Effectiveness Assessment of an Innovative Ejector Plant for Port Sediment Management

Maria Gabriella Gaeta,Cesare Saccani,Alessandro Guzzini,Marco Pellegrini,Renata Archetti,Arash Aghakhani

doi:10.3390/jmse9020197

Maria Gabriella Gaeta, Cesare Saccani + Show 4 more

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https://doi.org/10.3390/jmse9020197

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Abstract

The need to remove deposited material from water basins is common and has been shared by many ports and channels since the earliest settlements along coasts and rivers. Dredging, the most widely used method to remove sediment deposits, is a reliable and wide-spread technology. Nevertheless, dredging is only able to restore the desired water depth but without any kind of impact on the causes of sedimentation and so it cannot guarantee navigability over time. Moreover, dredging operations have relevant environmental and economic issues. Therefore, there is a growing market demand for alternatives to sustainable technologies to dredging able to preserve navigability. This paper aims to evaluate the effectiveness of guaranteeing a minimum water depth over time at the port entrance at Marina of Cervia (Italy), wherein the first industrial scale ejector demo plant has been installed and operated from June 2019. The demo plant was designed to continuously remove the sediment that naturally settles in a certain area through the operation of the ejectors, which are submersible jet pumps. This paper focuses on a three-year analysis of bathymetries realized at the port inlet before and after ejector demo plant installation and correlates the bathymetric data with metocean data (waves and sea water level) collected in the same period. In particular, this paper analyses the relation between sea depth and sediment volume variation at the port inlet with ejector demo plant operation regimes. Results show that in the period from January to April 2020, which was also the period of full load operation of the demo plant, the water depth in the area of influence of the ejectors increased by 0.72 mm/day, while in the whole port inlet area a decrease of 0.95 mm/day was observed. Furthermore, in the same period of operation, the ejector demo plant’s impact on volume variation was estimated in a range of 245–750 m3.

Highlights

The presence of anthropic activity in the coastal environment strongly modifies waves, currents and sediment transport regimes
The analysis was performed with the aim (i) of characterizing the extreme storm events mainly responsible for the short-term sediment movimentation occurring at the port entrance and (ii) of linking the amount of energy required for these events to the sediment movement at Cervia, in order to investigate the effectiveness of the ejector plant in 2019–2020, and to compare with the observations of the previous years (2017–2019), where no ejectors operated
Part of the sediment came from the surrounding area, and it is expected that natural sediment transport in the area produced by storm and longshore transport contributes

Summary

Introduction

The presence of anthropic activity in the coastal environment strongly modifies waves, currents and sediment transport regimes. Intense wave-induced currents and sediment transport rates are present around ports and commonly influence their commercial and recreational activities. The accumulated sediments reduce the admitted draft of the navigation channel on the one hand and generate erosional effects on the leeside coasts on the other. Harbours frequently require ordinary maintenance dredging to remove the accumulated sediments [1]. Dredging is a consolidated and proven technology, but involves considerable drawbacks [2,3,4,5], since it has a notable environmental impact on the marine environment, contributes to the mobility and diffusion of contaminants and pollutants already present in the settled sediments, and obstructs navigation during its operational phases.

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