action 2.8: report about appropriate dredging techniques

Progetto LIFE 08 ENV/IT 00426 COAST-BEST

Action 2.8: Report about appropriate dredging techniques

Envisan

Mid-term report LIFE+ - Project LIFE08 ENV/IT 000426 96 of 681

7.2.7 Action 2.8 (Report about appropriate dredging techniques)

LIFE Project Number LIFE08 ENV/IT 000426

LIFE+ PROJECT NAME or Acronym CO-ordinated Approach for Sediment Treatment and BEneficial

reuse in Small harbours neTworks” COAST_BEST

Deliverable: Report about appropriate dredging techniques (Action 2.8)

Envisan N.V. – Life COAST-BEST Final report - EN 1/39

Life COAST-BEST ENV/IT 426


ACTION 2.8. Review of appropriate dredging techniques on the basis of environmental and economic issues

T ABLE OF CONTENTS

Table of Contents .................................................................................................................. 2

1 Evaluation of the ports to be dredged........................................................................ 3

1.1 Introduction ........................................................................................................... 3 1.2 Port of Rimini........................................................................................................ 3 1.3 Port of Bellaria ...................................................................................................... 4 1.4 Port of Cesenatico ................................................................................................. 5 1.5 Port of Porto Garibaldi .......................................................................................... 6

2 Evaluation of the preliminary characterization data ................................................. 8

3 Overview of dredging techniques ............................................................................. 9

3.1 Overview techniques ............................................................................................. 9 3.2 CSD – Cutter Suction Dredger.............................................................................. 9 3.3 TSHD – Trailer Suction Hopper Dredger ........................................................... 12 3.4 BHD - Backhoe Dredger ..................................................................................... 17 3.5 Evaluation of the performances........................................................................... 21

4 Selection of the working method for LIFE-Best Coast........................................... 23

4.1 Summary of data ................................................................................................. 23 4.2 Selection of the type of dredging techniques ...................................................... 24 4.3 Mitigation measures during dredging ................................................................. 25 4.4 Control during dredging ...................................................................................... 26 4.5 Survey and special equipment on board of the dredger: ..................................... 28 4.6 Monitoring, Measuring and management of the dredging operations: ............... 33

5 Economical evaluation ............................................................................................ 34

5.1 General – reasons to dredge ................................................................................ 34 5.2 Relation between economical / environmental and other issues......................... 34 5.3 Project specific economical impact..................................................................... 34 5.4 Overall Economical issues .................................................................................. 35 5.5 Economical issues concerning item 1 - Dredging............................................... 35 5.6 Conclusion........................................................................................................... 36

List of figures and tables ..................................................................................................... 37

List of Attachments ............................................................................................................. 37

List of references................................................................................................................. 38


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 Porto Garibaldi). The evaluation has been done on the basis of site visits, areal pictures and the bathymetric charts. It follows below a short summary of the different ports.

1.2 Port of Rimini


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


Figure 2 - Areal view and marine chart Port of Bellaria

The Bellaria harbour 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


Figure 3 - Areal view and marine chart Port of Cesenatico

In the harbour 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 Porto Garibaldi


Figure 4 - Areal view and marine chart Port of Porto Garibaldi

The Porto 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.


2 Evaluation of the preliminary characterization data The following preliminary general data are available:

Port sand % Pollution Porto Garibaldi 61-92 Cesenatico 8-90 Zn, TPH (PAH's), Zn, As, Cu Bellaria 36-76 and 22-83 Zn, Cd Rimini 10 - 60 Zn, Cd, Cu

Table 1 - Data The following extra parameters are needed for a further detailed 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. Amount (m3) of dredged sediments disposed into the sea per year (1999 - 2008)

Harbour 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 Total

Bellaria 12,936 15,046 5,882 14,794 29,500 14,550 10,200 102,908

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 340.000 m³ for a period of 10 years, resulting in an average of 34.000 m³ pro year.


3 Overview of 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 of them, 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.

3.2.1 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


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


The table below gives the working sequence of a CSD.

Table 3 – Sequence of a CSD

3.2.2 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.


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.

3.3.1 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.


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,


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.


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


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.


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 limited (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.

3.4.1 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.


As the BHD is generally non-self-propelled it will be assisted by a tugboat for re-

positioning 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.

Figure 8 - CSD

General Working Principle

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.


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


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.

3.4.2 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.


3.5 Evaluation of the performances

Based on the above mentioned information; a first evaluation of the performances can be

made. In relation to the Life project it will be more the environmental performances that

prevail.

However we have also made a summary of the technical (operational) performances.

For the time being, it is nearly impossible to make a detailed evaluation in relation to the

Life Coast Best project; as not enough parameters are currently available.

Based on our general knowledge of the dredging industry and the equipment available on

the market, we can only provide a general evaluation of the different parameters.

It is quite obvious that new and modern equipment are having in general better

environmental performances (noise, accuracy, etc..)

3.5.1 Production performances (depth / output rates): In the table 4 an overview is given of the maximum production performances of the

different types of dredgers.

Dredging Depth

(max meter) * Output rate (m3/ hour) *

CSD 36 meters 200 – 5000 TSHD 155 meters Till 5000 BHD 32 meters 50 - 1000

Table 4 – Production performances

(*) based on the actual state of the art “standard” equipment.

3.5.2 Environmental performances A relation between the dredging techniques and the environmental performances is given

in the table below (table 5).

For the environmental performances the most imported parameters are covered; such as

accuracy, turbidity, mixing, spill, dilution, noise / sound.


The table 5 below does not take into account the influence of special modifications /

adaptations and other tools used in the environmental dredging world.

Accuracy Turbidity Mixing Spill Dilution Noise sound CSD + □ / + □ / + □ □ + TSHD - - / □ - □ - + BHD + - / □ + + + +

Table 5 – Environmental performances

+ : better then average - : less then average □ : average performance


4 Selection of the working method for LIFE-Best Coast

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 30.000 to 40.000 m³ to be dredged 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):


Figure 10 – treatment process

An important aspect to be considered during treatment is the 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 water discharge into 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


adopted BHD without auto propulsion. The main components are a hydraulic excavator

fitted with a environmental clamshell, as shown in figure 11, that will perform the dredging

operations, 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 the bucket correctly on the bottom in order to avoid over or under

dredging (precise removal of the contaminated sediments);

� minimise the amount of water added during the excavation.


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.

4.4.1 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.

4.4.2 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.


Figure 12 - DGPS and control system

NDR104

GPSantenna

PC2

TIDEreceiver

ShortRangeantenna

PC1 PC2

NDR104

RS232

RS485

RS485

RS232

RS232

RS485

RS485

RS232

RS485

RS232

RS485

RS232

RS485

RS232

RS485

RS232

PC1 PC2PC1 PC2PC1

IALAbeaconreceiver

DGPS receiverSercel NR203

DGPS receiverSercel NR109

DGPS receiverDSNP Aquarius 5000

LongRange

antenna

LongRange

antenna

ShortRangeantenna

GPSantenna

ShortRange

antenna

LongRangeantenna

ShortRangeantenna

GPSantenna

Survey PC

Survey Keyboard

Survey Monitor

Moxa board

VGA Splitter

SurveyTrackball

Serialinterfacing

Steer Monitor

Atlas Deso 14Echosounder



Odom 3200 MKIIEchosounder

Octans Gyro/heave/pitch/rollSensor

TSS DMS 2 seriesDynamic Motion Sensors


4.5 Survey and special equipment on board of the dredger:

It is quite obvious that control the operation is fundamental for environmental dredging.

As mentioned in the previous chapter (4.4.); it will be necessary to have state of the art

special equipment on board of the dredger and to implement an adequate survey

methodology.

In order to execute an accurate dredging (x,y,z) the necessary precautions and special

equipment has to be installed on board of the dredger.

It is quite obvious that the operator on board of a dredger; does not “see” what is going on

under water. Therefore the necessary tools have to be provided; so that operator can “see”

what he is doing.

In figure 13 we see some typical computer screen configuration for a BHD operator, that

the operators in the activities assist.

Figure 13 – Special equipment on board of the dredger

So it will be necessary to install the necessary equipment; such as power box, PC panel,

GPS system; Microdigger, pitch and roll sensors on board of the dredger.

If the dredger is a BHD, the necessary boom and stick sensors have to be installed.


Before the start of the dredging operations, all sensors and equipment have to be calibrated

in order to achieve a correct and well functioning dredging system.

• Calibration of the Pitch and Roll sensor

• Calibration of the Boom sensor

• Calibration of the Stick sensor


• Calibration of the Dogbone

• Bucket Angle

• Bucket flat Angle


The equipment described above, enables the operator of the dredger to “see” under water.

The tools at his disposition make it possible to execute the dredging operation with very

high accuracy.

Below some typical screenshots of the operators interface (Figure 14).


Figure 14 – Screenshots of the operators interface


4.6 Monitoring, Measuring and management of the dredging operations:

It is clear that not only the dredging technique is important; it is also the whole

management around the project that is important.

Today, environmental awareness is much higher then in the past.

It is not only the awareness that is important; it is also the implementation that is required.

So it is a whole concept of environmental management.

In this aspect the type of dredging technique is only a link in the chain.

The recent published information paper (June 2011) of CEDA is giving a good overview of

the following aspects:

• Dredging projects and the enviornment

• Environmental monitoring

• Environmental management

• Lessons learned from 15 years of dredging project experience.

A copy of this information paper is attached (attachment 1).


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, European, Italian and 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


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 30.000€ - 80.000€ Dredging in situ m³ 10€/m³ - 15€/m³ Demobilisation unit 30.000€ - 80.000€

Table 6 – Economical aspects of dredging


The costs related to the dredging activity are shown in table above 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. 40.000 m3/year) And taking a dredging rate of approx. 500 m3/day only a limit

days of work are required (approx. 50 – 100 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.


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 Porto Garibaldi........................................... 7 Figure 5 - CSD .................................................................................................................... 10 Figure 6 – working principle TSHD ................................................................................... 13 Figure 7 - TSHD.................................................................................................................. 15 Figure 8 - CSD .................................................................................................................... 18 Figure 9 – working principle CSD ...................................................................................... 18 Figure 10 – treatment process ............................................................................................. 24 Figure 11- Environmental closet bucket and CSD.............................................................. 25 Figure 12 - DGPS and control system................................................................................. 27 Figure 13 – Special equipment on board of the dredger ..................................................... 28 Figure 14 – Screenshots of the operators interface ............................................................. 32 Table 1 - Data........................................................................................................................ 8 Table 2 - Quantities ............................................................................................................... 8 Table 3 – Sequence of a CSD.............................................................................................. 11 Table 4 – Production performances .................................................................................... 21 Table 5 – Environmental performances .............................................................................. 22 Table 6 – Economical aspects of dredging.......................................................................... 35

List of Attachments Attachment 1: 2011 Ceda information paper environmental control on dredging projects


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 2010 www.european-dredging.eu www.envisan.com www.jandenul.com


Attachments:

A CEDA Information Paper - June 2011

1

Central Dredging Association

Environmental control

Marine and inland water-based infrastructure is a prerequisite for the sustainable development of economic bene� ts and public welfare. Dredging works are needed to realise and maintain such infrastructure. It is widely recognised that such projects create an impact on the environment and in recent years awareness of these impacts has grown – on the client side as well as among contractors.

The purpose of this paper is to share recent experience gained from the development of marine infrastructure projects in environmentally sensitive areas, with a particular focus on the realisation phase. The main emphasis is on lessons learned from 15 years of turbidity monitoring (see Figure 1) during dredging and sediment placement operations.

Dredging projects and the environmentEnvironmental aspects play an important role during the full cycle of project initiation, development, realisation and operation. While detailing the project at hand, legal frameworks such as the London Convention and the EU Water Framework Directive pose strict environmental controls. Any environmental effects – both adverse impacts and benefi ts – are evaluated as part of the environmental impact assessment, often in consultation with the legal commissioner. This evaluation may result in revision of the project design or the implementation of nature compensation measures.

Contractors are responsible for minimising environmental impacts during project realisation (process impacts). Sometimes, the use of environment-friendly work methods and robust environment management plans proves a decisive factor in project tendering. Once contracted, environmental monitoring schemes should be in place before construction works begin. Given the costs associated with these schemes and their strategic importance for environmental control,

development of these programmes should be integral to project preparation.

Environmental monitoringTo ensure the care and protection of surrounding ecosystems, while enabling the construction of marine infrastructure, environmental monitoring has become common on dredging projects since the Øresund Fixed Link Project between Denmark and Sweden (1996). Major marine infrastructure projects in, for example, Melbourne

Lessons learned from 15 years of turbidity monitoring

on dredging projects

Figure 1: Monitoring during dredging


�


Plume dispersion

Increased suspended solids

Increased light attenuation through water column

Decreased light in water column and on seabed

Reduced photosynthesis

Physiological and morphological changes in plants

Ecological consequences

Phy

sica

lB

iolo

gic

al

Seagrass

Source

Source reduction

Plumedispersion

Sunlight

Light attenuation

Lightattenuation

Seagrass response

(Australia), Rotterdam (Netherlands) or London (UK) have called for extensive environmental monitoring. Such large-scale programmes typically involve several types of monitoring, each with a different objective:• Surveillance monitoring or baseline monitoring: to assess

general project conditions and act as a reference for the interpretation of dredging impacts. Monitoring involves flora, fauna, hydrographic conditions, bed sediments and turbidity.

• Feedback monitoring or adaptive monitoring: to verify pre-project environmental assessments (model predictions, expert judgement) and to provide a base for possible adaptation of the project design, planning and/or work method.

• Compliance monitoring: to ensure compliance with the environmental restrictions endorsed for the project at hand. Each dredging project is unique and impacts vary

widely from one project to another, depending on local hydrodynamic conditions (tide, waves), natural turbidity levels, soil characteristics and dredging operations. Environmental monitoring is needed to gain insights into the actual relationship between impacts from dredging and the response of sensitive ecosystems such as coral reefs and sea grass. Such insights help to establish scientifically sound environmental limit levels for dredging operations.

Most present-day monitoring programmes are based on the assessment of turbidity levels, because the greater light attenuation in the water column resulting from the increase in suspended sediment concentrations is known to affect marine life (see diagram above and Figure 2 overleaf). Additional benefits of this parameter are its direct link to dredging and placement operations and its relative ease of measurement. Environmental restrictions typically involve limits on sediment plume size at dredging and disposal sites.

Recently, environmental restrictions have focused on other biological, chemical and/or physical parameters that directly reflect ecosystem health at a particular project site. However, limited capabilities for (operational) monitoring of such complex processes and insufficient understanding of the link to construction activities hamper widespread use of these criteria in present-day dredging practice.

Environmental managementManagement of environmental impacts has become a standard component of marine infrastructure projects. To avoid unforeseen delays and costs, environmental monitoring should be integral to project planning. An essential step is the compilation of an environmental management plan (EMP) to provide full details on:


3


• Monitoring requirements: what is needed to assure protection of the ecosystem? Includes a summary of environmental restrictions, including specifi cation of monitoring parameters and limit levels.

• Monitoring approach: how to ensure compliance with environmental standards? Includes an overview of work methods, including specifi cation of measurement equipment, data sampling (frequency, location, depth), data processing, data interpretation and dissemination of results.

• Mitigating measures: what operational measures can be taken in case of violation of environmental limits?

• Response procedures and responsibilities: what procedures are in place if environmental warning or limit levels are exceeded, and who is responsible for which action?Often, no previous practical experience is available for

a specifi c site. Where this applies, it is recommended to develop adaptive monitoring schemes, so that monitoring efforts can be adjusted (reduced, refi ned or expanded) if appropriate. It is important to realise that most ecosystems respond to prolonged, rather than instantaneous, turbidity impacts. For such cases, the use of time-averaged turbidity measures (for instance, six- or 12-hour rolling average) to assess impacts is justifi ed. This in itself adds signifi cantly

This document is presented by the Central Dredging Association (CEDA). an independent, international, easy-to-access platform for the exchange of knowledge and experience on all aspects of dredging and marine construction. CEDA publications are peer- reviewed by internationally acknowledged experts and represent high quality standards. Input for the document is obtained from all professional groups within the CEDA membership which represent a wide range of expertise, disciplines and nations. CEDA publications provide impartial, state-of-the-art information for academics, industry professionals, regulators, decision-makers and stakeholders. This document, or part(s) of it can be used freely by anyone, subject to reference made to CEDA as the author. For more information please refer to www.dredging.org

Central Dredging AssociationRadex BuildingRotterdamseweg 183c2629 HD Delft, The NetherlandsT: +31 (0) 15 268 2575E: [email protected]

Figure 2: Dredging plume dispersal

to the operational manageability of the environmental monitoring programme.

Lessons learned from 15 years of dredging project experienceEnvironmental monitoring has taught us:• Each project is unique. Nevertheless, with great care,

lessons learned from one project can be used for the next.• Dredging-induced turbidity impacts should be evaluated

as an increase above background level, not as absolute values. Environmental limit levels should be based on the resilience of the local ecosystem, while accounting for natural fl uctuations in turbidity level.

• Monitoring programmes should be designed in an adaptive manner, to allow for procedures to be reviewed and, if appropriate, adjusted.

• Environmental monitoring should be an integral part of project preparation and planning, to ensure effective mitigation of possible environmental effects.When made available to the outside world, environmental

monitoring data were also found to encourage stakeholder involvement and to improve public awareness.

In this way, environmental monitoring is directly relevant to the success of marine infrastructure projects and their apprecia-tion by the general public.

action 2.8: report about appropriate dredging techniques

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