Riverbank Instability Research Articles

Analysis of long-term and short-term bankline stability prediction considering seasonal variations: A study in lower Ganga Basin, India

River bank instability in the lower Ganga plain has been a major concern since the early 1850s due to its huge catchment flux and transboundary character, especially in the districts of Malda and Murshidabad. This study examines the seasonal dynamics of banklines in the upper and lower Farakka regions. The study assesses seasonal changes in the lower Ganga regions over 68 years (1955–2022) and projects trends for the next 22 years (2022–2044) using a GIS-based Digital Shoreline Analysis System (DSAS) approach. Long-term erosion prevails on the left bank at −19.38 ± 2.83 m yr^-1 (LRR method), with 38.61 % of transects showing a significant (p < 0.05) erosional rate, covering 58.85 % of total erosional transects. The right bank experiences accretion at a rate of 6.82 ± 2.83 m yr^-1, with 27.66 % of transects showing a significant erosional rate, covering 46.10 % of total erosional transects. Short-term fluctuations show erosion-accretion values surpassing the 50 % threshold, highlighting dominant erosion in 1975–1980 and 1985–2015. The non-cyclic erosion-accretion nature unveils erosional processes in 1975–2000 and 2010–2015 and accretional processes in 2000–2010 and 2015–2021 on the right bank during the monsoon season. The dynamics of the projected bank lines exhibit an accretional tendency over the right bank and an erosional trend over the left. Moreover, a strong correlation between the actual and expected bank lines is shown by the R2 value surpassing 0.95 for all seasons on both the left and right banks. The erosional trends are evident in Chachunda at a rate of −152.45 ± 198.92 m yr^-1, while Loharpur and Shikdarpur exhibit erosional rates of −237.88 ± 211.30 m yr^-1 and −243.59 ± 207.91 m yr^-1, respectively, in the lower Farakka. The seasonal long-term and short-term analyses are influenced by various forcing mechanisms like high sediment flux, enormous discharge, and drastic anthropogenic intervention that drives changing foci of erosion and accretion.

Effects of freeze–thaw on bank soil mechanical properties and bank stability

Riverbank instability in the seasonally frozen zone is primarily caused by freeze–thaw erosion. Using the triaxial freeze–thaw test on the bank of Shisifenzi Bend in the Yellow River section of Inner Mongolia, we investigated the changes in the mechanical properties of the soil at different freezing temperatures and freeze–thaw times, and analyzed the bank’s stability before and after freezing based on the finite element strength reduction method. The results showed that the elastic modulus, cohesion, internal friction angle and shear strength of the soil tended to decrease with the increase in the number of freeze–thaw cycles and the decrease in freezing temperature. After 10 freezing cycles at − 5 ℃, − 10 ℃, − 15 ℃ and − 20 ℃, the modulus of elasticity of soil decreased by 40.84 ~ 68.70%, the cohesion decreased by 41.96 ~ 56.66%, the shear strength decreased by 41.92 ~ 57.32%, respectively. Moreover, the stability safety coefficient of bank slope decreased by 18.58% after freeze–thaw, indicating that the freeze–thaw effect will significantly reduce the stability of bank slope, and the bank slope is more likely to be destabilized and damaged after freeze–thaw.

Around seven decades river course shifting and bank erosion susceptibility of river Mujnai

AbstractRiver bank erosion is a destructive fluvio‐hydrological hazard particularly inhabited flood plain of the dynamic Himalayan foreland basin. Every year during monsoonal months, morphology of the landscape is continuously modifying through the dynamic river system. The principal objectives of this study are (i) to identify the river bank erosion susceptibility through BESI (River Bank Susceptibility Index) model which has been modified from Rosgen's (2001) Bank Erosion Hazard Index (BEHI) model and historical reconstruction (from 1955 to 2021) of the river course of Mujnai and (ii) to examine the principal factors of river bank erosion particularly for the river Mujnai within Himalayan Foreland Basin. Sedimentary bank facies analysis has also been done to ascertain the causes of river bank instability. Hence, rate of bank migration, changes of channel width, channel sinuosity index (SI), channel length, erosion and accretion of the river bank, and so forth have been measured through geospatial techniques. Result showed that the younger Quaternary sediments are prone to erosion and BESI result illustrated that around 28% areas are under high erosion zones like Deoagaon, Dhulagaon, Hedayet Nagar, and Dalimpur villages in Alipurduar district. Average maximum width of the channel was recorded in 1980 (147.92 m). Additionally, the lateral migration in case of left bank was around 141.08 m (in the 1980) and 192.62 m in right bank (in 1980) while the shifting rate was 14.10 m/y and 17.51 m/y respectively. Quaternary bank materials, bioturbation and indistinct laminations of river bank are principal regulating factors behind bank erosion in this area. Monsoonal high‐velocity flow, bank full discharge and severe flood incidents accelerate the bank erosion vulnerability, particularly in this dynamic flood plain. Soft engineering techniques such as bioengineering, geo‐textile fabric, tree, grass and brush revetment should be implemented at high bank erosion vulnerable sites of river Mujnai.

Original

River bank erosion is a hazardous and common phenomenon in diara region near Malda district of North East India during monsoon and post-monsoon periods of every year. One of the significant causes behind the erosion is the textural composition and its arrangement along the river bank. The left bank of Ganga River is texturally very weak along diara region of Malda district. In the present study, the nature of riverbank soil textural composition has been measured by basis parameters analysis and mechanical analysis of soil and its erodibility level. Sieve analysis has been done on all collected soil samples and determines soil basic parameters. The nature of the soil has been derived through the mechanical analysis of particles after Folk and Worst method. Besides that, the degree of soil erodibility has been analyzed through the Bouyoucos Erodibility Index and ROM scale after Roslan and Mazidah. The results show that the erodibility levels become high to the moderate condition along the middle to lower extension of left bank line and relatively low along with upper extension according to ROM scale. Nature of soil along the left bank is dominantly sandy which also indicates the vulnerable condition of bank sites. Basic parameters of soil and its mechanical analysis also reveals that unstable condition exists along with the whole extension of the riverbank line but instability condition is increasing from upper to lower segment of bank line. So the risk of riverbank failure can be measured by determining the textural composition of the soil.

Flow control by pile-group groynes used for riverbank instability management

Smooth reduction of velocity from the mainstream to the bank is a desirable attempt when using a groyne for riverbank protection purpose. This can be achieved by applying modifications to groyne permeability or layout. In this study, the effects of different pile-group groynes on the flow deceleration were investigated experimentally. Different aspects including pile density, arrangement, row spacing and effects on the long downstream were considered. The results show that the pile arrangement pattern is an important factor on the control of flow magnitude and pattern behind a pile-group groyne. A gradual and smooth velocity reduction from the mainstream to the bank can be obtained by changing the arrangement of piles in a pile-group groyne.

Climatic Changes, Water Systems, and Adaptation Challenges in Shawi Communities in the Peruvian Amazon

Climate change impacts on water systems have consequences for Indigenous communities. We documented climatic changes on water systems observed by Indigenous Shawi and resultant impacts on health and livelihoods, and explored adaptation options and challenges in partnership with two Indigenous Shawi communities in the Peruvian Amazon. Qualitative data were collected via PhotoVoice, interviews, focus group discussions, and transect walks, and analyzed using a constant comparative method and thematic analysis. Quantitative data were collected via a household survey and analyzed descriptively. Households observed seasonal weather changes over time (n = 50; 78%), which had already impacted their family and community (n = 43; 86%), such as more intense rainfall resulting in flooding (n = 29; 58%). Interviewees also described deforestation impacts on the nearby river, which were exacerbated by climate-related changes, including increased water temperatures (warmer weather, exacerbated by fewer trees for shading) and increased erosion and turbidity (increased rainfall, exacerbated by riverbank instability due to deforestation). No households reported community-level response plans for extreme weather events, and most did not expect government assistance when such events occurred. This study documents how Indigenous peoples are experiencing climatic impacts on water systems, and highlights how non-climatic drivers, such as deforestation, exacerbate climate change impacts on water systems and community livelihoods in the Peruvian Amazon.

Riverbank stability assessment during hydro-peak flow events: the lower Osage River case (Missouri, USA)

ABSTRACT The fluctuation of water level downstream from dams due to hydropower flow releases can negatively affect riverbank stability. This research aims to investigate riverbank instability resulting from the outflow variation of hydropower plants, using Bagnell Dam and the lower Osage River (Missouri, USA) as the basis of analysis. The effects of the water releases from the Bagnell Dam were investigated by computing a series of safety factors in relation to outflow events for 78 cross sections along the 130-km stretch of the lower Osage River using the BSTEM algorithm integrated into the HEC-RAS model package. The results showed that the rate of change in the flow magnitude at each cross section impacts the calculated safety factor. The flow release fluctuations will change the value of the safety factor along the river over time, as the safety factor value closely follows the variation in the flow rate. Also, the results show that the cross sections closer to Bagnell Dam are subjected to be more unstable than those farther downstream of Osage River.

Multimodelling approach to the assessment of climate change impacts on hydrology and river morphology in the Chindwin River Basin, Myanmar

In the tropical region, climate change significantly affects the morphology of river channels as well as water resources. In this study, the climate change impact on hydrology and morphology is assessed in the Chindwin River Basin, Myanmar. Future climate data was developed by an ensemble of four Regional Climate Models (RCMs) using a performance-based weight method, under two Representative Concentration Pathways (RCP4.5 and RCP8.5). Two models were developed: a hydrological model (MIKE NAM) to simulate future discharge and a morphology model (MIKE 21 Flow Model) to simulate morphological changes under climate change scenarios. The results reveal that the mean annual discharge over the period from 2018 to 2040 (23 years) is projected to increase by 13.9 and 22.8%, under RCPs 4.5 and 8.5, respectively. The annual hydrograph shows a sharp rise and the recession of monsoon flood, with multiple peaks replacing the single peak observed during the baseline period (1975–2005) with a delay in peak of 8–10 days. The extreme events (floods) are expected to get more severe in the future in terms of frequency and magnitude compared to the baseline period. The study further shows that under extreme rainfall events, the left bank of the upstream areas is projected to experience severe morphological changes, accompanied by severe flood damage. As high flows become amplified due to climate change in the near future, morphological changes will exacerbate in the same period. Sediment deposition will increase the flood risk and river bank instability, constraining navigability in the river and adversely affecting riverine communities. The study reveals that mathematical modelling helps to identify the impacts of climate change on hydrology and morphology, and that knowledge coupled with an assessment of the vulnerability associated with lives and livelihoods, could help planners and policymakers to develop adaptation strategies and take meaningful action to mitigate the impact.

River bank instability from unsustainable sand mining in the lower Mekong River

Recent growth of the construction industry has fuelled demand for sand, with considerable volumes being extracted from the world’s large rivers. Sediment transport from upstream naturally replenishes sediment stored in river beds, but the absence of sand flux data from large rivers inhibits assessment of the sustainability of ongoing sand mining. Here, we demonstrate that bedload (0.18 Mt yr-1 ± 0.07 Mt yr-1) is a small (1%) fraction of the total annual sediment load of the lower Mekong River. Even when considering suspended sand (6 Mt yr-1 ± 2 Mt), the total sand flux entering the Mekong delta (6.18 Mt yr-1 ± 2.01 Mt yr-1) is far less than current sand extraction rates (50 Mt yr-1). We show that at these current rates, river bed levels can be lowered sufficiently to induce river bank instability, potentially damaging housing, infrastructure and threatening lives. Our research suggests that, on the Mekong and other large rivers subject to excessive sand mining, it is imperative to establish regulatory frameworks that limit extraction rates to levels that permit the establishment of a sustainable balance between the natural supply/storage of sand and the rate at which sand is removed.

Assessing the instability of Dong Nai River in Bien Hoa District using Bank Erosion Hazard Index (BEHI) and Remote Sensing and GIS

Abstract. In this study, a method for developing a quantitative prediction of river bank erosion in Bien Hoa district in Dong Nai River is presented. The river bank erosion hazard index (BEHI) was estimated to assess the stability of the river bank erosion in consultation with bank height, bank slope, rooting depth, rooting density and surface protection. The estimated BEHI of Dong Nai River in Bien Hoa district are high which indicates the riverbank instability. The estimated BEHI along the left bank is about 25–30. The satellite data of LANSAT TM 5, LANDSAT ETM 7 for the year 1995, 2005 and 2015 were used to assess the nature of shifting of the river bank and to estimate the land loss from river bank. All the derived images were transported on GIS environment to extract the course of the river. 13 sites were considered along the Dong Nai River in Bien Hoa District to estimate the leftward shifting of the bank line and to assess the shifting distance of the river bank line. There is a strong relationship between bank instability BEHI, shifting distance of the bank line and eroded bank area in this study.

Assessing the Instability of Dong Nai River in Bien Hoa District Using Bank Erosion Hazard Index (BEHI) and Remote Sensing and GIS

In this study, a method for developing a quantitative prediction of river bank erosion in Bien Hoa district in Dong Nai River is presented. The river bank erosion hazard index (BEHI) was estimated to assess the stability of the river bank erosion in consultation with bank height, bank slope, rooting depth, rooting density and surface protection. The estimated BEHI of Dong Nai River in Bien Hoa district are high which indicates the riverbank instability. The estimated BEHI along the left bank is about 25-30. The satellite data of LANSAT TM 5, LANDSAT ETM 7 for the year 1995, 2005 and 2015 were used to assess the nature of shifting of the river bank and to estimate the land loss from river bank. All the derived images were transported on GIS environment to extract the course of the river. 13 sites were considered along the Dong Nai River in Bien Hoa District to estimate the leftward shifting of the bank line and to assess the shifting distance of the river bank line. There is a strong relationship between bank instability BEHI, shifting distance of the bank line and eroded bank area in this study.

Bank instability along a weir pool of the River Murray

ABSTRACTRiver banks are an important transition zone between aquatic and terrestrial environments. This ecotone is highly vulnerable to natural and anthropogenic disturbances. Bank erosion is a common occurrence along the River Murray. Morphological features reflecting river bank instability form a near-continuous pattern along large tracts of the river. This study investigates the character and extent of bank instability along the Torrumbarry Weir Pool. Over 90% of the bank length in this weir pool was assessed as being actively eroding. Notch development was the dominant instability mechanism and it promoted other forms of bank instability. Erosion notches result from stable water levels and inherent soil instability of the river banks along the weir pool. The character and extent of river bank erosion recorded along this section of the River Murray is an artefact of flow regulation and not a reflection of the natural occurrence of bank erosion in river networks. Water level management in the upstream weir pool has significant implications for the management of river banks along regulated reaches of the River Murray.

Investigating effect of water level variation and surface tension crack on riverbank stability

During high flow season, the rise and fall of river water level could induce riverbank instability and threaten structural safety of flood-protection facilities on floodplains. Through a flume experiment, this paper investigates the influences of three factors (namely, drawdown rate of river stage, initial water elevation, and riverbank slope angle) on riverbank stability due to the fall of river water level. From the laboratory experiments it was observed that tension crack appeared in all riverbank failure cases and all failure patterns were of planar type. Moreover, this paper presents a riverbank stability analysis model that explicitly incorporates the integral effect of all forces acting upon the failure plane and tension crack. The prediction accuracy of the proposed model is examined by using experimental data obtained in this study and field data of the Hotophia Creek in the USA and the Sieve River in Italy. A comparison of model simulation results with and without considering tension crack clearly indicates the importance and necessity of including tension crack for achieving good accuracy in riverbank stability simulations. For practical application of the improved riverbank stability model, two empirical formulas for estimating tension crack location and failure plane angle were examined and modified to enhance their appropriateness in riverbank stability simulation. Finally, the improved model with the modified empirical formulas was verified to show its good prediction in riverbank stability analysis.

River bank burrowing by invasive crayfish: Spatial distribution, biophysical controls and biogeomorphic significance

Invasive species generate significant global environmental and economic costs and represent a particularly potent threat to freshwater systems. The biogeomorphic impacts of invasive aquatic and riparian species on river processes and landforms remain largely unquantified, but have the potential to generate significant sediment management issues within invaded catchments. Several species of invasive (non-native) crayfish are known to burrow into river banks and visual evidence of river bank damage is generating public concern and media attention. Despite this, there is a paucity of understanding of burrow distribution, biophysical controls and the potential significance of this problem beyond a small number of local studies at heavily impacted sites. This paper presents the first multi-catchment analysis of this phenomenon, combining existing data on biophysical river properties and invasive crayfish observations with purpose-designed field surveys across 103 river reaches to derive key trends. Crayfish burrows were observed on the majority of reaches, but burrowing tended to be patchy in spatial distribution, concentrated in a small proportion (<10%) of the length of rivers surveyed. Burrow distribution was better explained by local bank biophysical properties than by reach-scale properties, and burrowed banks were more likely to be characterised by cohesive bank material, steeper bank profiles with large areas of bare bank face, often on outer bend locations. Burrow excavation alone has delivered a considerable amount of sediment to invaded river systems in the surveyed sites (3tkm−1 impacted bank) and this represents a minimum contribution and certainly an underestimate of the absolute yield (submerged burrows were not recorded). Furthermore, burrowing was associated with bank profiles that were either actively eroding or exposed to fluvial action and/or mass failure processes, providing the first quantitative evidence that invasive crayfish may cause or accelerate river bank instability and erosion in invaded catchments beyond the scale of individual burrows.

Sediment Transport Dynamic in a Meandering Fluvial System: Case Study of Chini River

Sedimentation in river reduces the flood carrying capacity which lead to the increasing of inundation area in the river basin. Basic sediment transport can predict the fluvial processes in natural rivers and stream through modeling approaches. However, the sediment transport dynamic in a small meandering and low-lying fluvial system is considered scarce in Malaysia. The aim of this study was to analyze the current riverbed erosion and sedimentation scenarios along the Chini River, Pekan, Pahang. The present study revealed that silt and clay has potentially been eroded several parts of the river. Sinuosity index (1.98) indicates that Chini River is very unstable and continuous erosion process in waterways has increase the riverbank instability due to the meandering factors. The riverbed erosional and depositional process in the Chini River is a sluggish process since the lake reduces the flow velocity and causes the deposited particles into the silt and clay soil at the bed of the lake. Besides, the bed layer of the lake comprised of cohesive silt and clayey composition that tend to attach the larger grain size of sediment. The present study estimated the total sediment accumulated along the Chini River is 1.72 ton. The HEC-RAS was employed in the simulations and in general the model performed well, once all parameters were set within their effective ranges.

Understanding and managing the morphology of branches incising into sand-clay deposits in the Dutch Rhine Delta

In the Rhine-Meuse delta in the south-western part of the Netherlands, the morphology of the river branches is highly dependent on the erodibility of the subsoil. Erosion processes that were initiated after closure of the Haringvliet estuary branch by a dam (in 1970), caused a strong incision of several connecting branches. Due to the geological evolution of this area the lithology of the subsoil shows large variations in highly erodible sand and poorly erodible peat and clay layers. This study shows how the geological information can be used to create 3D maps of the erodibility of the sub-soil, and how this information can be used to schematize the sub-soil in computational models for morphological simulations. Local incisement of sand patches between areas with poorly erodible bed causes deep scour holes, hence increasing the risk on river-bank instability (flow slides) and damage to constructions such as groynes, quays, tunnels, and pipelines. Various types of mathematical models, ranging from 1D (SOBEK) to quasi-3D (Delft3D) have been applied to study the future development of the river bed and possible management options. The results of these approaches demonstrate that models require inclusion of a layer-bookkeeping approach for sub-soil schematization, non-uniform sediment fractions (sand-mud), tidal and river-discharge boundary conditions, and capacity-reduction transport modeling. For risk-reducing river management it has been shown how the development of the river bed can be addressed on a large scale and small scale. For instance, the use of sediment feeding and fixation of bed can be proposed for large-scale management, while monitoring and interventions at initiation of erosion can be proposed as response to small-scale developments that exceed predefined intervention levels.

Reply to the discussion by A.C. Londono on "Response of a residual soil slope to rainfall"

We would like to thank the discusser for her interest in our paper and appreciate her thoughts and views on our paper. In our paper we tried to present the responses of a residual soil slope (characterized through changes in infiltration, runoff, soil water content, and pore-water pressures) to various rainfall conditions and attempted to quantify the flux boundary conditions required for seepage analyses associated with rainfall-induced slope failures. The discusser compared results of our field studies on rainfall-induced slope failure to that of her study on riverbank instability. We find it particularly encouraging and reassuring to note that many of the findings in the discusser’s study support and validate findings from our study. We also appreciate that the discusser finds our contribution significant and useful. Such interests are encouraging and inspiring to the research community working in this area of research. We believe that more studies are needed in the search for better ways of addressing rainfall-induced slope failures.

SEDIMENT POLLUTANTS FROM A RIVER MEANDER REINSTATEMENT SITE : CONCENTRATIONS AND MANAGEMENT IMPLICATIONS

Since European settlement in the early 1800s, 66 artificial meander cut-offs have been created in the lower Latrobe River, Victoria. Contemporary waterway management practices include the reinstatement of a selection of these cut-off meanders to slow water flows and reduce river bed and bank instability. Infill sediments were collected from a range of depths from one of these meanders prior to its reinstatement to estimate the potential for remobilization of any sediment pollutants into the waterway. The characteristics of collected sediments were described and sediments were analysed for a range of pollutants including heavy metals, total petroleum hydrocarbons, monoaromatic hydrocarbons, organochlorine pesticides, polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs). Metal concentrations in the fine (<63 μm) sediment fraction increased with increasing sample depth; however, only increases in cadmium, chromium and mercury concentrations were statistically significant. Statistically significant increases in mercury concentrations with depth were also present in the entire sediment fraction. With the exception of mercury, concentrations of all metals assessed in meander sediments were similar to those reported as being at background concentrations. Mercury concentrations, although elevated, were below concentrations reported to adversely effect riverine biota. Concentrations of organochlorine pesticides, polychlorinated biphenyls, total petroleum hydrocarbons, monoaromatic hydrocarbons and polycyclic aromatic hydrocarbons were all below detection limits in the entire sediment fraction. As a consequence, reinstatement of the meander as part of a waterway management programme is unlikely to release significant quantities of sediment-partitioned pollutants into the mainstream waterway.

Prediction of tension crack location and riverbank erosion hazards along destabilized channels

AbstractRiverbank erosion, associated sedimentation and land loss hazards are a land management problem of global significance and many attempts to predict the onset of riverbank instability have been made. Recently, Osman and Thorne (1988) have presented a Culmann‐type analysis of the stability of steep, cohesive riverbanks; this has the potential to be a considerable improvement over previous bank stability theories, which do not account for bank geometry changes due to toe scour and lateral erosion. However, in this paper it is shown that the existing Osman‐Thorne model does not properly incorporate the influence of tension cracking on bank stability since the location of the tension crack on the floodplain is indirectly determined via calculation or arbitrary specification of the tension crack depth. Furthermore, accurate determination of tension crack location is essential to the calculation of the geometry of riverbank failure blocks and hence prediction of land loss and bank sediment yield associated with riverbank instability and channel widening. In this paper, a rational, physically based method to predict the location of tension cracks on the floodplain behind the eroding bank face is presented and tested. A case study is used to illustrate the computational procedure required to apply the model. Improved estimates of failure block geometry using the new method may potentially be applied to improve predictions of bank retreat and floodplain land loss along river channels destabilized as a result of environmental change.

Analysis of riverbank instability due to toe scour and lateral erosion

AbstractThis paper provides instruction in the use of the computer spreadsheet to undertake the calculations necessary to apply the Osman–Thorne bank stability analysis for steep, eroding riverbanks. The guide explains how to input the necessary parameters into the LOTUS 123 spreadsheet in order to: find the initial factor of safety of the bank with respect to slab‐type failure; test the sensitivity of bank stability to changes in the engineering properties of the bank material; analyse the response of bank stability to toe scour and/or lateral erosion and find the critical condition; find the geometry of the failure surface and failure block; analyse the response of bank stability to further toe scour and/or lateral erosion; find the geometry of the failure surface and failure block in subsequent failures.