DOCUMENTAZIONE

Purpose The paper aims to show the preliminary monitoring and field test results of the innovative technology tested in the
framework of theMARINAPLAN PLUS LIFE project for sustainablemanagement of sediment in harbour areas. The technology
is based on a patented jet pump thatwill be able to keep the seabed at a certain level over the time through a continuous removal of
silting sediments.
Materials and methods Preliminary field tests were performed to optimise the design of the demo plant and a monitoring plan
was devised to evaluate the technical, economic and environmental impacts of the technology, in particular in comparison with
dredging.
Results and discussion The preliminary tests showed promising results in terms of efficacy and efficiency of the sediment bypassing
device. At the maximum sediment removal capacity, the ejector tested in Cervia showed a sediment flow rate of about
2 m3 h−1, with an electric consumption of about 3.5 kW, and an influence diameter of about 5–7 m, after 15 days of working
operation. On the basis of the preliminary results, a 10-ejector demonstrator plant has been designed and realised, and it is now in
operation. The analysis of sediment and marine flora and fauna in the installation area in comparison with control areas indicates
the negative impact of cyclic dredging in the harbour inlet area.
Conclusions The innovative technology promoted by theMARINAPLAN PLUS LIFE project is a promising solution tomanage
sediment siltation in harbour areas through a cost-effective and low environmental impact technology. The monitoring of the
demo plant operation is fundamental to fully validate the technology and to demonstrate its efficacy and sustainability.

The presence of anthropic activity in the coastal or riverine environment modifies the wave as well as the water and sediment current regime. In particular, the body of water around ports is an area where intense currents and sediment transport rates are usually present and can be affected by low water velocities that take place close to the entrance and inside the port basin. Consequently, sediment can be entrained and accumulated in such areas, creating problems to navigation. Ports and moorings are filled with fine sediments due to deposition resulting from solid transport. In particular, silt particles settle because of the weak vertical and lateral shearing of the velocity field. The result is that harbours frequently require ordinary maintenance dredging.

The dredging process involves the removal of sediment in its natural deposited condition by using either mechanical or hydraulic equipment. Dredging is a consolidated and proven technology, but involves considerable drawbacks. In particular, dredging has a notable environmental impact on marine flora and fauna, contributes to the mobility and diffusion of contaminants and pollutants already present in the silted sediments, obstructs navigation and is characterized by relatively high and low predictable costs.

This paper aims to provide an original structured overview of technologies alternative to dredging that have been tested in the past 50 years. More than 150 articles have been analysed to compare standard dredging technologies with market-ready competitors from techno-economic and environmental perspectives. In particular, the paper focuses on anti-sedimentation infrastructures and on innovative plant solutions characterized by low maintenance costs and by a very limited environmental impact. The final aim of the paper is to describe the currently available technologies that prevent port inlet and channel siltation and to classify them through a techno-economic and environmental impact assessment. The comparison shows that dredging has both the higher costs and environmental impact, while fixed sand by-passing plants are characterized by the lowest environmental impact and operation costs that are competitive with dredging.

The management of sediment in aquatic ecosystem has been an important issue for water managers throughout history. The changing nature of sediment issues, due to increasing human populations, the increasing prevalence of man and recognition of the important role of sediment in the transport and fate of contaminants has meant that sediment management today faces many complex technical and environmental challenges. Sediment management is complex, involving a careful balance of science, policy and economics. So, there is not a single correct way to address a problem, but, rather, the approach should be driven by the ecological, political and economic goals of interested parties. When sediments are managed to achieve ecological goals (i.e. reclamation of the seabed next to former industrial areas), the main focus is on sediment contamination analysis, removal and treatment or disposal, thus involving sediment quality more than quantity. Trevi SpA, together with the Department of Industrial Engineering (DIN) of Bologna University designed, realized and tested a new dredging prototypal device, called Sludge Buster (SB), that has been designed for application where excavation accuracy and environmental impact minimization have particular relevance (i.e. contaminated sites). On the other hand, when sediments are managed to achieve socioeconomic goals (like navigational dredging or flood defense), the focus is on managing sediment quantity, because it is the presence or absence of sediment that is affecting final objective (for example, excess sediments in navigation channels) However, uncontaminated sediments have some ecosystems implications in terms of turbidity and/or habitat loss. In these cases, the movement of sediments is a given (if permitted), involving also management of removal, placement, disposal and/or treatment options. Trevi SpA, together with DIN designed, realized and a first commissioned a prototypal Pneumatic Flow Mixing (PFM) method plant. PFM method is a process for sediments transport and on-line consolidation (Oota et al., 2009).

The paper shows designing, prototyping and testing carried out since 2002 on an innovative plant for seabed maintenance, characterized by zero environmental impact and planned especially for harbour areas. The core of the technology is made up by a jet-pump device called "ejector". The ejector has been sized through both laboratory experiments and fluid-dynamic simulations. In 2005 the first full-scale experimental plant was designed and carried out in the port of Riccione (Italy). The results of the experimental campaigns demonstrated the functionality of the system itself, the cost-effectiveness and low environmental impact if compared to the use of the dredge. Finally, in 2011 the first industrial plant has been realized in the Portoverde Marina (Italy). This plant is characterized by better performances in automation and control higher than the first experimental plant. By these features it is possible to increase plant reliability and ensure a further reduction of the management costs.