Development of a Fluid-Mud Model and Its Application to Field-Scale Dredged Basins

In several Asian and Pacific ports, siltation in which navigation channels and basins are rapidly accumulated by muddy sediment obstructs smooth port operation. In coastal water where suspended sediment concentration is very high and composed of mud, in which settling is hindered, the fluid-mud process can become important and dominant in sedimentation. This bottom-concentrated, muddy layer can behave differently and mobilize independently from the upper water column, primarily in response to gravitational force, resulting in a fast siltation rate in topographic lows. In addition to the hindered effect, mud-bed fluidization induced by high waves is another vital mechanism generating a fluid-mud layer. Despite their significance in modeling siltation in navigation channels and berths, detailed inclusion of fluid-mud processes has been rather scarce. In this paper, a wealth of formulas has been selected to include in our fluid-mud model development (two-layer approach). Both fluid-mud generated mechanisms, so-called hindered settling and wave fluidization, have been considered. The model is tested against field data from test pits in Kumamoto port, Japan. Results show that the model can reasonably simulate fluid-mud movement to the bottom of the test pits, and also quantitatively estimate the siltation rates during the high-wave storm using sensible parameter values. Our analysis also details an evaluation of related timescales which are bed consolidation time, intervals of repeated survey scans, and the storm return period. Additionally, an analysis is performed satisfactorily to evaluate the contribution of fluid mud versus traditional suspended sediment (by advection–diffusion) in the siltation process.