Abstract Body

Preservation of a good navigability in harbours, ports and waterways is a challenging issue. Traditionally, the sediment that causes the problem is excavated, removed and relocated through maintenance dredging. Nevertheless, dredging is not effective in keeping navigability over the time. This objective may be reached through a higher frequency of dredging operations, but would result in higher costs and complex authorization/permit procedures. Maintenance dredging also has considerable environmental impacts: dredging i) greatly modifies underwater habitats and resident flora and fauna, ii) resuspends sediments and contaminants already present in the seabed, iii) impacts locally on greenhouse gas (GHG), pollutants and noise emissions, iv) generates a waste to be disposed, i.e. the dredged material. The “ejectors plant” technology has been developed as a sustainable alternative to maintenance dredging and has been recently tested by Trevi SpA and University of Bologna in two different applications in Cervia and Cattolica (Italy). Both plants were monitored for more than one year to assess i) water depth, ii) energy consumption, iii) maintenance costs, iv) seabed features and species diversity, v) equivalent CO2 emissions through LCA, vi) underwater noise impact. The minimum water depth required was guaranteed at the end of the monitoring period. Monitoring actions revealed that seabed features and species diversity were improved and that the impact on underwater noise was absent. Based on energy consumption, it was also demonstrated that an optimized ejectors plant, if fed by renewable power, could cut more than 80% of GHG emissions and guarantee near-zero pollutants emissions in comparison with traditional dredging. The ejectors plant technology has the potential to be widely applied for the ordinary maintenance of water infrastructures to prevent sedimentation as well as erosion, and the related impacts, like navigability hampering, flood risk, rivers and waterways embankment erosion.