River Channel Dynamics Research Articles

Assessing the effectiveness of “River Morphodynamic Corridors” for flood hazard mapping

In dynamic rivers the assessment of flood hazard related to geomorphological dynamics assumes crucial importance. Recently, some geomorphological approaches have been developed to assess channel dynamics in response to floods. In this study we explore the River Morphodynamic Corridors which include the current active channel and areas of the alluvial plain that may be (re)activated by channel dynamics during floods. In order to assess the effectiveness of such corridors for mapping flood hazard, we delineated the morphodynamic corridors along a river network of 74 km in the Cordevole River catchment (Italy) and compared the corridors with the channel changes that were triggered by a high-magnitude event (Vaia Storm) that hit the study area in October 2018. We observed that the morphodynamic corridors are capable to define areas where channel dynamics are most likely to occur and have proven satisfactorily effective in predicting channel widenings triggered by a severe flood. The results show that it is crucial to adopt different procedures for corridor delineation based on channel width, i.e., for small streams (width < 30 m) a more precautionary approach should be adopted that considers the entire alluvial plain as an area potentially affected by channel dynamics. The study highlighted an inherent limitation of the approach, since erosion that can affect valley slopes or fluvial terraces (i.e., widening of the alluvial plain) is not taken into account. This application represents the first validation of the River Morphodynamic Corridors approach through comparison with observed flood channel changes. Through this analysis, it can be inferred that, notwithstanding its relatively simple procedure, the approach allows a robust mapping and delineation of flood hazard due to river channel dynamics. The River Morphodynamic Corridors, when applied jointly with hydraulic model for assessing inundation processes, allow an overall assessment of flood hazard, particularly in dynamic river contexts.

Spatio-temporal analysis of riverbank changes using remote sensing and geographic information system

Fluvial hazards cause severe damage to human lives and properties. The increased intrusion of anthropogenic activities into natural hydrological cycles has increased hazard severity and confounded river channel dynamics. The present article studies the epochal channel erosion, accretion, and unaltered sites along the 42 km stretch between the Polavaram project and Dowleshwaram Barrage on the Godavari River. Geographic Information System (GIS) and Remote Sensing (RS) techniques were used to identify changes in river morphology. A total of five decades of Landsat images were analyzed, classifying the land use with a supervised learning Support Vector Machine (SVM) algorithm and an ISO cluster unsupervised algorithm to delineate the rivers and study the influence of land use land cover change (LULCC) on river morphology. Accretion and erosion channel changes during the assessment period were measured at all reaches, and the possible driving mechanisms of morphological alterations were studied.The results indicate the susceptibility of human dwellings and agricultural lands to floods due to the shifting of the highly vibrant river shoreline. The study provides the most recent information on Godavari River dynamics. These aspects of the river's evolution will aid in planning and management in the lower portions, which have not been well understood. River channel alterations can be quantitatively and economically analyzed using Remote Sensing (RS) and Geographic Information System (GIS) data.

Effect of Skewness Orientation on Morphological Adjustments in Alluvial Meandering Streams

Predicting morphological adjustments in alluvial meandering streams remains a challenging task due to the complex nature of the governing inter-related dynamic flow and sediment transport processes. This difficulty is increased in streams with irregular single-channel planform geometries, such as skewed meanders, where the meander apex is shifted in either the up-valley or down-valley direction relative to the meander centroid. Research in confined bank flume experiments has shown that the geometry difference affects flow characteristics and streambed development. The present study extends upon these findings by being the first to investigate the effects of skewness orientation in a wide-channel flume with a fully unconfined bed and banks. Three experiments were completed with an up-valley skewed, a down-valley skewed, and a non-skewed symmetrical channel, using well-sorted coarse sand and no sediment feed. The results had some variabilities in erosion and magnitude of morphological developments due to initial experimental conditions, but our analysis of the bedform positioning showed notable similarities and differences between the geometries. Bedforms typically formed upstream of the apex, with differences in their stream-wise direction extents. This research highlights how channel width-to-depth ratio and bank erodibility significantly impact river evolution, offering new insights into the dynamics of skewed meandering river channels. This study is a novel step towards a better understanding of skewed meandering rivers in unconfined alluvial channels and highlights opportunities for further research.

River channel dynamics and flooding: A case of motorable bridge collapse due to abrupt flood in Chhabdi Khola, Tanahun, Nepal

The monsoon season in Nepal brings calamitous events like riverbank erosion, toe cutting, and the structural failure of bridges due to floods. In July 2021, a motorable bridge in Bhadgaun, Tanahun district, Nepal, collapsed during a massive flood in Chhabdi Khola. The study aims to comprehensively document the aftermath, specifically focusing on the causal factors that led to the damage of the Chhabdi Khola Dovan Bridge. The study delves into an in-depth analysis of the stream's channel morphology, with the 5.85 kilometers Chhabdi Khola partitioned into 28 distinct segments, each spanning approximately 200 meters. These segments, sequentially labeled from Site 1 to Site 28, encompass the area extending from the upstream at Chhabdi Barah temple to the downstream at bridge’s location. Rigorous measurements of length, breadth, and depth at each site form the basis for volumetric assessments of the stream. The study revolves around contrasting paleo channel attributes with contemporary alterations within the Chhabdi Khola catchment. The analysis leverages precipitation data sourced from the Department of Hydrology and Meteorology (DHM) to discern precipitation trends within the Chhabdi Khola catchment area. The hydrographic data underwent trend analysis utilizing Mann-Kendall and Sen's slope method through R software (version 4.3.2). The collapse of the Chhabdi Khola Dovan Bridge resulted from intense water flow and debris due to heavy rainfall and a narrow outlet near the bridge, impacting the local population and land users facing the enduring aftermath of a catastrophic monsoon event. The study highlights the significance of understanding river dynamics in small streams and advocates for proactive disaster preparedness measures, even in seemingly small river channels.

Environmental drivers of spatio-temporal dynamics in floodplain vegetation: grasslands as habitat for megafauna in Bardia National Park (Nepal)

Abstract. Disturbance-dependent grasslands, often associated with hydromorphological and fire dynamics, are threatened, especially in subtropical climates. In the Nepalese and Indian Terai Arc Landscape at the foot of the Himalayas, natural and cultural grasslands serve a viable role for greater one-horned rhinoceros (Rhinoceros unicornis) and for grazers that form prey of the Royal Bengal tiger (Panthera tigris). The grasslands are vulnerable to encroachment of forest. We aimed to establish the effects of environmental drivers, in particular river discharge, river channel dynamics, precipitation and forest fires, on the spatio-temporal dynamics of these grasslands. The study area is the floodplain of the eastern branch of the Karnali River and adjacent western part of Bardia National Park. We created annual time series (1993–2019) of land cover with the use of field data, remotely sensed LANDSAT imagery and a supervised classification model. Additionally, we analysed the pattern of grassland patches and aerial photographs of 1964. Between 1964 and 2019, grassland patches decreased in abundance and size due to encroachment of forest. Outside the floodplain, conversion of grassland to bare substrate coincides with extreme precipitation events. Within the floodplain, conversion of grassland to bare substrate correlates with the magnitude of the annual peak discharge of the bifurcated Karnali River. Since 2009, however, this correlation is absent due to a shift of the main discharge channel to the western branch of the Karnali River. Consequently, alluvial tall grasslands (Saccharum spontaneum dominant) have vastly expanded between 2009 and 2019. Because the hydromorphological processes in the floodplain have become more static, other sources of disturbances – local flooding of ephemeral streams, anthropogenic maintenance, grazing and fires – are more paramount to prevent encroachment of grasslands. Altogether, our findings underscore that a change in the environmental drivers impact the surface area and heterogeneity of grassland patches in the landscape, which can lead to cascading effects for the grassland-dependent megafauna.

Assessment of river channel dynamics and its impact on land use/land cover in the middle Ganga plain, India

Assessment of river channel dynamics and its impact on land use/land cover in the middle Ganga plain, India

Assessing the impacts of current and future changes of the planforms of river Brahmaputra on its land use-land cover

River bankline migration is a frequent phenomenon in the river of the floodplain region. Nowadays, channel dynamics-related changes in land use and land cover (LULC) are becoming a risk to the life and property of people living in the vicinity of rivers. A comprehensive evaluation of the causes and consequences of such changes is essential for better policy and decision-making for disaster risk reduction and management. The present study assesses the changes in the Brahmaputra River planform using the GIS-based Digital Shoreline Analysis System (DSAS) and relates it with the changing LULC of the floodplain evaluated using the CA-Markov model. In this study, the future channel of the Brahmaputra River and its flood plain’s future LULC were forecasted to pinpoint the erosion-vulnerable zone. Forty-eight years (1973–2021) of remotely sensed data were applied to estimate the rate of bankline migration. It was observed that the river’s erosion-accretion rate was higher in early times than in more recent ones. The left and right banks’ average shifting rates between 1973 and 1988 were −55.44 m/y and −56.79 m/y, respectively, while they were −17.25 m/y and −48.49 m/y from 2011 to 2021. The left bank of the river Brahmaputra had more erosion than the right, which indicates that the river is shifting in the leftward direction (Southward). In this river course, zone A (Lower course) and zone B (Middle course) were more adversely affected than zone C (Upper course). According to the predicted result, the left bank is more susceptible to bank erosion than the right bank (where the average rate of erosion and deposition was −72.23 m/y and 79.50 m/y, respectively). The left bank’s average rate of erosion was −111.22 m/y. The research assesses the LULC study in conjunction with river channel dynamics in vulnerable areas where nearby infrastructure and settlements were at risk due to channel migration. The degree of accuracy was verified using the actual bankline and predicted bankline, as well as the actual LULC map and anticipated LULC map. In more than 90% of cases, the bankline’s position and shape generally remain the same as the actual bankline. The overall, and kappa accuracy of all the LULC maps was more than 85%, which was suitable for the forecast. Moreover, chi-square (x2) result values for classified classes denoted the accuracy and acceptability of the CA-Markov model for predicting the LULC map. The results of this work aim to understand better the efficient hazard management strategy for the Brahmaputra River for hazard managers of the region using an automated prediction approach.

Reconstructing backwater hydrodynamics from fluvial-deltaic deposits using stratigraphic inversion: An example from the Tullig Sandstone, Western Irish Namurian Basin, County Clare, Ireland

Fluvial-deltaic systems are subject to non-uniform backwater flow where rivers approach receiving basins. This hydrodynamic condition results in sediment aggradation on the channel bed and enhanced downstream fining. In turn, this impacts river channel dynamics, including lateral migration rates and the propensity for avulsion. The imprint of non-uniform flow on stratigraphy has been reported from field, numerical modeling, and experimental studies. This work provides key observations for evaluating the impact of non-uniform flow spanning length scales from those of sediment grains to delta lobes. However, reconstructing paleohydraulic conditions of non-uniform flow from fluvial-deltaic settings remains a challenge. Non-uniform flow is a defining characteristic of fluvial-deltaic environments, but most existing relations linking hydrology and the depositional record rely on the assumption of steady and uniform flow. Herein, we present a novel stratigraphic inversion technique, combining it with morphodynamic modeling and statistical analyses, to evaluate how backwater conditions manifest in the stratigraphy of the Tullig Sandstone, an ancient fluvial-deltaic deposit of the Western Irish Namurian Basin. Our analyses refine estimates of channel properties, including flow depth and bed slope, and are validated by field measurements of sandstone-facies properties, including grain size and stratal architecture. For example, bed sediment fines down-dip, commensurate with increasing cross set and bed thicknesses. These patterns indicate bed aggradation and are consistent with reconstructed morphodynamic conditions. This study pinpoints the extent of non-uniform flow and its influence on fluvial-deltaic stratigraphy and provides a framework for improving reconstruction techniques used to interpret the paleohydrology of ancient fluvial-deltaic systems.

Changes in River Channel Dynamics of the Satluj River, Punjab: Using a Geospatial Approach

Abstract River channel change is a dynamic process which involves erosion, accretion, lateral migration and changes in its width through the geomorphological process. Shifting of a river causes a direct impact on natural and manmade constructions which are located near the floodplain with consistent damage and devastation of the area. The objective of this study is to analyze the spatiotemporal variation along the Satluj river during the period 1990 to 2019 using Landsat TM, ETM+ and OLI satellite data. Spatiotemporal analysis of the river channel has been carried out to analyze the river channel change morphology, mid-line channel shifting and changes in surface water area of the Satluj river using twenty randomly distributed cross-sections (X1-X20). For surface water area change analysis, the satellite derived normalized difference water index (NDWI) has been used. The obtained results indicates that the river width increased by 0.033 km in overall cross-section (X1-X20) in the year 2019 as compared to the year 1990. Mid-line shifting of the river is mostly towards the left bank of the river. The maximum channel shifting of 1.364 km took place from Chak Bandala village in Jalandhar district to Madarpur village in Moga district between the years 1990 and 2019. However, the NDWI results indicate that the river surface area has been reduced by -90.33 km2 between the years 1990 and 2019. Additionally, the average shifting rate of the Satluj river during the period 1990 to 2019 is by 0.778 km.

Sentinel-1 Satellite Radar Images: A New Source of Information for Study of River Channel Dynamics on the Lower Vistula River, Poland

The amount of sediments transported by a river is difficult to estimate, while this parameter could influence channel geometry. It is possible to derive the bedload transport rate per unit width of the river channel by measuring the migration distance of bedform profiles over time and thickness of bedload layer in motion. Other possible methods include instrumental measurements using bedload traps and empirical formulas. It is possible to use remote-sensing techniques to measure the dynamics of bedform movements and geometries. Landsat images and aerial photographs have been used for this. A new source of remote-sensing information is radar satellite images. Sentinel-1 images have a temporal resolution of 2–3 days and spatial resolution of 25 m at middle latitudes, which make them usable on large rivers. The research area is the 814–820 km reach of the Lower Vistula River, where seven alternate sandbars were selected. The bank lines of the sandbars were delineated on Sentinel-1 images sensed during two low-flow periods of 4 August–26 September 2018 and 1 July–31 August 2019, when discharges at low flow were similar. From water stage observations at gauges, water elevations were assigned to every bank line of the alternate sandbars. The following morphometric parameters were calculated: alternate sandbar centers, volumes and longitudinal profile. Average daily movement of the sandbars in the period 4 August 2018–1 July 2019 was calculated as 0.97 m·day−1. A similar alternate sandbar movement velocity was obtained from a study of Sentinel-2 optical satellite images and hydro-acoustic measurements on the Lower Vistula River. Having depth of bedload in motion and alternate sandbar shift velocities, it was possible to calculate the rate of bedload transport according to the Exner approach formula. Rate of bedload transport was estimated as qb = 0.027 kg·s−1·m−1. This study shows a novel use of Sentinel-1 images to study the 3D geometry and movement rate of sandbars.

Modelling long-term alluvial-peatland dynamics in temperate river floodplains

Abstract. Peat growth is a frequent phenomenon in European river valleys. The presence of peat in the floodplain stratigraphy makes them hotspots of carbon storage. The long-term dynamics of alluvial peatlands are complex due to interactions between the peat and the local river network, and as a result, alluvial-peatland development in relation to both regional and local conditions is not well understood. In this study, a new modelling framework is presented to simulate long-term peatland development in river floodplains by coupling a river basin hydrology model (STREAM – Spatial Tools for River basins and Environment and Analysis of Management options) with a local peat growth model (modified version of DigiBog). The model is applied to two lowland rivers in northern Belgium, located in the European loess (Dijle (Dyle) River) and sand (Grote Nete River) belts. Parameter sensitivity analysis and scenario analysis are used to study the relative importance of internal processes and environmental conditions on peatland development. The simulation results demonstrate that the peat thickness is largely determined by the spacing and mobility of the local river channel(s) rather than by channel characteristics or peat properties. In contrast, changes in regional conditions such as climate and land cover across the upstream river basin have been shown to influence the river hydrograph but have a limited effect on peat growth. These results demonstrate that alluvial-peatland development is strongly determined by the geomorphic boundary conditions set by the river network and as such models must account for river channel dynamics to adequately simulate peatland development trajectories in valley environments.

Using Google Earth Engine to Assess Temporal and Spatial Changes in River Geomorphology and Riparian Vegetation

AbstractWe developed a new approach using a cloud‐based remote sensing and geospatial analysis platform, Google Earth Engine, to quantify temporal changes in river channel location and adjacent riparian vegetation extent and fraction. Our new method uses publicly available 1 m aerial images and eliminates manual processing need by incorporating an automatic image classification algorithm. Classification of riparian vegetation is enhanced by increasing the temporal resolution to monthly and by mapping vegetation at high spatial resolution. We illustrate the application of our method by characterizing temporal and spatial trends in riparian vegetation and river channel position for the mainstem of the Genesee River, New York, from 2006 to 2015. Annual change in riparian vegetation extent along the Genesee River ranged from a loss of 17% to a gain of 13%, and 64 km (28%) of the river demonstrated channel migration across consecutive aerial images. Our method also successfully distinguished differences between sections of the river above and below a dam. The enhanced capacity to map vegetation monthly allowed us to identify that seasonal active vegetation fractions along the Genesee River peaked at 75% in the summer and remained lower than 25% in winter. Our method allows stakeholders and managers to process remotely sensed imagery and investigate trends in river channel and riparian vegetation dynamics over time, while reducing the costs of data processing and storage.

Human impact on river planform within the context of multi-timescale river channel dynamics in a Himalayan river system

Rivers are dynamic landscape features which are often altered by human activity, making it difficult to disentangle human impact on geomorphic change from natural river dynamics. This study evaluated the human impact on river planform change within the context of short- and long-term river channel dynamics in the Himalayan Sutlej and Beas Rivers, by (i) systematically assessing river planform change over centennial, annual, seasonal and episodic timescales; (ii) connecting observed changes to human-environment drivers; and (iii) conceptualising these geomorphic changes in terms of timescale-dependent evolutionary trajectories (press, ramp, pulse). Landsat imagery was used to extract components of the post-monsoon active river channel (1989–2018), using the modified Normalized Differences Water Index to identify the wet river area, and visible red to determine active gravel bars. Findings were compared with a historical map to represent the pre-dam period (1847–1850) and with data on potential driving factors of change (discharge, climate and land cover). River planform characteristics changed significantly over all timescales, exhibiting strong spatiotemporal variation between and within both rivers. Dam construction likely caused channel narrowing and straightening at the centennial scale (press trajectory). In the Sutlej, this process has continued over the last 30 years, likely enforced by the cumulative effect of water abstraction and climatic changes (ramp trajectory). In the Beas, the pattern of change in river planform metrics was less pronounced over the same period and more variable along the length of the river, possibly linked to different dam operations that maintain a higher degree of flow variability and peak flows (press trajectory). High local erosion rates caused by aggregate mining (episodic) in the Sutlej were also observed (pulse trajectory). Expressed as evolutionary trajectories, the observed responses to human activity confirm the importance of legacy effects of human impact on river systems, and stress the dependency on spatial and temporal scales to determine trajectories of change. The multi-timescale assessment and conceptualisation provide insights into different dimensions of human impact on river planform change, which is pivotal to developing holistic management strategies.

Landuse change and sediment yield in an urbanised tropical deltaic catchment in Port Harcourt, South-South of Nigeria

River channel blockage due to high siltation is common in most urbanised catchments, leading to frequent flooding experiences. This is the case in the Woji River Basin. This study set out to investigate the changing landuse characteristics in the Woji River Basin and its effect on the river channel dynamics and sediment yield. Channel morphometry was determined from remotely sensed data and correlationship was measured using the Spearman ranks and Pearson's product moment co relational statistics. The result showed high influence of urban processes/landuse change on the river sediment yield, channel discharge regimes and channel morphometry characteristics. Other secondary effects of urbanisation on the river dynamics found include: urban encroachment into the floodplains; deposition of wastes into the river course; and high runoff occasioned by increasing basin surface imperviousness - culminating in downstream flooding events. Treatment of river channel and headstream wetlands protection was among recommendations.

Gilort river channel dynamics economic impact assessment in the 2010-2019 period Study case: The segment between Bălcești and Târgu Cărbunești

Gilort river channel dynamics economic impact assessment in the 2010-2019 period Study case: The segment between Bălcești and Târgu Cărbunești

A hydromorphic reevaluation of the forgotten river civilizations of Central Asia

The Aral Sea basin in Central Asia and its major rivers, the Amu Darya and Syr Darya, were the center of advanced river civilizations, and a principal hub of the Silk Roads over a period of more than 2,000 y. The region's decline has been traditionally attributed to the devastating Mongol invasion of the early-13th century CE. However, the role of changing hydroclimatic conditions on the development of these culturally influential potamic societies has not been the subject of modern geoarchaeological investigations. In this paper we report the findings of an interdisciplinary investigation of archaeological sites and associated irrigation canals of the Otrār oasis, a United Nations Educational, Scientific and Cultural Organization (UNESCO) World Heritage site located at the confluence of the Syr Darya and Arys rivers in southern Kazakhstan. This includes radiometric dating of irrigation canal abandonment and an investigation of Arys river channel dynamics. Major phases of fluvial aggradation, between the seventh and early ninth century CE and between 1350 and 1550 CE coincide with economic flourishing of the oasis, facilitated by wet climatic conditions and higher river flows that favored floodwater farming. Periods of abandonment of the irrigation network and cultural decline primarily correlate with fluvial entrenchment during periods of drought, instead of being related to destructive invasions. Therefore, it seems the great rivers of Central Asia were not just static "stage sets" for some of the turning points of world history, but in many instances, inadvertently or directly shaped the final outcomes and legacies of imperial ambitions in the region.

Degradation of multi-thread gravel-bed rivers in medium-high mountain settings: Quantitave analysis and possible solutions

Multi-thread gravel-bed rivers in Europe have undergone distinctive changes in morphology related to progressive narrowing and incision during the last 100 years. In many cases, the post-effects of multi-thread channel transformations are associated with sediment deficits caused by channelization, damming, or land use changes. Similar trends of channel narrowing and incision can be observed in the Morávka River in the Czech Carpathians, where damming, in particular, has led to sediment deficits and decreases in flood events. Evaluation of the planform dynamics of vegetation in the active channel, lateral and vertical erosion in the channel and calculations of the dominant discharge were used as tools to define potential measures for the protection and sustainability of the close-to-natural multi-thread Morávka River channel. The successive vegetation rapidly colonised originally non-vegetated gravel-bar patches, controlling sediment material reinforcement. This process strongly contributed to a decrease in the number of gravel bars in recent decades and a decline in multi-thread channel dynamics. The total volumes of approximately 36,000 m3 and 3000 m3 of sediment material were eroded in an approximately 1-km-long reach during a high-magnitude flood (with ~20-year recurrence interval of mean daily discharge) and the ordinal high-flow event (with ~1-year recurrence interval of mean daily discharge), respectively, which led to an overall sediment material deficit in the studied reach. No single value of dominant discharge for sediment transport was found by bedload transport simulations because the volumes of transported material continuously increased with the magnitude of a particular discharge and its duration. Based on these findings, the main potential measures for the protection and sustainability of multi-thread channels are recommended. The artificial disturbance of successive vegetation cover on gravel bars and the occurrence of artificial flooding are crucial factors that could increase the multi-thread Morávka River channel dynamics. The artificial supply of gravel- and cobble-sized sediment material is necessary to stop the propagation of the ‘hungry water effect’ and incision due to the present sediment deficit in the studied reach.

Морфодинамика и гидроморфология речных русел как разделы учения о русловых процессах

The article considers the structure of the study of channel processes (channel studies) as an independent section of river hydrology, which explores the effect of river runoff on the land surface. The main components of channel studies are the morphodynamics and hydromorphology of the channels. These sections are interacting with the dynamics of the channel flows and the theory of river drifts which depending on the content of the research are part of the channel science or the branches of knowledge unrelated to it. The basis of morphodynamics is the study of the morphology and dynamics of river channels, their technogenic changes, as well as river floodplains as derivatives of channel deformations, and the development of longitudinal river profiles. Hydromorphology develops hydrologic-morphological, hydromorphometric, morphometric and hydrologic-morphodynamic relations, establishes dependencies connecting the parameters of the channels among themselves, and with the hydrological and hydraulic characteristics of the rivers. It is shown that these dependencies are the basis for the development of forecasts of channel deformations as a result of the selfdevelopment of channel forms, natural and anthropogenically caused changes in the natural environment and climate. The methodology of managing channel processes and ensuring hydro-ecological safety during the development of river resources are based on regularities of channel deformations and forecasts of their development.

Assessment of spatial and temporal dynamics of the Selenga River channel deformation

The identification of spatio-temporal patterns of transformation of the Selenga river channel is an important task, which has both theoretical and practical importance. Dynamic seasonal and long-term changes in the levels and flow rates of water in the Selenga river, as well as significant kinetic energy of the flow cause a high intensity of channel processes, which must be taken into account in the construction and operation of hydrotechnical and shore protection, as well as other protective structures. A retrospective comparative analysis of the dynamics of channel deformation based on the thematic automated interpretation of Landsat satellite multi-temporal data is carried out. This, together with engineering hydrological calculations, allowed us to perform a qualitative and quantitative assessment of the results of the long-term manifestation of natural processes in a vast area occupying part of the Selenga valley from the state border to its delta. In the course of work, for the first time a map of the Selenga river channel dynamics. Areas with different types of channel stability have been identified, the channel classification has been carried out into meandering, straight and braided sections.

The Influence of River Channel Occupation on Urban Inundation and Sedimentation Induced by Floodwater in Mountainous Areas: A Case Study in the Loess Plateau, China

River channel occupation has made cities in the mountainous areas more vulnerable to floodwater out of river channels during rapid global urbanization. A better understanding of the influence of river channel occupation on urban flood disasters can serve as a reference in planning effective urban flood control strategies. In this study, taking a flood event that occurred on July 26th, 2017 in a city on the Loess Plateau as an example, field surveys, dynamics detection of the river channel using remote sensing technology, and scenario simulations with a two-dimensional flow and sediment model were utilized to quantitatively analyze the impacts of river channel occupation on urban inundation and sedimentation. The results show that river channel dynamics reduced by construction can be successfully detected using the combination of high-resolution images and Landsat time-series images. The variation of the water level–discharge relationship caused by the narrowing of the river channel and the increase of the flood-water level caused by water-blocking bridges/houses result in a significant reduction of the flood discharge capacity. The contribution of the narrowing of the river channel was 72.3% for the total area inundated by floodwater, whereas 57.2% of urban sedimentation was caused by the construction of bridges/houses within the river channel. Sustainable flood mitigation measures were also recommended according to the investigations and research findings in this study in order to reduce the social, environmental and economic damages caused by floods.