4. Discussion
Coastal oceans are dynamic, where ocean properties may change faster than in deep, open oceans away from land. As such, the size, shape, and extent of the plumes were quite variable. Measured by MODIS, plume area varied by tens of km2 over the course of several days. While some of this can be attributed to measurement uncertainties (see Section 4.2), there is undoubtedly large day-to-day variation in plume extent and severity. Indeed, even same-day RGB images from Landast and MODIS (Fig. 11) show large deviations in the observable plumes. The time difference between these images is just over 2.5 h, as Landsat typically overpasses this region at 15:50 UTC, while the MODIS Aqua overpass on those days is at 18:25 UTC. This variability could result from strong local currents (both tidal and non-tidal) advecting and dispersing sediments, and/ or rapid settlement of suspended sediments. Bokuniewicz and Gordon (1980) recorded descent speeds for dredging spoil as fast as 1.5 m s− 1, with lateral advection modulated by current velocity. No such characterization of sediment settlement velocities has been reported for this dredging event. However, reports of coral smothering (FDEP, 2014) indicate that settlement of particles explains least a portion of the day-to-day plume variability.