Gravel-bed Rivers Research Articles

Floodplain Forest Soil Series Along the Naturally Wandering Gravel-Bed River in Temperate Submontane Altitudes

Floodplain Forest Soil Series Along the Naturally Wandering Gravel-Bed River in Temperate Submontane Altitudes

Evaluation of flow resistance equations for high gradient rivers using geometric standard deviation of bed material

A dataset of 2184 field measurements reported in the literature was used to evaluate the predictive capability of eight conventional flow resistance equations to predict the mean flow velocity in gravel-bed rivers. The results reveal considerable disagreement with the observed flow velocities for relative submergence less than 4 and for the non-uniformity of the bed material greater than 7.5 for all the equations. However, the predictions made using the Smart and Jäggi (1983), Ferguson (2007), and Rickenmann and Recking (2011) equations were closer to the observed values. Furthermore, bedload sediment transport also reduces the predictive capability of the equations considered in this study except for the Recking et al. (2008) equation, which was developed considering active bedload transport. The performance of flow resistance equations improves when corrected by considering the geometric standard deviation of the bed material. Here we present an empirical approach using the whole dataset and its subsets for accounting for the additional energy losses occurring due to the wake vortices, spill losses, and free surface instabilities occurring due to the protrusions from the bed. The results obtained using the validation dataset shows the importance and usefulness of this approach to account for the additional energy losses, especially for the Strickler (1923) and Keulegan (1938) equations.

Using a statistical efficiency methodology for predictors’ selection in the bedload transport problem: A high gradient experimental channel case

Bedload transport rates for high-gradient gravel bed rivers has been studied through a physical model that replicated the typical features of these channels. A stepwise regression was performed to identify the best predictors from a set of independent variables. As independent variables channel slope, the ratio of area occupied by large particles to the total plan area, flow discharge, mean flow depth, mean flow velocity, water surface velocity, boundary shear stress, and shear velocity were considered. Different characteristic diameters (d16, d50, d84, and d90) were used to nondimensionalize the variables as well as to test the influence of grain size. A linear and a potential model were obtained for each characteristic diameter. Based on the correlation coefficients (R2) with the data used to build the models, the d50 and d84 linear and potential models were selected to perform further analysis. A set of independent data was used to verify the selected models. Better performance was observed for the potential models with 96% of the data falling within ½ order of the magnitude bands both for d50 and d84 . R2 for the d50 and d84 potential models were 0.63 and 0.76, respectively. Therefore, the d84 potential model can be selected as the present study representative model.

Sediment Production in French Alpine Rivers

AbstractGlobal compilations of river sediment loads show that mountainous areas produce a high proportion of the sediment transported to the oceans. However, because of the effort involved in measuring sediment fluxes in mountain river systems, the loads of these rivers are generally unknown. Here, we present estimates of contemporary sediment loads of 16 gravel bed rivers draining the Ecrins‐Pelvoux Massif in southeast France. Sediment production in this part of the Alps is relatively high and many river segments are either wandering or braided. We model sediment fluxes and annual sediment yields by coupling hydraulic‐based relations for sediment transport with hydrologic‐based relations for flow frequency. Bed load fluxes are modeled for a range of discharges using a function that relates transport rates to excess shear stress. Fluxes are then weighted by the frequency of individual discharges and summed to get the annual bed load for each site. The suspended load is estimated empirically as a fraction of the bed load. Results suggest that bed load fluxes at channel‐forming flows scale almost linearly with downstream increases in discharge. In addition, it appears that annual sediment loads (bed load + suspended load) scale linearly with drainage area. A complementary relation for specific sediment yield suggests that the load per unit drainage area is constant across the range of basins studied. The modeled sediment yields are comparable to previous field‐based estimates of modern sediment yields, and generally lower than estimates developed from analyses of cosmogenic radionuclides.

Infiltration Depth of Mineral Particles in Gravel-Bed Rivers

This article discusses the results of an experimental study of a spill of mineral particles in gravel-bed rivers due to mining accidents. The purpose of this research is to characterize the dynamics of the fine mining particles spilled on a bed of immobilized gravel as a hyper-concentrated mixture and to experimentally characterize the infiltration phenomenon. We analyzed the type of infiltration considering the dimensionless coarse to fine particle size relationship, the dimensionless weight of the fine particles, the relative density of the particles, and the relationship between the subsurface and surface velocities, in addition to the densimetric Froude and Reynolds numbers of the fine particles. We found that the dimensionless infiltration depth is not associated with hydraulic parameters or the weight of the fine sediment spilled; however, fine sediment deposition decreases with depth, and infiltration depth may increase if subsurface flow decreases over time. Finally, a relationship of the dimensionless maximum infiltration depth with the relative density of the mining particles, the ratio of the bed sediment and the mining particles sizes, and the ratio between the subsurface and surface velocities is established.

Spatial and seasonal change in algal community structure and its interaction with nutrient dynamics in a gravel-bed urban river

Harmful algal blooms frequently occur in urban rivers due to intense human activities. However, little is known about the change in algal community structure and its interactions with nutrient dynamics in gravel-bed urban rivers. In present study, water samples were collected from a gravel-bed River Xin’an, China for five months over four seasons and a rainy month to measure algal community structure, dissolved nitrogen gas (N2) and Argon (Ar) concentrations, and other water quality parameters. The results showed that the harmful Cyanophyta accounted for 31.6 ± 24.1% of the total community in the hot season while Bacillariophyta contributed more than 60% to the community in the other three seasons. The N2 was supersaturated in the moderate and cold seasons but it was unsaturated in the hot season, along with high concentrations of nitrogen-fixing cyanobacteria (Anabaena), indicating that the nitrogen fixation capacity was strong and even stronger than denitrification and anammox in the hot season. However, nitrogen fixation was not the main source of nitrogen in the water column. The concentrations of nutrients and Chla in the downstream river were significantly higher than those in the upstream river (p < 0.001 for nutrients and p = 0.029 for Chla), suggesting that human activities along the river greatly affected nutrient concentrations, as well as algal growth. Our study provides new insights into the algal community succession in a gravel-bed urban river and puts forward effective measures such as controlling exogenous nutrient input and dredging organic sediment for mitigating the harmful algal blooms in urban rivers.

Cycles of aggradation and degradation in gravel-bed rivers mediated by sediment storage and morphologic evolution

It has been observed that the relation between sediment storage and sediment transport rate in gravel-bed rivers exhibits counter-clockwise hysteresis, or aggradation-degradation cycles. Previous work has attributed these cycles to external changes to the sediment supply rate. We present a set of nine flume experiments that test the hypothesis that aggradation-degradation cycles can occur even under steady sediment supply conditions when the sediment transport rate temporarily nears the sediment supply rate. The experiments are designed to examine the transport-storage relations under a range of conditions with different initial bed condition, sediment supply rate, discharge, and supply material texture. The sediment transport efficiency of the experimental channel was strongly influenced by the existing bed morphology inherited from historical flows. The discharge and grain size distribution of the supply material played a secondary role, with higher discharge conditions and finer sediment feed material producing increased transport efficiencies. The transport-storage relations revealed that the transport rate of the channel changed with the volume of sediment stored and was, therefore, mediated by the channel morphology. Aggradation-degradation cycles were observed even under steady sediment supply and discharge conditions and were mediated by morphologic adjustments within the channel that temporarily led the transport rate to be near equal to the sediment supply rate. In other words, the probability of hysteresis in the transport-storage relation increases when the channel is near a transport equilibrium. The findings demonstrate the complexity associated with developing a unique relation between sediment transport and storage in gravel-bed rivers, and highlights the importance of considering the morphologic evolution and historical bed conditions.

Pioneer annual vegetation of gravel-bed rivers: first insights on environmental drivers from three Apennine streams

A huge knowledge gap exists on riverine pioneer herbaceous vegetation. Despite its relevance in regulating the C metabolism at the catchment scale, and the triggering role in shrubs and trees establishment along riverbanks, little data is available on its environmental determinants. Indeed, most existing knowledge in this field refers to woody species or aquatic macrophytes neglecting the ecosystem relevance of ephemeral herbaceous vegetation. Focusing on three gravel bed rivers located in northern Italy (Baganza, Nure and Parma streams), the present study is aimed to evaluate the riverine ephemeral plant richness, considering both native and alien taxa, and the role of hydrogeomorphological disturbance and sediment quality in the observed richness patterns. At higher disturbance rates (e.g., larger river sizes), our data indicates a progressive decrease in overall plant richness, but also an increase in the coverage-abundance rates mainly due to alien species. This evidence confirms that variations in hydrology imply changes in pioneer plant species richness at in-stream periodically exposed sediments. More attention must be given to the vulnerability of pioneer vegetation to climate change and direct human impacts to fully understand the functioning of lotic ecosystems, especially the non-perennial ones.

Experimental Study on the Riverbed Coarsening Process and Changes in the Flow Structure and Resistance in the Gravel Riverbed Downstream of Dams

Following the construction of a reservoir, sediment is intercepted, which greatly reduces the sediment concentration in the discharged flow. This reduction causes riverbed scouring and flow structure adjustments downstream, thereby impacting the river habitat. This study used the generalized flume test with different bed sand compositions and discharge rates to simulate the scouring adjustment process of a sand pebble riverbed channel downstream of a reservoir. The results show that the bed sediment composition affects the water surface gradient, scour depth, turbulence intensity, and sand resistance directly after final scouring. Coarse-grained bed sediment demonstrated the greatest final turbulence intensity and sand resistance, while bed sediments with reduced coarseness exhibited a greater scouring degree; the resistance for sand grains of moderate coarseness showed the greatest change. Sand resistance was exponentially and positively correlated with the median grain size and the fractal dimension of bed sediment mass. The mass fractal dimension expression was suitable for the analysis of bed sand grain-size distribution; it contributed to the calculation of grain resistance with fewer hydraulic parameters. The relationship between the mass fractal dimension and the adjusted grain resistance was also established, which can aid the calculation of the resistance changes in sandy gravel-bed river reaches downstream of reservoirs, enabling the prediction of their effects on aquatic habitats.

Predicting stable gravel-bed river hydraulic geometry: A test of novel, advanced, hybrid data mining algorithms

Accurate prediction of stable alluvial hydraulic geometry, in which erosion and sedimentation are in equilibrium, is one of the most difficult but critical topics in the field of river engineering. Data mining algorithms have been gaining more attention in this field due to their high performance and flexibility. However, an understanding of the potential for these algorithms to provide fast, cheap, and accurate predictions of hydraulic geometry is lacking. This study provides the first quantification of this potential. Using at-a-station field data, predictions of flow depth, water-surface width and longitudinal water surface slope are made using three standalone data mining techniques -, Instance-based Learning (IBK), KStar, Locally Weighted Learning (LWL) - along with four types of novel hybrid algorithms in which the standalone models are trained with Vote, Attribute Selected Classifier (ASC), Regression by Discretization (RBD), and Cross-validation Parameter Selection (CVPS) algorithms (Vote-IBK, Vote-Kstar, Vote-LWL, ASC-IBK, ASC-Kstar, ASC-LWL, RBD-IBK, RBD-Kstar, RBD-LWL, CVPS-IBK, CVPS-Kstar, CVPS-LWL). Through a comparison of their predictive performance and a sensitivity analysis of the driving variables, the results reveal: (1) Shield stress was the most effective parameter in the prediction of all geometry dimensions; (2) hybrid models had a higher prediction power than standalone data mining models, empirical equations and traditional machine learning algorithms; (3) Vote-Kstar model had the highest performance in predicting depth and width, and ASC-Kstar in estimating slope, each providing very good prediction performance. Through these algorithms, the hydraulic geometry of any river can potentially be predicted accurately and with ease using just a few, readily available flow and channel parameters. Thus, the results reveal that these models have great potential for use in stable channel design in data poor catchments, especially in developing nations where technical modelling skills and understanding of the hydraulic and sediment processes occurring in the river system may be lacking.

Abiotic predictors of fine sediment accumulation in lowland rivers

The delivery of excessive fine sediment (particles < 2 mm in diameter) to rivers can cause serious deleterious effects to aquatic ecosystems and is widely acknowledged to be one of the leading contributors to the degradation of rivers globally. Despite advances in using biological methods as a proxy, physical measures remain an important method through which fine sediment can be quantified. The aim of this study was to provide further insights into the environmental variables controlling sediment accumulation in lowland gravel bed rivers. We sampled 21 sites, during spring and autumn, selected to cover a gradient of excess fine sediment. Fine sediment was sampled using a range of methods including visual assessments, the disturbance method, and suspended sediment concentrations. A range of abiotic predictors was measured during sampling, and hydrological and antecedent flow indices were derived from local flow gauging station data. The results show reach scale visual estimates of fine sediment to be significantly and highly correlated with fully quantitative estimates of total surface sediment. Multivariate regression analysis showed that flow variables (regime, antecedent, and local flow characteristics) were strong predictors of deposited sediment metrics but poor predictors of suspended sediment. Organic content was shown to be relatively independent of total sediment quantity and is likely driven by other factors which influence the supply and breakdown of organic matter.

Alteration of gravel-bed river morphodynamics in response to multiple anthropogenic disturbances: Insights from the sediment-starved Parma River (northern Italy)

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.

Intelligent hybridized modeling approach to predict the bedload sediments in gravel-bed rivers

Intelligent hybridized modeling approach to predict the bedload sediments in gravel-bed rivers

Alluviation of a side-channel by bed material load. Field measurements and modelling

In this research, we explore the alluviation process of an artificial side-channel built in August 2015 and designed to alleviate bank erosion risks on the main river. The study area is located on the lower Gállego River, a meandering-wandering gravel-bed river draining the Southern Pyrenees. This river reach is still dynamic (i.e. chutes, meander migration and other riverine processes are often observed during floods) despite the presence of three dams in the upper catchment, encroachments and extensive mining during the 1960s–80s that led to severe incision. In this research, we focus on the effects of bankfull-like flood events (Qpeak = 354 m3/s) between February 2016 and February 2017, which alluviated 62% of the side-channel. This research aims at finding the physical mechanisms that explain the alluviation process and at putting them in the general context of the current geomorphic trend of the Gállego River in response to past and ongoing impacts.The causes of the alluviation are studied through collecting and analysing field data, which in turn, are used as input in a novel modelling strategy that includes one-dimensional hydraulic modelling, semi-empirical expressions to obtain the sediment supply entering the side-channel system and a morphodynamic model able to deal with granular sediment mixtures in compound channels. The analyses of the numerical results along with the recent history of impacts and general channel pattern adjustments help us understand about the morphodynamics mechanisms responsible for the alluviation of the side-channel.

Experimental study of boulder concentration effect on flow resistance in gravel bed channels

Previous studies demonstrated that for open channel flows the power velocity profile can be integrated to obtain the flow resistance law. In this paper the relationship between Γ coefficient of the power velocity distribution, the channel slope and Froude number (Eq. (9)) is firstly presented. Then the measurements carried out in a laboratory flume covered by hemispheric elements for two different hydraulic conditions (partially inundated and inundated) are used to calibrate this relationship. These elements are placed with a square arrangement and have a concentration range 4–64%. For the two investigated hydraulic conditions, this analysis demonstrates that the relationship to estimate the coefficient of the velocity profile is characterized by the same exponent of slope and Froude number while a different scale factor a has to be used. The effect of roughness element concentration Ch on flow resistance is also studied by the calibration of Eq. (9) for each experimental series characterized by a single value of Ch. For the partially inundated condition and values of the roughness element concentration less than 25%, the coefficient a increases with Ch while for Ch values ranging from 25 to 64% a decreases with concentration. For the submerged condition, the coefficient a increases with Ch and results almost constant for concentration values greater than 49%. The variability of the coefficient a with Ch is the effect of the variability of the reference plane for the water depth measurement with the concentration. Finally, the obtained relationships to estimate Γ function and the theoretical flow resistance law are verified by 205 measurements carried out in gravel bed rivers. In conclusion, the developed analysis demonstrates that an accurate estimate of the friction factor can be obtained for the investigated gravel surfaces by the proposed flow resistance equation and the obtained relationship to estimate Γ function.

Calculation Model to Predict the Static Armor Layer Size Distribution After the Reconstruction of a Gravel River Bed

The size distribution of armor layer in mountain rivers is an important factor that affects the stability of the river bed. However, there are relatively few studies on the prediction of armor layer size distribution in the reconstruction process after the previous static armor layer becomes unstable. In response to the above challenges, this study considers the incipient probability of sediment particles as the starting point, and comprehensively considers the coupling relationship between the initial bed materials, bed structure, armor ratio, and flow intensity, using a simple calculation model for predicting the static armor layer size distribution after reconstruction of a gravel-river bed. This paper introduces the concept of critical incipient particle size Dc, and considers that sediment particles smaller than Dc will incipient easily, resulting in a higher probability of being washed out, whereas the incipient probability of sediment particles larger than Dc (this part of the large-particle sediment includes not only the original particles on the bed surface, but also the large sediment particles exposed by the erosion of the bed subsurface) is relatively small. At the same time, this model also uses the armor ratio to reflect the impact of the bed surface structure. This study cites data from five sets of laboratory flume experiments to verify the calculation model, and the experimental results show that the model calculation results are in good agreement with the experimentally measured data, especially in predicting the median diameter D50 of the static armor layer. Our calculation model provides theoretical guidance for the study of mountain riverbed stability, earthquake prevention and disaster reduction.

Lateral and longitudinal flight dispersals of a stonefly, Alloperla ishikariana (Plecoptera, Chloroperlidae), from the hyporheic zone in a gravel-bed river in Japan

The life-history traits of amphibitic insects are not well understood. These insects inhabit saturated interstitial areas below the riverbed (hyporheic zone) at the larval stage, mate in terrestrial habitats, and return to rivers for oviposition, but there is no knowledge concerning their dispersal characteristics. We sought to address this by examining how far amphibitic insects disperse away from the channel (laterally) and along upstream or downstream (longitudinally) in a gravel-bed river. Alloperla ishikariana was selected as the focal species because it numerically dominates other amphibites in an 18-km study segment of a 4th-order gravel-bed river in Hokkaido, Northern Japan. Malaise traps were set at various distances from the channel towards the riparian forest to estimate lateral dispersal distances. An elevated stable nitrogen isotope ratio in downstream larvae, caused by the influence of effluent from a wastewater treatment plant, was used to assess longitudinal dispersal by identifying and tracking adult movements. Laterally, 50th and 90th percentile dispersal distances were 11.66 and 35.09 m for female A. ishikariana and 20.59 and 59.20 m for male, respectively; this overlapped with distances previously estimated for other aquatic benthic taxa. Longitudinally, 50th and 90th percentile dispersal distances were 0.74 and 1.43 km for female and 3.11 and 7.87 km for male, respectively. Alloperla ishikariana had one of the longest upstream traveling distances compared with other aquatic insects, and the longest among Plecoptera taxa known thus far where male exhibited a greater dispersal distance. A higher number of adults demonstrated upstream movement, suggesting an upstream bias in the longitudinal dispersal of A. ishikariana. Overall, amphibitic stoneflies did not exhibit distinct dispersal characteristics compared with the results of previous reports on presumably benthic taxa. Our findings support an improved visualization of a multi-dimensionally connected river ecosystem in terms of material flow, including vertical connectivity.

Additive Effects of Sediment and Nutrient on Leaf Litter Decomposition and Macroinvertebrates in Hyporheic Zone

Despite the fact that leaf decomposition constitutes an important function in rivers, how multiple environmental stressors simultaneously affect it remains largely unknown. This study investigated the interactive effects of fine sediments (particle size: &lt;2 mm; experimentally manipulated) and a specific nutrient (i.e., nitrate) on subsurface (hyporheic) leaf litter decomposition rate and macroinvertebrates in a gravel-bed river and its tributary in eastern Hokkaido, Japan. The experiment was conducted by measuring leaf litter decomposition of dried Alnus japonica leaves (3 ± 0.05 g) in benthic and hyporheic zones with and without sediment treatments at four sites that had a gradient of nitrate concentration. The decomposition rate was comparable between the two zones but was slowed down by sediment addition in the hyporheic zone. The functional responses were highly predictable for the individual stressors. Detritivore invertebrates were the main driving component of decomposition in the decreased leaf litter decomposition rate under a higher fine sediment condition, whereas higher nitrate accelerated the leaf litter decomposition rate by stimulated microbe-driven decomposition as well as detritivore feeding. Overall, the negative effect of fine sediment could be offset in the presence of nitrate while considering gross functional responses. We demonstrated the additive effects of fine sediment and nitrate on leaf litter decomposition in the hyporheic zone.

The estimation of bedload in poorly-gauged mountain rivers

Bedload transport is one major driver of gravel-bed river morphodynamics, and its quantification is capital for many environmental issues and river engineering applications, as well as for landscape evolution studies. To this point, bedload transport rates and volumes have been classically computed by means of sediment transport formulae. The most used bedload transport equations compute the bulk bedload mass based on section-averaged hydraulic parameters. However, due to the non-linear behavior of sediment transport, bedload formulae are sensitive to the input parameters. Then, some doubts arise when applying bedload equations on poorly gauged river reaches, i.e. rivers where there are no hydrological records and rating curves. In this paper, we assess the application of bedload equations in the case of poorly gauged river reaches, and we test a workflow to follow in such situations. This workflow consists of three steps: (i) Reconstructing the flow duration curve, based on gauging records from neighboring river basins; (ii) Solving the hydraulic geometry relations of the study-case river-reach, based on a flow friction equation; and finally, (iii) Computing bedload with a sediment transport equation. We tested this approach against the bedload information available in the literature for Idaho streams and we found that it could potentially approximate annual bedload volumes in ungauged reaches under certain conditions. To illustrate the potential of this workflow, we also computed bedload volumes for two ungauged river reaches from the Cantabrian mountains (NW Spain).

Experimental Study on the Shearing and Crushing Characteristics of Subaqueous Gravels in Gravel Bed River

Experimental Study on the Shearing and Crushing Characteristics of Subaqueous Gravels in Gravel Bed River