Journal of Waterway, Port, Coastal, and Ocean Engineering

A theoretical approach is applied to describe the diffraction of water waves by a structure in a channel of arbitrary configuration. The solution was achieved by applying the three-dimensional (3D) boundary element method and is valid for a structure of arbitrary shape. The derived model was applied to analyze the effect of the structure geometry and the configuration of the channel on diffracted wave field and on generalized wave-load components. The results show that the wave field in the channel and wave loads on a structure strongly depend on wavelength and the geometry of the structure. The far-field wave amplitudes and wave load components oscillate with increasing wave number, and for selected wave frequencies, the incoming waves are fully transmitted and forces on the structure simultaneously vanish. This result is of practical importance. The oscillations depend primarily on the length of the structure and are associated with the formation of partially standing waves in the subdomain along the structure, which affect wave reflection in the main channel and wave loads on the structure. The effect of the draft and width of the structure on the oscillations is very limited. However, the draft and width of a structure has a substantial effect on the magnitude of wave reflection and transmission, especially for narrow channels. Moreover, the draft and width of a structure has a substantial effect on wave-load components. The analysis of the results indicates that it is difficult to simplify a theoretical description because, even for a channel of a constant depth and ideal vertical walls, once a structure is present in the channel, the problem needs to be described by 3D formulation, which complicates the solution. Theoretical results are in reasonable agreement with experimental data.

The combined diffraction and refraction of long waves around a vertical cylinder with scour pit is studied analytically on the basis of a newly derived analytic solution of the mild-slope wave equation. The geometry of the scour pit around the cylinder is idealized to be axisymmetrical, and a simple power function is employed to represent its radial profile. The problem is solved in the polar coordinate system by separation of variables, and the resulting ordinary differential equation in the radial direction over the scour pit in this case can be transformed into the Bessel equation of real order. On the basis of the analytic solution obtained, the effect of the scour pit on wave scattering is investigated by comparing the cases with and without the presence of the scour pit. The scour pit contributes to reduce the wave run-up against the cylinder. In addition, the effects of the scour pit on wave run-up against the cylinder are more significant when the dimensions of the scour pit are larger or the incident wave is relatively shorter.

Urban flooding caused by heavy rainfall and high tides is a major problem in many coastal cities. For example, major cities in India have witnessed loss of life and property, disruption to transport and power, and incidences of epidemic during monsoon, most notable among them Mumbai in 2005, Surat in 2006, and Kolkata in 2007. Thus, an effective coastal urban flood simulation tool that can be used to identify flood vulnerability locations is needed. In this paper, the flood simulation of an urban catchment of Navi-Mumbai, India, is analyzed with the help of an in-house-developed simulation model that accounts for the tidal variation with the provision of a detention pond. The model uses FEM for flood simulation and geographic information systems (GISs) and remote sensing for database preparation. Overland flow and channel flow are simulated in one dimension by using the kinematic wave and diffusion wave approximations of St. Venant’s equations. The developed models have been verified with models from the literature and found to be satisfactory. The model has been used to simulate four rainfall events of the urban catchment. Out of four events, three were nonflooding and one was a severe flooding event. For the nonflooding events, measured data were available, and the model results were satisfactory. The model could simulate the flooding event showing the flooded stretch of the channel. By using the flooding event, the location and size of the possible detention pond are also simulated and their effects have been analyzed.

Floating breakwaters are typically used to protect small marinas or for shoreline erosion control on limited-fetch water bodies in which wavelengths are relatively short, such as lakes, reservoirs, and bays. In spite of the large amount of literature on floating breakwaters, there is still a lack of knowledge on the performance of cylindrical breakwaters, which, as a result of their simplicity, can minimize construction and material costs. In this paper, we describe a laboratory investigation of the hydrodynamic interaction of cylindrical breakwaters with monochromatic waves in deep and transitional water depths such as are found in small reservoirs. The tested breakwater models feature single- and multiple-cylinder cross sections combined with bottom-moored, arm-restrained (connected to shoreline), and pile-restrained configurations. When the breakwater models were fixed, the reflection was higher than in the partially restrained models, and the efficiency was strongly dependent on draft ratio ($z_d/d$, where $z_d$ is the draft and $d$ is the height of the structure). For partially restrained models, dissipation strongly influenced the transmission coefficients. For the measured range of waves, $z_d/d=0.7$ was the best of the tested draft ratios for the pile-restrained model. Horizontal restraint was found to be more important than vertical restraint in terms of improving breakwater efficiency.

A process-based numerical model has been used to study nearshore hydrodynamics on barred beaches. A laboratory experiment with an offshore bar migration case followed by an onshore bar migration is simulated. A new mechanism is incorporated in the model accounting for the breaking-wave persistence improving model performance for wave properties, particularly in the bar-trough region. A cross-shore variation of the breaking-wave parameter is introduced to the dissipation model. The effects of the surface shape parameter and a roller lag on radiation stresses and mean water-level predictions are investigated and found to improve the mean water-level predictions. The cross-shore variation of the momentum balance is presented to illustrate the variation of forcing for the undertow current. The persistence length and the roller lag mechanisms are shown to be important for predictions of the undertow currents on barred beaches and the current predictions are improved once both methods are used.

Marine sediments often contain sand-clay mixtures in widely varying proportions. This study presents the results of equilibrium scour and time variation of scour depths at circular piles embedded vertically in clay alone and sand-clay mixed beds under waves. Experiments were conducted in a wave flume with different proportions of sand-clay mixtures as bed sediments. Test results for the cases of steady current and sand alone under waves are used as references. The equilibrium scour depth reduces with an increase in clay proportion $n$ (by weight) in a sand-clay mixture. Interestingly, the scour depth reductions for $n=0.3$ and 1 are almost equal, suggesting that when the clay proportion in a sand-clay mixture becomes 0.3, the sand-clay mixture behaves as if it were a clay-alone mixture, in relation to scour depths. The dependency of equilibrium scour depth on the Keulegan-Carpenter number for different $n$-values can be expressed by an exponential law, using different coefficients and exponents. For time variation of scour, the nondimensional timescale increases with an increase in Keulegan-Carpenter number and clay proportion. However, unlike the near-equal scour depths, timescales are quite different for $n=0.3$ and 1.

Beach-nourishment requirements on the southwestern Spanish coast have led to a significant increase in offshore dredging. Following a new research line, assessment of changes recorded in physicochemical and biological parameters due to dredging and dumping operations was performed at the Cape of Trafalgar and Palmar Beach during June and July 2008. Turbidity, salinity, pH, dissolved oxygen, temperature, and suspended-sediment data were collected at 10 stations. At the end of the study, a three-campaign monitoring program was implemented for 1 year to assess the possible effects on biological communities and sediment properties. The relevant results, such as the average extent of the sediment plume ($<400\mathrm{m}$) and its persistence in the environment ($<10\min$), are discussed in this paper. A precise correlation between turbidity and suspended sediments and the recovery time of ecological balance were also established. Furthermore, minimal and reversible effects caused by dredging and dumping operations in this type of marine environment were identified.

Sea level estimates are important in many coastal applications and port activities. This paper investigates the ability of a neuro-fuzzy (NF) model to predict sea level variations at a tide gauge site in the Hillarys Boat Harbour, Western Australia. In the first part of the study, previously recorded sea levels were used as input to estimate current sea levels. The results showed an acceptable level of NF model accuracy. In the second part of the study, NF models were implemented to forecast sea levels averaged over 12- and 24-h time periods, three time steps ahead. The NF forecasts were compared with those of artificial neural networks (ANNs) for the same data set. The results show that the NF approach performed better than the ANN in half-daily 12-, 24-, and 36-h sea level predictions. The traditional linear regression and autoregressive models were also tested for comparison, and they demonstrated their inferiority to the results of other techniques.