Bank Toe Research Articles

Riverbank fascines mostly fail due to scouring: Consistent evidence from field and flume observations

AbstractThe willow fascine soil bioengineering technique is commonly used worldwide in river restoration projects to stabilize riverbanks, thanks to high theoretical shear stress resistance and adaptable configuration. Fascines are composed of bundles of living branches fixed between stakes. When positioned in meanders at bank toe, they are subjected to strong hydraulic constraints. Here, we present the field back‐analysis of 470 willow fascines alongside experiments in a small‐scale model (scale 1:25). We describe the dynamics of failure in various situations. The field analysis revealed that 78% of fascines present no signs of bank instability. No fascines were pulled out, and they rarely showed signs of destruction once vegetation had established. Flume experiments confirmed that the main mechanical process of failure is erosion at fascine toe and extremities (9% and 3% of occurrence in the field, respectively). The dynamics of failure occur through: (i) erosion at the fascine toe, removing materials under the bundle; (ii) bank sediments, sliding underneath the fascine; (iii) scouring, leaving stakes exposed to falling into the river. Based on these observations, the fascine toe should be protected sufficiently deeply against undermining to keep sediments in place while vegetation is established. Bank slopes should be reduced as far as possible to decrease scouring. Finally, the mean shear stress values used as reference when designing bioengineering techniques do not capture the local and continuous scouring processes leading to failure. Thus, bend curvature, degradation, grain sizes, and level of fascine implementation should be considered when adapting design.

Erosion mechanism of point bar retreat under the protection of a flexible mattress

Channel retreat can be responsible for the significant loss of banks, farmland, and wetlands, leading to drastic changes in fluvial sediment and local river regimes. Although current studies focus on the erosion process of natural river channels, the mechanism by which revetments, such as the flexible mattress, influence bank evolution is still unclear. Hence, by conducting a generalized model experiment, this study investigates the point bar failure process under the mattress protection, i.e., the episodic event when the soil reaches the static equilibrium state. Specifically, a scour hole develops at the junction between the soft and hard materials, causing mattress suspension on the bank toe’s side wall and resulting in a reduction coefficient for transverse scouring rate ranging from 0.08 to 0.15. Based on the theories of soil mechanics and river dynamics, the critical conditions for point bar instability were deduced, and a mechanical model describing its erosion process under the mattress protection was established. Furthermore, our model calculated the bank morphology and total erosion volume at different periods in the flume experiment, demonstrating a good agreement with the measured data. Additionally, variations in stability coefficient and forces exerted on soil (including shear strength, gravity, and fluid pressure) of the typical sections during point bar retreat were analyzed. Sensitivity analysis of the bank toe stability emphasized the controlling effect of soil mechanical properties and the negative feedback of mattress weight. The results reveal the interaction mechanism between the mattress protection and point bar failure, theoretically guiding the bank erosion strengthening and river management planning.

Higher-order turbulence statistics and multiscale characterization of morphodynamics in a riverbank section with an upstream mining pit

Channel dredging has become a common phenomenon across several fluvial systems. Pits dredged in the riverbank can influence the downstream turbulence and affect the bank slope and central channel morphodynamics. Erodible bed experiments were conducted in a laboratory flume having a riverbank cross section with three different bank slopes, i.e., 25°, 31°, and 40° with and without a mining pit. Flow over the bank slope and near the bank toe was most affected by the pit excavation at the channel upstream. Turbulence levels were amplified within the flow over the slope and near the bank toe. The logarithmic scaling range of higher-order fluctuations at the bank toe is greater for with pit case. The complex interaction of simultaneous processes like pit migration, sliding failure and bank erosion, and fluvial erosion was studied at multiple length scales and time scales. A wavelet cross correlation analysis was used to calculate the celerity of bedform migration at the bank toe along the flow. Statistical celerity of bedforms with smaller scales (up to 15 mm length scales) is significantly higher due to pit interaction. The study reveals that instream mining has notable effects on the inherent nature of higher-order turbulence statistics, especially near the bank slope and toe, as well as the multiscale morphological structures.

Turbulence structure and bank erosion process in a dredged channel

AbstractRiverbank erosion has significant geomorphological as well as anthropogenic consequences. The geomorphological impacts include form changes such as lateral channel migration, meanders, channel expansion, etc. The anthropogenic effects include the threat to floodplain human habitation, agricultural land, and stability of instream hydraulic structures and buried pipelines. Channel dredging for the extraction of sand and gravel has seen a multi‐fold rise in the last few decades. Therefore, riverbank erosion response to channel mining gains importance in river basin management. Sandpits dredged in the riverbeds can significantly impact the downstream riverbank stability. In order to assess these impacts, we conducted a series of experiments at a laboratory scale in a recirculating water flume. Three riverbank slopes, 25° (gentle), 31° (equal to the angle of repose of the bank sediments), and 40° (steeper than the angle of repose), were tested along with a sandpit. Remarkable changes in the turbulence structure of riverbank flow were found due to the channel pit. Pit excavation directly impacts the fluvial erosion characteristics of the riverbank. Pit action increases the Reynolds shear stress fields in the near‐bank flow, which causes progressive fluvial erosion of the berm at the bank toe. The erosivity of the main channel flow in the riverbank also leads to channel degradation, which increases the exposed height of the bank slope. Pit dredging leads to the generation of stronger ejection bursts which provide a mechanism for berm sediment mobility and erosion. The hydro morphological response of the riverbank due to sand mining was analysed, and process understandings are presented in the paper.

Field Measurements and Modelling of Vessel-Generated Waves and Caused Bank Erosion—A Case Study at the Sabine–Neches Waterway, Texas, USA

The Sabine–Neches Waterway (SNWW) is home to the largest commercial port of the United States military and of the refineries that produce 60% of the nation’s commercial jet fuel. The deposited sediments from bank erosion due to wake wash result in frequent dredging to keep the waterway operational. This study investigates vessel-generated waves and their impacts on bank erosion. Surface wave data at Golden Pass and the City of Port Arthur Park dock were measured using a 1 MHz Aquadopp Profiler. Bank properties such as soil strengths were measured and soil samples were collected. Acceptable predictive models for estimating the maximum wave heights caused by vessels sailing through the SNWW were developed and validated with recorded data. Vessel-generated waves are found to produce enough shear forces to mobilize bed sediments and cause bank erosion. The bed erosion rate increases with an increase in wave height or a decrease in water depth. Bank and bank toe erosion occurs at both monitoring locations. Bank stability and toe erosion model (BSTEM) results suggest that potential bank protection options are large woody debris and riprap at Port Arthur. However, other stronger stabilization methods are required at Golden Pass.

A three-dimensional experimental study on bank retreat: The coupled role of seepage and surface flow

The coupled role of seepage and surface flow on bank retreat has long been neglected, partly due to the concealment and complexity of seepage erosion. To fill this gap, we set up a three-dimensional laboratory experiment to explore bank retreat process in response to seepage and surface flow. During each experiment, we measured the changes of total soil stress, matric suction, and water content within the bank, as well as flow velocity and suspended sediment concentration near the bank. Results show that a rapid decrease in matric suction, the bank toe undercutting consequent to seepage erosion, the formation of tension crack on the bank top, and the occurrence of toppling or shear failure is the typical sequence of the observed bank retreat process under seepage flow. The inclusion of surface flow erodes slump blocks and so promotes cantilever formation, leading to additional bank failure. Compared with the case where only seepage is considered, the frequency of toppling failure under the coupled effect of seepage and surface flow decreases, but the contribution to the bank retreat increases by 37 %. The time taken to collapse in three-dimensional experiments is at least 1.5 h earlier than that of two-dimensional experiments, indicating the importance of preferential flow pathways of seepage. Overall, this research illustrates how surface flow interacts with seepage flow to control bank retreat process and is indeed a first step toward a fully understanding of multifactor-driven bank retreat.

Recognition of Fluvial Bank Erosion Along the Main Stream of the Yangtze River

Recognizing the risk of fluvial bank erosion is an important challenge to ensure the early warning and prevention or control of bank collapse in river catchments, including in the Yangtze River. This study introduces a geomorphons-based algorithm to extract river bank erosion information by adjusting the flatness from multibeam echo-sounding data. The algorithm maps 10 subaqueous morphological elements, including the slope, footslope, flat, ridge, peak, valley, pit, spur, hollow, and shoulder. Twenty-one flatness values were used to build an interpretation strategy for the subaqueous features of riverbank erosion. The results show that the bank scarp, which is the erosion carrier, is covered by slope cells when the flatness is 10°. The scour pits and bank scars are indicated by pit cells near the bank and hollow cells in the bank slope at a flatness of 0°. Fluvial subaqueous dunes are considered an important factor accelerating bank erosion, particularly those near the bank toe; the critical flatness of the dunes was evaluated as 3°. The distribution of subaqueous morphological elements was analyzed and used to map the bank erosion inventory. The analysis results revealed that the near-bank zone, with a relatively large water depth, is prone to form large scour pits and a long bank scarp. Arc collapse tends to occur at the long bank scarp to shorten its length. The varied assignment of flatness values among terrestrial, marine, and fluvial environments is discussed, concluding that diversified flatness values significantly enable fluvial subaqueous morphology recognition. Consequently, this study provides a reference for the flatness-based recognition of fluvial morphological elements and enhances the targeting of subaqueous signs and risks of bank failure with a range of multibeam bathymetric data.

Coupled modeling of bed deformation and stability analysis on a typical vulnerable zone on the Ningxia reach of the Yellow River during flood season

AbstractThe Ningxia reach of the Yellow River (NRYR) is wide and shallow, and instability and damages are likely to occur at its vulnerable zone. In this study, based on the one‐dimensional hydro‐sediment dynamics, two‐dimensional hydro‐sediment dynamics and vulnerable zone stability analysis model, a coupled model was established to analyze the scouring risk of the vulnerable zones in the NRYR during flood season. Considering the morphological change of bank slope at the vulnerable zones caused by flow erosion, the seepage stability of a typical spur dyke and protection embankment under the water level fluctuation conditions was analyzed. To fully reflect the coupled scouring effect of flow and sediment, the water flow scouring intensity index α is proposed. A significant increase of water flow scouring intensity index α will result in bank toe scouring, while its significant decrease will lead to silting of the bank toe. The probability of instability failure of the bank for the spur dyke slope is greater during the flood recession period. Compared with the influence of the change of river water level in the flood season, the slip stability of the bank slope is more sensitive to the change of bank toe erosion.

Riverbank stabilization based on the modulation of the near bank turbulence scales

Sundarban area of the lower Gangetic plain experiences embankment failure almost every year due to the formation of toe undercuts. Waves generated due to the continuous action of wind and tidal currents are paramount in the growth and development of these undercuts. Existing literature suggests that grids are effective in modulating the scales of turbulence. The present investigation is carried out with the objective of looking into whether grids can be effective in controlling the undercutting process and thereby restraining the failure of these embankments. To explore this artefact, laboratory flume experiments were carried out using cylindrical grid placed near the toe of a cohesive bank. Turbulent 3-D velocity was measured using micro-Acoustic Doppler velocimeter (ADV) at the junction of the grid and at the near bank region to get insight into the governing mechanism of grid-influenced flow on the bank. The present investigation revealed that the installation of the cylindrical grids at the toe region of the bank is effective in modulating the scales of turbulence. The scales of Reynolds shear stress fluctuations showed a reduced magnitude due to the presence of near bank grid. The results show that the grid breaks the large scales (larger eddies) of turbulence into smaller eddies through eddy cascading process and thereby modulate the turbulent shear stresses. This probably slowed down the erosion rate preventing the formation of the undercuts and thus restraining bank/embankment failure. Thus, it is envisaged that the proposed methodology on implementation at the riverbanks would serve as an effective measure in the protection of these embankments.

Effects of vegetation at a bar confluence on river hydrodynamics: The case study of the Arno River at Greve junction

AbstractRiver bars often form at river confluences due to variation in flow discharges or in sediment transport capacity; once these bars are grown, they constitute favourable habitats for vegetation development. In this work, we analysed the effect of vegetation above confluence bars on the hydrodynamics of a river reach. The case study considered is the Arno River reach at the Greve junction, where confluence bars expanded towards the opposite bank. A two‐dimensional hydraulic model was implemented through BASEMENT software varying the flow discharge. Three‐dimensional topographic data were used to generate the calculation mesh. Dendrometric surveys were carried out to describe the current state of the vegetation. Seven different vegetative scenarios were considered for numerical simulations, depending on different vegetation management conditions. Such scenarios are characterised by various plant densities, diameters, heights and species (herbaceous, shrub and arboreal), and, accordingly, different formulations were used to estimate the Manning coefficients. The outcomes of this study illustrate that the denser vegetation settled on confluence bars, the more the backwater effect is emphasised and the more the flow is shifted toward the opposite banks of the confluence thus inducing possible erosion phenomena at the toe of the outer bank. Moreover, the observed large bar extensions are surprising, when considering the mild confluence angle and the very low discharge ratio. We showed that the vegetation may be the key driver of the junction hydrodynamics and that vegetated confluences might not follow the classic hydraulics‐related models which may describe only a formative configuration.

Assessment of land use impact and seepage erosion contributions to seasonal variations in riverbank stability: The Iju River, SW Nigeria

The Iju (Atuwara) River is an important component of the Owo River catchment (ORC), which supports the livelihood of millions of people in Lagos and Ogun States of southwestern Nigeria. However, rapid urbanisation and numerous anthropogenic activities have caused significant changes in the natural flow regime of the river, resulting in serious bank erosion. In many riparian areas, accelerated bank erosion has been attributed to the combined effects of seepage erosion and fluvial undercutting of the bank toe due to the hydraulic stress of the river on the bank. This research, therefore, investigated the combined effects of seepage erosion, riparian vegetation (root cohesion), tension crack, and land use/land cover (LULC) change on the stability of riverbanks on the Iju River, Nigeria. Multi-temporal LULC datasets acquired from remotely sensed Landsat images of 1999, 2009, and 2019 were used to map LULC changes in the ORC. Laboratory tests were conducted to determine the geotechnical properties of the riverbanks followed by bank stability analysis and evaluation of the erosion potential of the riverbanks using the Bank Stability and Toe Erosion Model (BSTEM) and Bank Erosion Hazard Index (BEHI), respectively. The BSTEM results indicate that the factor of safety (Fs) decreased with an increase in seepage undercutting distance (du), irrespective of the bank angle. The correlation of Fs with root cohesion (cr) and depth of tension crack (zc) shows that Fs was positively correlated with cr but decreased with an increase in zc. LULC change results show that the natural flow regimes of rivers within the ORC have been adversely affected by the combined decrease in vegetation and wetlands, with a corresponding increase in the spatial extents of the built-up area and cultivated land/open spaces. These research findings are essential for the development of a watershed-scale natural disaster management framework for the southwest ecoregion of Nigeria.

Effect of bulk density, age, and water content on the erosional strength of streambank soils

The purpose of this study is to investigate the influence of physical properties, more specifically the bulk density and water content, to the erosional strength of streambank soils. Thirty (30) soil samples were extracted from the crest, midbank and toe of the bank at Clear Creek in Iowa City, Iowa. Out of those thirty (30) samples, six (6) samples were tested in the standard soil laboratory for obtaining their bulk density and particle size distribution, six (6) samples were tested their bulk density and heterogeneity using Gamma radiation scanning, and eighteen (18) samples were tested their erosional strengthr*f. In addition, six (6) pure Kaolinite-clay samples were constructed with various degrees of consolidation or age and water content for measuring their T>-:f using conduit flume technique. The results of the conduit flume tests revealed an increasing trend in magnitude of Hf moving from the crest to the toe of the bank. The T<--t values were 1.57, 1.53, and 1.92 Pa for the crest, midbank, and toe soils from the left bank. In similar order, the Tc.f values were 1.46, 1.47, and 1.83 Pa for the soils from the right bank. A similar trend was obtained for the bulk density based on standard laboratory test and gamma radiation scanning. According to standard laboratory test, the average bulk density values for the crest, midbank, and toe of the right bank were 1299, 1618, and 1880 kg/m3. Similarly, based on gamma radiation technique, the average bulk density values for the crest, midbank, and toe of the right bank soils were 1273 kg/m3, 1594 kg/m3 and 1863 kg/m3, respectively. This agreement in the trend of Tr-f and bulk density suggests a positive correlation between those to parameters. The results of Kaolinite-clay sample experiments demonstrated that samples with higher degree of consolidation or more age would have higher ^V. In addition, the Kaolinite-clay samples with higher water content would have lower rct. These findings suggest the presence of spatial and temporal variability in Ta of streambank soils. Therefore, incorporating this Tc,i variability in modelling streambank erosion will give more accurate results.

Bank stability and toe erosion model as a decision tool for gully bank stabilization in sub humid Ethiopian highlands

Gullies that are expanding at alarming rate are responsible for the majority of soil losses in the (sub) humid highlands of Ethiopia. Few affordable and effective methods for gully erosion control are available in the highlands. The objective of the study was to develop cost-effective measures to halt gully expansion by determining stable-bank conditions under a variety of environmental situations using the Bank Stability and Toe Erosion Model (BSTEM). The study was carried out in the sub humid Debre Mawi watershed, located 30 km south of Lake Tana. Input data for the BSTEM model were collected using field surveys and soil sampling. After the BSTEM was tested on actual measured soil data, soil cohesion and internal friction angle were calibrated against observed gully bank retreat. Using the calibrated parameters, the model evaluated the stabilization of the existing gully bank under different scenarios in which groundwater table, bank angle and bank height, tension crack depth, vegetation, and toe protection were varied. Finally, the head-cut of the study gully was treated based on the model recommendation. The simulated results showed that a 5 m deep gully was stable under fully saturated conditions when the bank toe is protected, its upper surface is vegetated, and its bank angles do not exceed 45°. If the depth of the gully is less than 5 m or if its water table is deeper than 0.5 m, only regrading the gully bank to an angle of 45° can stabilize the gully. BSTEM showed to be an effective tool that can be used to evaluate gully control measures.

The effect of instream logs on river‐bank erosion: Field measurements of hydraulics and erosion rates

AbstractThis is the first substantial field measurement of river‐bank erosion around fallen logs in rivers. Whilst numerous studies have established that living trees can stabilize river banks, and that fallen trees can cause scour of the river bed, knowledge of bank erosion effects from logs is largely restricted to qualitative observations. Recent flume studies suggest that a single log can increase near‐bank velocity (and thus erosion) and this increase is related to the blockage ratio of the log and the distance between the log and bank. However, hydraulic interactions between logs can reduce this increase or even decrease the near‐bank velocity. These theories, developed in a straight flume, have not been tested in the field. We measured erosion rates (relative to controls) on river banks adjacent to 35 large logs for 2 years, and velocity distributions around 11 logs during a near‐bankfull flow in anabranching channels of the River Murray, SE Australia. These channels have abundant large instream logs, consistent bank material, and consistent regulated high flows. The field results generally supported the velocity changes caused by single and multiple logs in the flume studies, with single logs increasing near‐bank velocity, but with the hydraulic interactions between successive logs tending to reduce this increase. Flow patterns caused by logs adjacent to curved banks were more complicated as the local effects of logs reinforced or weakened recirculating flows. Instream logs did not change overall, average, bank erosion rates, but they tended to shift the erosion from bank top to bank toe. However, individual logs increased or decreased bank erosion rates in patterns that generally concur with the near‐bank velocity changes predicted in flume studies: that isolated logs increased erosion rates whilst hydraulically interacting logs did not increase erosion rates. © 2020 John Wiley &amp; Sons, Ltd.

A decadal‐scale numerical model for wandering, cobble‐bedded rivers subject to disturbance

AbstractAlluvial rivers are composed of self‐formed channels which are sensitive to disturbances in their flow and sediment‐supply regimes. Regime changes commonly occur over decadal and longer timescales and can be caused by anthropogenic alterations such as dam construction and removal. Advances in numerical modeling have increased our ability to explore geomorphic adjustments over long timescales; however, many models designed to be run for decades or longer assume that banks are immovable or that channel width is constant. Since river channels often respond to disturbance by adjusting their geometry, this is a significant shortcoming. To investigate the impact of long‐term sediment supply alterations on channel geometry and stability, we have adapted MAST‐1D, a reach‐scale bed evolution model, to incorporate functions for bank erosion, vegetation encroachment, and local avulsions. The model is designed for medium‐large, coarse multithreaded rivers and can be run over long (decades–centuries) timescales. Bank erosion is a function of the mobility and transport capacity for structurally‐important grains which protect the bank toe. Vegetation growth is proportional to point bar width and occurs during conditions of low shear stress. Local avulsions occur when aggradation causes channel depth to drop below a threshold. We apply the model to the Elwha River in Washington, USA with the goal of investigating if and when the river recovers from dam emplacement and removal. The Elwha was dammed for nearly 100 years, and then two dams were removed, releasing a large pulse of sediment. We have modeled the set of reaches between the two dams. Our simulations suggest that channel response to dam emplacement occurs gradually over several decades but that the channel recovers to near pre‐dam conditions within about a decade following the removal. The dams leave a lasting legacy on the floodplain, which does not completely recover, even after two centuries. © 2019 John Wiley &amp; Sons, Ltd.

Distinct patterns of bank erosion in a navigable regulated river

AbstractDistinct bankline patterns appeared after the removal of protection works along a navigable reach of the Meuse River. A series of oblique embayments now dominate the riverine landscape after ten years of bank erosion, but their location and asymmetry cannot be explained yet. This work analyses and integrates field measurements of flow, ship waves, bank composition, bed topography and historical maps to explain the observed patterns along two reaches of the river. An extraordinary low‐water‐level event generated by a ship accident provided the unique opportunity to also analyse the subaqueous bank topography.The results indicate that the formation of oblique embayments arises from the combination of floodplain heterogeneity, structured by scroll‐bar deposits, and the regulation of water levels, resulting in ship‐wave attack at a narrow range of bank elevation for 70% of the time. Substrate erodibility acts on the effectiveness of trees to slow down local bank erosion rates, which is possibly enhanced by a positive feedback between woody roots and cohesive soil. The strong regulation of water levels and the waves generated by the intense ship traffic produce an increasingly long mildly‐sloping terrace at the bank toe and progressively dominate the bank erosion process. This study demonstrates the important role of floodplain and scroll bar formation in shaping later bank erosion, which has implications for predictive numerical models, restoration strategies, and understanding the role of vegetation in bank erosion processes. © 2019 The Authors. Earth Surface Processes and Landforms published by John Wiley &amp; Sons Ltd

Riverbank Stability Assessment under River Water Level Changes and Hydraulic Erosion

The dominant mechanism of riverbank cantilever failure is soil erosion of the bank toe and near bank zone. This paper demonstrates that the shape of the riverbank cantilever failure depends on the properties of the soil and the fluctuation of the river water level (RWL). With a stable RWL, a riverbank with higher resistance force leads to failure with larger and deeper overhang erosion width. When RWL rises, a less cohesive soil bank will be eroded over a larger width and riverbank failure will occur earlier. With a low rate of rising RWL, riverbank failure may happen in a type of mass failure. With a high rate of rising RWL, a riverbank will fail in a type of overhang riverbank failure, with the soil erosion rate being the main affected factor.

Sidewall shear stress distribution effects on cohesive bank erosion in curved channels

A series of experiments were conducted to reveal the effects of the sidewall shear stress distribution (SSSD) on homogeneous cohesive bank erosion processes in a U-shaped flume. The three-dimensional flow velocities were measured in detail and the turbulent kinetic energy method was employed to estimate the SSSD. The experimental results showed that the SSSD changed with the discharge and the point of the maximum shear stress varied within a range of 0·15–0·75 of the relative water depth. The variation of underwater bank topography was found to be consistent with the SSSD and the location of the maximum erosion point was not at the bank toe. The dominant failure mechanisms were observed to be tensile and toppling failures. Furthermore, a simplified bank erosion model (SBEM) was developed with consideration of the SSSD. Compared with the bank stability and toe erosion model, the SBEM can provide a more accurate simulation of bank erosion processes. This study is expected to enrich general understanding of cohesive bank erosion processes in curved channels, which will help to formulate effective strategies for river regulation.

Design of fascines for riverbank protection in alpine rivers: Insight from flume experiments

We present the results of flume experiments specifically designed to investigate the conditions required for successful bank protection using fascines, considered in the early and critical stage of their installation (no developed root system), in the alpine context. A total of 145 runs were performed with erodible banks, considering different combinations of protection design (no protection, rip-raps, twigs), bed mobility (with or without bedload), discharge (from low to exceptional floods), and bend curvature radius. None of the runs showed any direct fascine grabbing by the flow observed; all destruction was the consequence of bank scouring, erosion and collapse around the structure. In all cases, most destructive effects resulted from water recirculation inside the bank. Thus, we conclude that all measures aiming to reduce water circulations during the first stage of the fascine construction and development are recommended. This include large bend curvature radii (when possible), fining of the filling material, use of antiscouring twigs, optimisation of the programming of the works with consideration of the hydrology (shape of hydrographs) and regular survey of the structure. Our experiments show that anti-scouring twigs have a real protective effect by modifying the local hydraulics and promoting sediment deposition at the bank toe.

An Experimental Study on Mechanisms for Sediment Transformation Due to Riverbank Collapse

Riverbank erosion is a natural process in rivers that can become exacerbated by direct and indirect human impacts. Unfortunately, riverbank degradation can cause societal impacts such as property loss and sedimentation of in-stream structures, as well as environmental impacts such as water quality impact. The frequency, magnitude, and impact of riverbank collapse events in China and worldwide are forecasted to increase under climate change. To understand and mitigate the risk of riverbank collapse, experimental/field data in real conditions are required to provide robust calibration and validation of hydraulic and mathematical models. This paper presents an experimental set of tests conducted to characterize riverbank erosion and sediment transport for banks with slopes of 45°, 60°, 75°, and 90° and quantify the amount of sediments transported by the river, deposited within the bank toe or settled in the riverbed after having been removed due to erosion. The results showed interesting comprehension about the characterization of riverbank erosion and sediment transport along the river. These insights can be used for calibration and validation of new and existing numerical models.