Dredge Surveys & Modelling

Port and Harbour authorities have an obligation with respect to the Port Marine Safety Code to routinely survey their marine areas of responsibility to maintain safe passage and navigation, and in this regard engage dredging contractors to maintain desired water depths utilising modern marine plant and equipment.

Prior to commissioning any dredging works it is essential that there is an agreed baseline to enable progress to be monitored and we have the personnel, equipment and expertise to undertake a wide range of dredging support services, including pre & post dredge surveys and associated volumetric calculations, for both capital and maintenance campaigns.

These can be undertaken in any environment including canals and waterways, coastal regions, congested harbours and approach channels with 24 hour support available where required.

Equipped with software enabling 3D dredge models to be created, we can provide detailed and accurate volume calculations, quantify the amount of material removed and show areas of accretion or erosion.

In the image shown above Left, each of the coloured areas represents a different dredge level in a relatively complex dredging campaign, with the software used to calculate side slopes at any desired angle between areas of differing levels. Modern multibeam surveys provide a detailed 3D model of the seabed.

It is routinely accepted that data sets at 0.5m post spacing are issued as a standard output for dredging works, which is then used to create a very detailed 3D difference model between the current survey and the dredge model, referred to as an isopachyte, used in the calculation of dredge volumes.

This approach is far superior to previous sectional methods, allowing a very well defined measure of the material removed or built up between survey and design model or between successive surveys.

Prior to any dredging works taking place it is usual to retrieve grab samples or sediment cores of the material to be dredged and to have this analysed in a UKAS accredited laboratory. Analysis is commonly required to determine the physical and chemical properties of the dredge material, a pre-requisite for any dredge licence application.

With both grab sampling equipment and a vibrocore system available to carry out this type work in-house, we have well-established relationships with accredited laboratories to oversee the sample analysis and reporting process. See our Environmental pages for more information.

Should the contractor be required to contain the dredge arisings during the dredging process, we can assist via the installation of long term systems or periodic measurements of material in the water column (turbidity) in and around the area being dredged in order to prove containment is effective.

In areas where capital dredging is required it is often necessary to carry out sub-bottom profiling surveys and geotechnical investigations to quantify the depth that an area can be dredged to without resorting to rock blasting. This can be carried out with a variety of sensors, the choice dependent upon the expected material making up the overburden. See our Geophysical pages for more information.