scouring and filling process. The river reach just upstream or downstream to the river knot （e.g. Makou and Tianjiazhen river knot in this research） is dominated by filling process and the river reach in the river knot is dominated by the scouring process. Research results indicate no changes in the boundary of the river but the scouring and the filling magnitude in specific river channel is strong. The filling and the scouring process of the study river reach is greatly impacted by the sediments and water from the upstream of the study river reach. The construction of the Three Gorges Dam just up- stream to Yichang will cause further decrease of the release of the sediment load to the middle and the lower Yangtze River basin, which will further intensify the scouring process of the river channel in the study river reach.

Hydrodynamic Effect of the Regulation Project of Yangtze River Deepwater Channel Downstream of Nanjing

A two-dimensional flow numerical model of the tidal reaches, which total length is more than 700 km, is established from Datong to the Yangtze River estuary. The tidal levels, velocities, diversion ratios and dynamic axes before and after the separate regulation of each reach and combined regulation of all reaches are obtained. The comparative analysis shows that the regulation project of a separate reach basically has no impact on velocity distributions and variations of diversion ratios of upper and lower reaches, the variations of dynamic axes are only within the local scope of the project. The regulation project of a separate reach also has less impact on the water level in the lower adjacent reaches, but will make the water levels in the upper reaches rise. After the implementation of the regulation projects for all reaches, the rise of water level in the upstream reaches will have a cumulative impact.

The analysis on reservoir sediment deposition and downstream river channel scouring after impoundment and operation of TGP

According to the measured data after impoundment and operation of the Three Gorges Reservoir,the reservoir sediment deposition and downstream river channel scouring are described briefly and compared with the research results achieved in the demonstration stage.It is indicated through analysis that the reservoir sediment deposition and downstream river channel scouring during 8-year impoundment and operation are still within the original forecast,so the original forecasting results are feasible.The further observation and comparison should be conducted because the comparison between the observed data and the original forecast is not so sufficient in time and the prototype observation and related research work should be strengthened in the future.

River Channel Improvement and River Ecological Restoration

Recent years have seen the rapid development of China’s economy and urban construction. In this context, in order to meet the needs of people’s daily production and life for water resources, river channel improvement has become an important task. However, according to the analysis of objective factors, the way of human governance, which is contrary to the laws of nature, can lead to the destruction of river ecosystems. Based on this, this paper mainly discusses river ecological restoration around river channel improvement.

Causes and typical control model of wind-drift sandy lands in abandoned channel of the Yellow River

The historical formation and development of the abandoned channel of the Yellow River is reviewed and its causes of formation and present condition of prevention and control are analyzed in this paper. Based on this analysis, some ideas about control, critical problems and countermeasures in the next period are proposed with two typical control models as examples. We suggest that in preventing and controlling the wind-drift sandy lands in the region, the emphasis should be to develop, with a greatly expanded effort, a recycling economy. This should realize a combination of two ideas, i.e. integrate combating desertification with a structural adjustment of agricultural and an increase in the income of farmers.

Geomorphology Processes of Channel Planform Migration on Meandering Rivers

1 Introduction Morphological analysis on the planform migration structure of meandering river is an important basis for the reconstruction of evolution of paleochannel.Besides,it is a significant method for restoration of rivers through the

A New Method of Assessing Environmental Flows in Channelized Urban Rivers

Assessing environmental flows （e-flows） for urban rivers is important for water resources planning and river protection, Many e-flow assessment methods have been established based on species＇ habitat pro- vision requirements and pollutant dilution requirements, To avoid flood risk, however, many urban rivers have been transformed into straight, trapezoidal-profiled concrete channels, leading to the disappearance of valuable species, With the construction of water pollution-control projects, pollutant inputs into rivers have been effectively controlled in some urban rivers, For these rivers, the e-flows determined by tradi- tional methods will be very small, and will consequently lead to a low priority being given to river pro- tection in future water resources allocation and management, To more effectively assess the e-flows of channelized urban rivers, we propose three e-flow degrees, according to longitudinal hydrological con- nectivity （high, medium, and low）, in addition to the pollutant dilution water requirement determined by the mass-balance equation, In the high connectivity scenario, the intent is for the e-flows to maintain flow velocity, which can ensure the self-purification of rivers and reduce algal blooms; in the medium connectivity scenario, the intent is for the e-flows to permanently maintain the longitudinal hydrological connectivity of rivers that are isolated into several ponds by means of weirs, in order to ensure the exchange of material, energy, and information in rivers; and in the low connectivity scenario, the intent is for the e-flows to intermittently connect isolated ponds every few days （which is designed to further reduce e-flows）, The proposed methods have been used in Shiwuli River, China, to demonstrate their effectiveness, The new methods can offer more precise and realistic e-flow results and can effectively direct the construction and management of e-flow supply projects,

Some thermodynamic criteria for river channel changes

A theoretical model of river channel changes is presented, which shows some nonequilibrium thermodynamic criteria of a river channel to bedding and equilibrium.

Response of the distributary channel of the Huanghe River estuary to water and sediment discharge regulation in 2007

The water and sediment discharge regulation （WSDR） project, which has been performed since 2002 before flood season every year, is of great significance to the river management in China. Until 2007, six experiments have been fulfilled to evaluate the effect of the project on the natural environment. To fill the gap of investigations, a study on flood and suspended sediment transportation and channel changing along the distributary channel of the Huanghe （Yellow） River was conducted during the WSDR project period in 2007. The lower channel was scoured rapidly and the channel became unobstructed gradually several days after the flood peak water was discharged from the Xiaolangdi Reservoir. Within four days after the flood peak at 3 000 m3/s entered the distributary, the channel in the river mouth area was eroded quickly. Both the mean values of area and depth of the main channel were tripled, and the maximum flood carrying capacity increased to 5 500 m3/s or more. Then, the river channel was silted anew in a very short time after completion of the WSDR. Favored by the WSDR project, the fiver status in April 2008 became better than that of the year before. The adjustment ranges of main channel parameters were about 30%, 10%, and 10% at sections C2, Q4, and Q7, respectively. The process of rapid erosion-deposition was more active 15 km away in the channel from the fiver mouth due to the marine influence. It is reasonable for discharging sediment at concentration peak from Xiaolangdi Reservoir at the end of the flood peak. As a result, the sediment peak reached the river mouth about two days later than that of the water current. In addition, the WSDR project has improved the development of the estuarine wetland. Wetland vegetation planted along the river banks restrained the water flow as a strainer and improved the main channel stability. It is suggested to draw water at mean rate of 150 m3/s from the Huanghe River during flood periods, because at the rate the water in the wetland would be stored and replenished in balance. Moreover, we believe that cropland on the river shoal of the lower Huanghe River should be replaced by wetland. These activities should achieve the Huanghe River management strategy of ＂To concentrate flow to scour sediment, stabilize the main channel, and regulate water and sediment＂.

FISH ASSEMBLAGE RESPONSES TO DIFFERENT SECONDARY CHANNEL DESIGNS IN THE LOWER MISSISSIPPI RIVER,U.S.A.:A TEMPLATE FOR RIVER RESTORATION

The lower Mississippi River(LMR) has been heavily modified for multiple human purposes such as navigation, flood control, and bank stabilization. However, the LMR simultaneously supports a diverse fish fauna that includes recreational and commercial fisheries. Due to river training and diversion structures constructed during the past 80 years, the historic characteristics of the LMR have been drastically altered and have likely influenced fishes and fisheries in the system. One common restoration measure used throughout the LMR has been to "notch" wing-dike structures that close secondary(side) river channels. Dike notching allows year-round flows through secondary channels, which enhances habitat diversity and promotes biological productivity at the ecosystem scale. Although notching is presumed good for LMR fishes and other biota, few studies have examined its effects on fish assemblages. In this study, fish assemblages were sampled at seven LMR secondary channels spanning from river kilometer(rkm) 628(Louisiana-Mississippi, U.S.A.) upstream to rkm 1504(Missouri-Kentucky, U.S.A.). Four secondary channels were termed "permanent"(i.e.,with notched dikes) while three secondary channels were termed "temporary"(i.e., without notched dikes).Fishes were sampled by boat-mounted electrofishing conducted during falling and low stages from1995—1997. Fish assemblages differed between permanent and temporary secondary channels, and varied somewhat between falling and low stages. Gizzard shad(Dorosoma cepedianum), threadfin shad(D. petenense), and white bass(Morone chrysops) demonstrated consistent preferences for low-current conditions associated with temporary secondary channels. Conversely, blue catfish(Ictalurus furcatus), flathead catfish(Pylodictis olivaris), and freshwater drum(Aplodinotus grunniens) were more associated with permanent secondary channels. Future restoration strategies in the LMR should consider dike notching and resultant maintenance of permanent secondary channels in selected river reaches. However, temporary secondary channels also contain unique fish species, and also appear to be important sites of riverine primary production. Restoration strategies should consider a balance of both secondary channel types, which should support the greatest biodiversity for the LMR ecosystem.

TYPES AND DISTRIBUTION PATTERNS OF MODERN TIDAL CHANNELS ALONG THE HUANGHE RIVER DELTA COAST

There are three major types of tidal channels along the coast of the Huanghe (Yellow) River Delta: tidal inlets, tidal creeks, and tidal channels developed from abandoned river channels. The tidal inlets develop mainly in two areas with weak erosion and barrier islands. The tidal channels formed from abandoned river channels mainly developed in the area of the new delta lobes formed since 1934. Tidal creeks developed in the intertidal zone and distributed along almost all parts of the Huanghe River Delta coast, but their scales and features are different.

Evaluation of Fast Flood Diffusion through a Drainage Channel: A Flood Disaster Case Study of Japan’s Kinugawa River, September 10, 2015

On September 10, 2015, unprecedented flood was occurred in Kinugawa River basin located on eastern Japan. It inundated 40 km2 of flood plain in Joso city, Ibaraki Prefecture, and more than 4000 people there called for help despite supposedly having sufficient time to evacuate. Some said that small initial flood before main severe flood arrived made them make a mistake in deciding whether to evacuate or stay there, despite having to actually evacuate in reality. This study focused on flood behaviour in this area, in particular, the effect of a small drainage channel lying on the flood plain which caused fast flood diffusion in case of occurring huge overflowing. Field investigations starting on time of the disaster with high-resolution positioning system were conducted to obtain spatial maps of flood depth and height. For appropriate modelling of the effect of small channel, we applied simulation model coupling 1-dimensional (1D) and 2-dimensional (2D) hydraulic scheme on the field and compared results from the 1D/2D coupled model and model without 1D scheme. The models provided information that the flood could reach 4 hours earlier to the city central of Joso city comparing in case of model without 1D scheme. The water depth rose irregularly and it was more confusing and difficult for the victims to make appropriate evacuation act.

黄河下游花园口以上河段滞沙能力分析

黄河下游河床调整主要取决于来水来沙和河床边界条件,河床调整沿程不均衡特征明显,花园口以上河段床演变对水沙条件的变化响应尤为突出,泥沙冲淤调整幅度最大。基于河道冲淤及水沙演进特性、滞沙可行性、河槽几何特性等分析,提出了花园口以上河段可作为泥沙天然反调节“库”概念,结合黄河下游实测洪水资料,采用水力计算方法,计算了花园口以上河段的河槽排洪能力及不同河槽规模条件下河槽允许滞沙量,提出了反调“库”滞沙能力,可为小浪底水库排沙指标的确定提供依据,对维持小浪底水库有效库容、弥补后续清水河床沙源不足、改善黄河下游河槽冲淤不均衡现象具有重要意义。

Sarawak River Flow Behaviour after Matang Bypass Channel Construction during Low Tide Using InfoWorks River Simulation (RS)

Flood is occurring more frequently in Kuching nowadays due to the impact of climate change and rapid urbanization. The only discharge outlet for Sarawak River Basin currently is at Kuching Barrage and Shiplock. Sarawak State Government had decided to build Matang Bypass Channel from Sarawak River’s “Oxbow” to Batang Salak River for mitigating the flooding issues within Sarawak River Basin. Matang Bypass Channel had a bottom width of 250 m, 500 m reserve width and 8 Km in length. Flow behaviour with two discharge outlets during low tides are unknown yet. Therefore, this research is carried out to study Sarawak River flow behaviour after construction of Matang Bypass Channel using InfoWorks River Simulation (RS). Rainfall data used is January 2018. Four scenarios investigated are 1) Open two gates at Matang Bypass Channel opens and all gates at Kuching Barrage, 2) Open all gates at Matang Bypass Channel and Kuching Barrage, 3) Open gates at Matang Bypass Channel, but close all gates at Kuching Barrage, 4) Close all gates at Matang Bypass Channel, but open all gates at Kuching Barrage. Results revealed that when water gates are opened, sea water has the potential to backflow into Sarawak River basin through Kuching Barrage since sea level at Kuching Barrage discharge outlet is always 0.5 m higher than Matang Bypass Channel discharge outlet. When the gates at Matang Bypass Channel are fully opened and Kuching Barrage are closed, Kuching Barrage will retain the excess water and the river water will only be discharged into ocean through Matang Bypass Channel. In contrast, as the gates at Matang Bypass Channel are closed and at Kuching Barrage are fully opened, Matang Bypass Channel will store the excess water and river water will be discharged through Kuching Barrage alone.

初论黄河下游河道的河槽线

黄河白鹤镇至陶城铺河段两岸堤距宽,历史上河道冲淤变化迅速、河势游荡多变,经多年河道整治,总体上河势得到基本控制,滩槽逐步稳定。在此条件下,为促进黄河的生态保护和滩区发展,提高河道管理水平,将河道粗分为河槽与滩地,首次提出河槽线的概念,明确了河槽线的含义及绘制河槽线的原则,强调绘制河槽线要以防洪安全为前提,给出了河槽线的绘制方法及其现场标示办法,分析了河槽线的作用等。

Overbank Flow in a Multi-Staged Open Channel: Zonal and Overall Discharge Studies

An improved divided channel method has been proposed by modelling a parameter using the function of depth ratio for a multi-stage compound channel. Experimental data suggest that as the flow depth increases over the second stage floodplain, fractional contribution of the main channel and first stage floodplain under bankfull height plays a pivotal role in shear layer and momentum distribution. Therefore, a new mathematical model has been suggested for estimating the stage-discharge relationship for staged channels of more than one floodplain using the 1D technique of overall roughness correction. .

小浪底水库减淤调度模式探讨

小浪底水库在黄河中下游防洪格局中发挥着重要作用,长期保持库区较大库容、延长拦沙运用期,对黄河防洪保安具有重大意义。基于小浪底水库运用以来入库水沙条件变化以及调度实践分析,提出了近期小浪底水库减淤调度模式:前汛期洪水期考虑下游河道淤积和主槽过流能力,尽量利用大流量过程开展降低水位排沙运用,冲刷库区河槽新增淤积物,以恢复河槽过流能力,保持库区高效输沙通道;水库排沙运用过后,运用水位宜不高于库区较大滩地滩面,利用河槽输沙调沙能够有效减缓滩面淤积;后汛期在保证防洪安全的前提下,根据上游来沙情况择机开展水库回蓄,尽早将库水位蓄至HH37断面附近滩面以上,利用HH37断面以上库段临时调沙,减缓滩面淤积。

基于流域储水量精细化模拟的干旱指数构建及应用

为构建一种客观反映河道槽蓄量、水库蓄水量和土壤含水量联合亏缺的干旱指数,以秦淮河流域为研究区,基于500 m×500 m分辨率的VIC-FLASH模型,通过精细化模拟流域河道、水库和土壤中存储水量的变化过程,构建了标准化流域储水指数(SWSI),并应用SWSI对1980—2019年秦淮河流域历史干旱事件和干旱特征进行分析,验证了其可靠性和应用优势。结果表明:高分辨率VIC-FLASH模型可以较好地模拟流域储水量时空分布,流量过程模拟结果平均相对误差为10.6%,流域内6座水库实测与模拟蓄水量相关系数为0.53~0.86;SWSI可以准确识别干旱事件和反映区域干旱严重程度,干旱烈度与实际受旱面积的相关系数为0.88;1980—2019年逐日SWSI与标准化径流指数和土壤含水量距平指数的相关系数分别为0.89和0.98;SWSI不仅可以定量反映流域储水量的亏缺状态,而且可以更加客观地反映旱情时空演变过程。