Development of a Dredging Sensitivity Index, applied to an industrialized coastal environment in Brazil

Ports link world commerce via maritime routes, and dredging services are essential to establish and maintain these connections. However, one question is critical when dredging is being considered: where are the best places to do it? To try to answer this question, a Dredging Sensitivity Index (DSI) was developed as a management tool to be used in project planning steps. In order to diminish environmental damages and quality-of-life losses, DSI provides alternatives by identifying sensitivity areas. This new methodology quantifies impacts caused by the sediment removal step and points out favorable areas to dredge, with a simple map. Parameters such as fine-grain content (% < 63 μm), Acid Volatile Sulfides (AVS), Shannon-Wiener Index and fisheries, among others, were used to calculate the DSI. Formulas were used to weight and aggregate both, the parameters and the DSI itself. Sepetiba Bay was chosen to apply this methodology because of its relevant economic and environmental aspects. The methodology was applied to dredging situations, but it can be used to indicate areas for dredged material disposal, with a few modifications in the DSI formulas. A DSI map was a final result of this methodology, and showed that the northern portion of the bay, close to the littoral is a more sensitive area, where dredging should be avoided, or carried out very carefully. DSI is a very useful tool for reducing damages from dredging services, it contributes with zonation and it provides alternatives to decision-makers who manage these areas.