Coastal Engineering Journal

The deformation of nonlinear internal waves (NLIW) from depression to elevation waves during the shoaling process has been attributed to three key factors: wave amplitude, mixed-layer depth and water depth. This study examined the critical conditions for wave deformation by means of five strings of thermistors deployed at the Dongsha Atoll in the northern South China Sea (SCS). During a two-day experiment, four wave trains consisting of 78 solitons at five sites were identified. The parameters related to soliton transformation were formulated by applying the extended Korteweg–de Vries (eKdV) theory. The results indicated that the soliton energy dispersed dramatically along the sharp bottom slope, likely as a result of bottom friction and turbulence mixing. Large-amplitude depression waves were observed to transform into elevation waves before the thickness of the lower layer became equal to that of the upper layer. The ratio of the wave amplitude to the lower-layer thickness was found to be a good indicator of wave deformation. The critical conditions for the transition of the internal waves (IWs) occurred at the ratio approximately equal to $0.66\pm 0.2$. This means that a bottom-trapped elevation wave could form before passing through the theoretical critical point. The solitons felt the bottom and deformed when their amplitudes approached half of the lower-layer thickness. The solitons existed in the form of elevation waves when the waves were in contact with the bottom.

Field observations of the currents at a bending channel in the Abashiri River in Hokkaido, Japan have revealed an unexpected secondary circulation during flood tide with near-bed and near-surface currents toward the outer and inner banks of the bend, respectively. The direction of these cross-stream currents was reversed at the end of flood tide. The occurrence and shutdown of these observed unexpected secondary circulation were further investigated through the shape of the along-channel velocity profile by using a theoretical solution based on the steady-state momentum equation and the Stokes’s second problem for oscillating flow. Also, an advanced numerical model was used to quantify the unexpected secondary flow. It was shown from the theoretical analysis that vertical advection plays a great role in the momentum balance affecting the direction of secondary flows. The typical secondary flow was found to occur throughout ebb tide with a pronounced near-surface maximum velocity profile. Whereas, during flood tide, the longitudinal velocity profile was characterized by a near-bed and mid-depth maximum, resulting an upwelling flow near the outer bank. These findings were reconfirmed by numerical simulations that were conducted for the entire estuary.

On 16 September 2015, a Mw 8.3 earthquake occurred off the coast of Illapel, Central Chile, generating a tsunami that caused moderate damage along the coast of Central Chile. To investigate tsunami damage and evacuation responses, we conducted a post-tsunami field survey between La Serena and Concón. The average tsunami inundation height in the survey area was 3–4m; however, in the innermost corner of Coquimbo Bay, which was shielded from the tsunami source by the Coquimbo Peninsula, the tsunami inundation height was 6.0–6.2m, decreasing gradually along the coast away from the corner. This phenomenon was also confirmed around Tongoy Bay, which is geographically similar to Coquimbo Bay. Based on our results, we hypothesize that the tsunami was diffracted and refracted by the peninsula, and then converged on the innermost corner of the bay, located behind the peninsula. Interviews with local residents confirmed that most people evacuated immediately after feeling strong seismic motion, but before the tsunami warning and evacuation orders were issued. However, several people did not evacuate, either because they believed that they were located in a safe place, or because they wanted to protect their property.

A detailed laboratory study of swash zone sediment transport under dam-break waves on a fine sandy slope was carried out. A newly developed sediment transport measurement system was applied for simultaneous measurement of sediment concentration and transport velocity with a vertical resolution of 0.53 mm based on particle image velocimetry (PIV) and a light extinction method, respectively. Concentration data were combined with velocity data to produce sediment flux and were used to investigate the characteristics of sediment transport in the swash zone under dam-break waves. It was found that sand particles followed the flow well in the experiment. Phase difference between the maximum velocity and maximum concentration in the initial uprush was obvious. The maximum concentration varied significantly between different elevations. The onshore flux was much larger than the offshore flux, and the flux near the bed was much larger than that at the higher elevations. The net transport was offshore close to the bed, onshore in the middle layer, and almost zero in the upper layer. The measurement error between the mass change calculated from bed form evolution and the net sediment transport obtained from the measurement system was smaller than 20%.

Debris in high-volume, high velocity flows, such as tsunamis, storm surges, and dam breaks, cause widespread damage to coastal communities. Evaluating the motion of the debris within the flow is difficult due to the variety of variables that can affect the motion, therefore techniques must be developed to quickly and accurately track the motion of the debris within the flow. This paper presents an optical tracking technique to track the motion of debris over a horizontal bottom under laboratory conditions. The debris consisted of scaled-down shipping containers, made of polyethylene (PE), placed on a dry, raised, flat section of the basin floor. Container movement was measured using two overhead cameras and a novel object tracking and detection algorithm implemented in MATLAB. The algorithm was developed to be able to quickly and accurately track uniform containers throughout an experimental run. The algorithm combines image-processing techniques such as Color Thresholding and Blob Analysis with tracking methods such as the Kalman Filter and Hungarian (Munkres) Algorithm. The algorithm was evaluated by comparing the results to those from a manual tracking method. For experiments with one, three, and six containers, the algorithm showed good agreement with the results of the manual method. However, with nine containers, the increase in the amount of container–container collisions and the agglomeration of the containers resulted in poor results compared to the manual method. While the algorithm is only evaluated here to track the motion of the shipping containers, there is potential for its use in many other fields of hydraulic and coastal engineering.

In this paper, the combined use of satellite images and morphodynamic models is applied to assess the coastline changes of an erosion-prone deltaic zone in Northern Greece (Nestos River delta). Satellite images over the last 31 years were used to estimate the erosion rates at the eastern, central and western parts of the delta. The numerical model LITPACK, coupled with wave and hydrodynamic nearshore models, was calibrated based on these results, and was further utilized to predict the shoreline evolution with and without “hard” protection works. Results show that the model underestimated erosion rates over all studied sub-sections, but showed fair agreement to remote sensing analysis when focusing on the zones of major erosion. “Hard” coastal protection structures were tested to assess their mitigation efficiency in terms of longshore and cross-shore sediment transport reduction. LITPACK considered that the scenario of seven rubble-mound breakwaters with low seaward and lee-side slopes, positioned between 9m and 19m depicted the best results, even reversing coastline retreat process.

In this paper, a hybrid finite-volume-finite-difference scheme for the solution of the one-dimensional form of the Nwogu’s extended Boussinesq-type equations was developed to investigate the breaking of a solitary wave propagating over a fringing reef system. The adoption of a high-order finite volume WENO schemes with HLL Riemann solver for advection terms as well as the third-order Runge–Kutta time-stepping scheme makes the present scheme shock-capturing. From the validation case, it is shown that the present shock-capturing model could simulate the shoreline movement and wave breaking as well as bore propagation very well. In order to comprehensively understand the hydrodynamic characteristics when a solitary wave travels over a fringing reef system, a parametric study has been carried out to analyze the interaction process under various conditions. Effects of different physical parameters on wave breaking are analyzed and the reflection, transmission and dissipation (RTD) coefficients are calculated based on the integration of kinetic and potential energies in different zones.