Journal of Waterway, Port, Coastal, and Ocean Engineering

This paper presents the results of an experimental investigation on edge scour adjacent to a stone cover laid on a sandy bed. The three-dimensional flow over the edge of the stone layer has been investigated by the use of particle image velocimetry. The flow measurements show a significant amount of turbulence in the primary flow near the junction between the stone layer and the sand bed and the formation of complex secondary-flow structures. The results show that the flow and the edge scour process in a steady current are governed by the size of the roughness elements and to some extent the side slope of the berm. The edge scour is caused by the combined action of the primary flow and the secondary flow. The primary flow stirs up the sediment and puts it into suspension, and the secondary flow carries it away from the junction between the stone layer and the sand bed, resulting in a scour hole forming adjacent to the toe of the stone layer. The measured scour depth attained a constant level of approximately one times the stone size in the live-bed regime; further, the scour depth showed a slight decrease when the side slope of the berm was increased. Design diagrams are presented for the scour depth and the time scale of the scour process.

This paper presents the results of an experimental study on the mechanics of pipeline scour propagation in the spanwise direction. The experiments were conducted with uniform sediment under a unidirectional steady current in clear-water conditions. The study aims to provide a better understanding of how the differential pressure between the upstream and the downstream sides of the pipeline and local bed shear stress at the span shoulder affect pipeline scour propagation in the spanwise direction. The measured data show that a high differential pressure significantly enhances pipeline scour hole development in the spanwise direction. Its presence increases the propagation velocity of the scour hole and differentiates the rapid from the slack phase of development identified in previous studies. It may be inferred from the relationship of the propagation velocity on pressure gradient that the two factors, namely, the differential pressure and the local bed shear stress, vary proportionally with the strength of the local flow field. They combine to affect the propagation velocity of the scour hole at submarine pipelines in the spanwise direction.

Tropical cyclones deliver intense winds that can generate some of the most severe surface wave and storm surge conditions in the coastal ocean. Hurricane Irene (2011) crossed a large, shallow lagoonal estuarine system in North Carolina, causing flooding and erosion of the adjacent low-lying coastal plain and barrier islands. This event provided an opportunity to improve understanding of the estuarine response to strong and rotating wind forcing. Observations from acoustic sensors in subestuaries and water-level elevation measurements from a network of pressure sensors across the system are presented. Data are examined with two modeling techniques: (1) a simple numerical approach using a momentum balance between the wind stress, flow acceleration, pressure gradient, and bottom friction that gives insight into temporal variability in water levels through the passage of the storm; and (2) an advanced hydrodynamic model based on the full shallow water fluid momentum equations, coupled to a spectral surface wave model that accounts for the spatially varying bathymetry and wind field. The results indicate that both wind-generated surface waves and the wind-driven storm surge are important contributors to the total water surface elevations that induce flooding along estuarine shorelines under strong hurricane forcing.

The prediction of dredging productivity plays an important role in controlling the costs and optimizing the scheduling of the dredging process. However, it is very difficult to achieve satisfactory forecasting efficiency because there are so many uncertain variables, including the rock, soil, and water properties; the main performance index of the dredger; and environmental restrictions. In this paper, the authors have developed a quantitative classification model for dredging materials under complex conditions, in which the weight of the condition attributes is calculated using rough-set theory and conditional entropy. Then, by considering the effect of the rock and soil conditions, the main performance index of the dredger, and the influence of the underwater environment, a prediction model for dredger production efficiency was developed. This approach is applied to a land reclamation project in Tianjin, China. In the study case, the efficiency of the dredger production is predicted fairly well when compared with the realistic conditions, so this model provides a feasible method and a technical tool for dredging cost control and schedule planning.

The present paper focuses on a methodology for the optimal design of a rubble-mound breakwater using a probabilistic analysis. In this (optimization) problem formulation, the total construction cost is minimized, subject to the constraints related to geometry, safety margins in different failure modes (overtopping armor instability failure, toe erosion, and settlement failure), and acceptable yearly failure rate (a value indicating chance of failure). The aforementioned method is illustrated by its application to the design of a multilayer rubble-mound breakwater that is under construction at Thalai Fishing Harbour, Thalassery, Kerala, India. Then the derived optimal design is compared with the results of conventional design. The comparative study reveals that the proposed probabilistic design resulted in a better economical design.