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Proper estimation of sediment movement is very critical for the management of alluvial rivers. Computing the sediment transport with single particle size is possible. However, particles on the river bed and in transport have a size distribution. It is very important to estimate bed material size change, such as bed armoring, in case of scour. In this study, the applicability of the bed sorting method, which is available with HEC-RAS, was analyzed. Bed sorting methods divide the bed into two or three layers. Numerical simulations were conducted in the Geum River, Korea. The performance of the simulation with respect to bed sorting methods was evaluated by considering the temporal change of bed material size during the scour and armoring process. Three layer methods are not applicable for a natural river and had oscillatory temporal bed material size variation. The two layer method has stable temporal bed material size changes and predicts the armoring of the bed properly even with limited field data. Consequently, the active layer method is reliable for natural rivers to simulate the bed material size change while applications of three layer methods require sufficient investigation.

Because of multifunctional weirs installed as part of large river regulation works in Korea, water quality problems have arisen from environmental changes in tandem with decreased flow rates. However, there has been limited research into the green algae removal effect, water quality improvement in congested waters, dam and weir operations, and consequential riverbed changes. Studies regarding outflow in a basin, the application and development of sediment load output analysis methods, feasibility of related dam operations, and riverbed patterns have been separately performed. However, basins and rivers should be analyzed by an integrated method instead of an individual one. Therefore, in the present study, the effect of congestion on a river connected to a dam/weir and estuary bank was analyzed based on climate change scenarios HadGEM3-RA RCP 4.5 and 8.5, with the aim of integrating individual studies using watershed and river models. Flow was controlled by dam- and weir-related discharge simulations. Variations in the riverbed caused by the transfer of suspended load in the downstream region were analyzed for both long and short durations. The results of this analysis suggest that given future climate change scenarios, the width of the river and riverbed variations in the riverbed are expected to rise. HIGHLIGHTS Impact of long-term geometric variation in rivers.; Analysis of climate change scenarios.; Integrate watershed and river.; Variations in the riverbed for both long and short durations.; Analysis of both watershed runoff and sediment transport in a river.

International Roughness Index (IRI) is a key parameter in pavement performance evaluation. This study investigates developing a reliable prediction model that can be used to estimate IRI of rigid p...

Water scarcity can mean scarcity in availability due to physical shortage, or scarcity in access due to the failure of institutions to ensure a continuously regular supply or due to a lack of adequate infrastructure. Water scarcity will be exacerbated as rapidly growing urban areas place heavy pressure on water resources. To solve these problems, various solutions have been applied, but a fundamental solution has not been applied. Recently, a researched and developed infiltration rainwater drainage (IRD) system is being applied with consideration of its applicability. In this study, features of surface runoff and infiltration according to various flow patterns were analyzed using a three-dimensional CFD (Computational Fluid Dynamics) model for calculating water flow in the IRD system. To estimate the optimal setup, a permeability test and scaled model simulation were performed. The runoff characteristics of the IRD system with respect to rainfall intensity and duration were analyzed with dimensionless variables. With the prototype model, the drainage characteristics of the IRD system were analyzed over time using the hydrological curves. From the simulated results, it was found that the IRD system analyzed in this study was appropriate in the field by comparative analysis with the existing system based on peak runoff, internal storage, and lag time. Therefore, by applying the IRD system in the future, it is expected that the IRD has benefits, such as delayed lag time, surface runoff decrease, and an attenuation of the peak runoff.

Because river flooding and urban inundation due to extreme rainfall cause the severe damages on the infrastructure, it is necessary to develop an accurate prediction technique and to overcome the disasters. In this study, numerical simulation method was applied to predict urban inundation area with appropriate assumptions and hydrological data in the Lower Var valley region in France. The application site is located in the southeast of France and also geometrically complex with several hydraulic structures, such as weir and bridge piers from the mainstream of a river to the Mediterranean Sea. With complex geometrical consideration, numerical modelling of inundation was conducted separately with two steps. Firstly, the whole area of river reach with the urban area was simulated and analyzed. From the results, the smaller urbanized area was specified with consideration of the capacity of inundation. Two-dimensional hydrodynamic model, MIKE 21 FM (flow model) is applicable to simulations of river hydraulics and flood inundation including the urbanized properties. Upstream discharges for the boundary conditions were set up with based on the Gumbel distribution and SCHADEX method. From the numerical simulation, inundation area and river flow variation were analyzed and compared with respect to the upstream discharge scenarios. Furthermore, the effect of computational mesh resolution was analyzed with the urban model. Calculated flooded areas from the simulation results of the whole area model and urbanized models were compared and verified as a newly proposed and applied procedure of inundation analysis in the riverine area.

Changes in rainfall patterns due to climate change will change the hydrological elements in the stream and the riverbed changes that will occur consequently. In addition, dredging and multi-functional Weir installation was finished along the Nakdong River, South Korea in 2012 as a part of the Four Major River Restoration Project. Due to the project the river became wider and deeper with deeper water depth. If the characteristics of the watershed are maintained, it will return to the pre-maintenance stream, which is the dynamic equilibrium of the stream. Also, there are very few studies comparing and analyzing changes in river basins in connection with climate change. In this study, to develop the riverbed variation technique considering the climate change in the Nakdong River Basin. The fit of the model was analyzed by using GSTARS, which is a hydraulic model, by analyzing the changes of the riverbed according to the number of stream tubes and the sediment transport equation. As a result of the study, it was found that the riverbed change was appropriate when three stream tubes were used and the riverbed change was over estimated when the stream tubes were five. The Ackers and White and the Yang equations were found to be suitable for the riverbed changes. As the flow rate increases, the change of the riverbed becomes larger and the riverbed becomes narrower.

Flow simulation over a dune requires the proper input of roughness coefficients. This study analyzed a numerical simulation of open-channel turbulent flow over two-dimensional fixed dunes to reveal the effect of roughness on the dune bottom, and to determine the optimized combination of the turbulence scheme and the roughness height formula. The most appropriate roughness values and turbulence models were applied using Reynolds-averaged Navier&ndash, Stokes models. Seven methods were chosen to estimate the bed roughness properties at the inlet boundary section. The results of all cases calculated with the OpenFOAM toolbox were compared with laboratory experimental data for model validation. The performances of all bed roughness variations were evaluated according to the stream-wise and depth-wise directions with nondimensional values. Consequently, it was revealed that the combination of bottom roughness length scale at the inlet boundary and the k-&omega, shear-stress transport (SST) model was the most suitable for the flow separation zone and turbulent properties near the channel bottom.

Turbulence is one of the decisive parameters that cause scouring in the river bed and threaten the foundation of hydraulic structures. And choosing the right turbulent modeling scheme is the key to simulate this flow property accurately. This study investigated a turbulent flow in a scour hole developed in a channel by using OpenFOAM toolbox. Two different turbulence schemes, k−e and k−ω, were used to evaluate the performance of turbulent schemes in simulating the turbulence property in this complex region. Beside the main turbulence schemes, the difficulties in modeling the flow close to the wall also was solved by choosing the right wall function and boundary conditions. The results from these two models, the flow velocity profiles in streamwise and water-depth directions as well as the turbulent kinetic energy, were evaluated by comparing with the physical experimental data from previous research.

Reservoir sedimentation reduces the benefits from the storage of fresh water. The volume and distribution of sediment deposition must be predicted for a long term reservoir operation plan. Either or both experimental and numerical modeling can be applicable for an evaluation of reservoir sedimentation. Because sedimentation occurs along entire reservoirs and throughout the reservoir life span, a one-dimensional numerical sediment transport model, GSTARS, was considered in this study. Even though the model is not a truly two or three dimensional one, the model has capability of simulating channel geometric change in a semi-two dimensional manner using the stream tube concept. In this study, the effect of the number of stream tubes on the performance of the numerical simulation was analyzed using 14 years of real reservoir sedimentation data, and reasonable results were produced with three stream tubes. The densities of the deposited sediment depend on the reservoir operation scheme, especially for clay and silt. It was found that the predicted results vary with the density, and the prediction with various density with respect to location is required for a study reach where reservoir and river regions exit together.

Flow input from the basin will not remain the same as before due to climate changes. Since the predictions on river discharge due to climate change is given by scenarios, various discharge scenarios were prepared in this study. For a long term and reach prediction, semi-two dimensional sediment transport model, GSTARS, was used. The flood water surface elevations predicted by GSTARS model were analysed statistically and it was concluded that the model is applicable for the South Han River. Three stream tubes is the most suitable to simulate two dimensional river geometric change River geometric changes. For sediment load computation, Ackers and White equation and Yang equation were resonable. River will become narrower regardless of discharge variation, more discharge results in deeper channel.

Nguyen, T.H.T.; Park, S.W., and Ahn, J., 2020. Properties of rising multiple CO2 droplets under contamination of SO2: Understanding scenarios of leakage to seawater. Journal of Coastal Research, 36(4), 805–811. Coconut Creek (Florida), ISSN 0749-0208.Research on impacts of impurities on the rising of liquid droplets in other liquids is still quite limited, especially when it comes to the behavior of multiple particles. The properties of rising multiple CO2 droplets under contamination of SO2 are investigated in a scenario in which they may leak to the seawater from a pipeline or facility in a Carbon Capture and Storage (CCS) project. The interaction between droplets and their rising properties such as velocity were examined. The results of numerical simulation show that the presence of SO2 changes particles' shape and their rising velocities significantly compared with the single droplet case. This SO2 contamination also caused the repulsion of impure particles even when they were placed close to each other, which was observed as coalescence in the pure CO2 case. Results will help in understanding the impacts of contamination on the rise of multiple CO2 droplets such as that leaked by future CCS operations.

The flow around a single circular cylinder with splitter plate was investigated using Computational Fluid Dynamics. The present study investigated the effects of varying splitter plate length and the Reynolds numbers on flow characteristic, such as vortex shedding, drag force, lift force, separation point, pressure, and friction coefficients of the cylinder. It was revealed that the vortex shedding behind cylinder is completely suppressed when the splitter plate length is longer than the critical value, which is proportional to the Reynolds number. The variation of drag and lift coefficients with respect to splitter length can be classified into two patterns of a monotonic decrease and a general decrease but with small increase. We found that the first pattern occurs at Reynolds number ≤ 180 and higher Reynolds number gives the second pattern. When the splitter plate length is similar to the diameter of the cylinder, the vortex frequency, drag, and lift coefficients reach local minimum depending on the Reynolds number. A functional relationship between drag coefficient, length of splitter plate, and Reynolds number was determined.

A numerical simulation was used to compare the characteristics of flows past two cylinders in tandem versus side-by-side arrangements. Numerical experiments were performed at various Reynolds numbers and with different distances between the two cylinders. Diverse characteristics of flow, such as drag force, vortex shedding, and pressure distributions were investigated here. In tandem arrangement, at a certain distance, the drag coefficients of both cylinders change abruptly. However, at other distances, the drag coefficients vary somewhat linearly with the distance between cylinders. In side-by-side deployment, when the distance is more than three times the cylinders’ diameter, the higher Reynolds number has a smaller drag coefficient (as in the case of a single cylinder). At points where the flow pattern, drag, and pressure coefficients change significantly, the critical spatial ratios between the two cylinders were determined at different Reynolds numbers. In addition to the study of such changes in flow characteristics, the effect of flow pattern on the pressure field and drag force coefficients, as well as their relationship, was also investigated.

It is generally acceptable to assume that bed material load is equal to sediment transport capacity, if the exchange between bed and flow occurs instantaneously. However, for non-equilibrium sediment transport process, there are spatial and temporal delay effects. This is especially true for reservoir sedimentation processes. Recovery factor is a coefficient for non-equilibrium sediment transport. The determination of recovery factor can be obtained either experimentally or numerically. There is no consensus on the value of recovery factor in previous literatures. Numerical simulations with a semi-two dimensional sediment transport model, GSTARS4, were conducted in this study using various methods for the determination of recovery factor proposed by previous researches. Simulated results of a reservoir geometric change were sensitive to the selection of recovery factors. It was found that the recovery factor as a function of sediment size provided the most reasonable result. A functional relationship between recovery factor and sediment size was determined by comparing simulated and measured reservoir geometric change. Coarse sediment has small value of recovery factor.

The Soil and Water Assessment Tool 2012 (SWAT2012) offers four sediment routing methods as optional alternatives to the default simplified Bagnold method. Previous studies compared only one of these alternative sediment routing methods with the default method. The proposed study evaluated the impacts of all four alternative sediment transport methods on sediment predictions: the modified Bagnold equation, the Kodoatie equation, the Molinas and Wu equation, and the Yang equation. The Arroyo Colorado Watershed, Texas, USA, was first calibrated for daily flow. The sediment parameters were then calibrated to monthly sediment loads, using each of the four sediment routing equations. An automatic calibration toolIntegrated Parameter Estimation and Uncertainty Analysis Tool (IPEAT)was used to fit model parameters. The four sediment routing equations yielded substantially different sediment sources and sinks. The Yang equation performed best, followed by Kodoatie, Bagnold, and Molinas and Wu equations, according to greater model goodness-of-fit (represented by higher Nash-Sutcliffe Efficiency coefficient and percent bias closer to 0) as well as lower model uncertainty (represented by inclusion of observed data within 95% confidence interval). Since the default method (Bagnold) does not guarantee the best results, modelers should carefully evaluate the selection of alternative methods before conducting relevant studies or engineering projects.

The All American Canal transports water to southern California. There are two channels, the old one without lining and new one with lining to save water from the seepage loss. During the construction of the new canal, excavated sediments were piled on the right and left side banks of the old canal and the road between the new and old canals. Sediments fell into the old canal due to wind and gravitational forces. These sediment inputs to the old canal caused the flow to meander and the formation of side and middle bars. Numerical simulation of the lateral channel change was conducted using a semi-two dimensional model, GSTARS4, which is based on the stream tube concept and the theory of minimum energy dissipation rate. Both steady and unsteady flow simulations did not have significant difference of channel geometry. Application of theory of minimum energy dissipation rate, combined with stream tube concept, resulted in lateral migration of the channel, which cannot be simulated with truly one dimensional models, such as HEC-RAS and Fluvial-12. Channel meandering and the formation of middle bars were found from the semi-two dimensional GSTARS4 modeling.

Nguyen, T.H.T.; Park, S.W., and Ahn, J., 2020. Numerical method to determine upstream scour slope in relation to turbulence and particle movement. Journal of Coastal Research, 36(1), 189–195. Coconut Creek (Florida), ISSN 0749-0208.Several studies have been conducted to investigate the behavior of scour hole, which happens naturally at the end of the bed protections in the streams and rivers, because this phenomenon can result in the instability or destruction of man-made structures in the area. Some formulas or equations were introduced to calculate the upstream scour slope, one of the most important scour properties, but the application shows some difficulty because of the lack of data. This paper presents a simple but reasonable method to find upstream scour slope with the employing of a numerical simulation, in particular by considering the relationship between turbulence and particle movement.

Local scour at the downstream of the river bed protection is one of the most important parameters for the design criteria and sustainable management of the hydraulic structures. Previously, various researches on its process in the equilibrium state have been suggested with experimental and numerical approaches. In this study, relatively long-term laboratory experiments of local scouring at the downstream of fixed bed in an open channel were conducted with mono-granular sediment bed and analyzed about maximum scour depth and its temporal development. In particular, we conducted experiments with relatively low Froude number (less than 0.5) and their duration of tests was exceeded over 700 hours. We modified the relationship between the dimensionless time and length scales of the maximum scour depth of the local scour hole based on the turbulent shear layer thickness. A new functional relationship between dominant factors and the maximum scour depth in the equilibrium state were suggested and compared with previously suggested formula. Also, from the results by nonlinear regression, Froude number was founded as a dominant factor on the prediction of equilibrium maximum scour depth.

Lewis and Clark Lake is located on the main stream of the Missouri River. The reservoir is formed behind Gavins Point dam near Yankton, South Dakota, U.S.A. The Lewis and Clark Lake reach extends about 40 km from the Gavins Point dam. The reservoir delta has been growing since the closure of Gavins Point dam in 1955 and has resulted in a 21% reduction of storage within the maximum pool of the reservoir. Among several sediment management methods, drawdown flushing has been recommended as a possible management technique. The engineering viability of removing sediments deposited in the lake should be examined by numerical modeling before implementing a drawdown flushing. GSTARS4 was used for this study and calibrated by using measured data from 1975 to 1995. Channel cross-section changes and amount of flushed sediment were predicted with four hypothetical flow scenarios. The flushing efficiencies of all scenarios were estimated by comparing the ratios between water consumption and flushed sediment during flushing.

The assessment of the impact of climate change depends not only on quantitative changes in precipitation but also system characteristics that can be changed and enhanced. This study investigated the effect of building the shared network of a rainwater harvesting system as an adaptation to climate change scenarios. The performance of a rain barrel network under three climate change scenarios and three global circulation models (GCM) is examined. A sample community composed of four prospective users with individual storage is tested with various forms of shared connections. Most importantly, the results show that the benefit from shared rain barrels greatly increases under the climate change conditions compared with the historical rainfall data. Especially, for high reliabilities, the results indicate that the benefit of a rain barrel network increases under future climate change scenarios, whereas it does not show apparent improvement for low reliabilities. However, the performance of a rain barrel network is highly dependent on location and climate change scenarios. In contrast, the GCM does not considerably affect the performance of the shared network. The results of this study highlight the needs to establish sharing networks of rainwater harvesting systems under the climate change conditions, which would significantly increase the benefit of the entire community.

The deposition of hydraulically transported sediments occurs in all flow impoundments, whether they be naturally occurring or man-made. The natural system way of managing the deposition is to fill the impoundment with sediment until a point is reached where the flow of water finds a new path requiring less energy. This is very often caused by an impoundment completely or nearly full of sediment. If left in the current flow regime, Lewis and Clark Lake will eventually fill with deposited sediment, albeit more than 150 years in the future. The man-made reservoir, Lewis and Clark Lake, formed by Gavins Point Dam, has existing uses that preclude merely allowing the reservoir to fill up. The lake is used for hydropower, navigation re-regulation, recreation, water supply, and flood storage. In an effort to find ways to maintain all of the interests on the lake, management of the deposited sediments in the reach is vital. While the specific management process for the reservoir is yet to be determined, the Lewis and Clark Lake Sediment Management Study aims to develop tools to evaluate a wide variety of possible management proposals.