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River regulation by dams and embankments drastically reduce/alter flow, which affects the natural channel pattern. Existing braiding indices have seldom incorporated the effects of diurnal flow variations caused by hydropeaking, leading to over/underestimation of the braiding intensity. These indices consider only the visible wet channels, ignoring the existence of dry channels that are activated only episodically during phases of water release from hydropower dams. We have extracted the dry channels (those that are periodically wet) coursing across the channel belt of the highly regulated River Tista from Landsat images between 1977 and 2014, using Normalized Difference Wetness Index values. These were combined with existing wet channel widths and numbers to formulate the Regulated Braiding Index (RBi) for characterizing channel braiding in the Tista's course over the Himalayan foothill plains. Overall, the widths and numbers of wet channels decreased by 63% and 25%, respectively, during the regulated years (2003 and 2014) as compared to pre‐dam years (1977 and 1995) due to the collective operation of 14 upstream dams/barrages (having cumulative ~89 million m3 reservoir capacity), whose operations reduced the braiding intensity (eliciting lower RBi values). Further, the number of high braiding reaches decreased by half while low braiding stretches rose by 10% in comparison to the pre‐dam period due to reduced/regulated flow. Comparative analysis of derived RBi values with three existing braiding indices revealed that RBi values consistently decreased near barrages, bridges, and within embankment‐confined reaches, unlike the other indices, thus providing a better framework for assessing expected river regulation effects. [ABSTRACT FROM AUTHOR]

The use of water detection (WD) indices to infer daily discharge (Qd) has a great potential to enrich needed hydrological data for understanding fluvial processes driving the morphological changes of braided rivers. However, no consensus has been reached on which one stands out for use in mid-sized braided rivers. In this study, we compared the physical characteristics of three most commonly used WD indices, the Normalized Difference Water Index (NDWI), Modified Normalized Difference Water Index (MNDWI), and Normalized Difference Moisture Index (NDMI), for two mid-sized braided reach segments in the Qinghai-Tibet Plateau, China, that have different morphological structures. Relying on the Google Earth Engine web interface, we calculated the total mean water width (WWt) based on the detected surface-water areas (As) and braiding index (BI), as well as the mean values (m) of these indices over about four decades at the braided corridor scale (cs) (mNDWIcs, mMNDWIcs, and mNDMIcs). We then examined different responses of these indices to water and non-water features and their best threshold values for characterizing channel structures. Our analyses demonstrated that (1) NDWI and MNDWI perform well for detecting braided channel structures with the threshold of zero; (2) WWt is generally better correlated to Qd in a linear style than WD indices do, particularly when calculated from MNDWI; and (3) among WD indices calculated at the braided corridor scale, mMNDWIcs shows a better relationship with Qd than mNDMIcs does. Finally, we provided mechanisms that may explain these differences in terms of photometric discrepancies in calculating WWt and WD indices and the impact of image resolution on their calculations. [ABSTRACT FROM AUTHOR]

The objective of this paper was to presents potential implications of flooding on changes in channel width and braiding patterns within the nine study reaches upstream of the Shiroro Reservoir of River Kaduna, Kaduna Nigeria using standard methods for data acquisition and analysis. Preliminary findings reveal substantial alterations in channel morphology, characterized by an increase in channel width and a shift towards braided patterns in some of the study segments of River Kaduna. These changes are attributed to factors such as deforestation, urbanization, and land use changes within the river's catchment area resulting sediment released into the river. The hydrological consequences of these alterations, including increased flood risk in the upstream regions, sediment transport dynamics, and their implications for the functionality of the Shiroro Reservoir as a flood control mechanism has been pointed out. The outcomes of this study not only contribute to a better understanding of the evolving hydrogeomorphological dynamics of the Kaduna River but also provide valuable insights for sustainable river management practices and flood risk mitigation in the region. As Nigeria grapples with increasing challenges related to climate change and population growth, the findings presented in this paper hold significant relevance for policymakers, water resource managers, and communities living in flood-prone areas along River Kaduna. [ABSTRACT FROM AUTHOR]

The objective of this paper was to presents potential implications of flooding on changes in channel width and braiding patterns within the nine study reaches upstream of the Shiroro Reservoir of River Kaduna, Kaduna Nigeria using standard methods for data acquisition and analysis. Preliminary findings reveal substantial alterations in channel morphology, characterized by an increase in channel width and a shift towards braided patterns in some of the study segments of River Kaduna. These changes are attributed to factors such as deforestation, urbanization, and land use changes within the river's catchment area resulting sediment released into the river. The hydrological consequences of these alterations, including increased flood risk in the upstream regions, sediment transport dynamics, and their implications for the functionality of the Shiroro Reservoir as a flood control mechanism has been pointed out. The outcomes of this study not only contribute to a better understanding of the evolving hydro- geomorphological dynamics of the Kaduna River but also provide valuable insights for sustainable river management practices and flood risk mitigation in the region. As Nigeria grapples with increasing challenges related to climate change and population growth, the findings presented in this paper hold significant relevance for policymakers, water resource managers, and communities living in flood-prone areas along River Kaduna.

The current study explores the planform morphological changes that have occurred in the upper segment of the Yamuna River by using Landsat images from 1979 to 2019. The river segment was divided into 18 sections at equal spacing, viz., S1 to S18, and the centerline and bank line shifting, channel width, alterations in meander geometry and braiding characteristics in terms of sinuosity index (SI) and braiding index (BI) were evaluated. The results indicate a maximum centerline shifting eastward at section S-5 and westward at S17 during 1999, with respect to the base year of 1979. The average eastward and westward centerline shifting remained insignificant. The average west bank shifting ranged from 0.407 km to 0.892 km east and 0.440 km to 0.418 km west, indicating relatively higher west bank shifting towards east. The average east bank shifting ranged from 0.335 km to 0.505 km east and 0.344 km to 0.896 km west, indicating a narrowing of the bank width throughout the segment length. During the assessment period, the river segment exhibited sinuous characteristics and non-braided behavior. The outcomes of this study could be useful in predicting future trends in river shifting and developing sustainable land use planning strategies along floodplains. [ABSTRACT FROM AUTHOR]

The shifting pattern of the Ganges-Padma River in Bangladesh is examined using satellite images. The meandering Ganges-Padma River has recently transformed into a braided river. Satellite imageries from 1973–2016 are used to compute the sinuosity ratio and braiding index (two measures that allow for the trend analysis). It turns out that both the sinuosity ratio and the braiding index went up with time, surpassing the cut-off for meandering. Overall, the braiding index variation exceeds the sinuosity variation. [ABSTRACT FROM AUTHOR]

• Trend of channel braiding of a tropical river is assessed using braiding index, channel count and length indices. • The planform indices portray allometric growth patterns during the observation period (1990–2020). • The simulation of bar growth using ARIMA model indicates an oscillatory behaviour controlled by local morphotectonics. • The future forecast of bar growth for 2030 and 2050 has been tested with the RMSE and BIC. • The characterization of complex braiding patterns implies significant regional policy implications. Channel braiding is one of the fundamental fluvial processes in the context of sediment-energy nexus. The present study intends to simulate the channel braiding pattern of a tropical river (Jaldhaka River) on the Himalayan foreland plains. The grain size of the bed material in the Jaldhaka River decreases with distance from the mountain front, as does the surface gradient from the piedmont plains to the northern alluvial plains accompanied by the development of alluvial fans. Such assemblage results in multiple facets of hydro-geomorphic controls on channel planform dynamicity. This study is one of the pioneering attempts to characterize the spatial and temporal trend of channel braiding in any river running through the foreland region of the Sikkim-Bhutan Himalayas. The type of channel braiding is determined by the three indices – (1) Braiding Index (BI*), (2) Channel Count Index (BI), and (3) Channel Length Index (P t), in cases where no gradual and uniform trend of development has been seen. The spatial allometric growth of the channel braiding and time series association using the ARIMA model was examined on the twenty stretches of the river. The results depict nonuniformity in planform development with distance downstream during a 30-year time span (1990–2020). The nature of the planform value distribution concerning all three applied indices has projected a polynomial trend where certain intermediate channel segments break the general trend of the braiding intensity with downstream distance. Since the downstream braiding intensity of the Jaldhaka River hasn't decreased either linearly or exponentially, we were unable to find any significant relationship of it with surface gradient. The nature and association of the channel braiding of the Jaldhaka River point towards the influence of local controls (e.g. river terracing on the upper part and faultline controls in the middle part) on channel planform dynamicity. The prediction of channel braiding for 2030 and 2050 coupled with the model fitted with RMSE, and BIC bears great significance in revealing the future bar growth which may be useful for the different planners and stakeholders concerned with the river basin development. [ABSTRACT FROM AUTHOR]

The Cuarto River is an important watercourse in the Córdoba Province, Argentina. Its middle-low segment crosses the eastern plains of this province, one of the most populated and (agricultural-livestock) productive regions of the country. In this segment, the channel and fluvial belt morphometric parameters exhibit notable changes downstream. Understanding the morphodynamics of the Cuarto River allows the characterization and definition of channel reach with tendencies towards migration, aggradation and overflow. In this way, it is possible to identify critical channel reaches, a fundamental aspect for effective planning. This work aims to characterize the downstream changes in the fluvial belt, meanders geometry, channel pattern and channel slope, along the middle-low segment of the Cuarto River and link these modifications with authigenic (sediment supply and transport regime) and allogenic controls. Five channel reaches (R1-R5) were selected according to geological-geomorphological criteria and different geometric parameters (channel width, channel slope, braided index, meander geometry, confinement degree) were determined for each of them. Empirical equations were used to establish relationships between these geometric parameters. Although most parameters showed a generally downward trend towards downstream reaches, marked changes were observed. Particularly, in the R1-R2 reaches, the fluvial belt widens and is unconfined, and the channel width and braided index also increases. The relationship between meander length/channel width (Lm/w) and radius of curvature/channel width (rc/w) obtained were within the ranges for free meanders (8–14) and high mobility (2–3), respectively. These parameter values are associated with alluvial channels and suggest limitations in transport and conditions for sedimentation. However, in R3, R4 and R5, the fluvial belt narrows and becomes confined, with high sinuosity, a reduction in the width of the channel and the braiding index. This pattern is expected for reaches characterized by predominance of transport and a tendency to a mixed or suspensive load. Moreover, both groups of reaches also exhibit an abrupt contrast in bedload size (from very coarse sand/gravel in R1 and R2 to fine/very fine sand in R3, R4, and R5). The similarity between the exponents of the predictive functions (Lm/w, rc/w, and Lm/rc) and those obtained for the Cuarto River, in addition to the satisfactory regression coefficients of the measured parameters suggest an acceptable balance between meander geometry and channel width regime of sediment transport. The middle-low reach of the Cuarto River shows notable changes, which can be linked to regional-scale allogenic factors such as morphostructures and lithology (R1-R2 with elevated morphostructure, R3-R4 are transitional reaches towards depressed plains, while R5 with subsidence environments). Nonetheless, the river demonstrates the capacity to regulate these factors at the reach level through authigenic processes. Thus the variability of channel width, channel slope, braiding index, meander geometry and degree of confinement are explained mainly by downstream changes in sediment supply and transport regime (authigenic controls) and secondarily by changes in regional slope and banks lithology (allogeneic controls). • Relations between morphoestructal setting and fluvial belt mophology. • Use of empirical equations to analyze behaviour of alluvial channel regime. • Significant changes downstream in meanders geometry and channel pattern. • Good correspondence between meanders geometry relations and active river reaches. • Relations between morphological changes and bedload size downstream. [ABSTRACT FROM AUTHOR]

The shifting pattern of the Ganges-Padma River in Bangladesh is examined using satellite images. The meandering Ganges-Padma River has recently transformed into a braided river. Satellite imageries from 1973–2016 are used to compute the sinuosity ratio and braiding index (two measures that allow for the trend analysis). It turns out that both the sinuosity ratio and the braiding index went up with time, surpassing the cut-off for meandering. Overall, the braiding index variation exceeds the sinuosity variation.

Lateral migration of the Bhagirathi River temporally creates unavoidable geomorphic hazards in West Bengal, India. The Bhagirathi River flows SW for ~67.30 km between the confluence point of Ajay and Jalangi rivers in East Burdwan and Nadia districts of West Bengal. The course of Bhagirathi is notably migration prone and cultivates problematic changes along its course over time. In the study, we have looked into its migration tendency and unpredictability for past 238 years and then predicted the lateral shifting of river centerline using temporal satellite imageries — Landsat-5 (TM) of 1987 (8, December), 1995 (28, January), 2005 (7, January) and LISS-IV satellite imagery (2017, 5 January);SOI Toposheet — 1968-1969 (79A/2, 79A/3, 79A/6 and 79A/7) and Rennell's map of 1779. Other highlights are the quest of fluvial features, oxbow lakes, mid-channel bars, channel migration rate, meander geometry, channel sinuosity in different parts of river course and the parts that experience intensive bank erosion. The entire river course has been subdivided into three segments; viz. reaches A, B and C. Investigation displays that degree of sinuosity decreases from its anterior course (1968) to the existing course (2017). Reach-specific outputs display that reach B is highly sinuous (SI value 1.94 in 2017) and SI increases temporarily, whereas for reaches A and C it decreases with time. The rate of migration is higher in reach B than that in reaches C and A. The study displays a notably decreasing trend of migration in comparison with its previous lateral migration and shows that the migration nature over time is intensively inconsistent and unpredictable except very few portions of the river course. The nature of deposition within the river channel shows an unstable behavior during the entire period of the study. Meander geometry depicts a rapid change of river course innate to meander bends and shows a higher rate of migration by meander loop cut-off rather than lateral migration that reflects the inconsistency, erosion vulnerability and unpredictable nature of migration. The present work offers a valuable source to comprehend channel changes in Bhagirathi River and serve as an efficacious base for river-bank migration and erosion hazard planning and management. [ABSTRACT FROM AUTHOR]

Abstract: Estuaries typically show converging planforms from the sea into the land. Nevertheless, their planform is rarely perfectly exponential and often shows curvature and the presence of embayments. Here we test the degree to which the shapes and dimensions of tidal sandbars depend on estuary planform. We assembled a dataset with 35 estuary planforms and properties of 190 tidal bars to induce broad‐brush but significant empirical relations between channel planform, hydraulic geometry and bar pattern, and tested a linear stability theory for bar pattern. We found that the location where bars form is largely controlled by the excess width of a channel, which is calculated as the observed channel width minus the width of an ideal exponentially widening estuary. In general, the summed width of bars approximates the excess width as measured in the along‐channel variation of three estuaries for which bathymetry was available as well as for the local measurements in the 35 investigated estuaries. Bar dimensions can be predicted by either the channel width or the tidal prism, because channel width also strongly depends on local tidal prism. Also braiding index was predicted within a factor of 2 from excess width divided by the predicted bar width. Our results imply that estuary planform shape, including mudflats and saltmarsh as well as bar pattern, depend on inherited Holocene topography and lithology and that eventually convergent channels will form if sufficient sediment is available. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In the present study, instability of the river reach of Brahmaputra was analysed for braided belt width changes, braiding index and bar area. The river reach of the Brahmaputra from its confluence of Lohit, Dibang and Dihang to its confluence with the Tista river was studied from 1973 to 2009. The study was carried out using remotely sensed data from Landsat satellites at different dates. Discharge data synchronized with satellite data was collected by maintaining near-similar water level or discharge. Wavelet of the braided belt change was analysed to get the wavelet power and spatial extent of the changes. Finally, stream power was analysed from the average discharge data during the monsoon period to determine its effect on the instability of parameters considered. Results indicate that stream power does not directly relate to local changes in the braided belt or braiding index. However, with decrease in stream power, an increasing trend of bar area was found. Maximum wavelet power within a period showed a threshold behaviour at stream power of 5 W/km, beyond which the wavelet power raised sharply to a high value with increase in stream power. River response to the stream power was found at a global level rather than local level. Finally, a gradual decrease in stream power over time indicates the stable river reach. However, changes due to local bank erosion cannot be predicted using this analysis. [ABSTRACT FROM AUTHOR]

Estuaries show dynamic patterns of channels and bars, which are also valuable habitats, while channels provide access to harbours. In contrast with bars in rivers, we still lack explanations, theory and classifications for bars in estuaries. Theories for river bars show bar properties to be strongly dependent on channel width-to-depth ratio. For estuaries, only two physics-based theories are available. One predicts bar length to increase with flow velocity and tidal excursion length and the other with flow velocity and estuary width. However, these theories have not been tested for lack of data and experiments. Our objective is to determine bar shape and dimensions in funnel shaped alluvial estuaries and to provide predictive relations for bar shapes and dimensions. We present a new dataset measured in imagery and bathymetry with bar lengths spanning from centimetres (in experiments) to tens of kilometres. We visually identified and classified 190 bars and measured their width, length, height and number of cross-cutting barbs channels. Estuarine geometry and tidal characteristics were obtained from available databases and literature. We found that many compound bars can be seen as simple linear bars partly cut by barb channels, where partitioning of bar width collapses the data of bar length-to-width ratio. This is in agreement with the transverse wave form of bars assumed in linear stability theories that are supported by data in fluvial and coastal environments. Our empirical trend shows that sand bars in estuaries have similar length-to-width ratios as river bars but are more elongated. This trend was also found to hold for bars in numerical models and scaled laboratory experiments. Bar height is linearly related to local water depth. Natural bar length, bar width and braiding index are strongly correlated to estuary width. This relation is also evident in published data of bars in rivers and numerical models of rivers. The theoretical braiding index of tidal bars indeed depends on local width-to-depth ratio and is reasonably well predicted for our dataset. However, the theoretical models for tidal bar wave length and width surprisingly lack this correlation with estuary width and overpredict by an order of magnitude, pointing at a need to revisit tidal bar theory. The empirical relations provide a means of estimating bar dimensions when limited data are available and in order to evaluate results from numerical models and physical experiments. [ABSTRACT FROM AUTHOR]

Complex channel planform especially the dynamics of the multi-thread river is empirically examined using the three major dimensions - bar growth, channel length and channel count. To this end, many indices have been proposed to deal with the complex channel response in the context of sediment-energy synergistic scenarios. The existing methods are primarily concerned with the linear or 1D nature of the channel and bar. The present study introduced the areal or 2-D nature of the channel and bar to capture a more realistic picture because, with same length, area of the bar may differ greatly. Therefore, we proposed four indices on channel braiding taking into consideration the area of the channel and bar. We tested our indices to the 28 reaches of the Damodar River, India that showed a significant correlation (∼80%) with the existing standard method. The major highlights of the methods are outlined as follows. •Four novel indices were proposed considering the linear and areal dimensions of the channel and bar.•Proposed indices focus on the unit-free measures with known limits enabling pragmatic comparison with self and other channels.•New methods were tested using field data implying a significant correlation with the existing methods., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2023 The Authors. Published by Elsevier B.V.)

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 2009 was 31 × 10 m, 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 10.5 times. [ABSTRACT FROM AUTHOR]

The article provides information on geomorphological study on braided rivers which still lack consistency in measurement of the complexity of the braided pattern. It cites that several simple indices have been proposed and the channel count and total sinuosity are the most commonly applied. Moreover, none of the indices has there been an assessment of the sampling requirements and no systematic study of the equivalence of the indices to each other and their sensitivity to river stage has been made. Information on the series of experiments conducted, as well as the sampling criteria for braid indices, is discussed.