Dredging projects – from planning to execution

Dredging projects

“By failing to prepare, you are preparing to fail.”

This quote by Benjamin Franklin definitely applies to dredging.  As dredging projects are expensive and different stakes are involved, dredging projects are carefully planned and monitored, by both the employer and the contractor.

Dredge Engineering:  Employer and contractor

In dredging, the employer or client is the person or organization that requires the dredging work, such as a port authority or port owner, governments or municipalities. The contractor is the party that will execute the dredging work.

In general, a dredging project from start to finish includes the following steps:

* Project identification and decision-making process by the employer

* once the decision has been made that the project will follow through, the employer will start the Procurement strategy to select a contractor for the project

* Project preparation and mobilisation

* Execution of the dredging work and monitoring.

Project identification

Every dredging project starts with a certain need. A port authority might want to expand its existing port to accommodate the rise in global trade, or a government or municipality might express the need for coastal protection measures. Perhaps a property developer wishes to reclaim land for residential areas. Once the need for dredging works has occurred, a plan needs to be made.

This plan includes the objective and scope of the dredging project. Questions like: what is the purpose of the dredging activities? Which parties have a stake in the project? Who is responsible and who will act as the customer? What will the end result have to look like? What is the budget and what will the return on the investment be? When should it be ready, what hurdles are likely to be encountered, and do we have the necessary knowledge and equipment, or is a contractor going to do the work? These all have to be answered. Based on the preliminary project plan, the feasibility of the plan is assessed, so that the employer can decide on whether or not to go ahead with a project.

Dredging objective

Some of the most common types of dredging projects are:

* channel and port maintenance

* channel and port construction or deepening (capital dredging)

* coastal protection and beach nourishment

* land reclamation

* mining and aggregate dredging

* offshore works and pipeline trenches

* improvement of the environment


And as dredging can affect the environment and different interests, there might be opposition. As a result, usually it takes a considerable period of negotiations between the parties involved and political discussions before a final decision of approval is made. After approval, the procurement process is the next phase towards the start of the project.

During the decision-making process, a general plan containing the scope of work is drafted. Once the plan has been approved, it is time to select the right contractor.

Procurement strategy

In order to select a contractor, the project has to be specified in greater detail and the contracting and/or tender strategy has to be determined. The employer can decide on direct contracting, shortlist tender or open tender, with or without pre-qualification. If the financing of a project needs public funds, it is often standard procedure to invite more tenderers.

Procurement preparation by the employer

Contractors require detailed information on the project to be able to prepare a tender offer. Therefore, the employer will start to collect data for the tender documents. The employing party’s expert staff can prepare this information or they can leave most of these activities to a consulting engineering company. Information that is gathered includes:

* Dimensions of the works, including the alignment of the ports and channels, or other dredging areas, the designed depth in the specified areas and, in case of reclamation, the required level of the fill

* Detailed surveys of the areas to be dredged or reclaimed

* Types of soil, especially in remote areas where potential contractors have problems making their own site investigations

* Other physical conditions. Although basic information can be found in nautical charts, pilots and tidal almanacs, tenderers will be pleased with detailed information on tides, waves, currents and monsoons in the working areas

* Measurement and payment systems. The measurements of the dredged volumes can be done either in situ or by transported volumes. Payment can, for example, be based on the dredged volumes or on a fixed price

* Estimated quantities to be dredged and other project items to be executed

* For underwater disposal via hopper doors, the survey chart and coordinates of the area have to be included in the tender documents

* For reclamation, beach nourishment or other landfill, the dimensions and the required level must be determined. If settlement of the underground of the fill can be expected, soil investigations for the prediction of the settlement are to be made in order to achieve the correct level of the fill

* In case of contaminated dredged materials, the employer has to give instructions for storage. The contractors need to be informed about the rate of pollution in order to take measures for the protection of their personnel and equipment

* Deadlines – when does the project need to be completed?

* Maintenance work during the duration of the project. Some dredging projects require maintenance of the dredged areas until completion of the total projects. This should be included in the time schedule and cost estimation

* Cost estimation – after collection of all possible data of the project, a total cost estimation, including employer’s costs and contract costs, has to be prepared and compared with the available funds. In case of discrepancy, either the funds or the project specifications have to be altered

* Tender procedures and date – the employer has to determine the type of contract and the tender procedure. Depending on the urgency of the project, it is possible to make a choice for direct contracting, shortlist tender or open tender, with or without pre-qualification.

Invitation to tender

After preparing the tender specifications, the total packet of tender documents will be composed – including tender notice, form of tender, contract conditions, drawings, surveys, soil information, form of bid bond (if any), and form of performance bond. Then, contractors are invited to submit their tenders. In an open tender, all contractors can bid on the project. In a shortlist tender, only pre-qualified contractors or selected contractors are invited to submit a proposal.

Preparation of a tender by the contractor

Regardless of whether the employer opts for direct contracting, a shortlist tender or an open tender, the contractor will have to prepare a bid based on the information provided by the employer. Usually, there is an opportunity to ask questions. In this phase, the contractor will also check all possible general aspects, such as:

* Exchange rate and inflation

* Availability and costs of fuel

* Suppliers and repair facilities

* Availability of plant and equipment

* Local labour and the role of the unions

* Taxes, duties and fees

* Licences and permits

* Travel and accommodation costs.

Contractors generally have a local agent or representative who investigates a great deal of these matters. The contractor will start to put together a working plan to be able to calculate the costs and come up with a bid. Occasionally an employer will also ask for a technical proposal or design.

Awarding the contract

After the closing date of the tender, the employer will evaluate the bids and proposals. If necessary, additional interviews or questionnaires are carried out. The decision to opt for a certain contractor is generally not just based on price alone, but on the best value for money. The experience of the contractor, technical knowledge, dredging fleet, risk management, quality management, and health and safety records are, for instance, also taken into account.

Dredging contract

Once a contractor has been selected, the two parties will have to agree on the contract details. Different contract types are used in the dredging industry.After the contract has been signed, the contractor will start to plan the execution of the operation.

Project preparation

During the preparation of the tender offer the contractor already has an idea of the working method for the project and the availability of dredging equipment and personnel. When the contract is awarded the contractor starts planning the operation in detail and mobilisation will usually start as soon as possible.

Proper project management implicates accurate planning of the project execution, with the appointment of sufficient staff and reservation of the required equipment and auxiliaries. Office staff, the area manager, the project manager, the site manager and surveyors will all have to contribute their knowledge and experience to the preparation of the working method and planning of the operation, so that the project can be executed successfully.

Working plan and time schedule

Normally the contractor has to present a working plan with time schedule to the employer or his engineer. The working plan has to contain a description of the method of operation and the contractors project organisation.

Special attention can be given to the system of dredging and discharge, including:

* Working hours per day and per week

* In hopper dredging, the time for loading, sailing and discharging for the various sections in the dredging area, and the loading capacity for the various types of soil to be dredged

* System of discharge, via hopper doors or by means of a shore connection system

* Floating or submerged pipelines, land pipelines, spur dikes, water outlet and settlement markers.

Knowing the specifications of the equipment and the soil, it is possible to make estimations of the hourly dredging production in the different sections or layers of soil. From the total volumes and the available working hours per week, the overall number of operational weeks can be deduced.

The time schedule has to include:

* Mobilisation, arrival and site preparations

* Operations, specified in different sections

* Maintenance and completion

* Demobilisation.


Before equipment is shipped, it is worthwhile to investigate the availability in the project area. Hiring equipment locally can save time and money. In most countries, no real dredging equipment can be found, but additional equipment like pontoons and bulldozers can sometimes be hired.

Survey plant

Since all dredging activities are based on surveys, the survey plant and staff are very important. Sending the surveyors out before the total equipment arrives on site, helps maintain the momentum. Many dredging projects start with confusion on benchmarks, coordinates and tide gauges. It will be very useful to check the data together with the local surveyors and make sure that operational surveys can start directly on arrival of the equipment.

Shipping of equipment

If there is no certainty about the availability of local equipment, the contractor will bring his own equipment. Hopper dredgers are extremely mobile. Therefore, they can easily be sent from one part of the world to another and it is common practice to transport the additional equipment on board of the hopper dredgers as much as possible. Cutter suction dredgers are usually not equipped to sail themselves, so they have to be shipped. Most standardised cutter suction dredgers are dismountable for transport by road, rail or sea. Heavy stationary dredgers are transported by semi-submersible barges. Mobilisation ends at the moment that the complete equipment and auxiliaries are ready to use and production can start.

Project execution and monitoring

A successful project is a project that is complete in the shortest possible time. The production and output of the dredger(s), is an important factor, but even more important, is an effective dredging process. This often means that the working program has to be prepared in such a way that the bottom within the dredging area is deepened in regular layers, ending at the designed depth without leaving high or deep spots. To ensure the dredging is progressing according to plan, the dredging work is constantly monitored on the dredger(s) and regular surveys are carried out.

On board monitoring

The monitors on board the dredger indicate the alignment, the exact locations to be dredged (according to the survey data) and the position of the dredger. Recording the dredging tracks and comparing these with the survey results ensures the dredging is going according to plan.


Regular surveys of the dredging area are of vital importance to assess the progress. For these surveys, the following equipment is needed:

* Reliable positioning systems

* Accurate echo sounders in silt areas, together with a density measurement system, like Navitracker

* Automatic data processing

* Automatic tide gauges

* Levelling instruments for measurement of landfill and settle markers

* Adequate accommodation for processing unit and surveyors.

Every new survey chart can be reason to alter the dredging program. After the data has been processed and has been entered into the system onboard the dredger, the dredging works can continue according to the latest instructions.

Work supervision

In hopper dredging projects, the employer or his engineer, will usually appoint supervisors on board of the dredgers. It is common practice to keep records of:

* The dredging cycles – with times of sailing to the dredging area, dredging, sailing to the discharge area and discharge

* The dredged volumes as measured in the hopper and, in case of pumping out, the volume measurement from the integrated velocity and density meters in the pump room. The dredged volumes can be measured either in cubic meters or tons of dry material, depending on the payment system

* Dredging areas and sections

* Discharge locations

* Delays and type of delays. Depending the contract it is possible that the employer is responsible for some delays. Usually delays as a result of equipment failures are the contractor’s risk, but delays like extraordinary nautical traffic, instructions from the harbour master or waiting times for supervisors could be for the employer

* Performance of the equipment. Frequent causes of delays can be found from this registration and measures can be taken to prevent them.

Daily and weekly reports

The supervisors keep records of all the relevant data on daily reports. After one week the volumes, working hours, delays, dredging and discharge areas are added up on the weekly report. This report also has to contain information about arrival or withdrawal of plant and surveys.

In many contracts, both the engineer and the contractors’ representative or project manager have to sign the weekly reports. If the project manager disagrees with any of the items he still has to sign, but his remarks will be written in the report and can be discussed and settled in the progress meetings, or can even be reason for arbitration.

Progress meetings

At regular times the engineer and the project manager will meet for discussion of the survey results, the progress of the works, weekly reports, variation orders, etc. Records of these meetings become part of the project administration.

Payment certificates

The engineer will issue certificates of payment within the times required by the contract. Payments are usually made at intervals of four weeks.

Final report

The employers’ surveyor or engineer supervises the final survey works and he checks the raw data and the processing system. At port or channel dredging projects, often a national hydrographer will be present during the final surveys in order to use the data for corrections of the nautical charts.

After completion of the works, the engineer will prepare a final project report describing the works and the progress in time. In case of damages and/or variation orders during the project the engineer will include the circumstances and reasons in the final report. The main documents of the contract administration will be added as annexes. This report will also contain the engineers’ conclusions and recommendations for maintenance of the works and for future dredging projects.


After completion and acceptance of the works, the site can be cleared and the plant will be demobilized.