Search Results (82)

This study investigates biofilm–flow interactions in gravel-bed rivers using a novel numerical model. Traditional hydrodynamic models often overlook biofilm-induced roughness coupling, prompting the development of a mesoscopic Lattice Boltzmann Method (LBM) framework that dynamically links biofilm thickness to equivalent roughness. Key insights include a dual-phase mechanism: moderate biofilm growth reduces hydraulic resistance by smoothing gravel pores, while excessive growth increases resistance via flow obstruction. Validated against 65-day flume experiments, the model accurately predicted biomass (ash-free dry mass) and velocity profiles. Current limitations involve reliance on empirical biofilm formulas, lack of natural river validation (non-uniform substrates, dynamic flows), and computational barriers in 3D large-scale simulations. Future directions include integrating biogeochemical factors (temperature, nutrients), multiscale microbial-morphology frameworks, and GPU-accelerated high-resolution modeling. Full article

Watercress (Nasturtium officinale), a freshwater aquatic plant in the Brassicaceae family, is characterized by its high content of specialized metabolites, including flavonoids, glucosinolates, and isothiocyanates. Traditionally, commercial cultivation is conducted in submerged beds using river or spring water, often on soil or gravel substrates. However, these methods have significant environmental impacts, such as promoting eutrophication due to excessive fertilizer use and contaminating water sources with pesticides. This study aimed to explore two emerging cultivation strategies, i.e., hydroponics and aquaponics, to grow watercress and evaluate its specialized metabolite content using an untargeted metabolomic approach. The goal was to characterize metabolic profiles, identify component variations, and assess changes in metabolite accumulation at two harvest times. Two culture systems (hydroponic and aquaponic) and two harvest stages (‘baby leaf’ and traditional harvest) were examined. The results revealed 23 key metabolites, predominantly glucosinolates and flavonoids, that significantly influenced the metabolic profile discrimination, with the aquaponic system yielding the highest diversity and relative abundance of metabolites (variable importance in the projection (VIP) > 1). Important condition-related compounds were identified via cross-validation (area under the curve (AUC) > 0.7), including isorhamnetin sophoroside–glucoside and gluconasturtiin at the traditional harvest in the hydroponic system and glucoarabin at the ‘baby leaf’ stage in the aquaponic system. These findings highlight the potential of aquaponic and hydroponic systems as sustainable alternatives for watercress cultivation, offering environmental benefits and enhanced metabolite quality. Full article

Engineers, geomorphologists, and ecologists acknowledge the need for temporally and spatially resolved measurements of sediment clogging (also known as colmation) in permeable gravel-bed rivers due to its adverse impacts on water and habitat quality. In this paper, we present a novel method for non-destructive, real-time measurements of pore-scale sediment deposition and monitoring of clogging by using wire-mesh sensors (WMSs) embedded in spheres, forming a smart gravel bed (GravelSens). The measuring principle is based on one-by-one voltage excitation of transmitter electrodes, followed by simultaneous measurements of the resulting current by receiver electrodes at each crossing measuring pores. The currents are then linked to the conductive component of fluid impedance. The measurement performance of the developed sensor is validated by applying the Maxwell Garnett and parallel models to sensor data and comparing the results to data obtained by gamma ray computed tomography (CT). GravelSens is tested and validated under varying filling conditions of different particle sizes ranging from sand to fine gravel. The close agreement between GravelSens and CT measurements indicates the technology’s applicability in sediment–water research while also suggesting its potential for other solid–liquid two-phase flows. This pore-scale measurement and visualization system offers the capability to monitor clogging and de-clogging dynamics within pore spaces up to 10,000 Hz, making it the first laboratory equipment capable of performing such in situ measurements without radiation. Thus, GravelSens is a major improvement over existing methods and holds promise for advancing the understanding of flow–sediment–ecology interactions. Full article

The operation of large reservoirs significantly modifies flow–sediment regimes, and the reaches immediately downstream of the dams are the first to undergo responsive channel adjustments. Considering that the geomorphological responses are directly related to the flood control safety, channel stability and other sustainable functions of rivers, this paper explores the similarities and dissimilarities of the channel adjustments in the two reaches with gravel–sand beds immediately downstream of the Xiangjiaba reservoir and the Three Gorges Dam, respectively. The results show that major erosion primarily occurred during the initial years of reservoir impoundment. And then with the prominent reduction in washable sediment on the riverbed, the erosion intensity further weakened. It takes 6 to 13 years for the two reaches to reach a new state of relative equilibrium. In comparison, after the equilibrium state has been achieved, the reach with significant tributary sediment inflows exhibits alternating erosion and deposition dynamics, while the other remains relatively stable. The tributaries that transport a large amount of sediment during floods are the main sources of sediment deposition in the downstream reaches of the Xiangjiaba reservoir. However, the tributary inflow of the Qing River with low sediment concentrations has little impact on the riverbed evolution of the reaches from Yichang to Zhicheng immediately downstream of the Three Gorges Dam. These findings contribute to a deeper understanding of geomorphic adjustments near dams in response to upstream damming. Full article

The assessment of grain size and sediment output is crucial for analyzing the pace of sediment erosion, engineering dams and reservoirs, anticipating the impact of climate change and human activities on river systems, and comprehending the presence of trace and heavy metal pathogens and micropollutants. In July 2024, 16 samples of bed sediments were collected from the mainstream of Wadi Fatima and its tributaries in the Makkah region of Saudi Arabia to identify the depositional environments and the hydrodynamic conditions using Passega diagram, Linear Discriminate Function (LDF) and bivariate plots. The results indicate that the sediments being studied exhibit polymodal properties in both the upstream and midstream regions of the main channel of Wadi Fatima. However, in the downstream region, the samples show trimodal properties. Regarding tributaries, the WFT1, WFT2, and WFT4 sediments exhibit polymodal properties, except for WFT3, which is bimodal. Folk’s classification system categorizes the samples into four distinct classes/facies: gravel, sandy gravel, gravely sand, and sand, with respective proportions of 13%, 62%, 6%, and 19%. The sediments found in Wadi Fatima contain a range of graphic mean (M_Z) values, from −3.34 (indicating medium gravel) to 2.48 (indicating fine sand). On average, the M_Z value is −0.79, which shows extremely fine gravel. The standard deviation (sorting (σi)) values of the samples analyzed from Wadi Fatima vary between 0.71 (moderately sorted) and 3.44 (very poorly sorted), with an average of 2.00 (very poorly sorted). The data exhibits a range of skewness (Sk) values, ranging from −0.41 (showing a very coarse Sk) to 0.82 (representing a indicating a very fine Sk). On average, the data shows a Sk value of −0.02, indicating a symmetrical distribution. The kurtosis (K) values span from 0.51 (indicating a very platykurtic distribution) to 2.65 (indicating a very leptokurtic distribution), with an average of 0.95 (indicating a mesokurtic distribution). Full article

Shallow floodplains play a crucial role in river basins by providing essential ecological, hydrological, and geomorphic functions. During floods, intricate hydrodynamic conditions arise as flow exits and re-enters the river channel, interacting with the shallow vegetation. The influence and mechanism of shoal vegetation on channel hydrodynamics, bed topography, and sediment transport remain poorly understood. This study employs numerical simulations to address this gap, focusing on the Xiaolangdi–Taochengpu river section downstream of the Yellow River. Sinusoidal-derived curves are applied to represent the meandering river channel to simulate the river’s evolutionary process at a true scale. The study simulated the conditions of bare and vegetated shallow areas using rigid water-supported vegetation with the same diameter but varying spacing. The riverbed substrate was composed of non-cohesive sand and gravel. The analysis examined alterations in in-channel sediments, bed morphology, and bed heterogeneity in relation to variations in vegetation density. Findings indicated a positive correlation between vegetation density and bed heterogeneity, implying that the ecological complexity of river habitats can be enhanced under natural hydrological conditions in shallow plain vegetation and riparian diffuse flow. Therefore, for biological river restoration, vegetation planting in shallow plain regions can provide greater effectiveness. Full article

Riverbank erosion poses a significant threat to the stability and integrity of river training structures. River training structures such as groynes are important components of sustainable development as they play a crucial role in mitigating flood risks, controlling erosion, and supporting the habitat for aquatic organisms. The habitats vary largely according to the groyne type. A comprehensive comparative analysis of the flow field around the I, L, and T head groynes in the gravel bed is drawn. This study will be of immense use for riverbank protection in hilly terrain where streams are mostly dominated by the gravel bed. Laboratory experiments were conducted in a channel with a sediment bed as gravel of size 9.36 mm. Consistent flow conditions were maintained, with a flow depth (D) of 0.136 m and Froude no (Fr) of 0.61. The performance of these groynes, quantified using L_p (length of bank protection), was investigated. LHG and THG, notably, instigate more profound scour depths, recording values of 0.295 D and 0.29 D, respectively, while IHG trails with the value of 0.21 D. The complex flow field involving velocity peaks, decelerated, and negative flow is discussed and is attributed to flow separation at the groyne tip and the horseshoe vortex. The L_p for each groyne was estimated, with the IHG providing the maximum bank protection of 1.2 L₁, L₁ being the transverse length of the groyne. The cost–benefit analysis revealed IHG as the most cost-effective structure. These findings contribute to optimization of riverbank stabilization efforts, enhancing the resilience of hydraulic infrastructure and ensuring the safety and wellbeing of affected communities and ecosystems. The results also provide valuable insight into bank protection by various groynes and highlight their contribution to enhancing the resilience of river systems. Full article

Fine sediment infiltration and subsequent clogging in a gravel bed affect several fluvial, ecological, and biological processes, resulting in the degradation of the river ecosystem. Despite many experimental and a few numerical studies, the process is yet to be entirely understood. We employed a pure Lagrangian framework, called the Discrete Element Method (DEM), to numerically investigate the infiltration process. Special attention is given to tackling the issue of non-spherical and irregular particle shapes and particle size distributions (PSDs) in numerical simulations. Due to computational limitations, these aspects were either not considered or simplified in previous numerical studies. We implicitly included non-spherical and irregular shape effects through rolling resistance models, which do not cause excessive computational overhead. Our study shows that rolling resistance models greatly influence packing and fine sediment infiltration. However, they may also lead to unphysical particle behavior; thus, they should be carefully used in numerical simulations. Oversimplified PSDs do not mirror natural systems, and full PSDs pose computational challenges. Sufficient grain classes are needed to mimic the non-homogeneity and poly-dispersity found in natural fluvial sediments. The infiltrating characteristics of sand concerning PSD and shape effects are linked to size ratio D_15,Gravel/D_85,Sand, assuring physical and realistic modeling of the infiltration process. Full article

This paper aims to obtain a relation for estimating the median size of bed sediment, $d_{50}$, at the bends of meandering rivers based on real data. To achieve such a purpose, field data, including topographic, sediment sampling, and flow measurements, were collected from various rivers in Iran at different times of the year. Then, the Buckingham Π-theorem was applied to identify the effective dimensionless numbers such as the Shields function, Reynolds particle number, Froude number, submerged specific gravity of sediment, and aspect and curvature ratios. A correlation analysis was conducted between such factors to eliminate those dependent on others. In the following, three regression techniques, containing the power function approach, the general additive model (GAM), and the multivariate adaptive regression spline (MARS), were chosen to achieve the best relation. The obtained results indicated that the developed MARS model produced a better result than the others and was much more satisfactory, with a coefficient of determination (R²) of 0.96 and 0.95 and root-mean-square error (RMSE) of 140.64 and 140.47 for the training and testing phases, respectively. Furthermore, the MARS outputs were validated with an analytical method, which showed that MARS fitted with the field data much better. Consequently, the distinguished merit of this study is the development of a relation for determining $d_{50}$ that shows which geometric and hydraulic parameters have the most effect on sediment size in the river bend. Full article

Bedload transport in a river is a deeply analyzed problem, with many methodologies available in the literature. However, most of the existing methods were developed for reaches of rivers rather than for confluences and are suitable for a particular type of material, which makes them very inaccurate in cases where the sediments are comprised of a mix of different types of soil. This study considers the effect of two different bed sediment sizes, gravel and sand, in relation to bed load transport in a confluence. Five well-known and validated equations (namely Meyer-Peter and Müller, Parker + Engelund and Hansen, Ackers and White, and Yang) are applied to the case study of the Tagus–Alberche rivers confluence (in Talavera de la Reina, Spain), where main and tributary rivers transport different materials (sand and gravel). Field works in the area of the confluence were conducted, and a set of alluvial samples were collected and analyzed. The previously mentioned methods were employed to analyze the geomorphology in the confluence area and downstream of it under different flooding scenarios, concluding different trends in terms of deposition/erosion in the area under historic flooding scenarios. When the trends show erosion, all methods are very consistent in terms of numerical predictions. However, the results present high disparity in the estimated values when the predictions suggest deposition, with Parker + Engelund and Hansen yielding the highest volumes and Meyer-Peter and Müller the lowest (the latter being around 1% of the former). Yang and Ackers and White predict deposits in the same range in all cases (around 15% of Parker and Engelund Hansen). Yang’s formula was found to be suitable for the confluences of rivers with different materials, allowing for the estimation of sediment transport for different grain sizes. The effect of different flow regimes has been analyzed with the application of Yang’s formula to the Tagus-Alberche confluence. Full article

Measuring bathymetry has always been a major scientific and technological challenge. In this work, we used a deep learning technique for inferring bathymetry from the depth-averaged velocity field. The training of the neural network is based on 5742 laboratory data using a gravel-bed flume and reconstructed velocity fields, namely the topographies were obtained from real-world experiments, and the velocity fields were estimated using a statistical model. To examine the predictive power of the proposed neural network model for bathymetry inference, we applied the model to flume experiments, numerical simulations, and field data. The results showed the model properly estimates topography, leading to a model for riverine bathymetry estimation with a 31.3% maximum relative error for the case study (confluence of the Kaskaskia River with the Copper Slough in east-central Illinois state, USA). Full article

The formation of the Jinsha River drainage is a significant subject of concern in the geological and geomorphological fields. Among them, one key question is whether there was a regional paleo lake into which Lower Jinsha River drainage drained during the late Pliocene to early Pleistocene, due to massive fluvio-lacustrine sediments widely distributed in the Lower Jinsha River. Nevertheless, there has yet to be a consensus on the genesis of those fluvio-lacustrine sediments due to poor sedimentological and chronological data. In this study, to unravel the origin of those fluvio-lacustrine sediments and the formation model of the Lower Jinsha River, sedimentary characteristics, including spatial distribution, lithological composition, and stratigraphic contact relationship of those fluvio-lacustrine sediments were analyzed, and chronological determination of the fluvio-lacustrine sediments using Electron Spin Resonance and Optically stimulated luminescence method was conducted. The results show that in the Lower Jinsha River, the lacustrine sediments are mainly composed of silt and clay, with apparent horizontal bedding, stacked with fluvial cobble-gravel and sand, and are in unconformable contact with the underlying bedrock strata or paleo soil. The lacustrine sediments are spatially discontinuous and mainly distributed in the Shigu, Taoyuan, Panzhihua, and Longjie reaches. Downstream of these reaches are deeply incised gorges with an average slope >30°, and many landslide landforms and deposits can be identified here. In each reach, the lacustrine sediments were closely distributed along the trunk and tributary channels in the plane and were distributed at different altitudes, forming a sequence of lacustrine terraces. Chronological analysis shows that in different reaches, the deposition ages of lacustrine sediments are significantly different. In each reach, the deposition age of the lacustrine terraces of high altitude is older than that of low altitude. The above characteristics collectively indicate that the lacustrine sediments in the Lower Jinsha River were locally deposited by individual dammed lakes, probably induced by landslide rather than a regional paleo lake by tectonic activities. During the incision process of the river valley, landslides continuously block the river channel, forming dammed lakes, and then deposited lacustrine sediments at different elevations, forming lacustrine terraces. The lacustrine sediment of the topmost lacustrine terrace in Panzhihua reach was dated to be 1.78 Ma, combined with previous studies on the fluvial terraces, indicating the Lower Jinsha River existed and started to incise its valley before the early Pleistocene. The widespread dammed lake sediment indicates that the formation of the Jinsha River valley follows the pattern of “incision-landslide-damming-aggradation-incision”. Full article

River rehabilitation and ecological engineering are becoming critical issues for improving river status when ecological habitats and connectivity have been altered by human pressures. Amongst the range of existing rehabilitation options, some specifically focus on rebuilding fluvial forms and improving physical processes. The aim of this contribution is to illustrate how geomorphological expertise and process-based thinking contribute to river rehabilitation success. This semantic contribution is intended to feed the rehabilitation debate, particularly concerning the design of actions and the proposed references for monitoring target reaches and evaluating rehabilitation effects empirically. This article is also based on lessons learned from practical cases, mainly in gravel-bed rivers. Geomorphic understanding is needed at a local level to achieve an adequate diagnosis of river functioning, estimate human impacts and potential remnant river responsiveness, and to assess the gains and risks from rehabilitation, as well as to appraise success or failure through several pre- and post-project assessment strategies. Geomorphological studies can also be upscaled in a top-down manner (from high-order controls to small-scale processes, understanding detailed processes in their regional or basin-wide context), providing large-scale information at the regional, national, or even global level, information that can be used to diagnose the health of riverscapes in relation to local site-specific contexts. As such, geomorphological studies support strategic planning and prioritization of rehabilitation works according to specific contexts and river responsiveness, so as to move from opportunistic to objective-driven strategies. Full article

This paper describes how uncontrolled and illegal mining of sand and gravel can affect surface water and groundwater regimes in places where there is a hydraulic connection between them, based on a case study of the Velika Morava River in Serbia. Also, a change in cross-profile geometry, as a result of anthropogenic and natural factors, hinders the preparation of this river for inclusion among Serbia’s waterways. The Velika Morava River’s navigability would enable the development of waterborne transportation for both merchant ships and vessels of the Serbian Armed Forces River Flotilla. Correlations between water levels at gauging stations, as well as correlations between groundwater levels and river water levels at gauging stations, are used to show the dependence of these parameters on the change in the river bed profile after sand and gravel mining at the locations near gauging stations. In addition, the homogeneity of time-series of average annual elevations and the variance of the water levels of the Velika Morava River, measured in gauging stations during different periods, are statistically analyzed. The deepening of the Velika Morava riverbed where it was indiscriminately excavated in the 1980s led to the disruption of the groundwater regime and the hydraulic connection with the river, which lowered the water table of the aquifer used for the public water supply, as well as causing a number of other negative consequences. Full article