Life COAST-BEST ENV/IT 426

Transcription

1 Life COAST-BEST ENV/IT 426 Envisan N.V. Final report - engl 1/30

2 ACTION 2.8. Review of appropriate dredging techniques on the basis of environmental and economic issues TABLE OF CONTENTS Table of Contents Evaluation of the ports to be dredged Introduction Port of Rimini Port of Bellaria Port of Cesenatico Port of Garibaldi Evaluation of the preliminary characterization data Overview of the dredging techniques Overview techniques CSD Cutter Suction Dredger TSHD Trailer Suction Hopper Dredger BHD - Backhoe Dredger Selection of the working method for LIFE-Best Coast Summary of data Selection of the type of dredging techniques Mitigation measures during dredging Control during dredging Economical evaluation General reasons to dredge Relation between economical / environmental and other issues Project specific economical impact Overall Economical issues Economical issues concerning item 1 - Dredging Conclusion List of figures and tables List of references Envisan N.V. Final report - engl 2/30

3 1 Evaluation of the ports to be dredged 1.1 Introduction The following ports have been evaluated (Port of Rimini, Port of Bellaria, Port of Cesenatico, Port of Garibaldi). The evaluation has been done on the basis of site visit, areal pictures and the bathymetric charts. Below a short summary of the different ports. 1.2 Port of Rimini Envisan N.V. Final report - engl 3/30

4 Figure 1 Areal view and marine chart Port of Rimini The marina is bordered to the South with the harbour canal of Rimini and to the North with the beach of S. Giuliano. The marina is well protected. The seabed varies between 2.40 to 4.50 meters below sea level. 1.3 Port of Bellaria Envisan N.V. Final report - engl 4/30

5 Figure 2 - Areal view and marine chart Port of Bellaria The Bellaria harbor is situated at the mouth of the River Uso; its entrance is protected by two breakwaters of approximately 30 meters length. The seabed varies between 1.50 to 3.50 meters below sea level. 1.4 Port of Cesenatico Envisan N.V. Final report - engl 5/30

6 Figure 3 - Areal view and marine chart Port of Cesenatico In the harbor of Cesenatico there are a lot of fishing and pleasure boats and the seabed varies between 2.0 to 3.0 meters below sea level. 1.5 Port of Garibaldi Envisan N.V. Final report - engl 6/30

7 Figure 4 - Areal view and marine chart Port of Garibaldi The Garibaldi port is located on the final part of the channel Pallotta and is an important fishing harbour. The entrance is protected by two breakwaters. The seabed varies from 2.50 to 3.50 meters. Envisan N.V. Final report - engl 7/30

8 2 Evaluation of the preliminary characterization data The following preliminary general data are available. Table 1 - data Port sand % pollution Porto Garibaldi Cesenatico 8-90 Zn, TPH (PAH's), Zn, As, Cu Bellaria and Zn, Cd Rimini Zn, Cd, Cu The following extra parameters are needed for further detail technical evaluation: dry matter density organic matter The table below gives an overview of the dredging quantities during the last decade from the different harbours. Table - Amount (m 3 ) of dredged sediments disposed into the sea per year ( ) Harbour Total Bellaria 12,936 15,046 5,882 14,794 29,500 14,550 10, ,908 Cesenatico 11,248 24,800 36,048 Rimini 49,330 2,625 51,955 Riccione 21,150 5,000 4,100 5,380 35,630 Cattolica 18,270 24,040 1,400 14,250 10,855 16,960 85,775 Cervia 4,000 4,000 Porto Garibaldi 36,000 36,000 Table 2 - quantities The total quantities are approximately m³ for a period of 10 years. So an average of m³ pro year. Envisan N.V. Final report - engl 8/30

9 3 Overview of the dredging techniques 3.1 Overview techniques Preliminary to the selection of an appropriate dredging technique on the base of environmental and economic issues, it seems to us necessary to present an overview of the different options. For this a brief description of the different techniques are summarized below. Moreover we have made three videos to illustrate as good as possible the respective working principles. These videos were presented during a recent presentation in Bologna. In particular we have evaluated 3 types of dredging techniques: Cutter Suction Dredger (CSD) Trailer Suction Hopper Dredger (TSHD) Backhoe/pontoon Dredger (BHD) In what follows we summarise their working principles and analyze the strengths and weaknesses of each so that the reader can understand the choice we have made in relation to the object of study. 3.2 CSD Cutter Suction Dredger The CSD is used mainly for capital dredging in harder soil, which has to be removed in thick layers. The transport distance to the reclamation site should preferably be limited (max 5 to 10 km) to allow for an economical pipeline transport. In the case of an environmentally sensitive project, the dredging process must be controlled carefully. The disloading and hydraulic transport process must be carefully optimized. To achieve this, the optimum setting should be found by carefully varying cutting face height, step length, cutter rotation speed, swing speed, pump engine power and pipeline resistance Working Principles of a CSD The rotating cutter head will first cut out the materials to be dredged, in order to get them in a suitable state for removal by hydraulic means. The loosened material then enters the suction mouth, passes through the suction pipe and the pump (or pumps) and into the delivery line. The Cutter Suction Dredge is operated by swinging around the central work Envisan N.V. Final report - engl 9/30

10 spud using moorings leading from the lower end of the ladder to anchors. By pulling on alternate sides the dredge clears an arc of cut, and then moves forward by pushing against the work spud using the spud carriage. Once the spud carriage has reached its end position (6 or 9 m) the auxiliary spud will be lowered and the work spud raised, thus keeping the dredge in position. The main spud in its spud carriage will then be brought back in its original start position, where after the work spud will be lowered and the auxiliary spud raised in order to commence a new cutting arch. The side anchors are lifted and moved forward when the dredge has progressed far enough and the force on the anchors is not sufficient anymore. The anchors are shifted using the dredge s own anchor booms system or with an auxiliary anchor handling vessel. The control of the dredging process is maintained by means of the dredging computer and the use of a Differential Global Positioning System (DGPS). The output of this positioning system will be X and Y coordinates of the vessel. The Z coordinate is calculated by the dredging computer. Figure 5 - CSD Envisan N.V. Final report - engl 10/30

11 The table below gives the working sequence of a CSD. Table 3 sequence of a CSD List of CSD advantages and disadvantages: Good Accuracy of the excavated profile Increase of suspended sediments especially with fine grained material Dilution: due to the hydraulic character of the transport, water is added to the soil for transportation purpose. Depending upon the type of soil, the amount of added water varies. Envisan N.V. Final report - engl 11/30

12 3.3 TSHD Trailer Suction Hopper Dredger The TSHD is often used for maintenance dredging projects or for deepening existing channels. During such projects a limited thickness of softer material has to be removed, and reclamation and/or disposal sites are available at variable distances. This type of dredger is also used for the mining of sand and gravel offshore for reclamation projects such as beach nourishment or the creation of artificial islands. Selection of the optimal duration of the suction process and limiting overflow losses during dredging are the major factors related to the environmental effects of this type of equipment Working Principle of a TSHD A trailing suction hopper dredge is commonly used for dredging silty, sandy or gravely soils or soft clayey soils. While all other types of dredgers rely on other tools for transporting the dredged materials, a hopper dredge will store the dredged materials in its own cargo hold, called the hopper. The dredged materials can thus be transported over long distances. The TSHD is also able to unload its cargo by own means. Dredging activities can therefore be divided in the following consecutive activities: loading (dredging), sailing loaded, unloading and sailing back empty. A complete set of these four activities is called a dredging cycle. Envisan N.V. Final report - engl 12/30

13 Figure 6 working principle TSHD Sailing to the borrow area The dredging cycle starts with the empty hopper dredge sailing to the offshore dredging area guided by a navigation system. In this stage of the dredging cycle, the hopper dredge is regarded as a normal cargo vessel. Dredging The dredging systems of a TSHD consist of one or two suction tubes, each driven by a powerful centrifugal pump, called the sand pump. During the dredging, and in a process, Envisan N.V. Final report - engl 13/30

14 which is quite similar to the domestic vacuum cleaning, the lower ends of the suction tubes are trailing along on the seabed, while the sand pumps provide the suction power to lift the materials from the seabed into the hopper. Once the TSHD approaches the dredging area, the sailing speed is reduced and the suction tubes will be hoisted over board and lowered to the seabed. At the lower end of the suction tube, a special draghead is attached which is designed for maximizing the dredging production during the loading phase. The suction power is provided by the sandpump, which is normally installed in the pumproom in the engine rooms of the dredge. During the dredging, while the dragheads are on the seabed, the hopper dredge will maintain a low trailing speed. Such trailing speed is depending on the nature of the materials being dredged. The materials thus lifted (dredged) from the seabed, will be pumped into the hopper as a soil/water mixture. Care will be taken to minimise the water content in the mixture. Specialised operators control the dredging process. The dredge master and the navigating officer will, each one responsible for his area of control, co-operate closely. The computerisation covers all possible parameters involved in the dredging: dredging productions, engine and pump loads, draghead positions, hopper levels, etc Overflowing It is economic to allow a certain degree of overflowing. This means that, while the soils in the dredged soil/water mixture will settle in the hopper due to the gravity forces, the excess water is discharged via an adjustable overflow system. The overflow, which is built inside the hopper, consists of an in height adjustable funnel mounted on top of a vertical cylinder which ends under the keel of the dredge. The excess water is discharged under the dredge, which is the lowest level possible, thus minimising the dispersion of fines into the surrounding waters. Further, the design of the overflow is such that, by avoiding the entrapment of air in the overflow water, a minimum of turbidity is created. Envisan N.V. Final report - engl 14/30

15 In case where overflowing is contractually or environmentally prohibited, it is possible to monitor the filling process precisely using the highly computerised dredging process parameters. Sensors (so-called pingers) installed above the hopper will keep track of the height of fluids inside the hopper. By comparing this to the height of the overflow funnels, the filling process will be stopped when the fluids reach the funnel level. Sailing to the discharge / dumping point As soon as the TSHD is fully loaded, the suction tubes will be hoisted back onboard and course will be set towards the area for unloading the hopper dredge. During this transit the hopper dredge is sailing as a regular cargo vessel. Discharging / dumping There are several ways to discharge the hopper load. a) Bottom dumping The fastest way to unload the hopper is by discharging the load through the opened bottom doors of the hopper. When the hopper dredge has arrived on the spoil ground and the navigating officer is confident that the hopper dredge is exactly on the area where the hopper load is to be unloaded, the command will be given to open the bottom doors to dump the hopper load. Figure 7 - TSHD Envisan N.V. Final report - engl 15/30

16 Waterjets inside the hopper will ensure the hopper is completely empty and free of any dredged soil prior to closing the bottomdoors. A new dredging cycle can commence by sailing back to the dredging area. b) Pumping ashore Some TSHD are equipped with pumping ashore facilities. This enables them to pump the hopper load via a combination of a floating pipeline and shore pipelines directly into a reclamation area onshore. To this end a coupling system will be prepared consisting of a flexible floating pipeline with at its seaside end a special bow connection piece. The other end is connected to the shore pipeline. The hopper dredge, upon arrival at the coupling area, will be connected via the bow connection on board to this floating pipeline. Now the jets in the hopper will fluidise the sand in the hopper. The sand pumps will pump this fluidised mixture of sand and water through the pipelines to the reclamation or disposal area. For sections where the pipeline route has to cover large distances over water or where the pipeline has to cross a surf zone or a shipping channel, a submerged pipeline, resting on the seabed, will be chosen. c) Reclaiming with a spray-pontoon If the reclamation area is located under water and bottom-dumping the hopper load is not possible; the unloading is often realised using a spray-pontoon. The spraypontoon is connected to the hopper dredge using a similar pipeline system. This spraypontoon will, during the discharging of the hopper load, be moved over prescribed tracks, to deposit the load evenly over the required surface area. At the discharge end, by adequately controlling the discharge process, care will be taken to deposit the hopperload accurately within the set levels and horizontal boundaries. When the hopper has been emptied, a new dredging cycle can commence by sailing back to the dredging area. Envisan N.V. Final report - engl 16/30

17 3.3.2 List of TSHD advantages and disadvantages: The accuracy of the dredging depth is low compare with CSD, owing to the fact that the position of the suction pipe is flexible and more difficult to control. A vertical accuracy of approximately 15 to 25cm can be obtained provided sophisticated and steering equipment is used. Normal accuracy is around 0.5 to 1 m vertically and 3 to 6 m horizontally. The actual dredging process creates less suspended sediment compared with CSD as there is no rotating device in the draghead. Moreover, in the case of environmental projects, such overflow can be limitated (environmental valve, green valve reuse of the process water) or even prevented by stopping the dredging process earlier. The cutting process is strictly horizontal. As such, the mixing of soil layer can be controlled accurately. Significant amounts of water are added during the suction process. With modern monitoring and control equipment, this amount can be limited. 3.4 BHD - Backhoe Dredger The BHD is mainly used for the execution of relatively smaller dredging projects also in the harder soil as the mechanical cutting forces, which can be applied, are considerable. Recent developments in sophisticated monitoring and control equipment have improved the accuracy of this dredger considerably Working principles of a BHD General The backhoe dredger is a common type of dredger, generally non-self propelled. The main component is a hydraulic excavator, performing the dredging operation, mounted on a pontoon. The BHD mainly consists of a spud pontoon (a hull and spuds), a dredging excavator, an onboard workshop and a bridge/living quarters. The BHD is equipped with a computer system, used for on-line positioning and dredging monitoring. Envisan N.V. Final report - engl 17/30

18 As the BHD is generally non-self-propelled it will be assisted by a tugboat for repositioning during operations and towing during emergency situations. The tugboat needs enough power to ensure safe handling during towing. The same tug will be used as a supply boat to provide the BHD with the required consumables. General Working Principle Figure 8 - CSD Figure 9 working principle CSD The BHD is equipped with three spuds: one spud is located in the centre of the pontoon at the stern in a spud carriage system; this spud can be lifted and move along the centre line of the pontoon (or the pontoon can be moved with respect to the spud fixed onto the sea bottom); the two other spuds can only be lifted/lowered. Envisan N.V. Final report - engl 18/30

19 The working method of the backhoe dredger is as such that the dredger is towed into location by the assisting tug and is then fixed into position by its three spuds. Before lowering the spuds, the exact position as shown on the DGPS positioning system is checked in order to ensure that the spuds are lowered in the trench alignment. The dredger will then move into the exact starting position by using the spud carrier and the bucket. The dredger will excavate in steps 5 till 10 m length. When one step has been completed, the dredger will release the front spuds from the sea bottom and raise them approximately 2 m above the seabed. The spud carrier then shifts the dredger backwards in the dredging lane and then a new dredging cycle starts. Repositioning of the Backhoe Dredger using the spuds is done as follows: 1. The spud in the spud carriage is lifted and moved to the front of the carriage. 2. On arrival of the spud at the end of the carriage the spud is lowered. 3. The two fixed spuds are lifted from the sea bottom while the crane bucket is lowered onto the sea bottom. 4. The pontoon is then pushed against the spud in the carriage system backwards. 5. On confirmation of the correct alignment of the BHD the two fixed spuds are lowered to the sea bottom and the excavation operations can start. Dredging Control For horizontal positioning the dredger uses Differential GPS systems in combination with gyrocompasses, thus giving satisfactory accuracy. For controlling the bucket position, the dredger is fitted with IHC digviewer / Seatools Digmate systems or similar. These systems measure: - the angles for the boom, stick & bucket - the pontoon draught - the pontoon tilt - bearing The operator can follow the excavation operation on video screens, one for horizontal bucket position and the other for vertical bucket position. The system enables the dredge Envisan N.V. Final report - engl 19/30

20 operator to follow the exact movements and the depth of the bucket, and facilitates digging in a controlled manner to the designed limits. In this system the required dredging levels and slope angles can be pre-set in the computer so the operator can see the digging lines as well as the bucket position, in relation to the pre-set limits, on his video screens. Water level information is provided by a radio-linked tide gauge. The tide gauge is placed in the water close to the dredging area. The dredger is equipped with a radiolinked receiver to monitor the tide level during the dredging operation. The "digviewer system" receives the actual tide level several times per minute and the dredging depth is automatically updated. The supervisor or the main operator on each shift keeps a log for noting events of significance for the dredging operation, such as operation hours, breakdowns, repairs, production rates, weather conditions, dredging area, dredging depth etc. The area, which has been dredged during the last shift, is marked on specially designed dredging lay out drawings. The transportation of soil from the dredging areas to the dump area or quay wall is executed by means of propelled split barges List of BHD advantages and disadvantages: The accuracy is limited because the excavation bucket has to be repositioned at every cycle. However, such monitoring system exists and accuracy of 10cm can be obtained even if with reduced productivity. Suspended sediments are released during the raising of the material in open buckets as they move at a relatively speed through the water. In the case of fine grained materials these sediments remain in suspension for a long period and the accumulation can increase the turbidity at the dredging site above the natural background levels. Close buckets that limit spill are available. Thin layers can be excavated provided a good monitoring and control system is available. Dilution is highly reduced compared with CSD and TSHD. Envisan N.V. Final report - engl 20/30

21 4 Selection of the working method for the COAST-BEST project 4.1 Summary of data Based on the information mentioned in chapter 1 and 2, all the ports are characterized by the following aspects: Presence of small pleasure sailing and/or fishing boats Small areas / surfaces Presence of buildings and housing in the neighbourhood of the dredging area Organic and inorganic contamination Strong variation of the seabed Different distances to possible discharge area There is a need for approximately 30 to m³ dredging pro year. Moreover, the dredging system must allow for sufficient flexibility due to the lack of space and at the same time environmental dredging capability due to the contamination of the sediment. Summarizing, the characteristics must be: Dredge accurately (Accuracy +/- 10 cm); Low turbidity during the dredging activity (environmental bucket) Avoidance of spills of the dredged material; In addition, the treatment tests that will be performed in this Life project will be primarily based on separating the non-contaminated material from the contaminated one by a physical separation of the sand from the finer material in order to reuse it (below you can see a schematic picture): Envisan N.V. Final report - engl 21/30

22 Figure 10 treatment process :. An important aspect to be considered during treatment is management of the water coming from the treatment of the dredged sediment. This factor may play an important role in the whole economy of the process, particularly due to the foreseen continuous volumes to be dredged, the distances from the location of the treatment area and the need to comply with the regulations for their discharge to the sea after treatment. 4.2 Selection of the type of dredging techniques Therefore, according to us, another main objective in the selection of the appropriate dredging system, is to maximize the content of dry matter in the dredged material in order to avoid extra cost in the management of the water dredged. In this way it is possible to manage a lesser amount of water associated with the dredged sediments, to limit the space needed for treatment, to limit the size and investment costs for the necessary equipment for the water treatment and the costs associated with its running. Taking into account the explanations given above (chapter 4.1), we will describe below in detail the type of dredge that meets as much as possible these criteria, an environmental Envisan N.V. Final report - engl 22/30

23 adopted BHD without auto propulsion. The main components are a hydraulic excavator fitted with a clamshell of environmental type, as shown in figure 11, who will perform the dredging operations, the whole mounted on a spud pontoon. Figure 11- Environmental closet bucket and CSD The BHD is towed into location by the assisting tug and is then fixed into position by its spuds. 4.3 Mitigation measures during dredging In order to minimise any turbidity during the dredging activities the following measures will be adopted: position the bucket slowly on the bottom in such a way as to minimize the resuspension of sediment at the bottom; position correctly on the bottom in such a way as to obtain a continuous reading of the bathymetric that allows selective and precise removal of the sediments; minimise the amount of water added during the excavation. Envisan N.V. Final report - engl 23/30

24 4.4 Control during dredging To control the positioning, the dredge must be equipped with Differential GPS systems, which provide a satisfactory accuracy. In order to check the location of the environmental bucket or clamshell it is necessary to equip the dredge with a system digviewer or similar. This system allows the operator to follow the movements and the depth, and also facilitates the execution of excavation in accordance with the limits defined Vertical control of the water level The information on the level of water is supplied by a measuring instrument of the tides connected via radio. The instrument is placed in the water near the area to be dredged. The dredger is equipped with a radio receiver to monitor the level of the tides during the dredging operations. The system digviewer" will receive the level of sea in real time several times per minute updating automatically the depth of dredging Horizontal control The horizontal control is carried out through Differential GPS (DGPS). For this reason, the dredger and the vessel used for the measurements will be equipped with a receiver DGPS, while a receiver/transmitter differential is installed within or near the dredging area. Figure 12 shows a typical configuration used on board of the dredger. Envisan N.V. Final report - engl 24/30

25 TYPICAL CONFIGURATION OF THE DREDGER Figure 12 - DGPS and control system Short Range antenna Long Range antenna Short Range antenna GPS antenna Long Range antenna Short Range antenna GPS antenna Long Range antenna Short Range antenna GPS antenna NDR104 NDR104 TIDE receiver RS232 RS485 RS232 RS485 IALA beacon receiver RS485 RS232 RS485 RS232 RS485 RS232 RS485 RS232 RS485 RS232 RS485 RS232 PC1 PC2 PC1 PC2 PC1 PC2 PC1 PC2 DGPS receiver Sercel NR203 DGPS receiver Sercel NR109 DGPS receiver DSNP Aquarius 5000 Survey Monitor Steer Monitor Atlas Deso 14 Echosounder Atlas Deso 17 Echosounder Atlas Deso 25 Echosounder Odom 3200 MKII Echosounder VGA Splitter Serial interfacing Survey PC Moxa board Survey Keyboard Survey Trackball Octans Gyro/heave/pitch/roll Sensor TSS DMS 2 series Dynamic Motion Sensors Envisan N.V. Life Final report - engl 25/30

26 5 Economical evaluation 5.1 General reasons to dredge In general, there are different reasons to dredge, such as: Improvement of harbour capacity Improvement of inland waterways Reuse of material Infrastructure works (Energy and mining) It is clear that the reason to dredge the harbours mentioned in chapter 1; is to improve the harbour capacity (draft of ships) and to improve the seabed quality. 5.2 Relation between economical / environmental and other issues There is a strong synergy between economy and ecology. Also the legislation (International, EU, Italy, local) has an impact on the economical aspect. However the economical impact of dredging is only a fraction if the sediments are contaminated. In general it varies between 10 to 25% of the overall budget, this is of course depending on the level of contamination. 5.3 Project specific economical impact There is a strong link between dredging activities and sediment treatment (capacity, density, water content, and others). The possibilities on land (land based storage and treatment area) having a consequence on the economical aspect, such as: Availability Accessibility Distance (road / pipeline...) Opening hours Envisan N.V. Life Final report - engl 26/30

27 5.4 Overall Economical issues As mentioned before the economical impact of dredging and treatment of sediments can be divided in different items; i.e.: Item 1: Dredging Item 2: Pre-treatment and treatment of sediments Item 3: Reuse and disposal These items can be divided in the following sub-items: Item 1: Dredging: Item 1.1. Mobilisation cost (plant and auxiliary equipment) Item 1.2. Exploitation cost dredging spread o Equipment o Manpower o Consumables Item 1.3. Demobilisation cost (plant and auxiliary equipment) Item 2: Pre treatment and treatment of sediments Item 2.1. Mobilisation cost plant / infrastructure Item 2.2. Exploitation cost o Equipment o Manpower o Consumables o Water treatment Item 2.3. Demobilisation of plant Item 3. Reuse and disposal o Cost / benefit of re-use of material o Disposal cost of contaminated materials o Cost of water discharge 5.5 Economical issues concerning item 1 - Dredging In the table below the reader can see the cost range for the dredging activity as described above. description unit unit cost range Dredging Mobilisation unit Dredging in situ m³ 10 /m³ - 15 /m³ Demobilisation unit Table 4 economical aspects dredging Envisan N.V. Life Final report - engl 27/30

28 The costs related to the dredging activity are shown in the above table and they are related to a pontoon equipped with a hermetically sealed environmental bucket. In the case that the treatment area is located far from the dredging area the additional costs for the transport activity with hopper/carrier and the activities of unloading at the centre of treatment will have to be added. We underline that the overall evaluation is a function of several parameters as mentioned in chapter 5.3 and 5.4 and that at this stage of the project can not be specified in detail. 5.6 Conclusion In general we can conclude the following. Due to the relative small volumes to be dredged (approx m3/year) And taking a dredging rate of approx. 500 m3/day only a limit days of work are required (approx days/year or 2 to 5 months). It seems to us not opportune to have a dredger idle on site for a longer period. So the dredger has to be mobilised on a yearly base. Envisan N.V. Life Final report - engl 28/30

29 List of figures and tables Figure 1 Areal view and marine chart Port of Rimini... 4 Figure 2 - Areal view and marine chart Port of Bellaria... 5 Figure 3 - Areal view and marine chart Port of Cesenatico... 6 Figure 4 - Areal view and marine chart Port of Garibaldi... 7 Figure 5 - CSD Figure 6 working principle TSHD Figure 7 - TSHD Figure 8 - CSD Figure 9 working principle CSD Figure 10 treatment process Figure 11- Environmental closet bucket and CSD Figure 12 - DGPS and control system Table 1 - data... 8 Table 2 - quantities... 8 Table 3 sequence of a CSD Table 4 economical aspects dredging Envisan N.V. Life Final report - engl 29/30

30 List of references R. N. Bray Environmental Aspects of Dredging SIP 3D Proceedings of the International Seminar on Dredging, Dredging products and sustainable development Tunisia Envisan N.V. Life Final report - engl 30/30