Riverbank Stability Research Articles

Review on Riverbank Soil Collapse

Bank slope collapse is a kind of natural phenomenon which commonly existed on both sides of alluvial plain rivers. The mechanism of bank collapse is complex, and it is an interdisciplinary frontier research subject. The collapse of the bank slope will lead to the instability of river regime and frequent changes of erosion and siltation, which will cause great harm to river regulation and people's livelihood. Through review of river bank soil collapse at home and abroad, it is concluded that the main influencing factors of river bank soil collapse are the action of water flow and the soil structure of river bank. In addition, the stability of river bank and the numerical simulation of river bank collapse are also studied by scholars. In view of the above research results, the deficiencies of the current research are pointed out and the research directions that should be followed in the future are put forward.

Experimental study of riverbank protection with bio-engineering techniques

River management implies in many situation to control the river bank stability. Bio-engineering techniques are used as an alternative to rip-rap. These techniques are not new but a renewed interest was observed during the last decade. However the design of such bank protection is still largely based an expert evaluation of each situation, and we still crudely lack a real state of the art, based on mechanistic consideration of forces exerted by the river. We present the results of preliminary flume experiments aiming to study the resistance of river bank protections using bio-engineering techniques. The final applied objectives will be to propose a framework for a good use of such technique, accounting for the river morphodynamics context.

Modelling of the retreat process of composite riverbank in the Jingjiang Reach using the improved BSTEM

AbstractBank retreat in the Jingjiang Reach is closely related not only to the near‐bank intensity of fluvial erosion but also to the composition and mechanical properties of bank soils. Therefore, it is necessary to correctly simulate bank retreat to determine the characteristics of fluvial processes in the Jingjiang Reach. The current version of bank stability and toe erosion model (5.4) was improved to predict riverbank retreat, by inputting a dynamic water table, and calculating the approximation of the distribution of dynamic pore water pressure in the soil near the river bank face, and considering the depositional form of the failed blocks, which is assumedly based on a triangular distribution, with the slope approximately equalling the stable submerged bank slope and half of collapsed volume deposited in the bank‐toe region. The degrees of riverbank stability at Jing34 were calculated using the improved bank stability and toe erosion model. The results indicate the following trends: (a) the degrees of riverbank stability were high during the dry season and the rising stage, which led to minimal bank failure, and (b) the stability degrees were low during the flood season and the recession stage, with the events of bank collapse occurring frequently, which belonged to a stage of intensive bank erosion. Considering the effects of bank‐toe erosion, water table lag, and the depositional form of the collapsed bank soil, the bank‐retreat process was simulated at the right riverbank of Jing34. The model‐predicted results exhibit close agreement with the measured data, including the total bank‐retreat width and the collapsed bank profile. A sensitivity analysis was conducted to determine the quantitative effects of toe erosion and water table lag on the degree of bank stability. The calculated results for toe erosion indicate that the amount of toe erosion was largest during the flood season, which was a primary reason for bank failure. The influence of water table lag on the degree of stability demonstrates that water table lag was an important cause of bank failure during the recession stage.

Influence of riverbank stabilization techniques on taxonomic and functional macrobenthic communities

Riverbank erosion is linked to increasing risks in piedmont areas due to urbanization and hydromorphological alterations of rivers. Changes in riparian vegetation and in sediment dynamics modify aquatic macroinvertebrate communities. In this context, riverbank stabilization is a major issue in the conservation of stream ecosystem functioning. In this study, we aimed at assessing the impacts of riverbank stabilization techniques on the taxonomic and functional properties of benthic macroinvertebrate communities living in alpine mountain streams. For this purpose, the effects of four riverbank stabilization techniques (riprap, mixed, cribwall, and fascine) on the taxonomic richness and biological traits involved in the main ecological processes were tested and compared with natural bank conditions. Overall, the macroinvertebrate richness was lower in stabilized banks than in natural conditions, and communities welcomed on natural banks were significantly different from those found on managed banks. The biological trait composition such as “maximum potential size,” “life cycle duration,” “reproduction,” “feeding habits,” and “trophic status” differed significantly among riverbanks, especially between natural banks and the riprap, mixed, and cribwall trio. In a context of macroinvertebrate biodiversity and functional restoration, we can advocate the fascine technique as the most suitable technique tested.

Application of ecohydraulic bank protection model to improve river bank stability and biotic community in Surabaya River

Ecohydraulic river bank protection design was developed as ECO-RIPRAP model and has been applied along 100 meter length to restore accelerated erosion sites in Surabaya River at Wringinanom and Klubuk. The model combined re-profiled and re-vegetated bank with rock toe reinforcement and addition of log groynes at 10 meter length interval. Various native plant species were planted on bank slopes, including water plants Ipomoea aquatica and Pistia stratiotes , grasses and shrubs Ipomoea carnea, Pluchea indica, Saccharum spontaneum, Arundo donax, and native tree species Ficus glomerata, Bambusa arundinacea, Dendrocalamus asper, Bambusa vulgaris, Ficus benjamina, Dillenia indica, Psidium guajava, Arthocarpus camansi, Arthocarpus elasticus, Hibiscus mutabilis, Nauclea sp., Inocarpus edulis, and Syzygium polyanthum. The river bank morphology after ECO-RIPRAP application showed alteration from erosion to sedimentation due to rock toe enforcement, log groynes protection, and increase of plant cover on littoral banks that decreased near bank velocity. The macro-invertebrate community shown increase of taxa richness, EPT richness, %EPT and %Atyidae, but decrease of %Chironomidae at restored sites. The fish community shown increase of taxa richness, increase of abundance by 54.2%, increase of Pangasius micronemus abundance by 25.6%, and increase of Hemibragus nemurus abundance by 6.3 % at restored reach. Rare fish species thrive back at restored area, namely Oxyeleotris marmorata , Mastacembelus unicolor and Hampala macrolepidota .

Flow Hydrodynamics across Open Channel Flows with Riparian Zones: Implications for Riverbank Stability

Riverbank vegetation is of high importance both for preserving the form (morphology) and function (ecology) of natural river systems. Revegetation of riverbanks is commonly used as a means of stream rehabilitation and management of bank instability and erosion. In this experimental study, the effect of different riverbank vegetation densities on flow hydrodynamics across the channel, including the riparian zone, are reported and discussed. The configuration of vegetation elements follows either linear or staggered arrangements as vegetation density is progressively increased, within a representative range of vegetation densities found in nature. Hydrodynamic measurements including mean streamwise velocity and turbulent intensity flow profiles are recorded via acoustic Doppler velocimetry (ADV)—both at the main channel and within the riverbank. These results show that for the main channel and the toe of riverbank, turbulence intensity for the low densities (λ ≈ 0 to 0.12 m−1) can increase up to 40% compared the case of high densities (λ = 0.94 to 1.9 m−1). Further analysis of these data allowed the estimation of bed-shear stresses, demonstrating 84% and 23% increase at the main channel and near the toe region, for increasing densities (λ = 0 to 1.9 m−1). Quantifying these hydrodynamic effects is important for assessing the contribution of physically representative ranges of riparian vegetation densities on hydrogeomorphologic feedback.

Spatially Dependent Responses of a Large‐River Fish Assemblage to Bank Stabilization and Side Channels

AbstractThe alteration of rivers by anthropogenic bank stabilization to prevent the erosion of economically valuable lands and structures has become commonplace. However, such alteration has ambiguous consequences for fish assemblages, especially in large rivers. Because most large, temperate rivers have impoundments, it can be difficult to separate the influences of bank stabilization structures from those of main‐stem impoundments, especially because both stabilization structures and impoundments can cause side‐channel loss. Few large rivers are free flowing and retain extensive side channels, but the Yellowstone River (our study area) is one such river. We hypothesized that in this river (1) bank stabilization has changed fish assemblage structure by altering habitats, (2) side‐channel availability has influenced fish assemblage structure by providing habitat heterogeneity, and (3) the influences of bank stabilization and side channels on fish assemblages were spatially scale dependent. We developed a spatially explicit framework to test these hypotheses. Fish assemblage structure varied with the extent of bank stabilization and the availability of side channels; however, not all assemblage subsets were influenced. Nevertheless, bank stabilization and side channels had different and sometimes opposite influences on the fish assemblage. The effects of side channels on fish were more consistent and widespread than those of bank stabilization; the catches of more fishes were positively correlated with side‐channel availability than with the extent of bank stabilization. The influences of bank stabilization and side channels on the relative abundances of fish also varied, depending on species and river bend geomorphology. The variation in river morphology probably contributed to the assemblage differences between stabilized and reference river bends; stabilized alluvial pools were deeper than reference alluvial pools, but the depths of stabilized and reference bluff pools did not differ. The strengths of the relationships among fish assemblages, bank stabilization, and side channels were spatially scale dependent; optimum spatial scales ranged from less than 200 m to 3,200 m up‐ and downstream, suggesting that bank stabilization and side channels influenced fish assemblages across multiple spatial scales.Received October 7, 2016; accepted January 23, 2017 Published online July 31, 2017

COMPARAÇÃO DAS CARACTERÍSTICAS BIOTÉCNICAS DE <i>Sebastiania schottiana</i> (Müll. Arg.) Müll. Arg., <i>Phyllanthus sellowianus</i> (Klotzscg) Müll. Arg., <i>Salix humboldtiana</i> Willd., E <i>Salix</i> x <i>rubens</i> Shrank

O presente trabalho teve como objetivo fazer um estudo comparativo entre as características biotécnicas de Sebastiania schottiana (Müll. Arg.) Müll. Arg., Phyllanthus sellowianus (Klotzscg) Müll. Arg., Salix humboldtiana Willd., e Salix x rubens Shrank. Essas espécies apresentaram-se promissoras para estabilização de taludes fluviais e recuperação de cursos de água em estudos anteriores. O experimento foi instalado às margens de um arroio, em 2008 no município de São João do Polêsine, Rio Grande do Sul. As variáveis analisadas foram: taxa de sobrevivência no campo (%); número, diâmetro, comprimento, somatório dos brotos primários e comprimento do maior broto primário; número, comprimento dos brotos secundários e somatório do comprimento dos brotos secundários. Dentre as espécies analisadas, Phyllanthus sellowianus apresentou os melhores resultados para cinco características avaliadas, tornando-se assim, dentre as características avaliadas, a espécie mais indicada para a estabilização e recuperação de cursos de água na região estudada.

Multi‐criteria‐based Plant Species Selection for Gully and Riverbank Stabilization in a Sub‐humid Tropical Area

AbstractSelection of appropriate plant species for rehabilitation of degraded lands while fulfilling socio‐economic interests of local communities is one of the decision‐making challenges. This research was undertaken to select multipurpose trees, shrubs and grasses to stabilize degraded lands in the Gilgel Gibe catchment of Southwest Ethiopia, situated in the sub‐humid tropics. Two multi‐criteria decision analysis methods, analytical hierarchy process and simple multi‐attribute rating technique, integrated in the excel‐based multi‐criteria tree selection tool, were used. Focus group discussions were held with experts and local communities to prioritize 40 plant species from a preselected regional pool of 129 species, using six criteria groups containing 47 individual criteria. Root characteristics of the top 9 ranked plants were studied for triangulating the multi‐criteria decision analysis results. Both local communities and experts gave priority to indigenous trees over shrubs and grasses as the best five species for multipurpose use, whereas the top 5 species prioritized for riverbank stabilization contained both trees and grasses. In contrast, communities preferred indigenous trees, and experts selected grasses as the best five species for gully stabilization. The root system characterization revealed that the five top‐ranked multipurpose species also have the required root characteristics for effectively reinforcing unstable slopes. However, communities prefer to plant Eucalyptus and Grevillea trees because of their short‐term economic benefits although they understood the multipurpose value of indigenous plants. The trade‐off between direct economic benefit and multipurpose benefits could be solved by awareness creation, incentives to communities and policy re‐enforcement. Copyright © 2017 John Wiley & Sons, Ltd.

Modification of river meandering by tropical deforestation

Tropical forests are the only forest biome to have experienced increased rates of forest loss during the past decade because of global demands for food and biofuels. The implications of such extensive forest clearing on the dynamics of tropical river systems remain relatively unknown, despite significant progress in our understanding of the role of trees in riverbank stability. Here, we document rates of deforestation and corresponding average annual rates of riverbank erosion along the freely meandering Kinabatangan River in Sabah, Malaysia, from Landsat satellite imagery spanning A.D. 1989–2014. We estimate that deforestation removed over half of the river’s floodplain forest and up to 30% of its riparian cover, which increased rates of riverbank erosion by >23% within our study reaches. Further, the correlation between the magnitude of planform curvature and rates of riverbank erosion only became strongly positive and significant following deforestation, suggesting an important role of forests in the evolution of meandering rivers, even when riverbank heights exceed the depth of root penetration.

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.

Study on Mechanical Properties of Concrete with Manufactured Sand and Bagasse Ash

Background/Objectives: In the construction of structures river sand used as fine aggregate in concrete for centuries. River sand is not a renewable natural resource. In most of the area, river sand has been excessively exploited, which has endangered the stability of river banks and the safety of bridges, and creates an environmental problem. Hence, minimization of the use of river sand inevitable. Methods: In this study, the Manufactured sand (M-sand), produced by crushing rock depositions as a fine aggregate used in concrete. The M-sand is more angular and has rougher surface texture than river sand. In the M60 grade concrete, M-sand is used as fine aggregate and Bagasse Ash (BA) used as a pozzolanic material for the partial replacement of cement. Bagasse ash has partially replaced by the ratio of 0%, 10%, 20%, 30% and 40% by volume of cementation material in concrete. M-sand has been replaced by fully by volume of fine aggregate. In this investigation, to study the properties of concrete test likes Compressive Strength, Tensile Strength, Flexural Strength, Young’s modulus and Workability of concrete were carried out. The effects of M-sand on mechanical properties, studies with and without partial replacement of Bagasse ash were studies at the age of 7, 28 days. Findings: The test results show that the incorporation of Bagasse Ash up to 20% replacement level increases the mechanical properties of concrete. The variation in use of M-sand in concrete as compared to the river sand with the Bagasse Ash shows the minimum variation in the strength properties. Applications/Improvement: From this study, it is observed that the use of M-sand in high strength concrete can be use for the replacement of fine aggregate in M60 concrete. Use of Bagasse ash up to 20-30 % can be effectively used in concrete with or without the addition of M-sand, where the Bagasse ash available in plenty.

Impacts of river bank stabilization using riprap on fish habitat in two contrasting environments

AbstractRiverbank stabilization using rock riprap is commonly used for protecting road and bridge structures from fluvial erosion. However, little is known about how streams adjust to such perturbation or how this can affect fish habitat in different fluvial environments, particularly for non‐salmonid species in small streams. The objective of this study is to assess impacts of riprap on fish habitat quantity and quality through a pairwise comparison of 27 stabilized and non‐stabilized stream reaches in two physiographic regions, the Saint Lawrence Lowlands and the Appalachian highlands of Montérégie‐Est (Quebec, Canada). Both quantitative (Hydro‐morphological Index of Diversity, HMID) and qualitative (Qualitative Habitat Evaluation Index, QHEI) fish habitat assessment techniques are applied in order to compare results between methods. For each stream reach depth and velocity were measured to calculate HMID. In‐stream cover (woody debris, overhanging vegetation, undercut banks, aquatic macrophytes) and habitat units (pools, riffles, runs, glides) were also documented and used to determine QHEI. Results show that overall bank stabilization using riprap at bridge and stream crossings alters fish habitat characteristics. Loss of in‐stream covers and riparian vegetation lower QHEI scores at stabilized reaches, especially in more pristine Appalachian streams, but has less impact on already altered straightened Lowlands streams. In this latter context, some positive alterations of fish habitat were observed in riprapped reaches due to the coarsening of the substrate and an induced increase of slope. The two metrics (HMID and QHEI) revealed similar differences between stabilized and non‐stabilized sites for Lowlands sites, but their level of agreement was much less in the Appalachian streams, suggesting caution when interpreting habitat quality results based on a single metric. Copyright © 2016 John Wiley & Sons, Ltd.

Soil-Root System Withholding Strength for River Bank Stability

The ability of vegetation to stabilise soils is frequently employed in slope stabilisation projects including riverbank restoration activity. Soil block samples permeated with roots of Bermuda Grass commonly used for remediation and riverbank restoration were tested in a direct shear apparatus. Shear stress results of rooted soils were compared with results of un-vegetated soil bloc—s with similar soil types. The increase of shear strength was determined by comparing shear stresses at speciic horizontal displacements. The relative strength increase at the same displacement was 27.3 kPa compared to 19.1 kPa for un-vegetated soil at a displacement of 13.3cm (Location 3). The relative strength increase at the same displacement of 13.3cm was 43.5% for Location 1 and 42.4% for Location 2. The shear stresses in most of the blocks with roots were still increasing at the end of the test (maximum displacement of about 15cm). These conservative root biomass values and the shearing resistance obtained can be used in the assessment of the stability of the existing vegetated slopes and in the design of vegetated riverbanks.

On the role of partially saturated soil strength in the stability analysis of a river embankment under steady-state and transient seepage conditions

River flood risk is considered being one of the most costly hazards in Europe and under a further major potential impact of climate change, in combination with land-use changes and water management practices, flood risk is expected to increase for many river basins. In engineering practice, the design of river embankments is usually performed using simplified approaches, considering steady-state flow conditions induced by the retained water and almost neglecting issues related to partially saturated soils, thus leading to potentially heavily over conservative results of stability analyses. To provide a realistic assessment of river bank stability conditions and to get a more accurate prediction of flood risk it is necessary to consider river bank soil behaviour at different saturation degrees in connection with transient seepage flow. A numerical study on stability conditions of a specific river embankment focusing on the partially saturated soil strength contribution is presented herein. Seepage and stability analyses have been carried out using the information collected on river Secchia flooding case study, occurred north of the city of Modena (Italy) in January 2014. Limit equilibrium method has been adopted for assessing the overall stability in steady-state and transient flow conditions. Useful indications for accounting unsaturated soil strength in similar circumstances are finally provided in the paper.

Assessing River Embankment Stability Under Transient Seepage Conditions

The evaluation of riverbank stability is a fundamental problem in flood risk management, representing a critical task for engineering practice. Soil heterogeneity together with initial and boundary conditions are among the crucial issues that should be considered to obtain an accurate solution of the problem. Generally, attention and efforts are mostly devoted to the soil characterization, the hydrometric level forecasts and the estimation of the rainfall intensity, while in situ measurements usually receive less attention. Nevertheless, suction and soil water content have a strong influence on the reliability of seepage and stability analyses. A preliminary study aiming at the design of a monitoring system for the measurement of soil moisture and suction in the unsaturated silty soils of a river embankment has been carried out, with the purpose of linking the collected data to the boundary conditions and hence obtaining a more accurate estimate of the riverbank probability of failure. Furthermore, a general outline of the research project, its methodology and application are presented in the paper.

Human impact on plant biodiversity in functional floodplains of heavily modified rivers – A comparative study along German Federal Waterways

Rivers and their floodplains have been strongly influenced by human actions, such as river training measures, flow regulation, bank stabilization, or intensive land use. These alterations threaten the biodiversity of floodplains. While the effects of individual factors on plant species composition and diversity in riparian systems have been frequently studied, it is yet unknown how multiple stressors act in concert and whether the effects remain visible across regions.We chose the floodplains of German Federal Waterways (rivers with a high frequency of shipping traffic) to study the main drivers of plant species composition and biodiversity along heavily modified rivers and aimed to show whether natural differences obscure the effects of human alterations. We recorded the vegetation of river banks, grassland, and alluvial forest fragments in 20 study sites distributed across Germany.Species composition differed from natural floodplain alliances and showed a trend towards terrestrialization and an increase of common species that show no specific preference for floodplain habitats. Despite natural differences such as topography and climate having the strongest influence on plant composition and diversity, the effects of anthropogenic influence (e.g. land use, shipping traffic) remained visible. River construction tended to increase species diversity since the terrestrial species pool is bigger than the one of floodplain specialists. For restoration and ecological river management not only species numbers but their composition and ecological specifics should be considered, and local conditions need to be taken into account.

A comprehensive fluvial geomorphology study of riverbank erosion on the Red River in Winnipeg, Manitoba, Canada

Summary Riverbank erosion on the Red River in Winnipeg, Manitoba has raised concerns over the last 20 years and more. Although several recent studies have shown that fluvial erosion can reduce riverbank stability and promote geotechnical slope failure, there are too few that have focused on this phenomenon. The present study includes field measurements, experimental testing, and numerical modelling to quantify fluvial erosion through a 10 km reach of the Red River. Results have shown that seasonal freeze–thaw processes can dramatically reduce the critical shear stress and increase erodibility of the riverbanks. Moreover, a simple method has been employed using hydrodynamic numerical models to define the applied shear stresses on the river banks based on the river water level, which will be useful for further research and design purposes. The TEMP/W numerical model was used to define seasonal frost depth to estimate freeze–thaw effects. Finally all field measurements, experimental and numerical models results were used to predict annual fluvial erosion through this reach of the river.

Flow, turbulence, and drag associated with engineered log jams in a fixed-bed experimental channel

Engineered log jams (ELJs) have become attractive alternatives for river restoration and bank stabilization programs. Yet the effects of ELJs on turbulent flow and the fluid forces acting on the ELJs are not well known, and such information could inform design criteria. In this study, a fixed-bed physical model was constructed to assess the introduction of ELJs along the Big Sioux River, SD. Two ELJ types were examined, referred to as ELJ-1 and ELJ-2. Both types were deflector jams, where ELJ-1 was rectangular and ELJ-2 was triangular, and oriented with one side attached to the channel bank. They were deployed either as single structures or in groups of two or three on the same side of the channel and at different separation distances. Results show that (1) time–mean and turbulent velocities and bed shear stresses were measurably altered near the ELJ, but spatially averaged flow just upstream and downstream of the structure was unaffected; (2) streamwise drag forces measured for the ELJs were significantly larger than the transverse forces, and the derived drag coefficients for the single structures were 2.72±0.19 for ELJ-1 and 1.60±0.37 for ELJ-2; and (3) the presence of an upstream structure created a near-bank wake region that extended a distance of more than 30 flow depths downstream, which greatly reduced drag forces and drag coefficients observed for the downstream structure by as much as 80%. These observations are further evidence of the efficacy of ELJs in providing near-structure scour pool development and bank protection downstream, and they can be used to inform and assess the design of ELJs for use in river restoration and bank stabilization projects.

An endangered reed, Arundo donaciformis, in a dynamic urban environment: The need for interdisciplinary conservation proposals

The expansion of urban environments is a major cause of species decline. Regulatory protection of rare species leads however to major conflicts between urban development and species protection. Here, we develop an interdisciplinary study to address three main issues concerning a legally protected endemic reed, Arundo donaciformis (Poaceae), threatened by urban development of the town of Fréjus (Mediterranean France). First, we found an absence of genetic variation across the whole range of the species and that this species has a generalist ecological niche in ruderal habitats. These findings should facilitate its practical conservation. Second, a diachronic study revealed a decline of 50% of species distribution in the last twenty years. However, this species plays a dominant structural role in the urban network of green ways and on the banks of watercourses. It thus provides ecological services associated with riverbank stabilization and natural corridors between peripheral natural areas and urban green spaces. Third, sociological interviews revealed two contrasting perceptions of the species among local actors who view the plant either as a rare endemic species in regression or as a highly resistant, even invasive, weed of urban wastelands. Moreover, this protected species is quasi-absent from urban planning documents and local actors show little comprehension of the need for conservation management, illustrative of another case of the “knowing-doing” gap. In the dynamic urban environment of a Mediterranean town, this species requires pragmatic collaboration that complements scientific information with local knowledge and perceptions in order to enhance links among stakeholders and implement sustained conservation action.