Journal of Waterway, Port, Coastal, and Ocean Engineering

Ridge-runnel features can comprise large volumes of sand, and their migration can have a significant influence on the coastal sediment budget and beach recovery after a storm. Numerical modeling of ridge-runnel migration is challenging partly because of the strong interactions between the hydrodynamics and morphology and partly because of limited available field and laboratory measurements. This study investigated the effect of water ponding and runnel drainage on onshore ridge migration in an experiment in a sand flume where detailed free‐surface and velocity measurements were taken in the ponded water zone of the runnel and in the intermittently wet and dry zone on the ridge crest. The test scenario with a drained runnel showed a ridge migration speed five times larger than the scenario in which water and sediment could only exit the runnel as offshore return flow over the ridge. The time-averaged numerical model CSHORE was modified to include the ponded water effect in the sediment transport formulations. Results show the capabilities and shortcomings of CSHORE in reproducing the hydrodynamics, morphological evolution, and sediment transport rates measured during the experiment.

The present paper explores the possibility of exploiting sandpits at intermediate and shallow water depths by analyzing both the hydrodynamic and the morphodynamic response in the proximity of a dredged area. More precisely, a laboratory investigation was carried out to analyze the effects of the wave-current interaction over a borrow area, particularly in terms of the morphodynamic evolution of the pit. The influence of both regular and irregular waves on the current was analyzed. It was found that the flow is significantly influenced by such interaction in the presence of the borrow area. The morphodynamic evolution of the sandpit is mainly affected by the waves, while the superimposition of a current does not introduce qualitative modifications but increases the mobilization of sediments, with repercussions on the speed of the evolution process. The results of the experimental campaign suggested that the analysis of the morphodynamic evolution can be approached at a laboratory scale. Indeed, the volume infill rate resulted in agreement with the observations in real dredged sites (CNEXO pit); moreover, the same quantity can be interpreted in the light of literature relationships proposed to describe the time evolution of noncohesive sandy beds.

A set of fully nonlinear Boussinessq-type equations (BTEs) with improved linear and nonlinear dispersive performance is presented. The highest order of the derivatives is three in the equations, and they use the minimum number of unknowns: the free surface elevation and the horizontal velocity at a certain depth. The equations allow reduction of the errors both in linear frequency dispersion and shoaling below 0.30% for $\mathit{kh}\le 5$, and below 2.2% for $\mathit{kh}\le 10$, with $k$ as the wave number and $h$ as the water depth. The weakly nonlinear performance is also improved for $\mathit{kh}\le 2$. A simple fourth-order explicit numerical scheme is presented to test the linear and nonlinear behavior of the model equations against analytical and experimental results.

Extensive knowledge is available on the overtopping behavior of traditional smooth impermeable sea defense structures, such as mildly sloping dikes and vertical walls, both typically featuring a high crest freeboard to reduce wave overtopping. A particular design application emerges in the development of wave energy converters of the overtopping type, where maximization of wave overtopping is required, i.e., smooth impermeable steep sloping structures with low crest freeboards subjected to nonbreaking waves. To date, relatively limited knowledge is available on the overtopping behavior of those structures. In this study, the average overtopping rate obtained from new experiments has been analyzed and compared with existing prediction methods. This study contributes to a better knowledge on the overtopping behavior of the steep low-crested structures, which is positioned in between that of mildly sloping dikes and vertical walls and that of structures with zero crest freeboards and relatively large crest freeboards. The existing prediction methods seem unable to predict the significant effects of the slope angle and small relative crest freeboards on the average overtopping rate accurately. Therefore, a new set of prediction formulas is proposed based on the new experiments combined with existing data from literature. These formulas include wave overtopping at vertical walls subjected to nonimpacting waves and at structures with zero crest freeboard.

This paper uses two alternative economic analysis approaches, net present value (NPV) and real in options (RIO), to show how the failure to incorporate uncertainty and flexibility in the economic analysis of flood risk and coastal management strategies can result in maladaptive decisions. RIO offers a major development on the conventional NPV approach, because it integrates expected changes in future levels of uncertainty into economic analysis. This study applies RIO analysis to the semihypothetical case study of a coastal defense system to demonstrate its applicability for decision making on climate change adaptation. In the case study, two different adaptive strategies are analyzed, consisting of a hard and soft structural alternative. Soft strategies are often inherently more flexible than hard strategies. The results of the case study show that the NPV approach increases the relative cost of soft strategies for the two alternatives compared with hard strategies, because it does not account for the value of flexibility built into adaptive strategies. It is therefore recommended that RIO analysis be used for the choice between hard and soft strategies to avoid maladaptation. This is particularly significant in cases where there is both high climate uncertainty and high decision uncertainty concerning the best strategy.

Experiments on a large pipeline and a small pipeline in a piggyback configuration under regular and irregular waves are carried out. A comparison of the wave forces on the large pipeline and the small pipeline is made. The nondimensional force coefficients for the drag, inertia, and lift are obtained based on the Morison equation. The effects of the Keulegan-Carpenter (KC) number and the spacing ratio between the two pipelines on the force coefficients for the large pipeline, small pipeline, and piggyback pipeline system are investigated. The experimental results indicate that the variation tendencies of the drag coefficients and inertia coefficients with the KC number or the spacing ratio for the large pipeline, small pipeline, and piggyback pipeline system are similar. The variation tendency of the lift coefficient with the spacing ratio for the large pipeline is opposite to that for the small one.

The Bosphorus Strait is a typical example of a narrow sea strait and, in general, has a two-layer flow structure. Driven by the water level difference between the Black Sea (north) and the Sea of Marmara (south), a lighter upper layer flows from north to south. A denser lower layer flow is caused by the density difference between the adjacent seas and flows in the opposite direction. In this study, the three-dimensional (3D) flow structure of the Bosphorus strait was modeled using the MIKE 3 hydrodynamic numerical code. Selecting the drag coefficient $\left(c_f\right)$, buoyancy parameter $\left(c_{\varepsilon 3}\right)$, and turbulence Prandtl number $\left({\sigma }_t\right)$ as calibration parameters, the model was calibrated using genetic algorithms with available current measurements at three different depths for one given location. The root-mean-square errors of the calibrated model were calculated to be 0.266, 0.201, and 0.163 m/s at the depths considered, respectively. The model was also validated temporally, for four different time periods and spatially, at another location in the strait. The validated models show good overall agreement with the field measurements. This paper is also relevant to determining the hydrodynamic design criteria of marine structures, and safe marine navigation in the waterway will be considered.