Enhancing the performance of hazard indexes in assessing hot spots of harbour areas by considering hydrodynamic parameters

The hazard assessment strategies for harbour areas usually rely on tools able to predict environmental threats posed by contaminated sediments, mostly based on biological and chemical parameters and distinctly less on hydrological factors. Although ports are considered semi-enclosed and low-energy systems with scarce capacity to disperse contaminants to the open sea, the hydrological pattern established within the port basin cannot be neglected, especially when the localisation of hot spots is required for clean-up and remediation actions. In the present study we considered both approaches (biological/chemical and hydrological) for assessing hot spots of harbour areas. In particular, the relationship between the sediment hazard assessment c_NWAC (cumulative Normalized and Weighted Average Concentration) index (which is based on chemical and biological data) and a properly selected hydrodynamic parameter (the bottom shear stress) of the port area was investigated. This study demonstrates that marine currents influence significantly the fine-grained fraction distribution of the surficial sediments, and thus, the spatial and temporal variability of contaminant concentration. The evaluation of hydrodynamic parameters enhances the performance of hazard tools in the localization of areas of most concern and thus a detailed knowledge of the hydrodynamic features of the port seabed is advisable before defining a proper characterisation strategy for the harbour area.