Journal of Waterway, Port, Coastal, and Ocean Engineering

A theory on the horizontal spreading of contaminants in the surf zone is described in this paper. The surf zone is viewed as a narrow strip comparable to the characteristic wavelength, in which turbulence caused by wave breaking is strong. Flows inside the surf zone consist of both oscillatory motions and a steady current induced by breaking waves. The wave field in the shoaling zone is modeled by the linear theory for monochromatic waves, and it is assumed that the breaking wave height is proportional to the local depth in the surf zone. The simplest scenario of longshore current on a straight beach of constant slope is considered, for which the longshore current velocity is predicted by a slightly modified version of Longuet-Higgins' original theory developed in the 1970s. On the basis of the estimation that the time scale of horizontal diffusion is much longer than the wave period, the perturbation method of multiple scales is applied to derive the transport equation for the advective diffusion of a solute. The total advection velocity is found to be the sum of the steady current caused by radiation stresses and a contribution from the covariance of fluctuating velocity and concentration, which is the same as the Stokes drift in periodic waves. Numerical predictions for the movement of a solute cloud released, instantaneously or continuously, in a longshore current along a plane beach are examined. The solute is found to drift shoreward in addition to the expected transport along the shore. Computed examples are presented and comparisons with available laboratory experiments are also discussed.

A new fish reef block ensuring accurate placement by a free fall was developed to enable a more economical construction of nursery reefs for snow crabs. The block is based on a cube-shaped frame structure with extra shelf areas attached to the upper and lower frames to act as stabilizers. The falling behavior of the block in water was investigated by hydraulic model experiments and three-dimensional (3D) numerical computations. A stochastic model based on the experimental data was used to confirm a narrow distribution of the placement position as a result of the swing motion of the block during its fall. The numerical computation results indicate that the upper stabilizer produces a restoring moment for a tilted block and the lower stabilizer reduces instability in the wake of the falling block. In addition, a quick estimation method for the placement position was developed to determine the release point of the block during actual construction in the presence of ambient currents.

A laboratory experiment consisting of five tests was conducted to examine the effects of woody plants on erosion and overwash of high and low dunes. Scarping occurred on the foreslope for three high dune tests and no scarping occurred for two low dune tests. A narrow vegetation zone on a steep backslope of a high dune did not reduce wave overtopping and overwash in comparison with the corresponding bare dune. A wide vegetation covering the high dune reduced foreslope scarping, prevented wave overtopping initially, and reduced sand overwash after the initiation of wave overtopping. A wide vegetation zone covering an entire low dune reduced dune erosion by retarding wave uprush and reducing wave overtopping and overwash.

Despite its relatively small amplitude, the nodal tide can play a relevant role in several environmental processes, spanning from ecology to morphodynamics; in particular, field studies and numerical investigations indicate the nodal tide as the dominant factor in long-term and large-scale net sediment transport in some estuaries. Nevertheless, while some important results have been obtained about its morphological effect on estuary channels, the response of tidal flats and salt marshes is still to be investigated. In the present work, a two-dimensional (2D), vertically averaged, long-term morphodynamic model based on the concepts of intertidal dispersion and transport concentration has been applied to the case of a schematic lagoon forced by a nodally-modulated tidal range. The effect of such a periodic oscillation has been studied in terms of sediment fluxes, suspended sediment concentration, and morphology. The results of simulations, carried out starting from different equilibrium conditions in which a nodal perturbation was introduced in the tidal signal, were postprocessed via Fourier analysis to detect the characteristics of the nodal perturbation within the domain and to draw some considerations about the spatial differentiation, in terms of both amplitude and phase, of the morphodynamic response throughout the domain. Although taking into account the nodal contribution has little influence in a long-term (several decades to centuries) analysis, as shown in the current study, such a small oscillation in tidal range (approximately 4%) can locally result in bathymetric oscillations of relevant relative amplitude.

Landslide-generated impulse waves are considered a severe danger for humans and infrastructure. Design formulas following intensive laboratory research allow for a quick assessment of potential slide-event wave features. Unfortunately, prototype data are rare except for underwater slide deposits often corresponding to the only traces of a past event. If past events could be back-analyzed based on in situ scanned underwater slide deposits, the existing assessment approaches could be supported. Video recordings of 41 slide-generated impulse wave tests in a two-dimensional (2D) wave channel were analyzed regarding the underwater slide dynamics and their final deposition patterns. The underwater slide propagation process is described for three specifically selected tests. Correlation equations are presented for underwater slide front propagation and velocity, which are also useful for numerical modeling purposes. In addition, correlation equations are given for slide deposit features, including length and thickness, allowing for their estimation based on initial slide parameters.

This paper presents the results of an experimental study of the seabed liquefaction beneath standing waves. Silt (with $d_{50}=0.070\hspace{0.17em}\text{mm}$) was used in the experiments. Two kinds of measurements were carried out: pore water pressure measurements and water surface elevation measurements. These measurements were synchronized with video recording of the liquefaction process from the side. The ranges of the various quantities in the experiments were wave height $H=5.9–12.0\hspace{0.17em}\text{cm}$, wave period $T=1.09\hspace{0.17em}\mathrm{s}$, and water depth $h=30\hspace{0.17em}\text{cm}$. The experiments show that the seabed liquefaction under standing waves, although qualitatively similar, show features different from that caused by progressive waves. The pore water pressure builds up (or accumulated) in the areas around the node and subsequently spreads out toward the antinodes. The experimental results imply that this transport is caused by a diffusion mechanism with a diffusion coefficient equal to the coefficient of consolidation. The experiments further show that the number of waves to cause liquefaction at the nodal section appears to be equal to that experienced in progressive waves for the same wave height.

In 1999, two mooring dolphin platforms (MDP1 and MDP2), each with three suction caissons, were installed in the JZ9–3 field of the Bohai Sea of China. Before installation, penetration and retrieval tests for MDP1 were conducted near the design location site. In 2006, after being in service for 7 years, partial removal and repenetration prototype trials were performed for MDP2. The MDP1 platform has the same geometric structure and weight as MDP2, in which each suction caisson is 6 m in diameter and 9 m in height. Typical soil profiles at the site mainly consist of organic silt, silty clay, and clay. Records from the transducers were relevant to the installation and retrieval of the suction caissons, which were performed by controlling the pump discharge into/out of the caissons. The results show that skin friction decreases because of the seepage effect that occurs after applying the suction pressure inside the caisson. However, clayey or silty soils with low permeability required more time and suction to create a seepage flow to lower resistance in the penetration or removal phases. The setup effect caused by suction significantly increases the skin friction resistance by 62–84%, and the pump-out pressure equals 1.79–2.04 times the pump-in suction after 7 years. The on-site data are valuable for further study on the design and construction of platforms with suction caissons, especially regarding external skin friction.

Breakwaters can be broadly classified into overtopping and nonovertopping structures. In the case of a nonovertopping breakwater, either the crest level is designed in consideration with the maximum run-up level or a concrete crown wall is provided at the crest on the ocean side of the breakwater to avoid or minimize overtopping. It is essential to understand the wave-induced dynamic and uplift pressures exerted on the vertical face and base slab of the crown wall to incorporate this information in the design. The recently introduced armor block KOLOS, a modified version of DOLOS, is considered for detailed investigation of its hydrodynamic characteristics. Empirical relations have been proposed for the wave-induced pressures caused by regular waves on the crown wall fronted by KOLOS through a comprehensive experimental program. The overall results, compared with a breakwater fronted by natural rocks, indicate that the KOLOS armor layer offers better wave energy dissipation and results in minimal pressures induced on its crown wall.

The road toward a sustainable inland waterway network entails the installation of ecologically sound and technically effective bank protection. Heavy shipping traffic complicates the development of environmentally friendly bank protection on confined, nontidal waterways. Because in such conditions ship waves vary with ship design and operation, with topographic boundaries and locally changing hydraulic conditions, ship wave action is poorly understood. Therefore, a stand-alone field monitoring system was designed that accurately measures the impact on and response of environmentally friendly bank protection, consisting of off-bank timber piling and vegetation (reeds). Subsequently, the instrumentation was re-engineered and extended to a mobile version, enhancing the dynamic measurement possibilities. In this paper, the setup of both measurement systems is described, together with a detailed overview of the selected measurement instrumentation and good installation practices. The added value of these field monitoring systems is illustrated with an example of the monitoring system’s data output.

The current study experimentally investigates the wave-induced drift velocity of two-dimensional large floating objects (with $Lg/L>0.2$, where $Lg$ = longitudinal length of the floating objects, and $L$ = wavelength) under the action of regular waves. The focus is on the high-precision measurement of drift behavior and a wider range of parameters than what was previously reported in the literature. Stacked wood pieces with various submergences ($s$) were used to simulate the large floating objects on the water surface. An infrared-based motion monitoring system with two high-resolution cameras continuously recorded their motion in regular waves. The results show that the drift velocity increased quickly from the beginning and reached a quasi-steady mean value. The magnitude of the quasi-steady drift velocity increased with ratio of the pitch period to the wave period ($T_R/T$), until reaching a maximum when $T_R/T\approx 1$. After that, further increasing the ratio of $T_R/T$ did not lead to additional significant changes in the drift velocity. Three nondimensional submergences ($s/Lg$) of 0.0075, 0.022, and 0.036 were examined. The drift velocity typically decreased with larger submergence, which can be attributed to the larger added mass involved in the oscillatory motion.

Miter gates have been, and still are, widely used in hydraulic engineering as control devices for several types of locks (e.g., navigation, flood, tidal). For centuries, engineering practice has suggested a range of optimal values for the angle that the gate leaves must form pointing upstream, facing the current. According to experience and literature, this optimal range corresponds to an angle between the leaf and the normal to the lock wall that varies between 9.5 and 33.7°. It is confirmed here that in horizontally framed miter gates, which is the most usual arrangement, these optimal values depend only on the lock dimensions (span and height) and the geometric characteristics of the girder cross section. Using a simple dimensionless geometrical parameterization and static equilibrium considerations, a general approach for the preliminary dimensioning of miter gate leaves is developed, based on the optimization of the angle between the leaves for the three most commonly used types of girder cross section: square, rectangular, and I-beam (IPE series).