Dredging Intensity: A Spatio-Temporal Indicator for Managing Marine Resources

The sustainability of offshore sand reserves and the impact of their exploitation for coastal resilience can be assessed by resource managers via GIS. The GIS model to do this requires monitoring of the dredger location (including speed and displacement, if available). The designated borrow area is divided into grid cells, in this example, 100 × 100 m. The aggregate count of positions in each cell can be displayed in a graphic image called a "heat map" (or "density map" or "timeprint") where various intensities of colors represents the number vessel locations in each designated cell over the entire time period of interest as a surrogate for dredging intensity. Because sand dredging using a trialing hopper dredge is done at slow speeds, the aggregate time that a dredger spends in each cell can be modified by dredger speed to discriminate time spent actually removing sand from time spent in transit. If vessel displacements is also monitored, increases in displacement will also identify times and locations of active extraction. In this way, areas of disturbed benthic habitat can be identified, even if changes in bathymetry are not resolved.