River Morphology and River Channel Changes

River morphology has been a subject of great challenge to scientists and engineers who recognize that any effort with regard to river engineering must be based on a proper understanding of the morphological features involved and the responses to the imposed changes. In this paper, an overview of river morphology is presented from the geomorphic viewpoint. Included in the scope are the regime concept, river channel classification, thresholds in river morphology, and geomorphic analysis of river responses. Analytical approach to river morphology based on the physical principles for the hydraulics of flow and sediment transport processes is also presented. The application of analytical river morphology is demonstrated by an example. Modeling is the modern technique to determine both short-term and long-term river channel responses to any change in the environment. The physical foundation of fluvial process-response must be applied in formatting a mathematical model. A brief introduction of the mathematical model FLUVIAL-12 is described.

Impacts of Dredging on Fluvial Geomorphology in the Jamuna River, Bangladesh

Jamuna, a major braided river in Bangladesh, has an enormous hydrological impact on the surrounding areas and streams. Erosion and sedimentation in the Jamuna river cause a large flow fluctuation and floods round the year. Bangladesh Water Development Board has initiated a pilot capital dredging project in the Jamuna river in 2011-2012, aiming to guide the flow to reduce the risk of failure of the city area and right guide bundh of the Jamuna Bridge. This study explores the long-term role of dredging on river morphology us-ing erosion-sedimentation numerical modeling approaches. Primary data were employed in numerical models to estimate the erosion-sedimentation and compared outputs with the real-time cross-sectional variation at selected sections along the reach during 2012-2013. The analysis suggested that the rate of sedimentation is higher (60% to 80%), where the dredging alignment crosses through the existing sandbar/char. Moreover, a cross-section com-parison revealed that the channel near Sirajganj Hardpoint shifted towards the left (east) bank, and the channel within the study area developed very fast along the right (west) bank. However, satellite image analysis revealed that the major bankline shifting occurred from 2000 to 2010 and the channel shifting was observed from 2014 to 2018 along the reach, mostly, after the construction of some river training works. The variation of the channel per-sistence (40% - 100%) selected part of the study area in the channel inci-dence map, indicating the rapid dynamic behavior of the river morphology. This study showed a good agreement of measured data and simplified em-pirical relationships to predict the long-term morphodynamic behavior of the braided Jamuna river.

Sedimentary characteristics of distributive fluvial system in arid area: A case study of the Shule River distributive fluvial system, NW China

Based on detailed investigation of the modern sedimentation of the distributive fluvial system of Shule River and the data of unmanned aerial vehicle(UAV)aerial photography and satellite remote sensing,the sedimentary characteristics and differences of distributive fluvial system in arid areas are analyzed.By comparing the changes in slope,river morphology and sedimentary characteristics in different sections from the apex to the toe,the distributive fluvial system of Shule River can be divided into three facies belts:"proximal","middle"and"distal".The proximal belt has the largest slope and strongest hydrodynamic condition,mainly appears as large-scale braided river deposits;the fluvial bars in this belt are mainly composed of gravels,the gravels have good roundness and certain directionality,and are medium-large boulders,with low sand content;the main microfacies in this belt are braided channel and flood plain.The middle belt with slope smaller than the proximal belt,is mainly composed of braided bifurcating river deposits.Due to branching and infiltration,this belt has weaker hydrodynamic conditions,so some of the distributive rivers dry up,appearing as ephemeral rivers.This belt has small lenticular sandbodies,fine to medium gravels,higher sand content,and mainly braided channel,flood plain and aeolian dune microfacies.The distal belt has the smallest slope and flat terrain,where the river begins to transform from braided river to meandering river,the sediment is mainly sand.Due to the influence of slope,this belt has weaker erosion toward source and stronger lateral erosion,and point bars developing around the edge of the active lobes.In this belt,the river is completely meandering,and the main microfacies are braided channel,meandering channel,flood plain,aeolian dune,lake and swamp.

Unit stream power,minimum energy dissipation rate,and river engineering

Unit stream power is the most important and dominant parameter for the determination of transport rate of sand,gravel,and hyper-concentrated sediment with wash load.Minimum energy dissipation rate theory,or its simplified minimum unit stream power and minimum stream power theories,can provide engineers the needed theoretical basis for river morphology and river engineering studies.The Generalized Sediment Transport model for Alluvial River Simulation computer mode series have been developed based on the above theories.The computer model series have been successfully applied in many countries.Examples will be used to illustrate the applications of the computer models to solving a wide range of river morphology and river engineering problems.

Long-Term Impact of Extra Sediment on Notches and Incised Meanders in the Hoshe River, Taiwan

The extra sediment load induced by typhoons and rainstorms in the Heshe River, Taiwan, are the principal reason for severe sediment-related disasters. The total sediment load during Typhoon Morakot in 9009 was 31 x lo6 m3, accounting for 95% of the annual sediment discharge. Large amounts of sediment load entered the Hoshe River, causing the braiding index （BI） to increase. Subsequently, the BI became positively correlated with the channel width in the Hoshe River. The specific typhoon and rainstorm events decreased after Typhoon Morakot, the sediment input decreased, inducing the fluvial morphology of the braided river to develop into a meandering river. The extra sediment load induced the deposition depth to increase and produce a headward deposition in the main channel and its tributaries. In addition, the river bend and the topographical notch restrained the sediment from moving downstream and being stored locally, indirectly increasing the erosion density of the river banks from 2.5 to lo.5 times.

Functioning Hydraulic and Morphological Sustainability of River Training Works in Bangladesh

River dynamics play the most vital role in the socio-economic of the country. These rivers are highly dynamic in nature which causes extensive riverbank erosion. Active river bank erosion and bed scouring, is apprehended to change the scenario, leading to loss of limited valuable land of Bangladesh. River training is being practiced in Bangladesh since 1960s but the process is very expensive especially in the Ganges and the Jamuna Rivers. Five types of river training works were selected at different reaches. Hydro-morphological characteristics of the major rivers are being evaluated not only in engineering concepts but also in socio-economic and environmental aspects. PRA （participatory rural appraisal） tools were applied to evaluate protection safety, hydraulic and hydrological connectivity, ecological and environmental characteristics, causes of failure and social acceptability. This comparative study is being carried out for closing the gap between the modem river training works and in country experience through adaptation of research findings with a view to effectively arresting river bank erosion. Sirajganj Hardpoint, Chandpur Town Protection work and Nakalia Revetment are found to be suitable and effective. A technically suitable structure may not have good social acceptance without IWRM （integrated water resource management）.

Analysis of the Sedimentary Characteristics of a Modern Distributive Fluvial System:A Case Study of the Great Halten River in the Sugan Lake Basin,Qinghai,China

Understanding controls on river planform changes can help to build predictive models for distributive fluvial systems,and then guide the oil and gas exploration.To do this we have undertaken a detailed investigation of the modern Great Halten River distributive fluvial system from the Sugan Lake Basin,Qinghai,China.Unmanned aerial vehicle(UAV) photography,satellite remote sensing data and elemental analysis were used to determine differences in the sedimentary characteristics of the distributive fluvial system.From the apex to the toe,the changes in the slope,river morphology,sedimentary characteristics and element content in different regions were determined and three facies belts:“proximal”,“medial” and “distal” were identified.We found that the sedimentary structure and elemental content characteristics of each facies differ greatly.We compare the large-scale evolution of rivers from braided to meandering rivers,and the fine description of sedimentary characteristics in combination with each observation,we strengthen our overall understanding of the modern DFS from macro to micro scale.At the same time,we summarize the sedimentation model of the Great Halten River DFS,and our study provides a reference for establishing the sedimentary model in continental petroliferous basins.

Flow dynamics and sediment transport in vegetated rivers:A review

The significance of riparian vegetation on river flow and material transport is not in dispute.Conveyance laws,sediment erosion and deposition,and element cycling must all be adjusted from their canonical rough-wall boundary layer to accommodate the presence of aquatic plants.In turn,the growth and colonization of riparian vegetation are affected by fluvial processes and river morphology on longer time scales.These interactions and feedbacks at multiple time scales are now drawing significant attention within the research community given their relevance to river restoration.For this reason,a review summarizing methods,general laws,qualitative cognition,and quantitative models regarding the interplay between aquatic plants,flow dynamics,and sediment transport in vegetated rivers is in order.Shortcomings,pitfalls,knowledge gaps,and daunting challenges to the current state of knowledge are also covered.As a multidisciplinary research topic,a future research agenda and opportunities pertinent to river management and enhancement of ecosystem services are also highlighted.

3-D Seismic Identification and Characterization of Ancient Channel Morphology

It is easy to identify ancient fluvial morphologic types by the outcrop,log and core data.However,the horizontal distribution and geometry of the channels can only be identified and predicted by relying on the 3-D seismic data.The 3-D seismic horizon slices,especially,can play an important role in the sandstone prediction of meandering rivers,distributary channels and low-sinuosity channels.Every microfacies unit,including main channels,such as sinuous or branching channels,levee,crevasse channels,ligule crevasse splay and floodplain etc.can be identified.Braided channel sandstones are planar tabular lateral-connected sandbodies and the distribution of thick main channel belts can only be identified from 3-D seismic data.As the braided sandstones are ubiquitous,their occurrence and distribution do not need to be predicted.Generally,the coal velocity is so low that it can create a strong amplitude reflection in coal strata.It consequently conceals the amplitude respondence to anastomosing channel sandstone which could be identified from 3-D seismic inversion data sometimes.Case studies of mud-rich low-sinuosity rivers identified with 3-D seismic data indicate that the scales and width-to-thickness ratio of such sandbodies are small,laterally unconnected,and generally occurred on distant or further parts of an alluvial fan under dry climate conditions.Sometimes extraction of seismic attributes of every reflection event along horizons is expected to maximize expression of the spatial evolutions of ancient channels.

Study of Substrate and Physico-Chemical Base Classification of the Rivers of Nepal

The rivers in Nepal are classified in terms of geographical regions but a more scientific classification such as on the ba-sis of morphology is clearly lacking. This study was done in 9 rivers namely Jhikhukhola of the Koshi system, Aandhikhola, Arungkhola, East Rapti, Karrakhola, Seti and main channel Narayani of the Gandaki system, and two independent systems within Nepal, Bagmati and Tinau. Among the morphologies, river bed or the substratum was taken as the main variable for the analysis which was categorized into 7 types as rocks, boulders, cobbles, pebbles, gravels, sand and silt. There were 23 sampling sites each with 2 stretches of around 100m in those rivers. The data were taken as a percentage, and to avoid biases it was observed visually by the same person for a complete year in every season. With 23 sites each with 2 stretches and 4 replicates corresponding to 4 seasons, there are altogether 184 observations, each termed as a case, that constitute this work. Canonical Discrimination Analysis (CDA) which is most suitable when the data pool is huge was applied to see if the rivers studied distinguish themselves in terms of its morphology. The result was remarkably successful and was close to the established regional classification of the rivers. This kind of river classification has great application in the utilization, conservation and restoration of the most important natural re-source of the country.