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