Poojitha D. Yapa

SPEED model is a three-dimensional numerical model which can simulate sediment plumes released upwards (due to momentum of the mining tool) or downwards at a higher up release station. Both near-field dynamics phase and far-field passive advection-diffusion phase are considered. In the near field, the model is based on a Lagrangian integral control volume technique; for the far field, the Lagrangian discrete parcel method is applied. Both fixed source and moving source releases can be handled by the model. The effects of different particle sizes, sediment concentration and flocculation on settling velocities are taken into account. A multiple grid scheme is applied when the mining domain is very large or mining time is very long.

In addition to studying the sediment transport, the model simulates the chemical distribution due to sediment transport, estimates the mortalities of benthos due to deposited sediment and assesses the effects on photosynthesis due to sediment plume. The model is able to handle heavy metals, organic chemicals, nutrients and minerals. The partitions of chemicals between water and sediment are considered. The mortality of benthos is calculated based on LC50 and first order kill rate. The effect on photosynthesis of sediment plume in the euphotic zone is estimated based on the relationship between Photosynthetically Active Radiation and Net Primary Productivity.