Tree-demensional multi-layered mud transport model is presented. In Kumamoto Port which is under construction, extensive field measurements have been made to obtain detailed information on siltation mechanisms. A most remarkable result is the effect of a submerged dike on reducing the amount of deposition within the test trench.
　A multi-layered model is adopted to take into account the effects of submerged dikes and to be able to reproduce the vertical distribution of suspended mud concentrations.
　Numerical constants which govern mud transport process are estimated from the data obtained by the field observations and laboratory experiments. Finally, deposition rates within three trenches were used to calibrate the present model.
　As the dimension of the trenches is 70m×50m in area, the mesh size arround them should be small, about 10m, but the area apart from these places doesn't need as fine a mesh. To satisfy such contradicting requirements, a nested grid model is adopted and the supercomputer NEC SX-1E is used.
　After the calibration of the deposition rates is completed, calculations for the future plans are carried out to estimate the amount of deposition for cases with and without submerged dikes.
　It is predicted that submerged dikes 1m in height from the bottom will prevent siltation in the access channel and anchorages of Kumamoto Port by about 30% of the total deposition without submerged dikes.