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Sediment dredging has been an ever‐growing issue, especially in developing nations with high demand for concrete filler material. River systems are adversely affected by sediment mining, resulting in decreased stability of the riverbed and riverbanks. Nature‐based solutions for riverbank erosion have been a research topic that has led to the proposal of vegetation on the riverbanks. However, little is known about the extent of riverbank vegetation required to negate the devastating effects of sediment mining because dense vegetation severely affects the flow structure and becomes a waste trap. This experimental study uses sparsely dense, flexible, and bladed vegetation to study the annulment effects of vegetation against the existing mining pit. Near‐bed turbulence and sediment transport have increased in the test section in the presence of a mining pit. The increase in near‐bed streamwise and transverse Reynolds shear stresses helped us understand the increased sediment movement in streamwise and lateral directions. The morphology of the test section showed increased riverbed erosion at the beginning of the test segment. The entire cross‐section was levelled at the end of the test section, and aggradation was downstream of the test segment. In contrast, in the vegetated riverbank case, the initial profile of the bank was almost unchanged for the same discharge of flow and upstream sand pit. The sparse vegetation overperformed the intended negation effects. This study establishes that sparse vegetation would perform better in maintaining the channel morphology, which otherwise in dense vegetation would have faced a high erosion rate in the main channel while giving the same protection to the riverbanks. [ABSTRACT FROM AUTHOR]

Since the 2008 Wenchuan (Ms. 8.0) Earthquake, the foreland rivers of the Longmen Mountains have suffered from significant bed degradation, among which the Shi‐ting River has experienced the largest local degradation of more than 20 m in 7 years. Potential reasons of the dramatic degradation include: (a) sediment disconnectivity due to in‐channel weirs; (b) the mobilization effect on gravel of an increased sand supply as a result of earthquake‐induced landslides; and (c) sediment extraction due to intensive mining. In this paper, we study the complex interaction among the above‐mentioned factors in the Shi‐ting River, using a one‐dimensional river morphodynamic model. Simulation results show that in‐channel weirs can reduce bedload transport and lead to bed degradation that is proportional to weir height. When coupled with additional sand supply, the weirs preferentially trap gravel and deliver sand, augmenting the downstream mobility of gravel and thus the degradation. For the Shi‐ting River, the simulated bed degradation agrees well with the observation when an annual sediment mining of 16 million tons is implemented in the simulation, along with the effects of in‐channel weirs and sand supply. The contribution of sediment mining is one order of magnitude larger than the coupling effect of weirs and sand supply. Both the simulation and observation show that the largest bed degradation occurs downstream of the Renmin Weir, due to the large spatial interval between the Renmin Weir and the next grade control structure. Key Points: Sediment mining is likely the key factor causing dramatic bed degradation in the Shi‐ting River, ChinaThis degradation was abetted, but not primarily caused by earthquake‐derived sand mobilizing gravel, as proposed previouslyWeirs preferentially trap gravel and deliver sand, which enhances the mobility of gravel by sand [ABSTRACT FROM AUTHOR]

Excessive mining of gravel and sand from river bed leads to degradation, lowering of the groundwater table, environmental loss, damage to hydraulic structures, etc. The morphological process along the river can create a neurotic river system that reduces the lifespan of the hydraulic structures and flora and fauna. The sediment mining pit in the river is mobile due to the high exchange rate of local and transported material. This paper evaluates existing equations for predicting temporal and spatial migration of upstream nick of the sediment mining pits. The accuracies of the selected existing equations were checked using graphical and statistical approaches. The results reveal that the equation proposed by Lee et al. predicts the migration speed of upstream nick of the sediment mining pit better than the other equations with 37.04% of the total data within ±30% error lines. The equation proposed by Barman et al. stands at the second position based on correlation coefficient and other statistical indices values. The dimensionless parameters, the ratio of shear velocity and critical shear velocity, the ratio of pit depth to approach depth, and the ratio of pit length and width mostly govern the migration speed of upstream nick of the sediment mining pit. [ABSTRACT FROM AUTHOR]

Lignocellulose-bearing sediments are legacies of the previously unregulated wastewater discharge from the pulp and paper industry, causing large quantities of toxic organic waste on the Baltic Sea floor and on the bottom of rivers and lakes. Several km2 are covered with deposits of lignocellulosic residues, typically heavily contaminated with complex mixtures of organic and inorganic pollutants, posing a serious threat to human and ecological health. The high toxicity and the large volume of the polluted material are challenges for remediation endeavours. The lignocellulosic material is also a considerable bioresource with a high energy density, and due to its quantity, it could appeal to commercialization as feedstock for various marketable goods. This study sets out to explore the potential of using this polluted material as a resource for industrial production at the same time as it is detoxified. Information about modern production methods for lignocellulosic material that can be adapted to a polluted feedstock is reviewed. Biochemical methods such as composting, anaerobic digestion, as well as, thermochemical methods, for instance, HTC, HTL, pyrolysis, gasification and torrefaction have been assessed. Potential products from lignocellulose-bearing sediment material include biochar, liquid and gaseous biofuels, growing substrate. The use of a contaminated feedstock may make the process more expensive, but the suggested methods should be seen as an alternative to remediation methods that only involve costs. Several experiments were highlighted that support the conception that combined remediation and generation of marketable goods may be an appropriate way to address polluted lignocellulose-bearing sediments. [ABSTRACT FROM AUTHOR]

Excessive extraction of gravel and sand material from streams leads to major changes in ecosystems, failure of hydraulic structures, lowering of the groundwater table, morphological changes in rivers, etc. Experiments were conducted in this study to investigate spatio-temporal morphological changes in trapezoidal sediment mining pits of different dimensions and composed of cohesionless sediment. Sediment mining pit evolution is described in two phases, namely an expansion and a migration phase. At the initiation of the flow, the pit expands rapidly, and such expansion is higher for a deeper pit. During the expansion phase, maximum residual depth is found at the upstream edge of the pit. The migration speed of a pit during the migration phase is slow in the early flow stage and increases until the pit is filled with sediment. During the migration phase, the maximum residual depth decreases and shifts to the downstream edge of the pit. During the expansion phase, the downstream nick preserves a similar angle to the angle of repose of the bed material, but the upstream nick preserves a similar angle during the migration phase. The filling rate of a sediment mining pit is mostly determined by the pit depth and the bedload transport index. Regression relationships were proposed for estimating expansion rate, migration speed, upstream and downstream expansion lengths, filling and residual depths, and effective length of the mining pit. The existing equations for the computation of migration speed of the sediment mining pit were checked for their performance using the present study data. The performance results show that the proposed equation predicts migration speed more accurately than the existing equations. [ABSTRACT FROM AUTHOR]

Abstract: The development of alternate bars in channelized rivers can be explained theoretically as an instability of the riverbed when the active channel width to depth ratio exceeds a threshold. However, the development of a vegetation cover on the alternate bars of some channelized rivers and its interactions with bar morphology have not been investigated in detail. Our study focused on the co‐evolution of alternate bars and vegetation along a 33 km reach of the Isère River, France. We analysed historical information to investigate the development of alternate bars and their colonization by vegetation within a straightened, embanked river subject to flow regulation, sediment mining, and vegetation management. Over an 80 year period, bar density decreased, bar length increased, and bar mobility slowed. Vegetation encroachment across bar surfaces accompanied these temporal changes and, once established, vegetation cover persisted, shifting the overall system from an unvegetated to a vegetated dynamic equilibrium state. The unvegetated morphodynamics of the impressively regular sequence of alternate bars that developed in the Isère following channelization is consistent with previous theoretical morphodynamic work. However, the apparent triggering dynamics of vegetation colonization needs to be investigated, based on complex biophysical instability processes. If instability related to vegetation colonization is confirmed, further work needs to focus on the relevance of initial conditions for this instability, and on related feedback effects such as how the morphodynamics of bare‐sediment alternate bars may have affected vegetation development and, in turn, how vegetation has created a new dynamic equilibrium state. Copyright © 2018 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A large proportion of the uncertainty surrounding catchment sediment budget modelling has been attributed to sediment supplied from riverbank erosion. Some of the variables influencing riverbank erosion are bend curvature, specific streampower, riparian vegetation, and in some instances sand and gravel extraction. The empirical relationship between these variables and observed riverbank erosion across 78 km of the Upper Brisbane River, Australia was investigated. No significant relationship was found between curvature, specific streampower and riverbank erosion. The role of riparian vegetation relative to sediment supply from riverbank erosion varied with spatial location, susceptibility of a reach to erosion, and human disturbance such as sand and gravel extraction. Despite not having data on substrate type the model described approximately 37% of the variation in observed riverbank erosion. It appears that inclusion of a management practice factor in riverbank erosion models is justified, where appropriate, and may improve model performance. [ABSTRACT FROM AUTHOR]

This study aims to experimentally and numerically investigate the fluvial processes of channels disturbed through sand or gravel mining. A two-dimensional numerical model is applied to simulate flume experiments. A moving boundary-fitted coordinate system is used to describe the channel changes. As a numerical scheme, the cubic interpolated pseudoparticle method is used to calculate the flow field and bed changes, which introduces little numerical diffusion. The numerical model is verified with experimental data. The inflow sediment from the upstream is trapped into a pit and the sediment deposit wedge migrated to the downstream with a steep submerged angle of repose. The numerical and experimental results show that the sediment deposit wedge in the pit migrates to the downstream under the condition of steady state. The adjustment time within the disturbed channels increases as the dimension of the pit is increased. The sediment mining pit migrates with speed in the steep channel. Moreover, the numerical experiments show that the migration speed is proportional to the sediment inflow. And the disturbed channels by the sediment mining are affected by the sediment inflow conditions of the upstream and adjusted to the new state of equilibrium. [ABSTRACT FROM AUTHOR]

The article reports on the study conducted on Brenta River to reconstruct the channel adjustments of the river in Italy. The research was also undertaken to analyze the present condition of the water form in terms of bedload transport and sediment sources. Scientists found that dramatic channel adjustments occurred in response to an alteration of sediment fluxes caused by human intervention between 1950s and 1980s. Researchers found that dominant process undertaken in the river includes incision and different human activities in the place is responsible for the dramatic impact on the river including the impact on flow and sediment regimes. The results of the study conducted by researchers is useful in addressing channel maintenance and restoration of Brenta River.

In-stream sediment mining and feeding inevitably change the sediment budget of an alluvial river, and may substantially alter its hydraulics and morphology. These alterations can have variable effects on fluvial habitat. Minimization of the detrimental effects and maximization of the beneficial impacts require a quantitative understanding of the complicated interaction between flow, sediment transport and morphological evolution. However, existing numerical river models have been developed for purely natural fluvial processes, and are rarely, if ever, applicable where interactive sediment mining and feeding take place. This paper presents numerical models for alluvial rivers subject to interactive sediment mining and feeding, within the context of shallow water hydrodynamics. The theoretical framework of two- and one-dimensional models is provided from conservation laws, and closure requirements are briefly addressed. The present models are distinguished from previous ones because of the complete continuity equations for the water and sediment phases and bed material, which are scrutinized under idealized scenarios with known analytical features. The continuity equations contain terms arising from mass exchange, which, though less known to the majority of fluvial hydraulics community, may be significant not only scientifically but also under regimes of practical interests. To demonstrate the applicability of the present models, a numerical study is provided on the dynamics of an otherwise aggrading channel in response to sediment mining, showing the role of sediment mining in mitigating river aggradation. [Copyright &y& Elsevier]

The alteration of sediment transport regime represents one of the key factors controlling the response of fluvial systems to human impacts. Additional research efforts are required to define sound cause-effect relationships between the human pressures and the morphodynamic responses of sediment-starved gravel-bed rivers. This work deals with the evolution of the Parma River, a large Italian gravel-bed river affected over the last 160 year by multiple anthropogenic disturbances (i.e., land-use changes, in-channel mining and, more recently, the construction of a detention basin), which strongly limited the sediment availability to the high-plain portion of its course. The data collected allowed us to reconstruct the history of the impacts, the river morphological evolutionary trajectory, the sedimentological characteristics of the bed, and to estimate, leveraging a morphological approach, the variation in coarse sediment regime over the most recent period. After the cessation of intense in-channel mining in 1990s, the study sector located upstream from the detention basin shifted from a degrading (i.e., narrowing and incising) to a recovery phase, characterized by a mean coarse transport of 15,000–31,000 m3yr−1. These results demonstrate that the in-channel mining was the most impactful historical pressure acting on the river, and that a channel preserving some natural characteristics and passing from a condition of sediment-starvation to one of increasing sediment availability can recover an active morphodynamics within a short time period. The downstream sector was greatly affected by the reduction of sediment transfer that occurred in the 2000s caused by the construction of a detention basin. Its degradation continued over the most recent period and the coarse transport is currently very low (up to about 3000 m3yr−1 4 km downstream from the basin). This sector is characterized at the present by a morphodynamics defined as "slack", a condition induced by the complete evacuation of the mobile channel sediments, leading to extremely low bed material mobility and transport, and, consequently, to morphological degradation up to the achievement of a new quasi-equilibrium. We hypothesized that such an extreme state of alteration is relatively limited in space, affecting a gravel-bed river only at the reach scale in response to multiple overlapped impacts or because of an extremely severe perturbation (i.e., reduction) of the sediment availability and dynamics. • Human-induced sediment starvation causes alteration of gravel-bed river morphodynamics. • High armouring and low bed material load characterize a sediment-starved channel. • Increasing sediment availability can lead to a recovery of channel morphodynamics. • Multiple overlapped impacts can induce extreme morphodynamic alterations. [ABSTRACT FROM AUTHOR]

The present work discusses the problems and management options of beach wrack and dredged sediments. Beach wrack and dredged sediments near the shores have affected the coastal ecosystem, badly. The piles of beach wrack residues might be a significant emitter of greenhouse gases (GHGs) and dredged sediment is a substantial source of heavy metals and other pollutants. The recovery of valuable resources such as metals and nutrients from these so-called "wastes" is a sustainable strategy to enhance the resilience of the coastal ecosystem and management. The beach wrack meadows can be a potential source for green energy production. Even the demand for biodegradable polymers can be supplied by utilizing the waste beach wracks. The residues of beach wrack species like Posidonia oceanica, Zostera marina, Ulva spc. and Enhalus acorodies can be very beneficial species in terms of economic growth. Red algae have been the most favored and efficient candidate for methane yield. In case of dredged sediment, dewatering of sediment is an essential step for successful resource extraction. Although, extraction methods are almost similar to that applied for soil treatment, which includes pretreatment, physical partitioning, washing, thermal treatment, biological extraction, and immobilization. The fractionation study can be a beneficial tool for determining the metal species present in the sediment. Immobilization techniques are successful but continuous monitoring is required. The vitrification technique is highly effective but very expensive. Thermal treatment is useful for volatile metals such as mercury (Hg), but costs are high. Biological extractions are comparatively cheap but time-consuming. Henceforth, very few extraction methods are available for sediment and required further advancement in this field., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

It is a substantial challenge to quantify the benefits which ecosystems provide to water supply at scales large enough to support policy making. This study tested the hypothesis that vegetation could reduce riverbank erosion, and therefore contribute to reducing turbidity and the cost of water supply, during a large magnitude flood along a 62 km riparian corridor where land cover differed substantially from natural conditions. Several lines of evidence were used to establish the benefits that vegetation provided to reducing eleven riverbank erosion processes over 1688 observations. The data and analyses confirmed that vegetation significantly reduced the magnitude of the riverbank erosion process which was the largest contributor to total erosion volume. For this process, a 1% increase in canopy cover of trees higher than five metres reduced erosion magnitude by between 2 and 3%. Results also indicate that riverbank erosion was likely to be affected by direct changes to the riparian corridor which influenced longitudinal coarse sediment connectivity. When comparing the impact of these direct changes on a relative basis, sand and gravel extraction was likely to be the dominant contributor to changed erosion rates. The locations where erosion rates had substantially increased were of limited spatial extent and in general substantial change in river form had not occurred. This suggests that the trajectory of river condition and increasing turbidity are potentially reversible if the drivers of river degradation are addressed through an ecosystem restoration policy. Unlabelled Image • 1% increase in vegetation canopy cover reduced riverbank erosion by between 2 and 3% • Changes to longitudinal coarse sediment connectivity also affected riverbank erosion • Both drivers need to be addressed for effective ecosystem restoration [ABSTRACT FROM AUTHOR]

Sand mining in an active alluvial channel can compromise the streambed stability of the hydraulic structures nearby. This experimental study is aimed at investigating the effects of rectangular mining pit on the morphodynamics around circular tandem piers in a movable bed. A rectangular pit is excavated upstream of two circular piers embedded in the sand-bed in a tandem arrangement. The results are then compared to a case having only the piers without any mining pit. Turbulent stresses and mean velocities in the near-bed region rise significantly at the upstream region of the piers in the presence of a pit. Also, stronger flow reversal and horseshoe vortices have been detected at the base of the pier front. Due to these alterations in the nature of turbulence, erosion of channel beds upstream of the piers, increased scour depths, scour volume, and lateral erosion of the scour hole have been observed. Dynamic evolution of the local scour at various time scales has been studied using a wavelet cross-correlation method. Spatial evolution of local scour is found to be faster when a pit is excavated in the channel. Thus, mining activities near the piers can lead to significant changes in the flow-field, causing excessive scour around piers. [ABSTRACT FROM AUTHOR]