Yongping Chen

A 3-D WAVE-CURRENT DRIVEN COASTAL SEDIMENT TRANSPORT MODEL

Most of the existing sediment transport models are not synchronously driven by both the wave field and the flow field. This paper describes a 3D sediment transport model with waves and currents directly coupled within the model to continuously account for different-scale activities especially those that have significant contribution to local sediment transport processes such as formation of sediment plumes and turbidity maxima. A practical issue in modeling coastal sediment transport, besides the concern of model accuracy, is the efficiency of the model. In the present model, the wave action equation, instead of the computational demanding elliptic mild-slope equation, is used to calculate the wave parameters. The wave action equations take into account wave refraction and diffraction as well as the tidal hydrodynamic modification. The calculation of the wave and current forcing is coupled during the time marching process so that the effects due to short-term activities can be considered. The model has been verified against laboratory measurements and has also been applied to simulate actual sediment transport situations in the Pearl River Estuary (PRE), China. It has been quantitatively shown that the suspended sediment concentration in the PRE increases significantly when waves are present. Sediment deposition occurs at the upstream region of the PRE while erosion takes place mostly at the down-estuary region due to exposure to wave actions.

Suspended sediment fluxes in the radial sand ridge field of South Yellow Sea

ABSTRACT Zhang C. K., Yang Y. Z., Tao, J. F., Chen, Y. P., Yao, P., Su. M., 2013. Suspended sediment fluxes in the radial sand ridge field of South Yellow Sea. The radial sand ridge at the South Yellow Sea is one of unique geomorphic units in the world. It is famous of its radial current pattern and high suspended sediment concentration, forming abundant tidal flat resources which could be reclaimed for the land use. In order to make a scientific plan for the land reclamation, it is necessary to quantitatively understand the distribution of suspended sediment fluxes in this field. In this study, a 2D tidal current and suspended sediment transport model is developed and validated by the hydrologic survey data measured in 2006. The suspended sediment fluxes are calculated by the period-averaged multification of the simulated tidal current and sediment concentration in two consecutive tidal periods. The numerical results show that, in either winter or summer season, there has a positive sediment flux comes from the north and the south boundaries, indicating a net gain of sediment for the sand ridge field from both boundaries. The numerical results also show that a clockwise sediment flux system exists in the middle of the sand ridge field, but a small portion of sediment leaves the sand ridge area at the north wing. The overall gain of the sediment in this field is positive, implying that the radial sand ridge is still in the growing process.

Estimation of long-term wave statistics in the East China Sea

ABSTRACT Chen, Y. P., Xie, D. M., Zhang, C. K, Qian, X. S., 2013. Estimation of long-term wave statistics in the East China Sea. This study used a state-of-the-art approach to estimate the long-term wave statistics in the East China Sea. The wave climate in the past 60 years (1950–2009) was simulated by a third generation wave model driven by the NCEP/NCAR reanalysis wind data. Based on the statistical analysis of the numerical results, the mean wave fields and the extreme wave fields with 100-year and 50-year return period on the whole computational domain were obtained. The spatial variations of the wave fields show that the statistical waves decrease from south to north and from sea to coast in general, which can be associated with the local topography of the East China Sea. The seasonal variations show that the mean waves in the winter and autumn are slightly larger than those in the spring and summer, while the extreme waves in the summer are much larger than those in the other seasons, which is mainly due to the seasonal variation of monsoonal winds and the occurrence of typhoon events in the summer. The outputs of this paper are helpful to understand the distribution of mean and extreme waves in the East China Sea, and also useful to calculate the design waves in the coastal area if nearshore wave model like the SWAN model is introduced.

Modelling nearshore waves with presence of shore-parallel breakwaters

This paper presents the details of a Q3D numerical model and the preliminary results of its application to the coast in Norfolk, UK, with presence of 9 shore-parallel breakwaters. The intra-wave period model results were also compared with the measurements of an x-band radar installed at the site. The model results agree well qualitatively with the field observations. The impact of tides on the wave patterns high and low tidal levels is also presented.

Ensemble prediction of inundation risk and uncertainty arising from scour (EPIRUS)

This paper presents an integrated Cloud-to-Coast ensemble modelling framework of coastal flood risk due to wave overtopping and scour. It consists of three key components: meteorological forecasts, tide-surge-wave predictions and surf zone models. Using this integrated modelling approach, the flood risk in coastal areas from the extreme events can be accurately predicted and the associated uncertainties are assessed by creating ensembles of possible future storm events.

Modelling of a non-buoyant vertical jet in waves and currents

A generic numerical model using the large eddy simulation (LES) technique is developed to simulate a non-buoyant vertical jet in wave and/or current environments. The experimental data obtained in five different cases, i.e., one case of the jet in a wave only environment, two cases of the jet in a cross-flow only environment and two cases of the jet in a wave and cross-flow coexisting environment, are used to validate the model. The grid sensitivity tests are conducted based on four different grid systems and the results illustrate that the non-uniform grid system C (205×99×126 nodes with the minimum size of 1/10 jet diameter) is sufficiently fine for the modelling. The comparative study shows that the wave-current non-linear interaction should be taken into account at the inflow boundary while modelling the jet in wave and cross-flow coexisting environments. All numerical results agree well with the experimental data, showing that: (1) the jet under the influence of the wave action has a faster centerline velocity decay and a higher turbulence level than that in the stagnant ambience, meanwhile the “twin peaks” phenomenon exists on the cross-sectional velocity profiles, (2) the jet under a cross-flow scenario is deflected along the cross-flow with the node in the downstream, (3) the jet in wave and cross-flow coexisting environments has a flow structure of “effluent clouds”, which enhances the mixing of the jet with surrounding waters.

On the Long-term Changes of Extreme Wave Heights at the German Baltic Sea Coast

ABSTRACT Xu, Z.S.; Dreier, N.; Chen, Y.P., Fröhle, P. and Xie, D.M., 2016. On the long-term changes of extreme wave heights at the German Baltic Sea Coast. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 962–966. Coconut Creek (Florida), ISSN 0749-0208. The assessment of extreme wave heights is of great importance for the design of coastal protection strucutres. This paper aims to present long-term changes of extreme wave heights at several selected locations at the German Baltic Sea Coast. Annual maximum significant wave heights were selected from the hourly wave data obtained from a hybrid approach (wind-wave-correlations combined with numerical simulations on the basis of the SWAN model) for a total period of 140 years, spanning from 1961 to 2100. The future projections of wind data were dreived from the regional COSMO-Climate Local Model for two emission scenarios A1B and B1. The extreme wave heights at each location were estimated from the respective best-fitting distribution, log-normal or Weibull distribution. The results indicate that, the long-term changes of extreme wave heights are related to the emission scenarios used in the regional climate model, the distribution chosen for the estimating (up to +9.6%) and also the sample size for the extreme value analysis (up to +8.7%). These factors should be carefully considered in the future coastal structure design.

Modelling of extreme wave climate in China Seas

ABSTRACT Li, J.X.; Chen, Y.P., and Pan, S.Q., 2016. Modelling of Extreme Wave Climate in China Seas. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 522–526. Coconut Creek (Florida), ISSN 0749-0208.. Accurately estimating the extreme wave climate is important to the ocean and coastal engineering design. In this study, the long-term wave climate from 1979 to 2013 over the northwest Pacific Ocean, centred at the China Seas (including the East China Seas and the South China Sea), is hindcasted by using the spectral wave model WAMC4. The model is driven by the wind forcing obtained from the recently released 6 hourly ECMWF (European Centre for Medium-range Weather Forecasts) reanalysis data, with the spatial resolution of 0.125°×0.125°. For the typhoon events, the parametric typhoon wind fields are generated and blended in the typhoon affected area. The statistical analysis of the extreme waves with 100-year return period at several observation stations are carried out. The results show a good agreement with the observation data, indicating that using the blended wind field for the modelling of extreme wave climate in China Seas can considerably improve the accuracy of the predicted wave heights.

Modelling of sediment transport at Exe Estuary, Devon, UK

In this paper, results of sediment transport at Exe Estuary, Devon, UK, obtained from a process-based model under a number of wave and tide scenarios, are presented. This study uses a nested modelling system, which consists of an oceanic scale wave model WAM and a tide/surge model POLCOMS, to transform the meteorological information to nearshore wave and tide conditions for a fine resolution local coastal process-based model to carry out detailed predictions of nearshore hydrodynamics and morphodynamics at the study area. The work is focused on studying the impacts of yearly and 1 in 50 year return period storm events on morphology at the mouth of the Exe Estuary and the adjacent coasts. Comparisons of model results are made with the beach survey data carried out by the local authorities in March 2008, in addition to the model tests on both yearly calm and storm conditions in November 2006.

Postnourishment Evolution of Beach Profiles in a Low-Energy Sandy Beach with a Submerged Berm

AbstractSubmerged berms are an increasingly used coastal defense structure for beach nourishment because of their eco-friendly nature. A beach-nourishment project that included sand placement on th...