Journal of Waterway, Port, Coastal, and Ocean Engineering

In this paper, an analytical solution is given in the form of a Taylor series for long-wave scattering by a cylindrical island mounted on a general shoal, where the water depth in the shoal region can be a real constant plus a power function of the radial distance. In other words, the crest of the shoal is not restricted to be on the still water level. The distribution of singular points becomes complicated; therefore, the solution technique needs to be more sophisticated. Because of the generality of the location of the shoal crest, the analytical solutions find several classical analytical solutions to be its special cases, which include long-wave scattering by a cylindrical island mounted on an idealized paraboloidal shoal, a cylindrical island mounted on an idealized conical shoal, a cylindrical island mounted on an idealized shoal, and a cylindrical island located on a flat bottom. The present analytical solution covers a much wider range of problems, and therefore, is much more useful. Finally, the effect of the shoal size to the wave-scattering pattern is investigated using the present analytical solution.

In this paper, shear, effective stress and pore pressure distributions of two-layer porous soils subjected to harmonic waves are presented. The instability of the porous soil because of wave loading is investigated in terms of instantaneous liquefaction. The governing equations are written in their fully dynamic form, and possible simplifications are introduced. Finite-element models are developed for each formulation, and numerical results are verified with their corresponding analytical solutions, which are also developed here. Then, the problem of a two-layer soil under waves both in an open domain and in front of a vertical wall is studied in terms of dynamic response variations and regions of instantaneous liquefaction. Both linear and nonlinear waves are considered. Finally, a number of parametric studies to investigate the effect of a surface clay layer, inertial terms in the equations, various soil and wave parameters, and wave nonlinearity on the dynamic behavior and instability are carried out. The results indicate that the two-layer response is significantly different from that of a conventional single-layer approach. Inertial terms are partially important in terms of stress variations depending on the wave and seabed parameters. The clay layer reduces the amount of liquefaction protecting the underlying seabed, until it reaches a certain thickness beyond which the depth of liquefaction increases. Wave period, inertial terms, and wave nonlinearity affect the response for an open domain and in the presence of a wall, mostly leading to more liquefaction.

Motivated by existing damage accumulation modeling difficulties, some suggestions on how to build consistent stochastic models for damage accumulation in breakwaters are given. The models avoid the selection of easy to use mathematical functions, which are replaced by those resulting from a set of properties that are expected in the model. It is shown how an inadequate selection of damage progression models leads to inconsistencies, which are avoided by using the proposed consistent mathematical structures. Dimensional analysis, compatibility conditions, and the central limit theorem are the bases for building a model aimed at reproducing the stochastic damage progression on breakwater as a result of general random wave actions. Four elements are identified as essential for a damage accumulation analysis: (1) the statistical distribution of the initial damage, (2) the mathematical structure of damage growth curves, (3) the damage function, which accounts for how the variables affect damage, and (4) the integral form in which damage accumulates, which permits relating its random character to the normal distribution. These four elements are combined to derive a general structure of models for determining the damage produced by any wave history, and to obtain the evolution of densities of cumulative damage with time. Finally, the proposed methods are illustrated by means of a real case example, and one of the models proposed is shown to be convenient in reproducing damage progression in breakwaters. The proposed method is valid not only for breakwaters but to other evolutive processes appearing in the maritime and coastal engineering field.

Longshore sediment transport (LST) is a major driver of coastal evolution. However, despite the recognition that it presents an unsteady behavior at the seasonal scale, the variability at longer term scales (interannual and decadal) is still far from being properly acknowledged. The present work contributes to the understanding of the seasonal to decadal variability of the LST, benefiting from recent developments in wave hindcast modeling. This work was developed for the northwest coast of Portugal, which is fully exposed to the highly energetic wave regime generated in the Northeast Atlantic Ocean that induces unusually large LST rates. Hindcast offshore waves, between 1953 and 2010, were used as offshore forcing to deduce LST estimates. The mean annual LST, between 1953 and 2010, shows an irregular and noncyclic pattern. Computed mean annual LST, for this coastal stretch, is around 1 million cubic meters directed to the south, with yearly averages ranging from 108,000 to 2.24 million m³ year⁻¹ always directed to the south. The maximum observed annual LST magnitude exceeds the mean magnitude by more than 100%. The variability in LST magnitude was found to be mainly related to the LST magnitudes of autumn/winter months in response to the wave regime seasonality. Results show that to estimate the long-term LST within an error of about 20%, a period of about 10 years of data/observations is required. Interannual variability in the magnitude of the LST was found to be correlated (${\mathit{R}}^2=0.55$) with the annual North Atlantic Oscillation (NAO) index. In the years where the NAO index was higher, the mean annual LST was generally greater than the long-term average, while negative NAO index corresponds to lower than average LST estimates.

Our capability for predicting beach and dune erosion has improved in the last three decades, but the recovery of an eroded beach above the mean sea level (MSL) cannot be predicted at present. The cycle of beach erosion and recovery will need to be predicted for the long-term maintenance of a sand beach with a dune for coastal flooding reduction. The cross-shore numerical model (CSHORE) is extended and evaluated using natural beach erosion and recovery data along 16 cross-shore lines spanning 5 km alongshore for the duration of 272 days. The CSHORE predicts beach and dune erosion fairly well, as has been shown in previous comparisons. The bed-load formula used in the CSHORE is adjusted to predict the accreted beach profile with a berm. The computed beach profile evolutions are shown to be affected little by the alongshore gradient of the longshore sediment transport rate along the straight beach. The extended CSHORE predicts both erosion and accretion above MSL within a factor of about 2.

This paper presents results from laboratory experimental model studies investigating scour by waves around a pipeline attached to a flexible rubber plate or rigid spoiler. The rubber plate was placed between the submarine pipeline and bed, while the rigid spoiler is attached to the top of the pipe. The scour around pipelines with and without a rubber plate or a rigid spoiler under regular and irregular waves was observed and measured for a range of pipe sizes, wave amplitudes and frequencies, and the length of the plate/height of the spoiler. The experiments reveal that although the rigid spoilers can enhance the scour depth and extent (thus accelerating the self-burial of the pipe), they also have significant influence on both the upstream and downstream bed topography as sand ripples and dunes are formed. On the other hand, the rubber plates cannot only significantly increase the scour depth but also have little effect on the upstream and downstream bed. The experiments show that when the length of the plate is about 1.5 times the pipe size, it provides the optimum performance in terms of the largest scour depth while restricting the impact on nearby beds for the parameters investigated in this study.

This paper presents the results of studies of the physical processes observed in the coastal zone of the eastern part of the Gulf of Gdańsk, from the Vistula river mouth (Poland) to Cape Taran (Russia, Kaliningrad Oblast), because it is under severe environmental and anthropogenic pressure. We present investigations of wind climate, wind-driven currents, deep-water waves, nearshore sediment fluxes, engineering activities, and shoreline changes/response at eight study sites selected along the coast of the study area. Four of the sites are located on the Polish side and four on the Russian side of the state border. An assessment of the anthropogenic impact on coastal litho- and morphodynamics (local sediment fluxes and shoreline response) as a function of different local hydrodynamic climates is performed. Key coastal locations in the Gulf (the Vistula river mouth, the Baltijsk Strait with the harbor of Baltijsk, and the mining plants near Jantarnyj), where natural sediment morphological processes have been affected by human activities, are particularly analyzed. Even in the same system (Gulf of Gdańsk), sites located close to each other and subject to similar anthropogenic activities can display quite different evolutionary patterns. In some cases, anthropogenic effects may be secondary to natural background conditions.

The scour process around monopiles caused by breaking waves is studied experimentally using regular waves. The use of regular waves is conservative, which made it possible to avoid scour phenomena caused by nonbreaking waves such as scour generation and backfilling. The waves were breaking on a flat sand section after shoaling on a mildly sloping ramp. Various monopiles were exposed to plunging breakers that were breaking at various distances from the pile. It was found that the scour was caused by turbulence generated by the breaking and was diverted toward the bottom by the pile. The maximum scour depth found was approximately 0.60$D$. This was smaller than the scour observed around piles exposed to current; however, in some cases it was an order of magnitude larger than the scour caused by nonbreaking waves. This is apparently especially true for larger piles.