Hydromorphological Research Articles

Microplastics in the Hamburg port area-an analysis of sediment depth profiles along the upper Elbe river, Germany.

Harbours pose a unique environment of increased anthropogenic pressure and artificial river morphology that are of specific interest concerning microplastic release and accumulation. To address the specific situation in the Hamburg port area, a study in cooperation with the Hamburg Port Authority (HPA) was conducted. Sediment samples at different depth levels were taken at seven sites with similar flow velocity and underlying morphology. Two sites are located upstream and downstream of the port of Hamburg, while four sites are located in the centre area of the port. One additional site takes into account an estuary of a receiving stream flowing into the upper river Elbe. For the analysis of microplastic concentrations in the samples, the biogenic organic matter was removed by oxidative digestion followed by wet sieving and density separation. For identification, the Nile red staining method in combination with fluorescence microscopy was applied. A subset of identified synthetic polymers was investigated for polymer composition via µRaman spectroscopy. In addition, sediment parameters such as grain size distribution, organic matter and water content were analysed. In total, a number of 31 sediment samples divided into different depths below riverbed level were examined. In brief, 11,280 microplastic particles could be identified. Both the highest and lowest number of particles were detected at centre port sites ranging from 60 to 21,799 microplastics per kilogramme dry weight. Fragments are the dominating particle morphology throughout all locations, except for one centre harbour site where microbeads are most common. Frequently appearing synthetic polymers were detected to be polyvinyl chloride (34%) and polyethylene terephthalate (28%). Within this study, a significant correlation between microbead concentrations and the percentage of sand fractions (coarse, middle and fine sand) was detected.

Linking Suspended Sediment Conditions to Hyporheic Dissolved Oxygen and Fine Sediment Deposition in Salmonid Spawning Habitat Below an Irrigation Dam, Park County, Wyoming

ABSTRACTDams are essential for water resources management but impose notable effects on fluvial sediment transport and downstream river morphology by reducing or altering the timing of sediment loads. We explored the relationship between dam sediment management and downstream sediment dynamics in the context of riverine fisheries management. We quantified the effects of dam sediment management operations on downstream salmonid spawning habitat during two differing water‐level drawdown events: (1) an experimental drawdown leading to various high concentration sediment releases, and (2) a typical slower drawdown intended to minimize release of sediment. The experimental drawdown increased deposited fine sediment and decreased hyporheic dissolved oxygen levels. However, the typical drawdown did not increase fine sediment deposition or decrease hyporheic dissolved oxygen. We quantify the immediate impacts of dam operations using a number of water column and substrate metrics, and demonstrate the potential for sediment flushing operations to have short‐term seasonally persistent effects on salmonid spawning habitat. Common surrogates of suspended sediment concentration (i.e., turbidity) were poor indicators of salmonid spawning habitat, especially when sand was the dominant grain size. Instead, other measures of suspended sediment concentration such as acoustic backscatter and depth‐integrated samples, combined with discharge, appear to be better suited for monitoring and inferring the impacts of sediment releases on salmonid spawning habitat. We demonstrate the importance of understanding sediment particle sizes, monitoring relevant water column conditions in real‐time, and provide options for effectively monitoring the downstream impact of dam operations. This work can help managers balance dam sediment management operations with ecological priorities.

Transboundary hydropolitical conflicts and their impact on river morphology and environmental degradation in the Hirmand Basin, West Asia

The Hirmand Transboundary River Basin (HTRB), shared by Afghanistan, Iran, and Pakistan, is a hydrologically critical and politically sensitive region. This basin sustains livelihoods, ecosystems, and agriculture in a region plagued by climatic variability and geopolitical tensions. The Hirmand River, which forms the heart of this basin, faces severe morphological and discharge changes due to upstream water management, climatic shifts, and land use changes, directly impacting downstream ecosystems and human populations. This study examines the morphological changes in the Hirmand River and disentangles natural and human-induced drivers behind these shifts. Using the TWINS framework, the study assesses cooperation and conflict in hydropolitical relations, alongside the environmental repercussions of upstream activities on downstream ecosystems. Landsat imagery analysis (1987–2022) via Google Earth Engine reveals significant morphological changes, with 43% of river arcs shifting by 500–1200 m and an annual width reduction of three meters, even during wet periods. Further, prolonged droughts and upstream water diversions have desiccated the Hamoun Lake, obliterating ecosystems, displacing residents, and transforming exposed lakebeds into major dust sources. The TWINS analysis highlights hydropolitical dynamics as the predominant driver of these changes, outweighing climatic influences, and underscores the need for cooperative frameworks to address escalating environmental and social challenges in the basin.

Method for determining the bed load discharge by the parameter of the average depth of the layer of moving materia

The object of the study in this paper is the dunes form of transport of bed load in the channels of lowland navigable rivers. An accurate assessment of the bed load discharge is important when considering river morphology, conducting dredging and river regulation works to ensure navigational conditions, as well as when designing various engineering structures. This paper analyzes modern methods for measuring bed load discharge based on dune parameters. Considering the identified shortcomings and limitations of existing measurement methods, a new method for measuring bed load discharge is proposed. A distinguishing feature of the proposed method is the use of the average depth of the layer of moving material when determining bed load discharge. This parameter is defined as the ratio of the area of the moving material to the length of the moving material layer. Essentially, the moving material consists of dunes identified after filtering out minor bottom protrusions. The advantage of this method lies in using of the average depth of the moving material layer, which allows for all the dunes identified in the longitudinal profile to be accounted for when calculating the bed load discharge. The use of areal dune characteristics also enables the determination of bed load discharge in rivers where the bottom relief consists of deficit dunes.To confirm the effectiveness of this method, a series of experiments were conducted in the Channel Laboratory of the State Hydrological Institute in hydraulic flumes with a movable sand bed. The channel bedforms consisted of three-dimensional dunes. The flow regime in the flume was adjusted to replicate conditions typical of lowland navigable rivers. The experiments confirmed that even with the complex three-dimensional structure of the channel bedforms, the proposed method is highly accurate compared to existing methods.

Investigation of flow behavior within staggered vegetation patches of various shapes in an open channel

The flow dynamics and river geomorphology are influenced by vegetation patches, which naturally exist in various patterns. Previous studies have not explored the effect of vegetation patches with different shapes placed in a staggered arrangement with varying aspect ratio (AR: longitudinal to lateral patch length). We used a numerical method to examine the flow around rigid, emerged vegetation patches in a rectangular flume. The impact of different vegetation patch shapes (circle, square, and rectangle) was investigated using the Computational Fluid Dynamics (CFD) software FLUENT. The findings indicate a decrease in mean streamwise velocity downstream of patches, while flow relaxation occurs in the alternate (free) regions. The flow was significantly affected by the shape of the vegetation patches, with the circular configuration offering the maximum flow resistance. Vortex shedding, including primitive Kármán vortex (PKV) and large-scale Kármán vortex (LKV) streets, behind patches are found to be strong and prominent first for circular and then for rectangular patch (with AR = 2) shapes. Flow through the rectangular patch configuration with AR = 2 appeared more uniform with a higher efficiency of velocity reduction than that of rectangular patch configuration with AR = 0.5. The findings of this research are helpful in assessing flow structure influenced by vegetation.

Temporal Assessment of Recent Erosion and Accretion in the Ganga and Alaknanda Rivers in Parts of Garhwal Himalaya, India: Unveiling the Linkages with Anthropogenic and Climatic Events

ABSTRACT Unravelling erosion and accretion patterns of rivers with the application of remote sensing and GIS tools leads us to understand the river morphology and its behaviour. In the recent past, the catchment areas of river Ganga and its major tributary Alaknanda River affirmed some unprecedented anthropogenic interventions such as infrastructure boom, and deforestation as well as catastrophic climatic events. Considering these factors, the present study evaluates the erosion and accretion pattern of these river sections in the Garhwal Himalaya, India. The shape files of river sections of duration between 2017 to 2022 were extracted from high-resolution Sentinel-2, Land Use Land Cover (LULC) imageries. To understand their exactitude effect on river dynamics, these patterns are further correlated with recognised anthropogenic activities and natural events.

A Probabilistic Process‐Based Model of Bank Erosion and Its Application in the Middle Yangtze River

AbstractBank erosion in a natural alluvial river is influenced not only by near‐bank hydraulic conditions but also predominantly by bank soil properties. These factors exhibit considerable uncertainties, which are seldom considered in previous bank erosion models. Therefore, this study proposes a probabilistic process‐based model of bank erosion by embedding the probability distributions of different bank soil parameters. The model was applied to simulate the bank erosion process in the Middle Yangtze River (MYR), and it was validated against field measurements. Results show that: (a) bank soil parameters including critical shear stress, friction angle and cohesion, followed the Log‐Normal or Gamma distribution, with large variation coefficients of 0.44, 0.59, and 0.50; (b) the expected values of the calculated bank erosion widths agreed closely with measurements (with a relative error of 5%), and the high probability of mass failure occurred within a seasonal timescale (during September–November 2019), despite the high uncertainties in soil properties; and (c) the incorporation of water content variation into the stochastic model further increased the uncertainty of the results by several‐fold, indicating that considering more influencing factors in the model may reduce prediction accuracy. Besides, from a large‐scale perspective, the high diversity of river morphology (channel width) is also closely related to these uncertainties.

Mapping Turbidity Spatial Distribution of Monobe River in Kochi, Japan, Using Satellite Images and Existing Turbidity Data

ABSTRACTMaintaining the environment and functionality of rivers is crucial for the natural environment and socioeconomic activities. In Kochi Prefecture, field measurements of turbidity have been conducted to contribute to countermeasures against prolonged turbid water in the Monobe River; however, a detailed understanding of turbidity across the river has not yet been achieved. Therefore, we attempted to propose a simple turbidity estimation equation based on satellite remote sensing using existing data and visualized the spatial distribution of turbidity in the Monobe River. For turbidity of over 50 FTU, the mean absolute error and mean absolute percentage error (MAPE) of the proposed turbidity estimation equation were 9.9 FTU and 8%, respectively, showing higher accuracy than previous studies, while the accuracy in turbidity of under 50 FTU was not improved for practical use (MAPE was over 49%). By applying the turbidity estimation equation to satellite images, the spatial distribution of turbidity was visualized from the estuary of the Monobe River upstream to the Nagase Dam. The results were consistent with known findings on turbidity dynamics, such as decreasing turbidity in a straight section and increasing it in a curved section, and the spatial distribution of turbidity was considered to be reasonably estimated. The visualization also revealed cases in which turbidity fluctuated greatly in sections where field measurements were not conducted (e.g., increases or decreases in turbidity due to river morphology). In the future, it is expected that the turbidity estimation based on satellite remote sensing will be used in combination with the conventional field measurement of turbidity to understand and analyze the detailed situation of turbidity occurrence in the Monobe River.

River confinement and braiding loss in Canterbury region, Aotearoa New Zealand

AbstractIn relation to the wider concern that rivers in Aotearoa New Zealand have been narrowed by river control and land‐use encroachment, and that iconic braided patterns are being lost, nine braided rivers from the Canterbury region were studied to compare river width, pattern type and braiding intensity between the mid‐1900s and the present based on mapping from aerial images. Channel narrowing occurred along >90% (~490 km) of the length of the rivers studied, 375 km of which were historically braided. In total, the rivers narrowed by an average of 43% (48% for braided reaches). Coinciding with narrowing, braided reaches lost 1.3 channels, on average. Overall, 20% (over 100 km) length of the rivers recorded a change from braided to more simple pattern types including wandering (~18%) and single channel (~1%). The relationship of channel width and pattern change demonstrates the predictability of braiding change based on channel narrowing. As channels narrow, the likelihood of pattern simplification and change increases, although the amount of narrowing required to induce change depends on the initial width and pattern. Narrowing causes a reduction of braiding intensity even when the channel pattern remains braided. Based on these results, a predictor of channel pattern change and reduction of braiding intensity, based only on channel width and width change, can be applied to aid room‐for‐river management plans for conserving or restoring braided river morphologies. Channel width provides a general criterion for the prediction of braiding intensity and channel pattern threshold illustrating the scale‐related effects on channel pattern.

The effects of secondary currents in tight bends on large wood transport in rivers: Lesson learned from Versilia flood in 1996

AbstractThe presence and dynamics of large wood (LW) in river systems, particularly for streams flowing through forested areas, play a significant role in shaping river morphology and influencing flood events. This paper focuses on the numerical reproduction of observed LW trajectories during a flood event in the Versilia River in 1996 in Italy. The study reach, located near Pietrasanta in Tuscany, includes a tight river bend named S. Bartolomeo. During the event, more than two thousand cubic meters of transported wood were observed at this location. In addition, due to the collapse of the outer levee, six million cubic meters of water exited the river corridor, causing the flooding of Pietrasanta. The 2D Lagrangian model Iber‐Wood was used for the numerical simulation of this event. In particular, two versions of the model were used: the original one (IB‐NSC) and the enhanced version (IB‐SC) which simulates the effects of secondary currents on LW dynamics. The results validated the applicability of the enhanced version to simulate real‐world conditions and showed that the IB‐SC model improves the agreement between observed and simulated LW trajectories by more than 20% compared to the IB‐NSC model. Examining the influence of the breach on the LW trajectories, it appears that the presence of LW during the overtopping flow intensified and accelerated the erosion process, resulting in a rapid breach formation. This study therefore highlights the importance of including secondary current effects on LW transport for the development of flood risk assessments and river management strategies, particularly in channelized rivers with tight bends or meanders.

Analysis of Influencing Factors of Water and Sediment Condition Change in Fenhe River

Fenhe River is the second largest tributary of the Yellow River, and its water and sediment conditions have undergone tremendous changes in the age scale. The change of water and sediment conditions will inevitably lead to the change of river morphology, which poses a threat to the surrounding ecological environment and building safety. Firstly, this paper analyzes the changes of water and sediment conditions in Fenhe River through historical data. Secondly, according to the engineering measures and policies in the Fenhe River Basin, the influencing factors are put forward. Finally, the effects of rainfall, soil and water conservation, hydraulic construction, industrial water and coal mining on river flow and sediment conditions are considered. The results show that the increase of rainfall and inflow will weaken the sediment generation and carrying capacity, and further reduce the sediment yield. Soil and water conservation will effectively intercept runoff and sediment, reduce the content of the two in the river ; reservoir construction will regulate runoff and incoming sand to reduce the content of river sand. Industrial development and reservoir filling will reduce the amount of river water ; coal mining activities may aggravate the infiltration of the leakage area, resulting in a decrease in upstream runoff.

Knickpoints and fixed points: the evolution of fluvial morphology under the combined effect of fault uplift and dam obstruction on a soft bedrock river

Abstract. Rapid changes in river geomorphology can occur after being disturbed by external factors like earthquakes or large dam obstructions. Studies documenting the evolution of river morphology under such conditions have advanced our understanding of fluvial geomorphology. The Dajia River in Taiwan presents a unique example of the combined effects of a coseismic fault (the 1999 Mw 7.6 Chi-Chi earthquake) and a dam. As a result of the steep terrain and abundant precipitation, rivers in Taiwan have exhibited characteristic post-disturbance evolution over 20 years. This study also considers two other comparative rivers with similar congenital conditions: the Daan River was affected by a thrust fault Chi-Chi earthquake as well, and the Zhuoshui River was influenced by dam construction finished in 2001. The survey data and knickpoint migration model were used to analyze the evolution of the three rivers and propose hypothesis models. Results showed that the mobile knickpoint migrated upstream under the influence of flow, while the dam acted as a fixed point, leading to an increased elevation gap and downstream channel incision. Thereby, the narrowing and incision of the Dajia River began at both ends and progressively spread to the whole reach under the combined effects.

Sand bed river dynamics controlling microplastic flux

Microplastic contamination of river sediments has been found to be pervasive at the global scale and responsive to plastic and sediment bed properties, the flow regime and the river morphology. The physical controls governing the storage, remobilization and pathways of transfer in sand bed rivers remain unquantified. This means it is not currently possible to determine the risks posed by microplastic contamination within these globally significant river systems. Using controlled flume experiments we show that sand bed rivers can store up to 40% of their microplastic load within the sediment bed indicating that these environments can act as resilient sinks of microplastics. By linking bedform dynamics with microplastic transport characteristics we show that similarities exist between granular transport phenomena and the behavior, and hence predictability, of microplastic flux. Specifically, we demonstrate the inverse relationship between bedform celerity and microplastic retention within the bed can be used to predict microplastic flux. Further, we show that, in these environments, microplastic shape is more important than previously thought in controlling the fate of microplastics. Together, these findings are significant since they have important implications for the prediction and hence management of microplastic contamination in sand bed environments.

Optimization of Ecological Dispatch and Hydrodynamic Improvements in Tidal River Channels Using SWMM Modeling: A Case Study of the Longjin Yangqi Area in Kurama Mountain

Being tidal-sensitive, the river channel in the Longjin Yangqi area of Cangshan, Fuzhou City, is challenged further because of rapid urbanization. Thus, resultant remediation efforts are crucial. This study aims analyzes hydrodynamic characteristics of the area and, secondly, proposes an ecological dispatch solution with evaluation of its effectiveness through the Storm Water Management Model (SWMM). The chief tasks cover imitating rainfall runoff, optimizing sluice gate activities, reorganizing pump management, and reshaping river morphology to bolster flood control and water quality. Improvements were shown through ecological dispatch strategies, which suggested increasing the channel width for the river and deepening the riverbed, thereby increasing the flood duration, lowering water levels, and less frequent flood occurrences. Optimizing sluice gate settings improved efficiency in the regulation of water flow and reduced scour or siltation problems. Various adjustments to pumping operations scattered over various times were based on live-data analysis, therefore enhancing water flow and the self-purification capacity of the water body. The SWMM was directly applied in this tidal river for urban water resource management with data processing from over 100,000 points in simulations. Wherever needed, changes to model parameters were made to improve its capability and enhance its appropriate use in future urban settings. As a whole, this study presents a plan for sustainable water resource management paired with environmental conditions for the benefit of over 500,000 urban residents in the Longjin Yangqi area.

An Integrated Approach to Riverbed Morphodynamic Modeling Using Remote Sensing Data

River inlets, deltas, and estuaries represent delicate ecosystems highly susceptible to climate change impacts. While significant progress has been made in understanding the morphodynamics of these environments in recent decades, the development of models still requires thorough testing and data integration. In this context, remote sensing emerges as a potent tool, providing crucial data and the ability to monitor temporal changes. In this paper, an integrated approach combining remote sensing and morphodynamic modeling is proposed to assess river systems comprehensively. By utilizing multispectral or RGB optical imagery from satellites or UAVs for river classification and remotely derived bathymetry, echo sounder data for ground truth, and photogrammetric modeling of emerged areas, we outline a procedure to create an integrated and continuous digital terrain model (DTM) of a riverbed, paying particular attention to the wet–dry interface. This method enables us to identify the river centerline, its width, and its slope variations. Additionally, by applying a linear morphodynamic model that considers the spatial variability of river morphology commonly found in estuarine environments, it is possible to predict the wavelength and migration rate of sediment bars. This approach has been successfully applied to recreate the DTM and monitor the morphodynamics of the seaward reach of the Roya River (Italy).

Geo-spatial analyses of meandering rivers, assessing past and future impacts on bank landforms and LULC changes

ABSTRACT Morphological investigation of rivers is difficult but is one of the vital topics for the management of highly meandering river systems. The study employs a geographical information system (GIS) to analyse 32 years of Barak River data, addressing challenges in quantifying the morphology of meandering rivers. Earth observatory data from 1990 to 2022 track channel bank shifts and Land Use/Land Cover (LULC) alterations. Although the digital shoreline analysis system (DSAS) model identified long-term bank line migration analysis of shorelines, its use is very new for rivers, especially in terms of the meandering of rivers. Conversely, research on long-term meandering river morphology in the Barak River channel has not been conducted despite evident land-use changes. Using DSAS for bank positions and cellular Automata -Markov (CA -Markov) models for LULC, future projections until 2043 reveal ongoing Barak River bank shifts and significant LULC pattern alterations. The findings of the research were validated through root mean square error (RMSE), Student's t-test, chi-square, and the kappa coefficient. Forecasts indicate that rapid urbanization impacts river morphology. The methodology is crucial for managing highly meandering rivers, particularly in contexts involving vulnerable river systems.

Evaluating the continued significance of dam-induced vigorous downstream channel erosion in the context of projected climate change: a case study from Peninsular India

ABSTRACT Although erosion has naturally been driven by rainfall patterns, human activities have increasingly influenced erosion rates in recent times. However, as climate change alters precipitation, future erosion control may once again depend primarily on climate. The primary goal of this investigation was to ascertain whether the issue of escalated erosion, typically linked to downstream dam effects, could diminish in significance due to projected climatic shifts later in this century. An erosion potential index (Ep), formulated as the ratio of the mass of sediment influx from upstream to the frequency of the sediment-carrying flow events, was computed on a tributary of the Godavari River, located downstream of a dam. Using the Soil & Water Assessment Tool (SWAT), virtual experiments were conducted to distinguish the impacts of the dam from projected climate changes on river geomorphology. Two control scenarios were created using the current climate data and simulated regulated and unregulated states of the basin. Employing climate projections and various mitigation scenarios (SSPs) for the 2060s and 2090s, this study estimated Ep values exclusively under future climatic conditions in an unregulated state of the basin. Results indicate that, in the unregulated state without the existence of the upstream dam, future climate impacts on erosion outweigh the current effects of the dam, underscoring the growing influence of climate on geomorphology. It suggests that existing structural interventions may lose their geomorphic significance in the face of future climate conditions.

Flood Mapping using HEC-RAS and GIS: A Case Study of Palembang Watersheds

Flooding is a significant issue in Palembang City, affecting areas such as Gandus, Lambidaro, Boang, Sekanak, Bendung, Kidul, Buah, Juaro, Selinca, Nyiur, Aur, Sriguna, Kedukan, Keramasan, Kertapati and Jakabaring watershed. This research contributes to flood control measures by providing flood mapping and modelling for decision-makers and local authorities. The main objective of this paper is to perform a steady flow analysis to study the hydraulic characteristics of flow; velocity and water surface profile of the adjacent research areas. There are three processes involved in the data analysis: hydrological, hydraulic and spatial. The calculation of average rainfall is performed using the Isohyet method with the assistance of the IDW 3D Analyst tool in ArcGIS and the design discharge is calculated using the HSS Nakayasu method. The hydraulic analyses involve river morphology extraction using RAS Mapper tools in HEC-RAS. Steady flow simulations are conducted for normal water depth conditions and the highest tidal conditions. The simulation result is then reclassified and the flood location points are verified with observed data. For normal water depth conditions, the maximum water level in the Lambidaro watershed reaches 2,09 meters, which covers a flood area of 721,53 ha. Meanwhile, based on the highest tidal simulations, the maximum water level in the Selinca watershed reaches 3,21 meters, covering a flood area of 209,36 ha.

Altered flow and sediment transport impacts on the ecosystems of Chinese major rivers: An urgent call for eco‐fluvial dynamics

AbstractRiver ecosystems face challenges due to environmental degradation and alterations in flow and sediment transport resulting from climate change and other anthropogenic impacts. These changes may substantially affect river morphology, nutrient dynamics, wetland vegetation, aquatic habitats, and river ecological stability. This highlights the urgent need for systematic and quantitative studies on the interactions and feedback between changes in flow, sediment transport, and river ecology. In this study, we reviewed flow and sediment transport changes in major Chinese rivers, along with their resulting ecological impacts. We propose conducting eco‐fluvial dynamic studies, a potential solution that can guide the evaluation and restoration of ecological health impacted by physical processes. These studies can provide major benefits in balancing human and environmental needs in large river systems, which is crucial for the healthy and sustainable development of rivers.

A typology of potential hydraulic barriers to adult salmon migration in a bedrock river

Adult Pacific salmon (Oncorhynchus spp.) in the Fraser River, British Columbia, can die trying to retrace and ascend the river network to their natal spawning grounds due to hydraulic barriers, where encounter velocities exceed swim speeds of adult salmon. We evaluated river hydraulics, river morphology, and swimming ability to better understand these potential hydraulic barriers. A 375 km centerline velocity survey of the Fraser Canyon identified 22 high velocity locations where the distribution of velocity within the reach could produce a hydraulic barrier. We identified and studied three flow types associated with these 22 high velocity locations: 1) plunging flows, 2) rapids, and 3) overfalls, using drone footage at various discharges to examine flow structure and compare surface velocities with swimming modes. Complex flow within the major hydraulic features highlight the spatial locations requiring anaerobic swimming and areas of potential recovery that change with discharge. This approach can be used to improve the understanding of fish migration limits in a natural river system and aid in future mitigation.