Mathematical Modeling and Simulation of Ocean Disposal of Harbor Dredged Materials

Ocean disposal of wastes such as dredged materials causes the concentrations of contaminants and some other water quality parameters in the water column to change. In this study, the STFATE (short-term Fate) system, a model developed by the U.S. Corps of Engineers for managing automatic dredging and disposal of the dredged materials, was used to model and simulate the deposition, dispersion, and accumulation of the dredged material disposed at an ocean site. Additionally, aerial photographs taken from a helicopter on dispersion of the disposed materials were used to calibrate and verify the modeling results for evaluating its applicability in predicting the influence of disposing dredged materials on the surrounding seawater quality. Simulation results indicate that after $4\mathrm{h}$ of ocean disposal, the dredged material showed negligible adverse influence on the seawater quality $(\mathrm{SS}=3–4\mathrm{mg}∕\mathrm{L})$ . Results of simulating the dispersion of dredged materials revealed that $20\mathrm{s}$ disposal duration resulted in smaller influence distance and range but a longer time for the seawater to recover to its original state. A longer disposal time of $\mathrm{1,200}\mathrm{s}$ would cause a larger distance and range of influence but a shorter recovery time. The verification results demonstrate that simulated values on the dispersion length, width, area and shape generally comfort to the trends of monitored data; the average error is around 27.8%.