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This article focuses on developing models that estimate suspended sediment concentrations (SSCs) for the Lower Brazos River, Texas, U.S. Historical samples of SSCs from gauge stations and satellite imagery from Landsat Missions and Sentinel Mission 2 were utilized to develop models to estimate SSCs for the Lower Brazos River. The models used in this study to accomplish this goal include support vector machines (SVMs), artificial neural networks (ANNs), extreme learning machines (ELMs), and exponential relationships. In addition, flow measurements were used to develop rating curves to estimate SSCs for the Brazos River as a baseline comparison of the models that used satellite imagery to estimate SSCs. The models were evaluated using a Taylor Diagram analysis on the test data set developed for the Brazos River data. Fifteen of the models developed using satellite imagery as inputs performed with a coefficient of determination R2 above 0.69, with the three best performing models having an R2 of 0.83 to 0.85. One of the best performing models was then utilized to estimate the SSCs before, during, and after Hurricane Harvey to evaluate the impact of this storm on the sediment dynamics along the Lower Brazos River and the model's ability to estimate SSCs. [ABSTRACT FROM AUTHOR]

Scour is a significant contributing factor to bridge failures, and when a bridge fails, it totally or partially loses its serviceability, causing fatalities, delays in emergency transportation and evacuation efforts, and economic losses. The mechanism of scour in riverine environment is different from those in areas under wave action, that is, coastal, and lacustrine environments. A total of 38 experiments were conducted in the laboratory under wave-alone, current-alone, and waves–current combined conditions to investigate the flow pattern and geometry of scour holes around bridge piers. Under these conditions, different flow parameters were considered and the influence of these parameters on the scour hole geometry was observed. The results showed that the combination of wave and current produced scour depths larger than those of the wave-alone experiments but smaller than those created by the current. Particle image velocimetry was used to investigate the flow field around piers and observe changes in vortex characteristics due to the change in flow conditions. Finally, an attempt was made to relate the size and shape of vortices to the scour process. It was concluded that the strength of wake vortices, the relative direction of the flow and wave, and the distances of waves from the channel bottom influenced the scour geometry and the downstream deposition pattern. [ABSTRACT FROM AUTHOR]

The frequency and intensity of recent flood events demonstrate the need for investigating the forces exerted on inundated bridges. The hydrodynamic force coefficients for bridge superstructures are well established in the literature, but they can be significantly affected by the accumulation of debris upstream and the presence of substructures (e.g., piers, bent caps). The aim of this study is to evaluate the effects of debris-damming and substructures on hydrodynamic forces exerted on bridge superstructures. For this purpose, a series of laboratory experiments on the small-scale bridge and debris models was performed, and the lift and drag forces and overturning moments on bridge decks with debris and substructures were measured and compared to the hydrodynamic forces generated by the flow on superstructures without blockages. The total streamwise and vertical forces and overturning moment were used to investigate the effects of debris and substructures on superstructure forces. Results are also presented on drag, lift, and moment coefficients, as they revealed a considerable change in the hydrodynamic force and moment coefficients because of the additional flow blockages created by debris and substructures. Maximum drag coefficients were observed for a flat plate debris model, combined bridge model (i.e., superstructure, debris, and superstructure), partially submerged model, and a substructure-superstructure model of a fully submerged bridge. Maximum lift and moment coefficients occurred for the substructure and wedge debris models, respectively. • Scale model of the typical bridge superstructures is assessed. • The effect of woody debris and bridge substructures is reported. • Debris and substructures are found to impact the hydrodynamic forces considerably. [ABSTRACT FROM AUTHOR]

Stream-crossing bridges are designed to pass the design flow while maintaining a minimum freeboard; however, flood events are reported as the most frequent cause of bridge failure in the U.S. and around the world. Floodwater exerts significant forces on bridges, shearing and overturning their decks, which may cause them to fail. When a bridge fails, it loses its total or partial serviceability, causing fatalities, delays in emergency transportation and evacuation efforts, and economic losses. An accurate estimation of hydrodynamic forces on a bridge superstructure, therefore, is vital to assess its vulnerability to flooding. The purpose of this study is to investigate the effects of bridge geometry and flow conditions on hydrodynamic forces. A series of experiments on bridge scale models were performed in a laboratory flume to analyze the response of the drag, lift and moment coefficients to bridge geometry (deck width, and girders height and shape) and flow conditions (inundation ratio, proximity ratio, blockage ratio, and Froude number). The experimental results showed that hydrodynamic force and moment coefficients are dependent on the extent of the bridge submergence, Froude number, and proximity of the bridge to the streambed. The relationship between bridge geometry and force coefficients indicated that the geometric features of bridges have a large influence on flow field as well as drag, lift, and moment coefficients. [ABSTRACT FROM AUTHOR]

The existence region plan of alternate bars, multiple bars, meandering and braiding, introduced by da Silva in 1991 and presented in its most recent form by Yalin and da Silva in the 2001 IAHR monograph Fluvial Processes, is updated and revised. For this purpose, the plan is extended by adding available laboratory and field data from the recent literature, as well as earlier data that only recently became available to the authors. Data from two series of laboratory runs conducted by the authors are also included. These were conducted to fill in a gap in the existing data, pertinent to the definition of the existence region of alternate bars. This work led to a revision to the location of the boundary lines of the existence regions of both alternate bars and meanders. An attempt was also made to reveal the existence regions of different types of multiple bars. [ABSTRACT FROM PUBLISHER]

The size of the largest horizontal coherent structures (HCSs) of turbulence in open-channel flows is investigated experimentally on the basis of three series of flow velocity measurements. These are further used to explore the dynamics and morphological consequences of HCSs. The flow velocity measurements were carried out in a 21 m long and 1 m wide channel, with a bed formed by sand with average grain size of 2 mm. The bed surface was flat. The turbulent and subcritical flow under investigation was uniform, with a flow depth of 4 cm. The bed slope of 0.0015 was such that, for the present flow depth, the bed shear stress acting on the bed was substantially below the threshold for initiation of motion, thus ensuring that the bed remained flat throughout the measurements. To the knowledge of the writers, this work is a first attempt to systematically investigate HCSs in open-channel flows. It should be viewed as an extension to the case of horizontal structures of work previously carried out by a number of authors on large-scale organized turbulence motion in open-channel flows, so far focusing exclusively on vertical coherent structures (VCSs). The horizontal burst length was found to be between five and seven times the flow width. A slight internal meandering of the flow caused by the superimposition of burst sequences on the mean flow was detectable. Both of these findings lend support to the longstanding belief expressed by many prominent researchers that the formation of large-scale river forms is directly related to the large-scale turbulence. In particular, the present measurements for the first time provide some direct evidence in support of hypotheses previously raised by Yalin and da Silva regarding the formation of alternate bars and meanders through the action of HCSs on the mean flow and the mobile bed and banks. [ABSTRACT FROM AUTHOR]

• Suspended Sediment Concentration (SSC) was estimated from digital imagery. • The effect of sediment color on the estimation of SSC was assessed. • Regression models were developed between visible wavebands reflectance and SSC. • The models were developed for four sediment samples with different colors. • Strong relationships were observed between red waveband reflectance and SSC. Satellite remote sensing has been extensively used for estimating the suspended sediment concentration (SSC) in coastal and inland waters. The application of this method to smaller waterbodies, however, encounters several limitations, such as the coarse temporal and spatial resolution of satellite images, cloud coverage intercession, and inaccessibility during emergency periods. Conventional digital cameras are used for monitoring the water quality parameters in inland waters, but their application for remote sensing of SSC in inland waters is still under development. The empirical models developed to estimate SSC from digital imagery are usually site-specific and do not consider the effect of the sediment properties such as grain size and shape, sediment color, and types of minerals. The performance of digital cameras for estimating SSC is assessed in this study, and the effect of sediment color on the accuracy of this method is investigated. A series of laboratory experiments were conducted using four different colors of sediment: light gray, dark gray, light brown, and dark brown. The results showed that the red waveband reflectance of digital imagery was more sensitive to the variation of SSC than that of blue and green waveband. The sediment color evidently affected the correlation between the measured SSC and waveband reflectance, even with the same particle size distribution. Sediment with darker color showed the lowest reflectance values, whereas lighter-color sediment has the highest reflectance values. The performance of the developed SSC-reflectance regression models for all sediment colors was assessed at two river sites, i.e., Village Creek, and the West Fork Trinity River. The correlation between measured and predicted SSC for Village Creek, that had the same sediment size and color as the light gray soil, was high ( R 2 = 0.98). The correlation was relatively low ( R 2 = 0.55) for the West Fork Trinity River and dark gray soil water samples which had a similar color and different sediment sizes. The difference in sediment sizes could explain why the SSC-reflectance model derived from the dark gray soil exhibited poor performance in predicting the SSC for this site. This study demonstrated that consideration of sediment color effect in developing a remote sensing algorithm from digital imagery would result in more accurate estimations of SSC in riverine environments. [ABSTRACT FROM AUTHOR]

Freshwater unionid mussels are among the most imperiled fauna in North America, and their decline has been partially attributed to sediment from anthropogenic activities. However, there remains a debate regarding the role played by sediment in mussel declines due to a lack of field and laboratory evidence. If sediment is responsible for mussel declines, then a lack of information will likely impede efforts to mitigate species declines and protect remaining habitat. However, if the impacts of sediment are overstated, time and resources may be wasted on a threat that has little bearing on mussel declines or habitat loss. Given this knowledge gap, the purpose of this paper is to review the literature focused on the potential impact of suspended sediment and sedimentation on freshwater mussels. We focused our search on suspended sediment, expressed either as suspended sediment concentration (SSC) or total suspended solids (TSS), and sediment deposition and scour. We found increases in suspended solids could impact mussels by decreasing food availability, physically interfering with filter feeding and respiration, and impeding various aspects of the mussel–host relationship. We also found mussel–sediment thresholds, wherein certain concentrations of sediment caused significant declines in population performance, which could serve as reference points for ecological research and management. Specifically, we found clearance rates (a measure of feeding) were negatively impacted by TSS concentrations >8 mg/L, and respiratory stress occurred at ∼600 mg/L. Declines in fertilization success and glochidial (i.e., mussel larvae) development were observed at TSS values of 15 mg/L, and reproductive failure occurred at 20 mg/L. Impacts on host fish attachment and glochidial encystment occurred at TSS concentrations of 1250–5000 mg/L. Impacts on fish varied depending on the biological endpoint but typically occurred at TSS values ranging from 20 to 5000 mg/L. We also found mussels were sensitive to smothering and mortality occurred at depths as low as 0.6–2.5 cm of substrate. Finally, we found relative shear stress (RSS) values >1, which is a measure of substrate stability in response to scour and entrainment, resulted in significant declines in mussel biodiversity. [ABSTRACT FROM AUTHOR]

In this article, the authors acknowledge Kourosh Babaeyan-Koopaei for complementing their work by plotting laboratory and field data. They also appreciate his result which highlights that belonging to the meandering regions of the plan is not sufficient to determine the meandering of a stream. They also consider author A.S. Shakir's criterion for braiding and for the division into n sub-channels described in his book.

River ice complicates river hydraulics and morphodynamics by adding a new boundary layer to the top of the flow. This boundary layer affects the velocity distribution throughout the depth due to increased flow resistance, and varies the local boundary shear stress on the bed (lower boundary) by adding new shear stress on the upper boundary (under surface of the ice). Variation of shear stress plays an important role in incipient motion of upper and lower boundary materials: sediment motion and transport are directly affected by local boundary shear stress, as are ice cover thickness, condition, and progression. This paper provides estimates of upper and lower boundary shear stress during stable ice cover and the important stage of ice cover breakup using available methods based on continuous field measurements of velocity profiles obtained with a bottom-mounted acoustic Doppler current profiler in the Nelson River, Canada. Boundary shear stresses varied dynamically with transformation of the ice cover, including the presence and removal of slush ice and formation of the ice jams. Estimated upper boundary shear stress varied between 0.52 and 23.87 N=m², whereas lower boundary shear stress varied between 1.51 and 2.40 N=m², with the highest values observed during breakup. These values are compared with estimates from previous laboratory experiments. [ABSTRACT FROM AUTHOR]

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

This paper explores use of acoustic Doppler current profiler backscatter amplitude as a surrogate for total suspended solids concentration. Total suspended solids concentration and acoustic Doppler current profiler data were collected at the Lower Nelson River and Red River in Manitoba, Canada, during both ice-covered and open water periods such that acoustic Doppler current profiler backscatter data could be calibrated to predict TSS concentrations. Several novel calibration schemes were evaluated, including multiple linear regression models that involved flow parameters determined from acoustic Doppler current profiler data in addition to acoustic backscatter intensity. The inclusion of the average of the friction velocities of the channel bed and ice cover, calculated from time-averaged velocity data, in a multiple linear regression was found to improve model performance in both studied rivers and during both ice-covered and open water periods. [ABSTRACT FROM PUBLISHER]