Hydrographic Surveys

Catering to this specialist area, SEP offers comprehensive hydrographic survey services in house, provided by sister company SEP Hydrographic.

Established in 2020 to meet a growing need from our clients for combined land and marine solutions, SEP Hydrographic applies a sensible and practical approach to even the most complex survey requirements.

Their leadership team benefit from a combined 50+ years of experience and expertise in highly challenging environments. From their dedicated survey vessel, Pulsar, SEP Hydrographic perform high-quality, efficient surveys using the latest technology available from leading equipment suppliers.

What is hydrographic surveying?

Simply put, hydrographic surveying is the process of acquiring, processing and presenting detailed bathymetric information on the seafloor, including ports, harbours and inland waterways. Multibeam sonar uses sound waves that travel downward through the water column and bounce back up off the seafloor (or other seabed features). These echoes are captured onboard survey vessels, which record their strength and timing.

Hydrographic information can be used for a variety of uses, including navigation, shipwreck discovery and charting, planning cable routes and offshore wind farms, construction of piers and docks, locating seafloor hazards such as rocks and reefs, as well as supporting search and rescue operations at sea.

When are hydrographic surveys required?

Hydrographic surveys are performed in both inshore and offshore marine environments, informing pre-construction and post-construction projects.

Pre-construction surveys include the initial data acquisition to provide those involved in a project with a good knowledge of the seafloor. Depending on the stage of the project, the data may be acquired alongside geophysical sensors to inform planning, design and engineering decisions.

Other datasets at the pre-construction phase may include:

  • Side Scan Sonar
  • Sub Bottom Profiler
  • Magnetometer
  • Geotechnical sampling (Boreholes, Vibrocores, Cone Penetrometer Testing (CPT))
  • 2D and 3D UHR seismic surveys
  • Seabed benthic sampling and video transects

Post-construction surveys provide a detailed record of the physical changes made to an area as well as creating a baseline from which to monitor future change. Datasets collected during these phases may be combined with those acquired as part of initial pre-construction phases. Post-construction surveys are performed after construction has been completed to monitor movements of the seabed over time, perform environmental monitoring, monitor critical assets on an ongoing basis such as subsea cables, inform maintenance and repair operations and plan any decommissioning work.

What kind of data is collected during a hydrographic survey?

Depending on the nature of the contract work and stage of marine construction, hydrographic surveyors will typically acquire single beam and multibeam bathymetry during the survey, and may also acquire backscatter and water column data.

What equipment is used for hydrographic surveying?

Modern hydrographic surveying techniques use state of the art electronic survey and global positioning systems, as well as onboard inertial positioning systems, single beam and multibeam echo sounders.

These instruments are capable of producing accurate and reliable information on the water depth and seafloor in real-time, presenting this information with centimetre-level accuracy.

What are the benefits of performing hydrographic surveys?

Hydrographic surveys contribute to increased safety on the water by providing accurate depth measurements and highlighting previously unknown underwater hazards with precise positioning such as rocks or wrecks that may pose a danger to vessels navigating in the area.

The data acquired through surveys is used to inform the design and construction of new marine projects such as ports, piers and marinas; offshore renewables projects, oil and gas developments, or can be used to improve open water navigation for larger vessels. Hydrographic surveys and data are also used by scientists and engineers for scientific research and ocean modelling purposes.

What is involved in planning hydrographic surveys?

As with any activity in the marine environment, effective planning for hydrographic surveys is essential and takes place in several stages:

  1. Review and understand the requirements - A dedicated project manager will be assigned to each survey project and will liaise directly with the client to understand their requirements, define objectives and identify any potential issues that may arise.
  2. Operational Planning -  The operational planning process involves ensuring personnel and equipment availability, planning for transit to the site, investigating environmental conditions and local ports. There may also be potential legal issues to consider such as protected areas/species (e.g. seabed habitats, protected species), as well as distributing a Notice to Mariners (NtM)
  3. Detailed risk assessment - A detailed risk assessment is performed in line with our integrated management system. The output is a comprehensive health and safety management plan, emergency response plan and project HIRA that outlines how the project should be managed from a health and safety. All offshore personnel go through extensive industry-standard emergency training and need to pass a medical examination.
  4. Project mobilisation - Depending on the status of the vessel and the equipment onboard, the project mobilisation will either take place before or after the transit to the local site. A project kick off meeting may be arranged with the project team and the client representative, and any equipment calibration or verifications will be performed.
  5. Survey acquisition  - Depending on the project requirements and scale of the site, data acquisition can take days, weeks or even months to complete. The survey spread will dictate the survey acquisition speed and - combined with the size and stability of the vessel - the weather tolerance. Hydrographic surveyors will design the line plan to be optimised for efficiency and quality, taking into account environmental limitations. Any technical queries or
  6. Data processing and reporting - This phase varies significantly depending on the project requirements. For simple, short-duration projects, the resultant datasets could be delivered in a matter of days, but for larger-scale multi-discipline projects it is likely to take longer. The data is processed to deliver the agreed mapping datasets and to produce detailed plans.

Types of Hydrographic Surveys

Inshore surveys

Inshore surveys are performed in protected areas such as estuaries or sheltered bays. Inshore surveys are generally performed using a small vessel or RIB, which provides the flexibility to conduct surveys in tight spaces where larger vessels cannot operate. The shallow nature of inshore survey areas, along with seabed features such as sandwaves and tidal currents often makes data processing challenging.

Offshore surveys

Offshore hydrographic surveying is performed in areas where conditions are more challenging, such as exposed coastlines and deep water. In these regions, a larger vessel is often required with specific features that allow it to operate safely in the marine environment. In deep water, multibeam systems provide higher-resolution data compared to single beam instruments when operating at low speeds.

What is the future of hydrographic surveying?

Advances in technology have allowed for a significant shift from analogue equipment to integrated survey systems which provide efficiency and accuracy within this field. In the not-so-distant future, survey technology will continue to advance with increased automation of equipment and sampling techniques reducing risk to the crew, allowing for longer periods at sea and further increasing efficiency.

How much do hydrographic surveys cost?

The costs involved with hydrographic surveys will vary significantly depending on the type of survey being undertaken, the survey location and how much hydrographic data is required.

Get in touch with our team for a quick, no-obligation quote.

Specialist technical support for hydrographic surveys

At SEP Hydrographic, the team of hydrographic surveyors have provided expert survey services to clients from a range of industries including offshore renewables, ports and harbours, and offshore oil and gas. With multi-discipline survey expertise, SEP is well placed to support your project throughout the entire survey process. Get a quote now by emailing info@sephydrographic.com.