Coastal Ocean Forecasting: science foundation and user benefits

The advancement of Coastal Ocean Forecasting Systems (COFS) requires the support of continuous scientific progress addressing: (a) the primary mechanisms driving coastal circulation; (b) methods to achieve fully integrated coastal systems (observations and models), that are dynamically embedded in larger scale systems; and (c) methods to adequately represent air-sea and biophysical interactions. Issues of downscaling, data assimilation, atmosphere-wave-ocean couplings and ecosystem dynamics in the coastal ocean are discussed. These science topics are fundamental for successful COFS, which are connected to evolving downstream applications, dictated by the socioeconomic needs of rapidly increasing coastal populations

Coastal Ocean Forecasting: science foundation and user benefits

The advancement of Coastal Ocean Forecasting Systems (COFS) requires the support of continuous scientific progress addressing: (a) the primary mechanisms driving coastal circulation; (b) methods to achieve fully integrated coastal systems (observations and models), that are dynamically embedded in larger scale systems; and (c) methods to adequately represent air-sea and biophysical interactions. Issues of downscaling, data assimilation, atmosphere-wave-ocean couplings and ecosystem dynamics in the coastal ocean are discussed. These science topics are fundamental for successful COFS, which are connected to evolving downstream applications, dictated by the socioeconomic needs of rapidly increasing coastal populations

The application of the numerical wind wave model SWAN to a selected field case on the South African coast

Thesis (MScEng (Civil Engineering))--University of Stellenbosch, 2002.198 leaves double sided printed, preliminary pages i-xx and numberd pages 1-1-12-6.Includes bibliography. List of tables, figures and appendices and acronyms. Scanned with a HP Scanjet 8250 Scanner to pdf format (OCR).ENGLISH ABSTRACT: In this study the numerical short wave model SWAN is evaluated for application to a selected coastal region in South Africa. The aim of this study was to evaluate the degree of accuracy with which SWAN can simulate prototype nearshore wave spectra and wave parameters (e.g. wave height, mean wave direction and mean wave period) for an Algoa Bay field case. Algoa Bay represents a typical deep, sheltered embayment on the South African south coast, which is exposed to high-energy swell. Sensitivity analyses on various wave-related processes were also done, with the aim of establishing the dominant physical processes and appropriate model setup for the Algoa Bay field case. With the dominant wave-related processes and appropriate model setup for the Algoa Bay field case established, selected final runs were performed to determine the degree of accuracy with which SWAN can simulate prototype conditions, by comparing its results with available field recordings. This study comprises a review of the SWAN evaluation work conducted to date by others, an overview of South African coastal conditions, and numerical model simulations. The model simulations, which represent the main focus of this study, were conducted for a selection of available offshore wave conditions (at 85 m water depth) observed during the Algoa Bay field case and were compared to available nearshore observations (at 17 m water depth). Environmental conditions of waves, wind and currents were included in these simulations. The study focuses on model application and sensitivity analysis, rather than model development, and includes evaluation of all relevant processes, without focussing on any specific model aspect. The results of this study show that SWAN simulations correlated well with observations at the nearshore station in Algoa Bay, both in wave spectral shape and its associated parameters. Dominant processes identified for the field case were depth-induced refraction, bottom friction and directional spreading. This finding agrees with those of previous evaluations of SWAN and previous modelling experience by others. It is shown that high-energy swell is relatively more sensitive to the choices of model setup than wind sea. Based on the simulation results of high-energy swell, it is concluded that the calculation of depth-induced refraction in SWAN seem to contain a degree of inaccuracy. It is also concluded that the findings of this study could be used as a guideline to SWAN modelling studies along the South African south coast.AFRIKAANSE OPSOMMING: In hierdie studie word die toepassingsmoontlikhede van die numeriese kortgolf model SWAN vir 'n geselekteerde gedeelde van die Suid-Afrikaanse kuslyn beoordeel. Die doel van hierdie studie is om die vlak van akkuraatheid waarmee SWAN prototipe golfspektra en golfparameters (bv. golfhoogte, gemiddelde golfrigting en gemiddelde golfperiode) in die vlakwater kan simuleer te beoordeel, vir 'n Algoabaai gevallestudie. Algoabaai verteenwoordig 'n tipiese diep, beskermde baai aan die Suid-Afrikaanse kuslyn, wat blootgestel is aan hoe-energie deining. Sensitiwiteitstoetse is ook uitgevoer vir verskillende golfprosesse, met die doel om die dominante fisiese prosesse en gepaste modelopstelling vir die Algoabaai gevallestudie te vind. Nadat die dominante golfprosesse geidentifiseer is, en die toepaslike modelopstelling gevind is, is finale simulasies uitgevoer vir geselekteerde gevalle om die mate van akkuraatheid te bepaal waarmee SWAN prototipe kondisies kan simuleer, deur simulasie resultate met beskikbare veldmetings te vergelyk. Hierdie studie bestaan uit 'n samevatting van die evaluasiewerk verrig op SWAN deur andere, 'n samevatting van golf-, wind- en stroomtoestande aan die Suid-Afrikaanse kus en numeriese modelsimulasies. Die modelsimulasies, wat die hooffokus van hierdie studie is, is uitgevoer vir 'n seleksie van beskikbare diepsee golftoestande (in 85 m waterdiepte) uit die Algoabaai gevallestudie en is vergelyk met beskikbare vlakwater metings (in 17 m waterdiepte). Omgewingstoestande van golwe, wind en seestrome is ingesluit in hierdie simulasies. Die studie fokus op modeltoepassing en sensitiwiteits-analise, eerder as modelontwikkeling, en behels die beoordeeling van alle toepaslike modelprosesse, sonder om te fokus op enige spesifieke model aspek. Die resultate van hierdie studie toon aan dat die SWAN simulasies goed korrileer met vlakwater meetings in Algoabaai, vir beide golfspektraalvorm en verwante golfparameters. Bodemrefraksie, bodemwrywing en rigtingsspreiding is geidentifiseer as dominante modelprosesse. Hierdie resultaat kom ooreen met bevindings van vroeere beoordeling van SWAN en modelleer-ervaring deur andere. Dit word aangetoon dat hoe-energie deining relatief meer sensitief is vir modelopstelling as wind-see. Gebasseer op resultate van simulasie met hoe-energie deining, word die gevolgtrekking gemaak dat die berekening van bodemrefraksie in SWAN 'n mate van onakkuraatheid toon. Die gevolgtrekking word ook gemaak dat die resultate van hierdie studie as riglyn gebruik kan word vir modelleerwerk met SWAN aan die Suid-Afrikaanse suidkus

Nonstationary SWAN simulation in the Wadden Sea

The spectral wind wave model SWAN plays a key role in the estimation of the Hydraulic Boundary Conditions (HBC) for the primary sea defences of the Netherlands. Since some uncertainty remains with respect to the reliability of SWAN for application to the geographically complex area of the Wadden Sea, a number of activities have been initiated under project H4918 \u91Uitvoering Plan van Aanpak SBW-RVW Waddenzee\u92 (Plan of Action on the Boundary Conditions for the Wadden Sea) to devise a strategy for the improvement of the model. In this context, a number of hindcast studies have been carried out with SWAN for the Amelander Zeegat in the Wadden Sea. In all of these studies, the stationary simulation mode of SWAN was applied, since this is the approach currently followed in the computation of the HBC. Although the Wadden Sea interior is relatively small \u96 typically making stationary simulation appropriate - the wave boundary conditions and the local wind and current forcings vary relatively rapidly, so that stationary simulation may become inaccurate. Furthermore, if the model domain would be extended offshore to compute the HBC for the entire Wadden Sea, nonstationary simulation could become necessary. The aim of the present study is to compare the results of nonstationary and stationary hindcasts with SWAN in the Wadden Sea, for typical W to NW storm conditions. In addition, the effect of including morphological changes in the computations is considered. This study has shown that, when simulating over a large spatial domain that includes the entire Dutch coast and a portion of the North Sea, a notable difference between the results of these two simulation modes is the absence of a phase lag between offshore and the nearshore wave conditions in the case of stationary simulation. Over these relatively large spatial scales, both the nonstationary and stationary modes of SWAN strongly underestimate energy at the spectral peak nearshore of the barrier islands. When simulating on the scale of the Wadden Sea, notable differences between the results of nonstationary and stationary simulations are found in the Amelander Zeegat tidal inlet. However, along the Frisian coast, differences between the two simulation modes are relatively small. In nonstationary simulations on the scale of the Amelander Zeegat, the inclusion of morphological changes has little effect on the wave conditions at the Frisian coast. Based on the results of this study, it is recommended to continue the use of the stationary mode of SWAN for simulations on the scale of the Amelander Zeegat.SB

Direklesende ontledingsmetodes vir die edelmetale

Tesis (M. Sc.) -- Universiteit van Stellenbosch, 1964.Full text to be digitised and attached to bibliographic record

Multidirectional wave transformation around detached breakwaters.

The performance of the new wave diffraction feature of the shallow-water spectral model SWAN, particularly its ability to predict the multidirectional wave transformation around shore-parallel emerged breakwaters is examined using laboratory and field data. Comparison between model predictions and field measurements of directional spectra was used to identify the importance of various wave transformation processes in the evolution of the directional wave field. First, the model was evaluated against laboratory measurements of diffracted multidirectional waves around a breakwater shoulder. Excellent agreement between the model predictions and measurements was found for broad frequency and directional spectra. The performance of the model worsened with decreasing frequency and directional spread. Next, the performance of the model with regard to diffraction–refraction was assessed for directional wave spectra around detached breakwaters. Seven different field cases were considered: three wind–sea spectra with broad frequency and directional distributions, each coming from a different direction; two swell–sea bimodal spectra; and two swell spectra with narrow frequency and directional distributions. The new diffraction functionality in SWAN improved the prediction of wave heights around shore-parallel breakwaters. Processes such as beach reflection and wave transmission through breakwaters seem to have a significant role on transformation of swell waves behind the breakwaters. Bottom friction and wave–current interactions were less important, while the difference in frequency and directional distribution might be associated with seiching

Wave propagation under influence of currents

The present study aims to assess the prediction of wave penetration into tidal inlets under ambient current in SWAN. The performance of SWAN in the modelling of wave-current interaction was studied for two field cases, namely Port Phillip Bay Heads, Australia, and the Amelander Zeegat in the Dutch Wadden Sea. In-situ wave observations were available for both field situations. In addition, the Amelander Zeegat field case includes recently obtained marine (X-band) radar fields of a number of variables over the tidal inlet. The ambient current was shown to have a significant effect on the wave parameters. The addition of enhanced current-induced whitecapping using the expression of Deltares (2010b) has an important, but comparatively smaller impact, which is mainly seen in the significant wave height and mean period. In the Port Phillip Bay field case, which features near-idealised swell and wind sea conditions, the enhanced dissipation term clearly reduces Hmo during ebb, for which negative current gradients are found, improving the agreement with observations. For slack and flood, which feature positive or small negative current gradients, generally small impacts on wave height were found. By contrast, in the Amelander Zeegat, reductions in Hmo were found during ebb, but also for slack and flood, since negative gradients in the current field were found during all tidal phases. Although the results for Hmo improved with the application of the enhanced currentinduced dissipation, T m-1 ,O remains underestimated in the Amelander Zeegat field case. The optimal value for the proportionality coefficient Cds3 in the enhanced current-induced dissipation term has not been found yet. For some situations Cds3 = 0.8 is better, for others Cds3 = 1.6, suggesting that the parameterisation of Deltares (2010b) should be further refined. Therefore, calibration for specific situations is recommended at present. Comparison of SWAN results with the spatial fields processed from the radar observations has given valuable insight into the spatial performance of SWAN. Furthermore, qualitative agreement has been found between the observed wave lengths and computed values.SB

Observed finite depth wave growth limit in the Wadden Sea

The spectral wind wave model SWAN (Booij et al. 1999) plays a key role in the estimation of the Hydraulic Boundary Conditions (HBC) for the primary sea defences of the Netherlands. Since some uncertainty remains with respect to the reliability of the wind wave model SWAN for application to the geographically complex area of the Wadden Sea, a number of activities have been initiated under the project \u91SBW Waddenzee\u92 to devise a strategy for the improvement of the model. This activity is carried out in parallel with a measurement campaign that is being undertaken in the Dutch Wadden Sea to provide observational data for the calibration and validation of SWAN (\u91SBW-Veldmetingen\u92). The present study aims to compile a reliable set of observations (waves, water depth and wind) from three westerly storms recently observed in shallow regions in the Dutch Wadden Sea (Royal Haskoning 2007), and from three field experiments in shallow lakes, with which to calibrate SWAN for finite depth wave growth in the Wadden Sea. Firstly, the reliability of the observations taken during the mentioned westerly storms in the Wadden Sea interior was assessed, and improved in terms of the interpretation of the wave buoy observations (which were taken in small water depth, namely 1.5-2.0 m) and the modelling of water levels. Whereas Royal Haskoning (2007) reports maximum Hm0/d ratios in excess of 0.6 for the Wadden Sea (0.55 if a plotting error is removed), the present study has shown maximum Hm0/d ratios to rather be in the order of 0.43. It is recommended to reduce the uncertainty of this result further by verifying finite depth wave buoy observations with alternative instrumentation, such as pressure sensors or capacitance probes, and by measuring water depths at the wave buoy locations. Secondly, this data set was compared with the above-mentioned data sets from shallow lakes representing depth-limited wave growth, from which a reasonable agreement was found. In this regard, the empirical relationships for the growth limit proposed by Young and Babanin (2006) appear to be applicable for Lake George and Lake Sloten, but not for the overall data set. Thirdly, a selection of 30 calibration cases of depth-limited wave growth for SWAN has been made from the data sets of the four geographical areas considered. It is recommended to investigate the performance of SWAN for these field cases by hindcasting, and to subsequently apply them in the calibration and validation of the model.SB