Bart T. Grasmeijer

The predictability of cross-shore bed evolution of sandy beaches at the time scale of storms and seasons using process-based Profile models

Deterministic and probabilistic Profile models have been compared with hydrodynamic and morphodynamic data of laboratory and field experiments on the time scale of storms and seasons. The large-scale laboratory experiment is a pure 2D case and offers and ideal test case for cross-shore Profile models, as disturbing alongshore non-uniformities are absent. The field experiments are performed at the Egmond site (The Netherlands) during the EU-COAST3D project and represent storm time scale (Oct.–Nov. 1998) as well as seasonal time scale conditions (May 1998–Sep. 1999). The objective of the paper is to present information of coastal processes on these time scales and to assess the predictive capabilities Coastal Process-based Profile models with respect to hydrodynamics and morphodynamics at sandy beaches on the time scales of storms and seasons. Profile models can quite accurately (errors smaller than 10%) represent the cross-shore significant wave height distribution in the surf zone, if the wave breaking model is properly calibrated. The wave breaking coefficient should be a function of local wave steepness and bottom slope for most accurate results. Profile models can reasonably represent the cross-shore and longshore currents (undertow) in a pure 2D case and in 3D field conditions. Profile models including cross-shore mixing effects and breaker delay effects do not produce better predictions of the longshore and cross-shore current velocities. Profile models using default settings can quite reasonably simulate the behaviour of the outer and inner bars on the storm time scale; the behaviour of the beach cannot be modelled with sufficient accuracy on the storm time scale. Profile models can reasonably simulate the post-storm onshore bar migration, provided that the near-bed orbital velocities and wave asymmetry-related sand transport are represented in a sufficiently accurate way (using non-linear wave theories). Profile models cannot simulate the beach recovery processes on the post-storm time scale, because these essentially 3D processes are not sufficiently known to be included in the models. Profile models using default settings cannot simulate the behaviour of the outer and inner bars and the beach on the seasonal time scale; the behaviour of the outer bar on the seasonal time scale can only be represented properly after tuning using measured bed profiles. The simulation of the inner bar and beach morphology on the seasonal time scale could not be improved by tuning.

Modeling of waves and currents in the nearshore parametric vs. probabilistic approach

This paper introduces a hydrodynamic model that can predict the cross-shore transformation of wave height, on- and offshore orbital motion, and time-averaged cross-shore and longshore currents in a parametric and probabilistic mode. In the parametric mode, the computations are based on the root-mean-square wave height, the peak period, and the energy-weighted mean angle of incidence, while in the probabilistic mode a discrete number of classes with their own wave height, period, and angle of incidence is prescribed. Predictions of the two modes differ marginally and result in about the same error statistics when compared to data from laboratory and field experiments. Consistent with other probabilistic wave models, measured wave height distributions inside the surf zone were not reproduced accurately by the present probabilistic model. Although this could be remedied by introducing some variability around the breaker parameter, predictions of the other hydrodynamic parameters did not improve as a result. From a hydrodynamic point of view, it appears superfluous to use the rather time-consuming probabilistic mode for morphodynamic modeling; the parametric mode suffices.

BREAKER BAR FORMATION AND MIGRATION

Detailed studies have been undertaken to assist in the design of major extensions to the port of Haifa. Both numerical and physical model studies were done to optimise the mooring conditions vis a vis the harbour approach and entrance layout. The adopted layout deviates from the normal straight approach to the harbour entrance. This layout, together with suitable aids to navigation, was found to be nautically acceptable, and generally better with regard to mooring conditions, on the basis of extensive nautical design studies.Hwa-Lian Harbour is located at the north-eastern coast of Taiwan, where is relatively exposed to the threat of typhoon waves from the Pacific Ocean. In the summer season, harbour resonance caused by typhoon waves which generated at the eastern ocean of the Philippine. In order to obtain a better understanding of the existing problem and find out a feasible solution to improve harbour instability. Typhoon waves measurement, wave characteristics analysis, down-time evaluation for harbour operation, hydraulic model tests are carried out in this program. Under the action of typhoon waves, the wave spectra show that inside the harbors short period energy component has been damped by breakwater, but the long period energy increased by resonance hundred times. The hydraulic model test can reproduce the prototype phenomena successfully. The result of model tests indicate that by constructing a jetty at the harbour entrance or building a short groin at the corner of terminal #25, the long period wave height amplification agitated by typhoon waves can be eliminated about 50%. The width of harbour basin 800m is about one half of wave length in the basin for period 140sec which occurs the maximum wave amplification.Two-stage methodology of shoreline prediction for long coastal segments is presented in the study. About 30-km stretch of seaward coast of the Hel Peninsula was selected for the analysis. In 1st stage the shoreline evolution was assessed ignoring local effects of man-made structures. Those calculations allowed the identification of potentially eroding spots and the explanation of causes of erosion. In 2nd stage a 2-km eroding sub-segment of the Peninsula in the vicinity of existing harbour was thoroughly examined including local man-induced effects. The computations properly reproduced the shoreline evolution along this sub-segment over a long period between 1934 and 1997.In connection with the dredging and reclamation works at the Oresund Link Project between Denmark and Sweden carried out by the Contractor, Oresund Marine Joint Venture (OMJV), an intensive spill monitoring campaign has been performed in order to fulfil the environmental requirements set by the Danish and Swedish Authorities. Spill in this context is defined as the overall amount of suspended sediment originating from dredging and reclamation activities leaving the working zone. The maximum spill limit is set to 5% of the dredged material, which has to be monitored, analysed and calculated within 25% accuracy. Velocity data are measured by means of a broad band ADCP and turbidity data by four OBS probes (output in FTU). The FTUs are converted into sediment content in mg/1 by water samples. The analyses carried out, results in high acceptance levels for the conversion to be implemented as a linear relation which can be forced through the origin. Furthermore analyses verifies that the applied setup with a 4-point turbidity profile is a reasonable approximation to the true turbidity profile. Finally the maximum turbidity is on average located at a distance 30-40% from the seabed.

Wave-Related Suspended Sand Transport in the Ripple Regime

This paper presents results of an experimental and theoretical study on wave-related suspended sand transport under irregular waves in the ripple regime. Experimental data were analysed to determine the mean and oscillating suspended transport components. The analysis results clearly show the influence of the particle diameter on the wave-related transport. The second part of the study is related to a I DV model, which simulates the instantaneous velocity and sand concentrations from close to the bed up to higher in the water column. The model is based on the classical diffusion approach taking both the turbulence-related and the effective wave-related diffusion into account. It shows that the time-averaged sand concentrations can be simulated reasonably well in the ripple regime using the calibrated equations.

Wave-Related Transport and Nearshore Morphology

This paper discusses the simulation of nearshore bar migration using the CROSMOR profile model. Two sediment transport formulations have been used : the method of Van Rijn and that of Van der Werf. The model has been applied to two large-scale laboratory experiments in the Delta flume of Delft Hydraulics. Both transport models can represent the trends observed in the laboratory experiments.

Hydrodynamics and Morphodynamics in the Surf Zone of a Dissipative Beach

Abstract: Two profile models have been compared with field data measured at the Egmond sandy beach site (The Netherlands) within the framework of the European COAST3D project. Three hydrodynamic storm events and two morphodynamic events (storm and post-storm periods) have been selected for model comparison. The two profile models UNIBEST-TC and CROSMOR are process-based models; the UNIBESTTC model is a deterministic model, whereas the CROSMOR model is probabilistic model based on a ‘wave by wave’ approach. The models show reasonable results for wave height, longshore current and offshore bar migration.

Effect of channel deepening on tidal flow and sediment transport—part II: muddy channels

Natural tidal channels often need deepening for navigation purposes (to facilitate larger vessels). Deepening often leads to tidal amplification, salinity intrusion, and increasing sand and mud import. These effects can be modelled and studied by using detailed 3D models. Reliable simplified models for a first quick evaluation are however lacking. This paper presents a simplified model for sand transport in prismatic and converging tidal channels. The simplified model is a local model neglecting horizontal sand transport gradients. The latter can be included by coupling (as post-processing) the simplified model to a 2DH or 3D flow model. Basic sand transport processes in stratified tidal flow are studied based on the typical example of the tidal Rotterdam Waterway in The Netherlands. The objective is to gain quantitative understanding of the effects of channel deepening on tidal penetration, salinity intrusion, tidal asymmetry, residual density-driven flow, and the net tide-integrated sand transport. We firstly study the most relevant tidal parameters at the mouth and along the channel with simple linear tidal models and numerical 2DH and 3D tidal models. We then present a simplified model describing the transport of sand (TSAND) in tidal channels. The TSAND model can be used to compute the variation of the depth-integrated suspended sand transport and total sand transport (incl. bed-load transport) over the tidal cycle. The model can either be used in stand-alone mode or with computed near-bed velocities from a 3D hydrodynamic model as input data.

APPLICATION AND COMPARISON OF TWO DIFFERENT FINE COHESIVE SEDIMENT TRANSPORT MODELS IN DELFT3D

This paper discusses the application of two different fine cohesive sediment transport models in Delft3D, i.e. the classical method of Partheniades (1965) & Krone (1962) and the new unified sediment transport model of Van Rijn (2007). Both models were applied to simulate suspended silt concentrations for two complicated sediment environments, namely the Ems estuary in the northeastern part of the Netherlands and the Yangtze River in China. Good agreement between computations and observations may be obtained by modifying the free model parameters in both methods. However, the PK method is more complicated. There are much more parameters that have to be validated for the PK method than for the VR method, which makes the PK method more complex to apply.

MEASURED AND PREDICTED SUSPENDED SAND TRANSPORT ON A SANDY SHOREFACE

This paper describes on site field measurements of sand transport with two different types of instruments at 13 m water depth at a location 2 km off the coast of Noordwijk aan Zee, The Netherlands. The measurements are compared with results from four practical model combinations using different predictors for the combined current and wave-related shear stress, the reference concentration and the wave boundary layer thickness. Measurements are also compared with results from the Bailard suspended load sand transport model. Best overall predictions of the measured suspended transport rates are made with the Bailard model. Read More: http://ascelibrary.org/doi/abs/10.1061/40855%28214%2986