Papers by Jacco Groeneweg
Journal of Flood Risk Management
In this study two statistical methods for computing timeand space-evolving extreme events are imp... more In this study two statistical methods for computing timeand space-evolving extreme events are implem ented and assessed. The implementation and application of the methods are carried out with a view towards the sa f ty assessment of water defences. With this type of app lication in mind, the methods are used to produce t im and space-varying extreme wind fields, which are needed to force wave and hydrodynamic models. Furthermore , th results of the two methods are compared and effects of the choice of distribution, threshold and refer nce location on the resulting wind fields are assessed. Although th e wind fields produced by the methods show more err atic spatial variations, due to the associated uncertainties, th an ose of the observed wind fields, they seem rea listic and can in principle be used to drive wave and hydrodynamic mo dels. However, an assessment of the results of thes e statistical methods in terms of the underlying physics still ne eds to be carried out and is part...
INTRODUCTION Dikes protect large parts of the Netherlands against storm surges and wave attack. A... more INTRODUCTION Dikes protect large parts of the Netherlands against storm surges and wave attack. As described in Van Dongeren et al. (2007), these primary coastal defenses must be checked every five years by the best available methods to verify whether they comply with the required level of protection on the basis of Hydraulic Boundary Conditions (HBC). For a location along a primary coastal defense the HBC consist of a combination of normative wave conditions and water levels. Presently, a number of model studies are carried out in the framework of the SBW (Sterkte en Belasting Waterkeringen: Strength and Loads on Water Defenses) with the overall aim to improve the quality of the models and methods used to derive these HBC in the Wadden Sea. This is a shallow sea in the north of the Netherlands and protected from the North Sea by a number of barrier islands (Figure 1). Tidal flows enter and leave the Wadden Sea via a number of tidal inlets. North Sea waves may also penetrate through...
Ocean Wave Measurement and Analysis (2001), 2002
A procedure is presented for the dynamic handling of the boundaries of Boussinesq‐type wave model... more A procedure is presented for the dynamic handling of the boundaries of Boussinesq‐type wave models that enables to control the reflection properties. The main purpose of the procedure is the reduction of spurious reflections at open boundaries. The procedure also allows, ...
Coastal Engineering 2002 - Solving Coastal Conundrums - Proceedings of the 28th International Conference, 2003
Abstract: An extensive data set of waves propagating over a shoal on a beach has been obtained fr... more Abstract: An extensive data set of waves propagating over a shoal on a beach has been obtained from measurements in a three-dimensional physical model. The data set has been used to validate the two-dimensional Boussinesq-type wave model TRITON. In particular the performance of the implemented wave-breaking model has been investigated. Since the unique data set contains a variety of wave regimes, also the modeling of other wave aspects, such as linear dispersion and shoaling, as well as nonlinear wave-wave ...
Coastal Engineering 2008, 2009
Past and future changes in the North Sea extreme waves are investigated in this article. Estimate... more Past and future changes in the North Sea extreme waves are investigated in this article. Estimates obtained from non-stationary extreme value analyses, expressing the extreme value distribution parameters as functions of time and wind speed related covariates, are given. The results show that there is a significant trend of about 9 mm/yr in the current climate extremes of significant wave height and a trend of 1 mm/yr in the projections from 2001 to 2100. The characteristics of the extremes of wave period depend on whether swell or wind-sea events are considered. If both types of events are considered, the extremes are dominated by swell events and no present or future changes are identified. Considering wind-sea events only, a trend of less than 0.01s/yr in the present climate wave periods and a trend an order of magnitude smaller in the projections from 2001 to 2001 were detected.
Simulation Practice and Theory, 1995
This paper deals with the implementation of a domain decomposition method for the threedimensiona... more This paper deals with the implementation of a domain decomposition method for the threedimensional shallow water equations. The domain decomposition method belongs to the class of generalized additive Schwarz methods. It is based on a local coupling mechanism that allows for a flexible formulation of subdomain interfaces. For a real-life application in the Netherlands numerical results are presented. The experiments are carried out on a HP workstation and on a CRAY C90.
Journal of Fluid Mechanics, 1998
The generalized Lagrangian mean (GLM) formulation is used to describe the interaction of waves an... more The generalized Lagrangian mean (GLM) formulation is used to describe the interaction of waves and currents. In contrast to the more conventional Eulerian formulation the GLM description enables splitting of the mean and oscillating motion over the whole depth in an unambiguous and unique way, also in the region between wave crest and trough. The present paper deals with non-breaking long-crested regular waves on a current using the GLM formulation coupled with a WKBJ-type perturbation-series approach. The waves propagate under an arbitrary angle with the current direction. The primary interest concerns nonlinear changes in the vertical distribution of the mean velocity due to the presence of the waves, but modifications of the orbital velocity profiles, due to the presence of a current, are considered as well. The special case of no initial current, where waves induce a so-called drift velocity or mass-transport velocity, is also studied.
Coastal Engineering, 2007
The Guyana coastal system is characterized by very thick deposits of Amazon mud and high mud conc... more The Guyana coastal system is characterized by very thick deposits of Amazon mud and high mud concentrations in its coastal waters. The mud deposits can be quite soft and may liquefy under incoming waves. Subsequently, the liquefied mud damps the incoming waves effectively. This paper presents a simple model to predict wave attenuation over soft (fluid) mud beds. This model is based on the two-layer approach by Gade [Gade, H.G., 1958, Effects of a non-rigid, impermeable bottom on plane surface waves in shallow water, Journal of Marine Research, 16 (2) 61-82.] which is implemented in the standard version of the state-of-the-art wave-prediction model SWAN. Input to the mud wave damping module consists of the extension, thickness, density and viscosity of the liquefied (fluid) mud layer. The model is validated against small-scale wave attenuation measurements carried out in a laboratory wave flume. The model predictions agree favourably with the experimental data. Next, the model is applied to predict wave height and wave attenuation in the Guyana coastal system. Extension and thickness of the liquefiable layer could be assessed from dual-frequency echo soundings. In the absence of field data, the density of the liquefied mud layer is obtained from literature, whereas the value of the mud's viscosity had to be established by trial and errorthe selected value, though, is in the range of literature values. The model predicts significant wave attenuation. The computed changes in wave energy spectrum agree qualitatively with measurements in Surinam, whereas the decrease in significant wave height agrees more or less with historic observations along the Guyana coast.
Coastal Engineering Proceedings, 2011
Over the last five years a research program has been carried out to assess the performance of the... more Over the last five years a research program has been carried out to assess the performance of the spectral wave model SWAN in the Wadden Sea so that it may be used for the transformation of offshore wave conditions to wave boundary conditions near the sea defenses (dikes and dunes). The assessment was done on the basis of extensive wave measurements conducted in Ameland inlet and the Dutch Eastern Wadden Sea, as well as relevant data from lakes and estuaries. After a first round of assessment, we found that SWAN performed reasonably well for storm conditions but three aspects required further attention. Firstly, focusing on the main channel, SWAN formulations needed to be modified in order to eliminate overprediction of the significant wave height in opposing currents. Secondly, the primary spectral peak of North Sea waves penetrating into the inlet was underpredicted. Best results were obtained when the refraction of low-frequency waves was limited and the bottom friction coefficie...
Journal of Coastal Research
Coastal Engineering, 2016
Coastal Engineering 1998, 1999
Journal of Waterway, Port, Coastal, and Ocean Engineering, 2015
In compliance with the Dutch Water Act the strength of the Dutch primary water defences must be a... more In compliance with the Dutch Water Act the strength of the Dutch primary water defences must be assessed periodically for the required level of protection against hydraulic loads with return periods of up to 10,000 years. In the determination of the hydraulic loads, typically only one instant during a storm is considered, e.g. the instant at which the maximum water level is achieved in the region of the dike section of interest. For the determination of the required water defence crest level this is an appropriate approach, since the maximum wave overtopping rate is typically obtained at the maximum water level. For failure mechanisms other than overtopping, the instant of the maximum water level does not necessarily lead to the critical load on the water defence. Furthermore, failure mechanisms such as dune retreat and erosion of revetments typically depend on the temporal, and therefore also spatial, variation of the storm. In order to produce temporally and spatially varying hydr...
Coastal Engineering 2000, 2001
The theory and implementation of the dominant wave effects in a 3D mean flow model are described.... more The theory and implementation of the dominant wave effects in a 3D mean flow model are described. The effects considered are the wave-induced mass flux, waveinduced turbulence, the effects of streaming and forcing due to wave breaking. To model the wave-induced mass flux we have used the GLM method. This method is a hybrid Eulerian-Langrangian approach that also enables the inclusion of a vertically non-uniform mass flux distribution. The model shows good agreement with measurements. It was found that the application of a vertically non-uniform mass flux improves the model predictions considerably. An important conclusion is that with minor modifications any Eulerian-based 2DV, 2DH or 3D flow model can be upgraded to a more physically correct GLM-based model.
Coastal Engineering Proceedings, 2011
In 2011 new Hydraulic Boundary Conditions must be established for the statutory assessment of flo... more In 2011 new Hydraulic Boundary Conditions must be established for the statutory assessment of flood protection in the Wadden Sea area, which is a complex tidal system in the northern part of the Netherlands. The aim is to base these normative wave conditions on the wave simulation model SWAN and the probabilistic method Hydra-K, to be consistent with other systems as the Holland Coast and the Zeeland Delta. Assumptions made for the latter water systems, like steady state wind forcing, uniform water levels and neglect of currents, are not valid in the tidal basin of the Wadden Sea. A schematic temporal variation of both wind direction and wind speed is applied to define wind fields that drive the hydrodynamic computations. Both wind fields and resulting water level and current fields form the input of SWAN computations for a large number of combinations of basic wind speed and wind direction, offshore surge level and phase difference between tide and maximum wind speed. The result is...
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Papers by Jacco Groeneweg