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Zero environmental impact plant for seabed maintenance

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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.
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I2SM 2014 Ref no: ID 146
ZERO ENVIRONMENTAL IMPACT PLANT FOR SEABED MAINTENANCE
Bianchini Augusto, Pellegrini Marco, Saccani Cesare
Department of Industrial Engineering (DIN) – University of Bologna
ABSTRACT
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.
Keywords: Seabed maintenance, Dredging zero environmental impact, Jet pump, Industrial
dredging plant, Automation and control.
1. INTRODUCTION
Harbours and tidal inlets located on coastal areas have one common characteristic: the
need to avoid littoral materials collected nearby the entrance. Bypassing can occur
naturally, but in the natural process the harbour entrance becomes unusable for
commercial and navigation purposes and, in the worst cases, the inattention results in the
complete closure of the port itself. The dredging equipment represents the most common
solution for sand bypassing and for keeping harbour and inlets right depth. This kind of
equipment is rugged and reliable; it has been proved over and over and appears to be
irreplaceable for many applications and locations. On the other hand, there are locations
and situations for which this equipment is not suitable and may be detrimental or
prohibitively expensive in terms of costs. Moreover, dredging operation obstructs the
normal navigation operations. Furthermore, dredging operation can have high
environmental impact on marine flora and fauna [1,2] and can contribute to mobility of
contaminants and pollutants [3,4] already present on the seabed.
Need for improved operations and maintenance techniques and equipment for sediment
bypassing is a profitable sector for research and development applications [5]. Among
other technologies, jet pump has a great potential as primary component in sand
bypassing system, since it requires limited personnel, is able of great portability and can
be assembled at reasonable cost: moreover, the technology is reliable since has been
applied starting from 1976 for coastal application [6]. A jet pump (Figure 1a) is a device
that transfers momentum from a high speed primary jet flow to a secondary flow. The
primary jet flow contacts the suction fluid at the nozzle exit and drags it into the jet pump,
thus starting up and sustaining the secondary flow of suction fluid from surrounding water
mass. If present, solid particles are entrained in the secondary flow, thus being introduced
in the mixing chamber, where jet stream and suction fluid are further mixed, exchanging
momentum and recovering pressure. The slurry then pass through a diffuser and into a
discharge pipe for delivery to a discharge point (or into a booster).
Figure 1: a) Schematic of a jet pump; b) Schematic of the “ejector” developed by DIN.
Department of Industrial Engineering (DIN) of Bologna University, in collaboration with two
Companies, Elettromeccanica Muccioli Marco Srl (Rimini, Italy) and Plant Engineering Srl
(Bologna, Italy) developed and tested an innovative plant for seabed maintenance
characterized by the fact that the main element, called “ejector” (Figure 1b), is an open jet
pump (i.e. without closed suction chamber and mixing throat) with a converging section
instead of a diffuser. The ejector can be used as a fixed or mobile device [7]: the paper
focuses on fixed ejectors application. When used as a fixed device, one ejector works on a
limited area whose diameter depends on the sediment characteristic as, for example, the
angle of repose. By ejectors integration in series and in parallel it is possible to create a
seaway. The paper shows laboratory, first experimental plant and first industrial plant
activities and main results achieved over the years. A spin-off company of Emilia
Romagna Region (Italy), named Plant Engineering Srl, has been created to promote the
widest technology dissemination and to design and manage new industrial applications.
2. LABORATORY DEVELOPMENTS AND TESTING
The one-dimensional jet pump theory is well known and described by several models,
improved and implemented over the years [6, 8]. The ejector suction effect is due by the
behavior of a fluid jet in free outflow from a hole (nozzle diameter d) towards an open
environment. A jet under these conditions increases its flow, from inlet to outlet section,
due to the flow absorbed within the jet itself from the surrounding environment: the high
velocity of the jet creates a low pressure area out of the nozzle leading the pumping of the
second flow toward this minimum pressure point. Consequently, there is an exchange of
momentum between the two streams resulting in a uniform mixed stream flowing at an
intermediate velocity between the primary and secondary flow ones.
On the other hand, it has been demonstrated that jet pump performance calculation needs
to be validated by experimental test in order to overcome the uncertainty on the
determination of the value of some fundamental parameters such as friction coefficients or
convergent-divergent drag coefficient [9, 10]. Starting from 2002 and up to 2013, several
ejectors (Figure 2a and 2b), characterized by different geometries, have been tested in
DIN laboratory to verify theoretical performance in a real environment (Figure 3a and 3b):
inlet and outlet ejector streams pressure were measured by pressure gauges, while inlet
and outlet volumetric flow were measured by level variation in the water and discharge
tanks, respectively. Experimental test has been integrated with computer fluid-dynamic
simulation. The results of the preliminary tests have led to the design and realization of an
ejector (Figure 2b) characterized by an implemented secondary flow nozzles system. The
primary nozzle jet pressure is the one described above and is responsible for the action of
water-sediment mixture suction from the surrounding environment; this latter has been
integrated with a series of inclined radial secondary nozzles, positioned at the two edges
of the ejector and fed by the same duct of the primary nozzle, with the aim of increasing
the solid concentration in the mixture through an effect "spade-shovel" in which the
secondary nozzles shake the sediment on the backcloth and the primary nozzle removes
it.
Figure 2: a) Picture of two of first series ejector prototypes (2002-2004); b) Picture of second series ejector
prototype (2004-2005, the one used in Riccione harbour), during laboratory test.
Figure 3: a) Picture of experimental set arrangement; b) Schematic of experimental set arrangement.
Starting from 2005 and up to 2013, the ejector has been tested in order to forecast its
performance at different working and boundary conditions. Operational characteristics of
the ejector have been described by two jet pump dimensionless ratios, flow ratio Q and
head ratio H defined as Q=QD/QP and H=HD/HP, respectively, where QP and QD are
primary volumetric flow and delivery volumetric flow and HP and HD are primary flow
pressure and delivery flow pressure. Ejector efficiency η has been defined as η=Q×H.
Examples of laboratory test results are shown in Figure 4a and 4b: results are given for
different ejectors (different ratio between nozzle diameter d and discharge diameter D) at
the same inlet pressure and with water-water environment (no sediment). The results in
Figure 4a show that, being D a constant value, a higher d decreases the ejector suction
capacity (measured by Q). On the other hand, a higher nozzle diameter d allows reaching
higher pressure at the converging outlet, thus increasing sediment transport distance.
Furthermore, Figure 4b shows that ratio d/D does not affect ejector efficiency. The results
are in line with the theoretical forecasts for the behavior of the jet pump [6]. Moreover,
ejector performance (Figure 5a and 5b) has been characterized as a function of inlet
pressure (measured by adimensional inlet pressure coefficient p, that is the ratio between
measured HP and maximum primary pressure HPmax allowed) and as a function of
equivalent discharge pipe length (measured by adimensional factor Lp, that is the ratio
between equivalent discharge pipe length L and equivalent maximum pipe length Lmax
allowed) through the suction efficiency Ψ, defined as the ratio between the secondary
volumetric flow QS and the delivery volumetric flow QD, that is the sum of primary flow QP
and secondary flow QS (Equation 1). Figure 5a shows Ψ values for a d/D=0,24 ejector,
while Figure 5b is for d/D=0,32.
Ψ=QS/QD=QS/(QP+QS) (1)
Figure 4: a) H as a Q function; b) η as a Q function.
Figure 5: a) Ψ as a p and Lp function for a d/D=0,24 ejector; b) Ψ as a p and Lp function for a d/D=0,32 ejector.
Figures 5a and 5b show how, in the same boundary condition, the lower is the ejector
nozzle diameter the higher is the suction efficiency. On the other hand, when the ejector
works in real environment, suction efficiency shall be controlled to avoid discharge
clogging risk due to sediment deposition along the pipe. Figure 5b also shows an
interesting property of ejector: when Lp increases due to pressure drop in the discharge
pipeline (for instance, by the presence of sediment), since the ejector is fed at constant
rate, suction efficiency can reduce up to 0%, that means no secondary flow is present and
only clean water (the one that feeds the ejector) is present in the discharge pipeline. So,
when delivery flow becomes critical due to a high sediment transport, the ejector reduces
itself the secondary flow and, consequently, its suction efficiency, thus realizing a self-
control of secondary flow rate.
3. FULL-SCALE EXPERIMENTAL PLANT RESULTS
In 2005 the first full-scale experimental plant (Figure 6a and 6b) has been realized in the
port of Riccione (Italy). 15 ejectors have been provided, with a variable distance between
one device and the other, to cover the 65 meters of the inlet canal (Figure 6a), in order to
maintain a constant depth in the middle of the canal. The authorization process for plant
installation and operation involved three main actors: (1) Riccione Municipality authorized
State property land use, (2) Rimini Port Authority approved the project with regard to
safety of navigation and (3) Emilia-Romagna Region authorized plant installation and
operation without considering sediment discharge as nourishment but only as a sediment
displacement, since the plant moves the sediment that is transported naturally in its area
of influence.
This last authorization represents a powerful advantage over dredging. The experimental
phase went on for the whole summer season and the functioning of the experimental plant
ensured sufficient water depth (over 3 meters) for navigation without dredge operation
[11], event that has never happened before that time. The pump was a 90 kW centrifugal
pump. At the pump suction there was a grid filter. Downstream of the pumping system
there was a purging manual hydrociclones battery (placed inside the pumping system
cabin). Water feeding filtration is necessary since ejector radial nozzles could be subjected
to clogging. A manifold with 15 pipes for ejectors feeding was present downstream the
pump. Along each of the feeding lines one manual valve VI (to balance the lines) and one
Y-filter were present (see experimental plant P&ID in Figure 6b).
The experimental plant didn’t have the characteristic of a continuous working and
automatized plant, since it was realized mainly to test ejectors performance in real marine
condition. So, the plant was put into operation only when the manual operator was on site
and for time intervals between 60 and 210 minutes. Before and after plant operation
bathymetric surveys were performed in order to evaluate plant impact. Figure 7 shows an
example of bathymetric, made before and after experimental plant functioning and a sea
storm. After 75 minutes of functioning, the experimental plant was able to restore the water
depth (4-4,5 m) preceding the sea storm of August 7th and 8th 2005. Finally, the effect of
ejector operation on water turbidity was monitored too: it was demonstrated that the
ejector produces a very limited turbidity zone, confined in a volume of about 200 litres near
the ejector itself, and no sediment resuspension was observed. So, ejector technology
reduces to zero the environmental impact of seabed maintenance if compared with
dredging technology.
Figure 6: a) 3D image of Riccione port experimental plant lay-out; b) Riccione experimental plant P&ID.
Figure 7: 3D image of Riccione experimental plant bathymetric done between August 5th and 9th 2005.
The experimental campaign was concluded successfully. Nevertheless, ejector and more
in general the plant needed further development to reach higher efficiency and industrial
reliability.
4. INDUSTRIAL PLANT RESULTS
In 2012 the first industrial plant was realized in the Portoverde Marina (Italy). Plant
installation and operation authorizations were achieved by the same procedure described
for the plant in Riccione. This plant represents the natural evolution of Riccione
experimental plant: thus, even if the ejector has been further developed, the re-design
process focused on the whole plant engineering with the final goal of realizing a fully
automated and remotely accessible plant. Figure 8 shows Portoverde plant P&ID: two
ejectors were installed to protect the dock inlet. The plant layout is similar to the one
shown in Figure 6a, except for the manifold that is inside the pumping cabin and not along
the wharf. The three main plant implementations are: automatic control of the water
feeding flow rate of the ejectors on two different values, design level (also called “flushing”)
and maximum level; automatic balancing of water feeding flow rate of the ejectors;
automatized cycle for pump downstream filter purging. An inverter and a PLC integrated
the 30 kW centrifugal pump in order to reach the first plant implementation: on each
ejector water-feeding line has been installed a flow meter consisting of orifice plate and
differential pressure transducer (PT4 and PT5 in Figure 8). The PLC compares the total
measured flow rate with the target one and controls the pump inverter in order to adjust
the total flow rate to the desired value. The second plant implementation is realized by the
integration of two control electro-valves (VR in Figure 8) in the PLC flow control system: in
fact, the PLC controls the total flow by acting on the pump inverter and balances the flow
through the two ejectors by opening or closing the electro-valves. By the way it is possible
to automatically manage equal or different flow rates in the two ejectors for flushing and/or
maximum flow condition. The third plant implementation is able to give both high water
feeding filtration and continuity to plant operation. Water filtration is guaranteed by an auto-
purging disk filter with 400 μm limit. Auto-purging cycle is started by PLC when pressure
drop through the filter (measured by PT3 in Figure 8) overcomes a set value. Auto-purging
is also timed.
Figure 8: Portoverde Marina plant P&ID.
The shift from the maximum flow to the flushing one and vice versa is controlled by a PLC
fully automated cycle. The flushing flow rate is the design flow rate and corresponds to the
flow rate able to guarantee the cleaning of ejectors and discharge pipelines. In this
condition the ejector carries out a delivery of slurry that is very poor in terms of solid
matter: so, this kind of operation is suitable for uncritical sea weather condition in terms of
sediment supplying in the area of influence of the ejectors. Nevertheless, the plant
operates continuously 24/7, thus over time produces anyway a positive effect in terms of
sediment removal. On the other hand, when critical conditions are reached (i.e. sea
storm), the water feeding flow rate needs to be shifted on the maximum value (that is
higher than flushing) and that realizes a denser slurry by increasing ejector suction
efficiency. Critical sea weather is recognized by the PLC through the measurement of wind
speed and direction. Moreover, over the cabin a web-camera is installed, oriented on dock
inlet: so, the operator can remotely access to PLC control panel and, after checking the
weather and sea conditions, can change the operating mode. Furthermore, two control
signals on delivery flows have been added. The first one is a turbidity measurement,
realized by photoelectric sensor transmitter and receiver (PER and PET, respectively, in
Figure 8) installed in the pipeline discharge. In presence of the on-off turbidity signal, the
PLC sets the flow rate on maximum value. The second one is a delivery flow
measurement, realized by a Doppler effect flow meter (FS in Figure 8) installed in the
pipeline discharge. In presence of the on-off flow signal, corresponding to the overcoming
of the minimum delivery flow allowed, once again the PLC sets the flow rate on maximum
value. Both photoelectric sensors and Doppler effect flow meter are placed inside a
metallic box installed near the discharge point and their signals are transmitted to the PLC
by a wireless LAN bridge (distance about 150 meters). Besides, in the plant there are a
series of automated cycles to protect the pump and the auto-purging filter: the pressure
transducer PT1 (Figure 8) measures pump suction pressure to verify if critical condition for
pump cavitation are reached, while the pressure transducer PT2 (Figure 8) is used to
relieve both high discharge pump pressure (if pressure is too high it may cause damage
on filter and pump) and low discharge pump pressure, as a detector of a leak downstream
of the pump. Finally, the PLC acquires data recorded on the plant in continuous and saves
them in the form of spreadsheets, downloadable from remote.
Marina Portoverde plant has been tried out from April 26th to September 19th 2012. In
particular, in this period the automated management of the plant was tested and
developed. As results of this test period, some improvements were introduced: PLC
software implementation, selection of different sensors through installing and testing,
pipeline substitution (from stainless steel to polyethylene) and reliable anchoring of
ejectors and pipes at seabed. A further trying out session was realized from February 20th
to March 20th 2013 to verify the new implemented solutions. After plant optimization
process, the attention was refocused on the ejector: in particular, new laboratory test were
carried out to increase ejector energy efficiency and a new updated version was realized.
Starting from September 21st 2013 and up to May 1st 2014, the plant worked continuously
and maintained between 2,5 and 3,0 meters depth at the dock inlet for all the winter
season. Table 1 summarizes design, installation and commissioning costs of the industrial
plant; moreover, Table 1 shows management cost, divided into operating costs, ordinary
and extraordinary maintenance costs, projected into a one year functioning (8.600 h).
Average electric energy consumption is reduced of 41% from about 5,50 kW per ejector
[12] to 3,25 kW. Electrical energy cost is calculated by considering a 0,20 €/kWh cost.
Ordinary maintenance costs are mainly due to pump suction filter manual cleaning (at
least to be performed every six months) and to little maintenance and monitoring activities
realized by sub-personnel on the underwater installation. Finally, extraordinary
maintenance activities were computed: they were mainly due to the sea storm on 10th, 11th
and 12th November 2013, that damaged pipelines anchors on wharf, and to undersea
pipeline breakdown, made by external cause, that had led to the replacement of the
pipeline. An yearly management cost of about 17.000€ is competitive with dredge, with the
great advantage that ejector plant ensures the navigability throughout the year.
Item Quantity
Design, installation and commissioning costs 70.000€
Electrical energy consumption 55.900 kWh/year
Operating cost (energy consumption) 11.180€/year
Ordinary maintenance costs 1.800€/year
Extraordinary maintenance costs 4.000€/year
Table 1: Design, installation and commissioning costs, plus operating, ordinary and extraordinary yearly
maintenance costs of Marina Portoverde plant.
5. CONCLUSIONS
The ejector technology has been demonstrated to be an efficient and reliable system and
proved to be more competitive in the industrial scale than the dredging technology both in
economic and environmental perspectives. A further ejector redesign is currently in
progress with the aim of obtaining even more efficient performance in terms of energy
consumption and of increasing ejector reliability in the long-term operation.
ACKNOWLEDGEMENTS
The research activities and plants design and realization were co-financed by Emilia-
Romagna Region.
REFERENCES
[1] Paul L.A. Erftemeijer, Bernhard Riegl, Bert W. Hoeksema, Peter A. Todd. Environmental
impacts of dredging and other sediment disturbances on corals: A review. Mar Pollut Bull.
2012; 64: 1737-1765.
[2] Paul L.A. Erftemeijer, Roy R. Robin Lewis III. Environmental impacts of dredging on
seagrasses: A review. Mar Pollut Bull. 2006; 52: 1553-1572.
[3] Carlos Vale, Ana M. Ferreira, Cristina Micaelo, Miguel Caetano, Eduarda Pereira, Maria J.
Madureira, Elsa Ramalhosa. Mobility of contaminants in relation to dredging operations in a
mesotidal estuary (Tagus Estuary, Portugal). Water Sci Technol. 1998; 37: 25-31.
[4] Yuchuan Bai, Zhaoyin Wang, Huanting Shen. Three-dimensional modelling of sediment
transport and the effects of dredging in the Haihe Estuary. Estuar Coast Shelf S. 2003; 56:
175-186.
[5] P.K. Boswood, R.J. Murray. World-wide Sand Bypassing Systems: Data Report. Coastal
Services technical report R20, Conservation technical report No. 15. ISSN 1037-4701. 2001.
[6] E.C. McNair Jr. A sand bypassing system using a jet pump. A sand bypassing system using a
jet pump. In: ASCE. Coastal Engineering. Proceedings of Fifteenth Coastal Engineering
Conference; 1976 July 11-17; Honolulu, Hawaii (USA); 1976.
[7] A. Bianchini, M. Pellegrini, G. Preda, C. Saccani, D. Vanni. Integrated technologies for
sediment treatment. Environ Eng Manage J. 2013; 12:253-256.
[8] S.H. Winoto, H. Li, D.A. Shah. Efficiency of jet pumps. J Hydraul Eng. 2000; 126: 150-156.
[9] A.H. Hammoud. Effect of design and operational parameters on jet pump performance. In:
WSEAS. Proceedings of the 4th International Conference on Fluid mechanics and
aerodynamics; 2006 August 21-23; Elounda (Greece); 2006.
[10] Ibrahim R. Teaima. A central-type jet pump model for wheat grains removing from water
channels. In: IWTC. Proceedings of the 16th International Water Technology Conference; 2012;
Istanbul (Turkey); 2012.
[11] G. Amati, C. Saccani. Experimental plant for sand removal from harbor areas seabed
(Impianto sperimentale per il desabbiamento dei fondali nelle aree portuali, in Italian). In:
ANIMP. Proceedings of the Thirty-second Engineering and Plants National Symposium; 2005;
Rimini (Italy); 2005.
... In 2005, the first experimental plant [13] was realized and tested in the port of Riccione (Italy). In 2012, a second experimental plant [14,15] was realized in the Portoverde Marina (Italy). The first industrial scale demo is now running in Cervia (Italy), and the activities include a complex monitoring schedule to validate the technology in terms of both economic and environmental impact [16]. ...
... By ejector integration in series and in parallel it is possible to create or to maintain a channel at the desired water depth. Figure 3. Sketch of the ejector, reproduced from [14]. ...
... In fact, if it is well known from literature that, in the same boundary condition, the lower is the ejector nozzle diameter d the higher is the suction efficiency Ψ (defined as the ratio between the secondary flow QS and the delivery flow QD). On the other hand, suction efficiency Ψ must be controlled to avoid discharge clogging risk due to sediment deposition along the pipe [14,16]. The accurate knowledge of ejectors operation in different operating conditions allowed to reach a stable near-zero impact condition, i.e., neutral mass balance in the area of influence-the ejector removes as much sediment as it receives. ...
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... without closed suction chamber and mixing throat) with a converging section instead of a diffuser and a series of nozzles positioned circularly around the ejector. The technology has been under development since 2001 and has already been applied in two experimental plants in Italy (Amati and Saccani 2005;Bianchini et al. 2014): the ejector works on a limited circular area created by the pressurised water outgoing from the central and circular nozzles, whose diameter depends on the sediment characteristics such as, for example, the repose angle. By ejector integration in series and in parallel, it is possible to create or to maintain a seaway. ...
... Ejector design has been optimised over the years to achieve the maximum effectiveness with the minimum power consumption. The first result was achieved through a continuous redesign of the ejector geometry, while the second result was implemented through a sophisticated automatic control strategy of the water pumping plant (Bianchini et al. 2014). Moreover, ejector design has been refined to reach a stable near-zero impact condition, i.e. neutral mass balance in the area of influence-the ejector removes as much sediment as it receives. ...
... Moreover, ejector design has been refined to reach a stable near-zero impact condition, i.e. neutral mass balance in the area of influence-the ejector removes as much sediment as it receives. Specific information about the impact of design parameters can be found in Bianchini et al. (2014). A new version of the Fig. 3 Map of sampling locations (Mercator projection, geodetic datum WGS84). ...
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... In 2012, a second plant was realized in the Portoverde Marina (Italy). The Portoverde plant represented the natural evolution of the Riccione experimental plant, with the final goal of realizing a fully automated and remotely accessible plant (Bianchini et al., 2014). Furthermore, two control signals on delivery flows were added (Pellegrini and Saccani, 2017). ...
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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.
... Moving away the sediments that are depositing in the basins, the "ejector" technology aims to restore the natural flow of sediments altered by human activities and infrastructures. Furthermore, based on its working principle, the sediments can also be continuously moved in those areas affected by coastal erosion without environmental impact ( Bianchini et al., 2014). Therefore, justified by the potentials, the paper aims to present the main experimental and field performances of the technology. ...
... Although several technical strategies were developed through the years to counteract both sediments accumulation and coastal erosion (de Jonge and Neal, 2018;Gracia et al., 2018;van Rijn, 2011;Williams, 2018;Batuca and Jordaan, 2000), many doubts are still present about their environmental, economic and social consequences ( Bianchini et al., 2019). Therefore, considering these factors as an essential target, an innovative solution called the "ejector" was designed, experimentally tested and successfully operated during on-field tests ( Bianchini et al, 2013;Bianchini et al., 2014;Pellegrini & Saccani, 2017 coasts situation were often investigated by several Authors ( Bruno et al., 2019). In particular, a critical situation was assessed at Rodi Garganico where an alteration of the natural sediments transport regime occurred resulting in a very negative impact to local economy. ...
... In 2012, a second plant was designed and installed at the dock inlet of Portoverde Marina (Italy), figure 4. A fully automated and remotely accessible plant was realized ensuring the recognition of critical sea weather ( Bianchini et al., 2014) and of delivery flow conditions (Pellegrini and Saccani, 2017) through dedicated sensors allowing primary flow rate control to the ejectors. In addition to these plants, one more plant was realized in July 2019 by Trevi SpA in Cervia (Italy) thanks to the LIFE Programme funding ensuring the evaluation of technical performances and real environmental as well as social outcomes ( figure 5). ...
... In the last decade an innovative technology for seabed plant management has been developed, designed and tested with the contribute of the University of Bologna [1,2]. The main element of the plant, called "ejector" (figure 1), is an open jet pump (i.e. ...
... 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. In 2011 [2] a small scale 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. ...
... It was found that the minimum opacity set with the potentiometer in the lower position corresponds to a 10% of sand in mass per kg of discharge flow (that is, more or less equal to a 5% of sand in volume per liter of discharge flow). This value is compatible with the working characteristic of ejector [2]. So, photo-electric sensors were set at the minimum value of the potentiometer and several tests were conducted with three different pairs of sensors in the same working conditions (i.e. ...
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The paper describes the experimental apparatus and field tests carried on to remotely control through non-invasive and non-intrusive instruments turbidity and flowrate of a water-sand mixture flow conveyed by a pipeline. The mixture flow was produced by an innovative plant for seabed management. The turbidity was monitored by thru-beam infra-red photo-electric sensors, while flowrate was monitored by an ultrasonic Doppler flow switch. In a first phase, a couple of photo-electric sensors and a mechanical flow switch were preliminary tested in laboratory to verify installations concerns and measurement repeatability and precision. After preliminary test completion, photo-electric sensors and mechanical flow switch were installed in the real scale plant. Since the mechanical flow switch did not reach high reliability, an ultrasonic Doppler flow switch was identified and tested as alternative. Then, two couple of photo-electric sensors and ultrasonic Doppler flow switch were installed and tested on two pipelines of the plant. Turbidity and minimum flow signals produced by the instruments were integrated in the PLC logic for the automatic management of the plant. The paper also shows how ultrasonic Doppler flow switch measurement repeatability was negatively affected by the presence of the other ultrasonic Doppler flow switch working in a close pipeline and installed inside a steel casing.
... The ejector works on a limited circular area created by the Italy. In 2012, a second experimental plant (Bianchini et al., 2014;Pellegrini and Saccani, 2017) was implemented in Marina di Portoverde in Italy. Both installations were realised at harbour entrances and designed to handle sand. ...
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In June 2019, the research team of the LIFE MARINAPLAN PLUS project began operating the first-of-a-kind demonstration plant installation at the harbour entrance of Marina di Cervia (Italy). Fulfilling the project’s objective to apply at industrial scale a reliable technology for the sustainable management of sediment in marine infrastructures, this technology prevents harbour silting through the use of submerged devices called ‘ejectors’ installed on the seabed.
... In 2005, the first experimental plant was realized and tested in the port of Riccione (Italy). In 2012, a second experimental plant [15,16] was realized in Portoverde Marina (Italy). Both installations have been realized at port entrances and were designed to handle sand. ...
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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.
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Preservation of a good navigability in harbours, ports and waterways is a challenging issue. Sediment is currently removed through maintenance dredging, but without being 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, iii) impacts locally on greenhouse gas (GHG), pollutants and noise emissions. The “ejectors plant” technology has been developed as a sustainable alternative to maintenance dredging and has been recently tested in two different applications in 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) CO2 emissions, 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. Finally, 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 has the potential to be widely applied for the ordinary maintenance of water infrastructures. The paper explores the opportunity to integrate the technology with nature-based solutions and for the combined generation of renewable heating and cooling for buildings.
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Purpose The paper aims to show the monitoring results of an innovative technology, the ejectors plant, tested in the MARINAPLAN PLUS LIFE project framework for sustainable sediment management in harbours. Materials and methods A monitoring plan has been designed to evaluate the technical, economic and environmental impact of the ejectors plant demonstrator for 15 months, located in Cervia (Italy). In particular, the demonstrator’s effectiveness and efficiency have been assessed to determine the yearly operation and maintenance costs. Results and discussion The techno-economic analysis shows promising results in terms of efficacy and efficiency of the ejectors plant. The ejectors plant guaranteed navigability for the whole period of operation with a yearly cost reduction compared with traditional dredging. Conclusions The innovative technology promoted by the MARINAPLAN PLUS LIFE project is a promising solution to manage sedimentation in harbours through a cost-effective and a low environmental impact technology. The monitoring actions validated the technology fully and demonstrated its efficacy and sustainability, highlighting the further improvements needed.
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To mitigate coastal erosion and harbors siltation, new strategies are required in the immediate term. In fact, even if many traditional solutions are available, their application is usually limited due to economic, environmental and social reasons. This situation is particularly evident in the case of small marinas or in those areas where the local economy is strongly affected by harbor operation such as in the case of the port of the municipality of Cervia (Italy). To solve the problem occurred in this specific case, an innovative device, called the "ejector", is proposed and implemented in a dedicated experimental plant characterized by low operative costs and no environmental impact. Starting from the description of the technology, the paper aims to show the ejector's potentials with respect to siltation and erosion problems. For the purpose the first results derived from the application in the case study at the municipality of Cervia are reported.
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All harbors and tidal inlets that are located in coastal areas have one characteristic in common—the need to bypass littoral materials that collect nearby. If natural harbors and tidal inlets are left unattended, bypassing will often occur naturally, but in the process, the harbor or inlet is usually rendered unfit for commercial or navigation purposes. Quite often, the inattention results in the total closure of the inlet. Therefore, at almost all harbor entrances and controlled tidal inlets, the natural bypassing must be augmented by secondary, usually mechanical, means. The customary technique for bypassing sand and maintaining harbors and inlets is the use of floating dredge equipment. This equipment is rugged, reliable, has been proved over and over, and appears to be irreplacable for many applications and locations. However, there are many locations and situations for which this floating equipment is not suitable and may, in fact, be detrimental or prohibitively costly. Waves of even moderate height, moderateto- high tidal excursion and currents, draft limitations, limited maneuvering area, and interference with normal navigation operations are examples of conditions which decrease the desirability and application of floating dredge equipment. Small volumes of material to be bypassed are an economic liability for the floating plant since mobilization and demobilization costs contribute extraordinarily to the unit cost for bypassing work.
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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).
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This report was prepared in 1996/97 as background information for the assessment of bypassing systems for the Tweed River Entrance Sand Bypassing Project. The information contained within this report has been obtained from a number of sources. The authors wish to thank all those who have provided assistance. In particular, the advice and feedback from project personnel within the Queensland Environmental Protection Agency, NSW Department of Land and Water Conservation, and Brown and Root as well as Queensland Transport, was greatly appreciated.
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Experimental observations for the performance of a jet pump are presented with two different suction configurations and designs. The experimental rig was constructed in such a way it can be used with up feed (negative suction head) or down feed (positive suction head). During experimental programme water is used in both motive and pumped sides. The effect of nozzle-to-throat spacing to nozzle diameter ratio "X", on the jet pump performance was also tested, with different flow rates and motive pressures, in both cases (up feed and down feed). It was found that the best efficiency for the jet pump is attained with the up feeding configuration.
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A review of published literature on the sensitivity of corals to turbidity and sedimentation is presented, with an emphasis on the effects of dredging. The risks and severity of impact from dredging (and other sediment disturbances) on corals are primarily related to the intensity, duration and frequency of exposure to increased turbidity and sedimentation. The sensitivity of a coral reef to dredging impacts and its ability to recover depend on the antecedent ecological conditions of the reef, its resilience and the ambient conditions normally experienced. Effects of sediment stress have so far been investigated in 89 coral species (~10% of all known reef-building corals). Results of these investigations have provided a generic understanding of tolerance levels, response mechanisms, adaptations and threshold levels of corals to the effects of natural and anthropogenic sediment disturbances. Coral polyps undergo stress from high suspended-sediment concentrations and the subsequent effects on light attenuation which affect their algal symbionts. Minimum light requirements of corals range from <1% to as much as 60% of surface irradiance. Reported tolerance limits of coral reef systems for chronic suspended-sediment concentrations range from <10 mg L(-1) in pristine offshore reef areas to >100 mg L(-1) in marginal nearshore reefs. Some individual coral species can tolerate short-term exposure (days) to suspended-sediment concentrations as high as 1000 mg L(-1) while others show mortality after exposure (weeks) to concentrations as low as 30 mg L(-1). The duration that corals can survive high turbidities ranges from several days (sensitive species) to at least 5-6 weeks (tolerant species). Increased sedimentation can cause smothering and burial of coral polyps, shading, tissue necrosis and population explosions of bacteria in coral mucus. Fine sediments tend to have greater effects on corals than coarse sediments. Turbidity and sedimentation also reduce the recruitment, survival and settlement of coral larvae. Maximum sedimentation rates that can be tolerated by different corals range from <10 mg cm(-2) d(-1) to >400 mg cm(-2) d(-1). The durations that corals can survive high sedimentation rates range from <24 h for sensitive species to a few weeks (>4 weeks of high sedimentation or >14 days complete burial) for very tolerant species. Hypotheses to explain substantial differences in sensitivity between different coral species include the growth form of coral colonies and the size of the coral polyp or calyx. The validity of these hypotheses was tested on the basis of 77 published studies on the effects of turbidity and sedimentation on 89 coral species. The results of this analysis reveal a significant relationship of coral sensitivity to turbidity and sedimentation with growth form, but not with calyx size. Some of the variation in sensitivities reported in the literature may have been caused by differences in the type and particle size of sediments applied in experiments. The ability of many corals (in varying degrees) to actively reject sediment through polyp inflation, mucus production, ciliary and tentacular action (at considerable energetic cost), as well as intraspecific morphological variation and the mobility of free-living mushroom corals, further contribute to the observed differences. Given the wide range of sensitivity levels among coral species and in baseline water quality conditions among reefs, meaningful criteria to limit the extent and turbidity of dredging plumes and their effects on corals will always require site-specific evaluations, taking into account the species assemblage present at the site and the natural variability of local background turbidity and sedimentation.
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During the construction of a New Bridge over the Tagus estuary 2.5 million tons of sediments were dredged, part of this quantity being contaminated material. The extension and intensity of the water turbidity associated with dredging operating varied with the tidal conditions but the resuspended material collected near the bucket dredger did not present a concentration increment in metals and PCB, when compared to the estuarine suspended sediments. The calculated distribution coefficients suggest that some contaminants in solids near the dredger were not in equilibrium with the water. A 24-hour laboratory experiment demonstrated the complexity and quickness of anoxic sediments oxidation. In such a short period of time metals in the solids change their fractionation. A second laboratory simulation showed that mussels accumulate metals and PCB congeners when placed in turbid aerated water.
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A theoretical analysis and an experimental study on the efficiency of water jet pumps, where water is used for both the primary and secondary flows, are presented in this paper. The theoretical efficiency equations for such jet pumps were first derived based on one-dimensional formulation, and the theoretical maximum ideal efficiency of 100% was obtained. An experimental rig was designed and constructed to conduct the experimental study in which a commercial water jet pump was used. The effects of different area ratios of nozzle to mixing throat as well as different nozzle cross sections, which include square and triangular nozzles, on the jet pump performance were then investigated. The best nozzle cross section for the jet pump was found to be circular, and for high efficiency, the area ratio was found to be around 0.30.
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During the construction of a New Bridge over the Tagus estuary 2.5 million tons of sediments were dredged, part of this quantity being contaminated material. The extension and intensity of the water turbidity associated with dredging operating varied with the tidal conditions but the resuspended material collected near the bucket dredger did not present a concnetration increment in metals and PCB, when compared to the estuarine suspended sediments. The calculated distribution coefficients suggest that some contaminants in solids near the dredger were not in equilibrium with the water. A 24-hour laboratory experiment demonstrated the complexity and quickness of anoxic sediments oxidation. In such a short period of time metals in the solids change their fractionation. A second laboratory simulation showed that mussels accumulate metals and PCB congeners when placed in turbid aerated water.
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The Haihe Tide Lock was constructed on the Haihe River in 1958 to stop salty and muddy water intrusion. Nevertheless, tidal currents carry sediment, which is eroded from the surrounding silty coast, into the river mouth and, thus siltation of the channel downstream of the tide lock becomes a major problem. Employed are trailer dredges, which stir up the silt and subsequently moves it out of the mouth with ebb tidal currents. While the application of this method is encouraging there are still problems to be studied: how high is the dredging efficiency, how far can the resuspended sediment be transported by the ebb currents, and is the sediment carried back by the next flood tide? This paper develops a 3-D model to answer these questions. The model employs a special element-interpolating-function with the σ-coordinate system, triangle elements in the horizontal directions and the up-wind finite element-lumping-coefficient matrix. The results illustrate that the efficiency of dredging is high. Sediment concentration is 4–20 times higher than the flow without dredging. About 40–60% of the resuspended sediment by the dredges is transported towards the sea 3.2 km off the river mouth and 10–30% is transported 5 km away from the mouth. Calculations also indicate that the rate of siltation of the river mouth is about 0.6 Mm3 per year. If the average discharge of the river runoff is 0, 200 or 400 m3 s−1 the mouth has to be dredged for 190, 99 or 75 days every year so to maintain it in equilibrium. The dredging efficiency per day is 0.53–1.31%.
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Main potential impacts on seagrasses from dredging and sand mining include physical removal and/or burial of vegetation and effects of increased turbidity and sedimentation. For seagrasses, the critical threshold for turbidity and sedimentation, as well as the duration that seagrasses can survive periods of high turbidity or excessive sedimentation vary greatly among species. Larger, slow-growing climax species with substantial carbohydrate reserves show greater resilience to such events than smaller opportunistic species, but the latter display much faster post-dredging recovery when water quality conditions return to their original state. A review of 45 case studies worldwide, accounting for a total loss of 21,023 ha of seagrass vegetation due to dredging, is indicative of the scale of the impact of dredging on seagrasses. In recent years, tighter control in the form of strict regulations, proper enforcement and monitoring, and mitigating measures together with proper impact assessment and development of new environmental dredging techniques help to prevent or minimize adverse impacts on seagrasses. Costs of such measures are difficult to estimate, but seem negligible in comparison with costs of seagrass restoration programmes, which are typically small-scale in approach and often have limited success. Copying of dredging criteria used in one geographic area to a dredging operation in another may in some cases lead to exaggerated limitations resulting in unnecessary costs and delays in dredging operations, or in other cases could prove damaging to seagrass ecosystems. Meaningful criteria to limit the extent and turbidity of dredging plumes and their effects will always require site-specific evaluations and should take into account the natural variability of local background turbidity.