Coastal Engineering Journal

Based on a re-analysis of the existing undertow models and the experimental results, a proper explicit model is proposed for computing undertow profile inside the surf zone. The model has been derived by using the eddy viscosity approach. The model is examined using published laboratory data from six sources covering small-scale and large-scale experiments, i.e. the experiments of Nadaoka et al. (1982), Hansen and Svendsen (1984), Okayasu et al. (1988), Cox et al. (1994), CRIEPI (Kajima et al., 1983) and SUPERTANK (Kraus and Smith, 1994). The present undertow model is considerably simpler than most of existing models. Although the model is simple, it shows good agreement with the experimental results above the bottom boundary layer. The calculation is so simple that the undertow profile can be calculated by using a pocket calculator.

The present analysis, as a kind of case study, deals with the experimental research at two different coast sites of the South Baltic. The analysis of the driving forces caused by wave fields and so on, and the responses, like current circulations, sediment transport and morphological coastal changes, gave rise to the attempt of empirical description of environmental site-specific coastal features and their large-scale interactions. In the present study, the name "large-scale" refers to the processes having the longshore scale of the order of kilometres and the cross-shore scale of hundreds of metres. Time scales lie in the range from months, seasons up to a few or dozen or so years at most. The above investigations provide an insight into the specific hydro- and morphodynamical processes occurring in coastal zones of the Baltic Sea. These processes can be regarded as representative for other small seas.

The reliability-based risk assessment and structural design model (REBAD) (Balas, 1998) introduced in this paper, is a worthwhile tool in the preliminary design of maritime structures which are portrayed by vast failure consequences and significant resource expenditures. REBAD model in which the Second-Order Reliability Method (SORM) is utilized together with a cost-optimization algorithm, is implemented to Mersin yacht harbor which is constructed near the city of Mersin located on the Turkish coast of Mediterranean Sea. SORM is established on a more correct approximation of the failure surface than the first-order method. The failure mode probability is predicted by approximating the failure surface by a quadratic surface with the identical curvature at the design point. First, REBAD is implemented to the main breakwater by utilizing the Hudson failure function to determine the size of armor units, then failure mode response functions were obtained for the fixed exceedance probability of several damage levels. Combining with the hydraulic model study carried out by Ergin and Özhan (1994) and REBAD outcome, the trunk section of main breakwater and design functions were determined. The second order reliability-based sensitivity study was also carried out to systematically compare limit state equations of Hudson and Van der Meer.

Authors concluded that, Van der Meer failure function is a more reliable design function for this case study which illustrated the affect of uncertainties encountered in Turkey on the design practice of rubble mound breakwaters. Since REBAD enabled the first application of reliability-based design practice for coastal structures in Turkey, it is the commencement for the development of a national reliability-based design standard of maritime structures.

In this paper, at first results of experiments in sheet flow conditions under nonlinear asymmetric irregular oscillations with and without long wave components are presented and a method for estimating the net transport rates is proposed. Then the importance of phase lag between free long waves and irregular short waves as well as the effect of steady currents on the magnitude of transport rate are discussed. Implications of the results are further demonstrated by applying the proposed formulation to calculating the cross-shore distributions of sediment transport rates on a sheet flow dominated beach under incident irregular waves with low frequency components. It is found that long waves can significantly enhance the seaward transport of sediments inside the surf zone during a storm. It is also shown that the presence of a standing long wave system may lead to large spatial gradients in the cross-shore transport rates and eventually, to formation of a multiple longshore bar system.

This paper proposes a one-dimensional and a horizontally two-dimensional random wave transformation models based on a spectral wave equation with a probabilistic bore-type energy dissipation term, and examines the validity of the wave models by comparing the predictions with the observations. The present spectrum-based prediction models with a probabilistic dissipation term are rather heuristic but robust to use. Since the present random wave transformation models consist of spectral and probabilistic models, the wave model can be called as a hybrid random wave transformation model. The model solves the spatial evolution of complex Fourier amplitudes from which energy spectra are calculated. In addition, water surface elevations are obtained from the calculated complex amplitudes by using the inverse Fast Fourier Transform. Furthermore, representative wave heights and periods are obtained from the water surface elevations.

We apply the one-dimensional wave model to predict transformations of double peak spectral waves, small and prototype scales' experimental waves and field waves over uniform slope and arbitrary bathymetry. In addition, the horizontally two-dimensional wave model is applied to predict transformations over an elliptic shoal, a conic shoal and field bathymetry, and also employed to investigate the mach-reflection. The comparison between the various observations by laboratory and field experiments and the predictions by the wave models shows good agreements.