Journal of Waterway, Port, Coastal, and Ocean Engineering

Microorganisms have been used to delay fluid mud consolidation and to keep fluid mud navigable. However, bacteria and extracellular polymer substances (EPSs) that delay sediment consolidation have not been studied widely, and it has taken many years to make inorganic chemoautotroph bacteria and EPSs effective. To understand the effect of EPSs on consolidation and to find new methods of applying EPSs at nautical depths, a strain of bacteria, Burkholderia vietnamiensis, was recently isolated and screened from sediment; it was cultured to secrete EPSs to be added directly to fluid mud in a series of consolidation experiments. The experimental results showed that the EPS consisting of polysaccharides as the main component can greatly reduce sediment settling and consolidation velocity. Also, when the EPS content was relatively high, the fluid mud consolidated at a slower rate. A self-weight consolidation in the settling regime was best predicted by an exponential equation, and a permeability regime was best predicted by a logarithmic equation. The equilibrium density of mud in the effective stress regime decreased exponentially with increasing EPS content. The application time of the nautical depth might be delayed greatly by adding 0.68 g/L EPS directly into the Cangnan Power Plant Harbor, Zhejiang Province, China. The new concept of direct EPS addition into fluid mud might be a solution to the problem of slow growth of inorganic chemoautotroph bacteria and EPSs, and it might be helpful to promote the application of EPSs at nautical depths in new harbors.

This study explored the use of automatic identification system (AIS) data to assess the sheltering effectiveness of three inlet structures in the coastal United States: Columbia River at the border of Oregon and Washington; Freeport, Texas; and the Savannah River at the border of Georgia and South Carolina. Archival AIS data from 2012–2014 were assembled into distinct vessel transits and partitioned into sheltered and exposed segments. Vessel-performance metrics were defined and compared for the exposed and sheltered segments during high- and low-wave conditions, based on offshore wave information study data. Vessel-performance metrics were statistically analyzed to identify the sheltering effect of the inlet structures. The results show a quantifiable, statistically significant positive impact of jetty sheltering on vessel performance in all three study areas. The procedures developed in this study are intended to quantify jetty functionality from a vessel-performance perspective such that a portfolio of structures may be prioritized for maintenance.

The design of flexible floating anticollision systems (FFAS) against collision by uncontrolled vessels is based on quasi-static considerations, in which the maximum loading is taken to occur when the vessel is brought to a standstill and its kinetic energy is completely transferred to the strain and frictional energy of FFAS. The dynamic loading during the collision process due to system response characteristics of the FFAS is typically ignored. In the present study, the authors demonstrated through an experimental investigation that it is critical to consider both quasi-static and dynamic loadings to design against possible failures of the system. The experimental investigation was performed as a case study for a FFAS to protect a chemical wharf at Zhangzhou Port, China. The system consisted of a row of floating buoys connecting and mooring with steel chains. Extensive physical modeling tests were performed to quantify the motion of the collided buoy and the tensions of selected block and mooring chains when the FFAS was struck by a 5,000-DWT (deadweight tonnage) vessel model with different initial velocities. The results showed that the transient impact force on the system had multiple dynamic peaks during the collision process. Most importantly, the maximum loading on the FFAS (and the reaction impact force on the vessel in the opposite direction) occurred at a dynamic peak prior to when the vessel was halted to a standstill, and the magnitude was larger than the maximum quasi-static loading based on energy transfer principle alone. Thus, the case study highlighted the importance of including the dynamic loading and responses into the design considerations of FFAS.

In this study, measurements were used to characterize the dry–wet seasonal factors that control hydrodynamics and sediment transport in the Deepwater Navigational Channel (DNC) located in the North Passage of the Yangtze Estuary. The measured data showed the following: (1) The estuarine turbidity maximum (ETM) location remained in the middle and lower reaches of the DNC, regardless of season or tide, and (2) density stratification and saltwater-intrusion length were found to significantly impact seasonal differences in the estuarine turbidity maximum. Subsequently, a physical-based three-dimensional numerical model was developed to simulate seasonal variations in fine-grained suspended sediment dynamics in the Yangtze Estuary. A series of numerical experiments focused on river discharge, seasonal wind, and mean sea level was performed to explore the primary mechanisms. Finally, the complexity of water circulation and sediment dynamics related to the seasonal variability of channel siltation in the channel was determined. The modeling results showed that (1) river discharge has a strong impact on the horizontal and vertical distribution of residual currents, especially near the bottom during the wet season; (2) seasonally varying wind can significantly alter residual currents near the riverine limit, and the wind in the dry season favors the delivery of sediments from river to sea; and (3) seasonally varying mean sea level and wind climate jointly shape the saltwater-intrusion length near the estuarine front. This study represents a preliminary exploration of physical phenomena and their contribution to siltation of the Yangtze Estuary navigation channel. The results of this study provide crucial data for the development of measures to mitigate channel siltation.