Journal of Waterway, Port, Coastal, and Ocean Engineering

A detailed mathematical model for sedimentation of dredged channels, based on a detailed representation of all relevant transport processes such as convection, mixing and settling, is presented. This is an important advantage compared with the traditional prediction formulas, which are based on a rather strong schematization of the transport processes. A sensitivity analysis is presented showing the influence of the streamline refraction effect and the wave shoaling effect in the channel on the sedimentation process. Two applications of the proposed mathematical model are given and show reasonable agreement between measured and computed concentrations and sedimentation rates. Finally, a set of graphs is presented which can be used to get a rough estimate of the trapping efficiency of dredged channels.

For several decades, the Belgian East Coast has posed problems of a sedimentological nature. Off the coast, a gully (called “Appelzak”) has developed to a depth of 8 m below low‐water and has shifted dangerously near the existing seadike, causing severe beach erosion. In 1976 the Belgian Government decided to sizeably enlarge the outer harbor of Zeebrugge seaward to a distance of 3.5 km from the coast, and to proceed with a significant beach restoration of about $8.5\mathrm{million}{m}^3$ of sand. An extensive observation program is carried out to study beach changes and to indicate unexpected developments, so that counter‐measures can be taken in good time. Results of observations over the period June 1979 until February 1981 are examined using survey data from bathymetric soundings, aerial photogrammetry and terrestrial beach measurements.

A simple representation for a tidal basin with freshwater input is described. By assuming the conditions are well‐mixed within the basin, it is possible to develop an elementary analysis for predicting salinities in the basin and sediment transport between the estuary and the basin due to density exchange flow. The results of the analysis are presented in a generalized manner and this enables first estimates for some prototype situations to be made easily and with a minimal amount of field data. Some very simple physical model tests, described in the paper, have confirmed the validity of the analysis. An example of the use of the engineering model is given in which the dredging requirement at a small dock system is examined; this reveals some interesting and important features, and it is likely that these features apply at other tidal basins.

The maintenance and deepening of existing waterways and navigational channels by dredging are vital to the nation's economy. Cutterhead dredges share the major burden of dredging in the United States. Sediments in the waterways have become polluted over the years and this has become a matter of concern. A substantial increase in turbidity has been observed in the vicinity of cutterhead dredges. A need exists, therefore, to study the complex nature of flow around the cutterhead, and to investigate the factors contributing to turbidity generation and ways of reducing the turbidity. Hydraulic model studies provide an ideal tool for studying the flow around a cutterhead. Systematic studies of cutterhead design carried out in the past decade were mainly related to the establishment of a similitude criteria for flow at the suction intake of a cutterhead, the sediment pickup behavior at the intake of a suction pipe, and the cutting ability of cutterheads of different shapes. Previous investigations were extended in the current investigation to include studies on flow field and sediment pickup at the cutterhead intake. The flow field studies provide a means to predict velocity field at the cutterhead intake. The sediment pickup phenomenon was found to follow the Reynolds type similitude relationship. The study on sediment resuspension at the cutterhead has helped to identify various parameters related to the sediment resuspension mechanism at the cutterhead.