Sediment Transport Parameters Research Articles

Insights into nearshore sandbar dynamics through process-based numerical and logistic regression modeling

Process-based nearshore morphodynamic models are commonly used tools by coastal engineers and planners to predict the nearshore morphology change of sandy beaches across various spatiotemporal scales. Accurate modeling of the morphological response on medium and long time scales is imperative for quantitative assessments of coastal infrastructure over a project’s intended life-span. However, most previous modeling applications have focused on single/sub-seasonal storm events and are often limited to an assessment of the subaerial beach (i.e. berm and dune). This not only leaves uncertainty concerning the quality of morphology predictions on extended (> weeks) time scales, but also the capacity of process-based models to emulate realistic nearshore sandbar dynamics and the corresponding exchange of sediment between the nearshore-beach system. To shed light on these meso-scale dynamics, CSHORE, a 1D phase-averaged, process-based nearshore morphodynamic model, was applied on an annual scale to a multi-barred, dissipative beach in Oysterville, WA, USA. Thousands of unique sediment transport and hydrodynamic parameter combinations were executed during model calibration. A large portion of these simulations displayed physically realistic sandbar dynamics, including the growth, decay, and migration of intertidal and subtidal sandbars. To explore the model mechanisms enabling realistic bar behavior, the binary and multinomial logistic regression model were used to quantify the relationship between model parameter selection and the probability of various categorical bar configurations occurring in the final predicted profile. The results indicate the most sensitive parameters associated with barred morphology, in this study, and support the use of separate sediment transport parameters for low and high wave energy conditions. The co-utilization of numerical and statistical modeling outlined in this publication is generalizable to future exploratory modeling and/or calibration routines concerned with categorical outcomes.

Estimation of Sediment Transport Parameters From Measured Suspended Concentration Time Series Under Waves and Currents With a New Conceptual Model

AbstractIn‐situ observations of hydrodynamics and suspended sediment concentrations (SSCs) were conducted on an abandoned lobe in the northern part of the modern Yellow River Delta, China. The SSC record at the site is found to be the superposition of a general trend (fast increase and slow decrease cycle) caused by storm waves (SubSSC1) and relatively smaller fluctuations caused by tidal currents (SubSSC2). Physically, this indicates that storm waves eroded the bottom sediments while tidal currents then re‐suspended and advected the suspended sediments in the study area. To further obtain the suspended sediment transport parameters, first, SubSSC1 is modeled with significant wave height which incorporates a “memory curve” to consider the remaining impacts of historical waves. It is detected that waves in the past 75 hr still influence the present SSC which is reasonable because 75 hr is roughly the typical duration of a normal storm. Second, SubSSC2 is modeled with tidal excursion and trigonometric functions with measured periodicities. Finally, some sediment transport parameters, for example, the background SSC, the horizontal SSC gradient, the tidal constituents that advect it, and their relative time lags are optimized from the best fits of the measured and modeled SSC time series. The proposed framework for model construction and parameter optimization can be extended to other sea areas for inferring sediment transport parameters from field SSC time series at a specific station.

Development of a Quantitative Approach for Morphodynamic Assessment of Extreme Flood Event in Lokoja

Abstract – This study developed a quantitative approach for the morphodynamic assessment of River Niger at Lokoja. The study involves the collection of twenty-one years daily discharge and water level at the gauging station. The data were collated and outliers were removed. The missing data were fitted using the Least Square Method. The flood generating processes were investigated by computing the bankfull discharge of selected reach as well as collecting river bed samples at six (6) different locations along the river reach. Based on these, the specific gravity and mobile D50 and D90 of the bed materials were obtained. The preliminary investigation of the river morphodynamics was studied by computing the sediment transport parameters such as Shield parameter, bed shear velocity, sediment fall velocity amongst others. These parameters are significantly important due the high flow rate associated with the river. Based on criteria by two well-known sediment transport capacity formula, the river reach is characterized as sandy-bed River in line with Eugelund and Hansen’s Formula (E-H-F). The entire flow generation parameters and mobile river bed materials failed the Meyer and Peter- Muller criteria. Hence, the sediment transport capacity of the river was computed using (E-H-F). The results show that understanding the morphodynamics of the rivers play a significant role in the understanding of flooding.

Testing sea-level and carbonate production effects on stratal architecture of a distally steepened carbonate ramp (Upper Miocene, Menorca): A 3D forward modelling approach

Although distally steepened carbonate ramps have been studied by numerous researchers, the processes that control the development of these carbonate systems, including tectonics, differential carbonate production along the ramp profile, or antecedent physiography of the slopes, are an ongoing discussion. We use a stratigraphic forward model to test different hypotheses to unravel controls over distally steepened ramp development, referenced to the well-known Upper Miocene Menorca carbonate ramp (Spain). Sensitivity tests show that distally steepened ramps develop under complex interaction among accommodation, carbonate production and sediment transport parameters. Ramp slope initiation is favoured by still stands and falls of sea-level, in a setting with high-frequency sea-level fluctuations with amplitude between 20 m and 40 m. Low-frequency and higher amplitude sea-level fluctuations of about 115 m tend to form models with no significant slope development. The impact of antecedent slope on the geometry of ramps is determined by the paleoslope inclination, with flat to subhorizontal paleosurfaces resulting in ramps that mirror the antecedent slope. In contrast, steeper paleosurfaces tend to result in ramps with well-defined slopes. Our models, therefore, show that the ramp profile becomes more influenced by the depth constraints on the carbonate sediment producers than by the geometry of the underlying topography as the inclination of the paleosurface increases. The presented models also show that seagrass-dominated shallow carbonate production tends to result in steep slopes due to the low-transport characteristic imposed by seagrass trapping. This steepness can, however, be altered by the introduction of high transport sediment grains from deeper carbonate producers, which fill the slopes and more distal sections of the ramp profile.

Matematičko modeliranje tečenja i pronosa nanosa - primjer brane na rijeci Tisi

High flow velocities downstream of the Tisa Dam at Novi Bečej (Serbia), produced by the large difference between water levels in the upstream and downstream reaches, cause bank erosion by the right bank immediately downstream of the emergency spillway, threatening stability of the dam itself. Due to complex interaction between the parameters of flow and sediment transport at the given location, an approach involving a spatial (3D) mathematical model of flow and sediment transport, aimed at solving such complex processes, is investigated in this paper. An optimum solution meeting all requirements for the stability of structures in question has been reached by the model, through comparison of the results generated by the existing conditions with the result provided by the measures proposed to fix the problems.

GEP- and MLR-based equations for stable channel analysis

Abstract For decades, research on stable channel hydraulic geometry was based on the following parameters: river discharge, dimensionless discharge, the median size of bed material and the slope. Although significant research has been conducted in this area, including applied machine learning to increase the geometry model prediction accuracy, there has been no remarkable improvement as the variables used to describe the geometry relationship remain the same. The novelty of this study is demonstrated by the parameters used in the stable channel geometry equations that outperform the existing equation's accuracy. In this research, sediment transport parameters are introduced and analysed by applying the multiple linear regression (MLR) and gene expression programming (GEP) methods. The new equation of the width, depth and bed slope can give much-improved results in efficiency and lower errors. Furthermore, a new parameter B/y is introduced in this study to solve the restriction issue, either in width or depth prediction. The results from MLR and GEP show that in addition to the existing hydraulic geometry parameter, the B/y parameter is also able to give high accuracy results for width and depth predictions. Both calibration and validation for the B/y parameter yield high R2 and NSE values with low mean squared errors and mean absolute errors.

Research of Impacts of the 2018 Hokkaido Eastern Iburi Earthquake on Sediment Transport in the Atsuma River Basin Using the SWAT Model

Landslides, debris flows, and other secondary disasters caused by earthquakes threaten the safety and stability of river basins. Earthquakes occur frequently in Japan. Therefore, it is necessary to study the impact of earthquakes on sediment transport in river basins. In this study, considering the influence of reservoirs, the Soil and Water Assessment Tool-calibration and uncertainty program (SWAT-CUP) was employed to analyze the runoff parameter sensitivity and to optimize the parameters. We manually corrected the sediment transport parameters after earthquake, using the Soil and Water Assessment Tool (SWAT) model to assess the process of runoff and sediment transport in the Atsuma River basin before and after the 2018 Hokkaido Eastern Iburi Earthquake. The applicability of the SWAT model to runoff simulation in the Atsuma River basin and the changes of sediment transport process after the earthquake were studied. The research results show that the SWAT model can accurately simulate the runoff process in the Atsuma River basin, the Nash–Sutcliffe efficiency coefficient (NSE) is 0.61 in the calibration period, and is 0.74 in the verification period. The sediment transport increased greatly after the earthquake and it is roughly estimated that the amount of sediment transport per unit rainfall increased from 3.5 tons/mm/year before the earthquake to 6.2 tons/mm/year after the earthquake.

Field measurements on alluvial watercourses in light of numerical modeling: case studies on the Danube River.

Adequate monitoring and data acquisition of proper hydraulic, sediment, and constituent parameters in alluvial watercourses have become crucial aspects of human interaction with the environment. Conducting well-organized, comprehensive, and meaningful field measurements on natural watercourses are of great importance when assessing its hydraulic, morphological, and ecological state. However, this paper presents a methodology for field measurements on alluvial watercourses in light of numerical modeling. The proposed methodology focuses on collecting field data sets to calibrate numerical models for flow, sediment, and heavy metal transport. The proposed approach targets the simultaneous measurement of hydraulic, sediment transport, and heavy metal transport parameters that are key for calibrating constants and exchange mechanisms in contemporary numerical models. Using the principles laid out in this paper, two sets of measurements were carried out on the Danube River, one on a reach near Mohács in Hungary and the other on a reach near Belgrade in Serbia. The first case study discusses the measurement and results of comprehensive hydraulic and sediment parameters. The second case study considers hydraulic and sediment measurements complemented with trace metal measurements for zinc, lead, and mercury. These measurements were used for calibrating numerical models for flow, sediment, and heavy metal transport, as a proof of concept. It has been demonstrated that the gathered data sets contain key parameters that are strongly linked through physical laws and are needed for calibration purposes, as well as parameters that can allow the newly calibrated coefficients to be confirmed through other measured phenomena. Therefore, the proposed methodology provides minimal data sets with detailed measurements for calibrating numerical models for flow, sediment, and heavy metal transport. Guidelines for future measurements that can suffice the increasing need for numerical modeling and monitoring of natural watercourses are also offered.

Hydrodynamic modeling and radiotracer investigations in Kolkata Port Trust, Kolkata, West Bengal, India

In this study, hydrodynamic modeling and radiotracer investigations were conducted in Kolkata Port Trust, Kolkata, West Bengal, India to investigate the dispersion of sediments and to evaluate the suitability of three different dumping sites (Upper Auckland, Lower Auckland and Eden) for dredged sediments along a navigation channel. Scandium-46 (148-240 GBq) comprising scandium glass powder with a particle size distribution ranging from 75-100 μm was used as a radiotracer. The radiotracer was injected onto the seabed at the selected site using a remotely operated injection system and its movement on the seabed was tracked over a period of three months using waterproof NaI(Tl) scintillation detector. The tracer concentration curves were plotted on a site map of the area for different trackings and isocount contours were plotted. Qualitative information was obtained from the isocount contours such as the general direction of movement and spread of the radiotracer. The isocount contours showed that the sediment predominantly moved away from the navigation channel. From the isocount, a transport diagram was plotted based on isocount counter and sediment transport parameters such as the general direction of movement by sediments on the seabed, transport velocity, transport thickness and bed load movement rate were determined for all the sites. The dispersion patterns obtained for the sediments by modeling were compared with the experimental results and they were found to be similar. Thus, the model results were validated and the proposed sites were found to be suitable for dumping the dredged material because the sediments did not return to the navigation channel.

A new approach for scaling beach profile evolution and sediment transport rates in distorted laboratory models

Laboratory wave flume experiments in coastal engineering and physical oceanography are widely used to provide an improved understanding of morphodynamic processes. Wave flume facilities around the world vary greatly in their physical dimensions and differences in the resulting distortion of the modelled processes are reconciled using scaling laws. However, it is known that perfect model-prototype scaling of all hydro and morphodynamic processes is rarely possible and there is a lack of understanding to what extent distorted models can be used for direct morphological comparison. To address this issue, distorted scale laboratory flume experiments were undertaken in three different facilities, with the aim to measure and compare beach profile evolution under erosive waves and increasing water levels. A novel approach was developed to transform and scale the different experimental geometries into dimensionless coordinates, which enabled a direct quantitative comparison of the beach profile evolution and sediment transport rates between the differing distorted experimental scales. Comparing results from the three experiments revealed that the dimensionless scaled morphological behaviour was similar after the same number of waves – despite very different degrees of model distortion. The distorted profiles appeared to be suitable for comparison as long as a modified version of the Dean number is maintained between them. The new method was then validated with two further published datasets, and showed good agreement for both dimensionless profile shape, dimensionless sediment transport and morphodynamics parameters. The new approach scales the sediment transport by the square of the runup, proportional to HL, rather than H2, and yields good agreement between the datasets. It is further shown that the new scaling method is also applicable for comparing distorted profile evolution under water level increase, as long as the water level is raised in a similar way between the experiments and by the same total increment relative to the significant wave height (Δh/Hs).

Improved lithology prediction in channelized reservoirs by integrating stratigraphic forward modelling: Towards improved model calibration in a case study of the Holocene Rhine-Meuse fluvio-deltaic system

Stratigraphic forward modelling (SFM) provides the means to produce geologically coherent and realistic models. In this paper, we demonstrate the possibility of matching lithological variability simulated with a basin-scale advection-diffusion SFM to a data-rich real-world setting, i.e. the Holocene Rhine-Meuse fluvio-deltaic system in the Netherlands. SFM model calibration to real-world data in general has proven non-trivial. This study focuses on a novel inversion process constrained by the top surface and the sand proportion observed at specific pseudo-wells in the study area. Goodness-of-fit expressed by a new fitness function gives the error calculated as the average of two calibration constraints. Computational efficiency was increased significantly by implementing a new optimization process in two hierarchical steps: a) optimization in terms of sediment load and discharge, which are the most influential parameters having the largest uncertainty and b) optimization with respect to the remaining uncertain parameters, these being sediment transport parameters. The calibration process described allows for the most optimal combination of achieving acceptable levels of goodness-of-fit, feasible runtimes and multiple (non-unique) solutions to obtain synthetic stratigraphic output best matching real-world datasets.By removing model realizations which are geologically unrealistic, calibrated SFM models provide a multiscale stratigraphic framework for reconstructing static models of reservoirs which are consistent with the palaeogeographic layout, basin-fill history and external drivers (e.g. sea level, sediment supply). The static reservoir models that are matched with highest certainty therefore contain the highest geological realism and may be used to improve deep subsurface reservoir or aquifer property prediction.The new methodology was applied to the well-established Holocene Rhine-Meuse dataset, which allows a rigorous testing of the optimization; the calibrated SFM allows investigation of controls of the Holocene development on the sedimentary system.

Variability in Onshore Sediment Transport on a Natural Beach during a Central American Cold Surge Event

Briggs, T.R.; Figlus, J.; Torres-Freyermuth, A.; Puleo, J.A.; Warren, W., and Alrushaid, T., 2020. Variability in onshore sediment transport on a natural beach during a Central American cold surge event. Journal of Coastal Research, 36(3), 487–497. Coconut Creek (Florida), ISSN 0749-0208.Beaches facing the Gulf of Mexico along the northern part of the Yucatan Peninsula experience frequent Central American cold surge events, or northerly storms locally called “Nortes,” which interrupt the usual daily patterns of sea- and land-breeze–dominated nearshore dynamics. These perturbations of prevailing hydrodynamic forcing conditions also affect sediment distribution and transport parameters in the surf and swash zone, which are critical elements in understanding and modeling complex morphodynamic processes during storm events. However, detailed measurements of sediment characteristics throughout the water column during a storm event are scarce. This study presents field measurements of bottom and suspended sediment transported in the onshore direction during a 24-hour storm event impacting the Yucatan Peninsula. Sediment load data within the water column collected in 3 hour intervals via vertical arrays of streamer traps, deployed at two cross-shore locations in the inner surf zone, are compared with sediment data from collocated bottom grab samples. Time series of grain size distributions, sediment statistics, and respective vertical variations throughout the water column are related to measured bed-level changes to verify applicability of simple erosion and accretion predictors. Results indicate that bottom sediment and sediment distributions throughout the water column deviate substantially due to storms, highlighting the complexity and difficulty of assessing sediment transport and morphodynamic processes with a single-parameter sediment characteristic. Calculated total onshore transport rates during the Norte were on average one order of magnitude higher than during nonstorm conditions.

Modeling Mud and Sand Transfers Between a Macrotidal Estuary and the Continental Shelf: Influence of the Sediment Transport Parameterization

AbstractCoastal environments are directly influenced by terrigenous inputs coming from rivers through estuaries. Quantifying the amount of nutrients and contaminants transported by sediments from continental areas to the sea is crucial for marine resources protection. However, the complexity of estuarine dynamics makes it difficult to quantify sediment fluxes from field measurements alone and requires numerical modeling. Thus, using a realistic 3‐D hydrodynamic and sediment transport model, this study aims at evaluating the influence of model empirical parameters on sediment fluxes and estimating uncertainties on mud and sand transfers at a macrotidal estuary mouth. A sensitivity analysis, considering changes in sediment transport parameters, revealed that the system is sensitive not only to settling and erosion parameterizations but also to the spin‐up period and the sediment sliding process. Both estuarine circulation and tidal pumping induce a residual up‐estuary transport, which is balanced by seaward export during spring tides. Although more fine sediments are exported within the surface turbid plume during high river discharge, the net mud transport is directed up‐estuary due to increased baroclinic circulation. Besides, model results highlighted a strong seasonal variability in sediment fluxes with a short and high import during high river flow and a long and weak export during low river flow. Uncertainties associated with the simulated fluxes were about 93% for mud and 51% for noncohesive classes, based on the best performing parameter sets for surface suspended sediment concentrations. These results can be reliably extrapolated to similar macrotidal estuarine systems.

Scale‐Dependent Evanescence of River Dunes During Discharge Extremes

AbstractDuring high river discharge extremes, the growth of dunes can reach a maximum beyond which a transition to upper stage plane bed may occur, enhancing the river's conveyance capacity and reducing flood risk. Our predictive ability of this bedform regime shift in rivers is exclusively built upon high Froude number flows dominated by asymmetric dunes with steep downstream‐facing slipfaces that are rare in natural rivers. By using light‐weight polystyrene particles as a substrate in an experimental flume setting, we present striking dune morphodynamic similarity between shallow laboratory flow conditions and deep rivers, preconditioned that both flow and sediment transport parameters are accurately scaled. Our experimental results reveal the first observation of upper stage plane bed in a shallow laboratory flume that is reached for a Froude number well below unity. This work highlights the need to rethink widely used dune scaling relationships, bedform stability diagrams, predictions of flow resistance, and flood risk.

Effects of shrub patch pattern on runoff and sediment yield

Understanding the changes of runoff, sediment transport, and hydrodynamic parameters of slopes under the influence of landscape patch coverage and connectivity is of great significance for revealing the hydrodynamic mechanism and hydrological connectivity of slope soil erosion process. In this study, the changes of runoff, sediment transport and hydrodynamic parameters of downhill surface in different coverage levels (0%, 20%, 40%, 60%, 90%) and different connectivity modes (vertical path, horizonal path, S-shaped path, random patches) of shrublands were analyzed by field artificial simulated rainfall test. The results showed that, with the increases of shrub cove-rage, runoff yield and sediment yield decreased exponentially. When the coverage increased to more than 60%, the capacity of shrubs to reduce runoff and sediment became stable. With the increases of shrub coverage, flow velocity, flow depth, Reynolds number, Froude number, stream power, and flow shear resistance significantly decreased, while Manning's roughness coefficient and Darcy-Weisbach resistance coefficient increased significantly. When shrub coverage increased to more than 60%, there was no significant difference in the eigenvalues of hydraulic parameters. The runoff rate under the four connectivity modes followed the order of vertical path > S-shaped path > horizonal path > random patches. The sediment rate was the largest in the vertical path, followed by the S-shaped path, and the horizonal path was not significantly different from the random patches. The path with poor connectivity (horizonal path, random patches) exhibited stronger resistance of hydraulic transmission and poor hydraulic sedimentation capacity than the well-connected path (vertical path, S-shaped path). Our results could provide important theoretical basis for soil erosion control on the Loess Plateau and high-quality development of the Yellow River basin.

Determination of influential parameters for prediction of total sediment loads in mountain rivers using kernel-based approaches

It is important to have a reasonable estimation of sediment transport rate with respect to its significant role in the planning and management of water resources projects. The complicate nature of sediment transport in gravel-bed rivers causes inaccuracies of empirical formulas in the prediction of this phenomenon. Artificial intelligences as alternative approaches can provide solutions to such complex problems. The present study aimed at investigating the capability of kernel-based approaches in predicting total sediment loads and identification of influential parameters of total sediment transport. For this purpose, Gaussian process regression (GPR), Support vector machine (SVM) and kernel extreme learning machine (KELM) are applied to enhance the prediction level of total sediment loads in 19 mountain gravel-bed streams and rivers located in the United States. Several parameters based on two scenarios are investigated and consecutive predicted results are compared with some well-known formulas. Scenario 1 considers only hydraulic characteristics and on the other side, the second scenario was formed using hydraulic and sediment properties. The obtained results reveal that using the parameters of hydraulic conditions as inputs gives a good estimation of total sediment loads. Furthermore, it was revealed that KELM method with input parameters of Froude number (Fr), ratio of average velocity (V) to shear velocity (U*) and shields number (θ) yields a correlation coefficient (R) of 0.951, a Nash-Sutcliffe efficiency (NSE) of 0.903 and root mean squared error (RMSE) of 0.021 and indicates superior results compared with other methods. Performing sensitivity analysis showed that the ratio of average velocity to shear flow velocity and the Froude number are the most effective parameters in predicting total sediment loads of gravel-bed rivers.

Hydraulic Parameters for Sediment Transport and Prediction of Suspended Sediment for Kali Gandaki River Basin, Himalaya, Nepal

Sediment yield is a complex phenomenon of weathering, land sliding, and glacial and fluvial erosion. It is highly dependent on the catchment area, topography, slope of the catchment terrain, rainfall, temperature, and soil characteristics. This study was designed to evaluate the key hydraulic parameters of sediment transport for Kali Gandaki River at Setibeni, Syangja, located about 5 km upstream from a hydropower dam. Key parameters, including the bed shear stress (τb), specific stream power (ω), and flow velocity (v) associated with the maximum boulder size transport, were determined throughout the years, 2003 to 2011, by using a derived lower boundary equation. Clockwise hysteresis loops of the average hysteresis index of +1.59 were developed and an average of 40.904 ± 12.453 Megatons (Mt) suspended sediment have been transported annually from the higher Himalayas to the hydropower reservoir. Artificial neural networks (ANNs) were used to predict the daily suspended sediment rate and annual sediment load as 35.190 ± 7.018 Mt, which was satisfactory compared to the multiple linear regression, nonlinear multiple regression, general power model, and log transform models, including the sediment rating curve. Performance indicators were used to compare these models and satisfactory fittings were observed in ANNs. The root mean square error (RMSE) of 1982 kg s−1, percent bias (PBIAS) of +14.26, RMSE-observations standard deviation ratio (RSR) of 0.55, coefficient of determination (R2) of 0.71, and Nash–Sutcliffe efficiency (NSE) of +0.70 revealed that the ANNs’ model performed satisfactorily among all the proposed models.

Assessment of Water Flow and Sedimentation Processes in Irrigation Schemes for Decision-Support Tool Development: A Case Review for the Chókwè Irrigation Scheme, Mozambique

Water flow and sedimentation processes have been significantly erratic at the Chókwè Irrigation Scheme (CIS) and have affected its hydraulic performance. Given its expansion there is need to understand these processes taking place on-site and along the channels of the scheme. CIS being the biggest project of its kind in Mozambique requires proper management of water flow and sedimentation processes. Therefore, the effect of water flow, sediment transport and deposition parameters on the performance of the CIS is needed. In order to determine the effect of spatial and temporal water flow and sediment distribution trends along the irrigation canals, there is need to establish a correlation between these parameters. Determining the influence of water flow velocity on sediment settling rate at different depths along the canal reaches is important in managing the CIS. In addition, a developed decision-support tool to predict sediment deposition is required. For this reason, it is therefore crucial to carry out a timely assessment of water flow and sedimentation processes in CIS in a review concept. From the current review, some gaps that exist for more focused research on Chókwè Irrigation Scheme have been identified. In this regard therefore, there is need to develop an effective support tool for managing water flow and sediment deposition along the canal reaches with a view to increasing crop production in CIS.

Physical and coupled fully three-dimensional numerical modeling of pressurized bottom outlet flushing processes in reservoirs

Sediment deposition in reservoirs is an important research topic in engineering practice. Reservoir sedimentation has the potential to affect flood levels, drainage for agricultural land, pump station and hydropower operation as well as navigation. This paper describes the development of a coupled fully three-dimensional (3D) numerical model for the prediction of the local sediment flushing scour upstream of the bottom outlet. The presented numerical model solves the Navier-Stokes equations in conjunction with the k- ɛ turbulence model which includes both sediment transport and hydrodynamic parameters. The proposed coupled fully 3D numerical model is used to simulate experimental tests based on non-cohesive sediment. The geometric features of the scour hole (temporal and spatial hole development) upstream of the bottom outlet were reasonably well predicted compared to the experimental data. Furthermore, the velocity field upstream of the bottom outlet was in good agreement with measurements. The proposed numerical model for bottom outlet flushing was, therefore, validated because of its ability to accurately predict the scour hole development during the flushing process. The proposed numerical model can be considered reliable provided that the model is correctly calibrated and set up to reflect the conditions of a particular case study.

Storm Impact on Morphological Evolution of a Sandy Inlet

AbstractObservations of waves, currents, and bathymetric change in shallow water (<10‐m depth) both inside and offshore of a migrating inlet with strong (2–3 m/s) tidal currents and complex nearshore bathymetry show over 2.5 m of erosion and accretion resulting from each of two hurricanes (offshore wave heights >8 m). A numerical model (Delft3D, 2DH mode) simulating waves, currents, and morphological change reproduces the observations with the inclusion of hurricane force winds and sediment transport parameters adjusted based on model‐data comparisons. For simulations of short hurricanes and longer nor'easters with identical offshore total time‐integrated wave energy, but different peak wave energies and storm durations, morphological change is correlated (R2 = 0.60) with storm intensity (total energy of the storm divided by the duration of the storm). Similarly, the erosion observed at the Sand Engine in the Netherlands is correlated with storm intensity. The observations and simulations suggest that the temporal distribution of energy in a storm event, as well as the total energy, impacts subsequent nearshore morphological change. Increased storm intensity enhances sediment transport in bathymetrically complex, mixed wave‐and‐tidal‐current energy environments, as well as at other wave‐dominated sandy beaches.