Hydrographic Survey

What You Need to Know About

Hydrographic Surveys

Hydrographic surveys are a critical element of marine management. Hydrographic surveys measure water depth and detect submerged features. They are essential for:

  • Maritime navigation
  • Marine construction
  • Dredging
  • Offshore oil exploration/drilling
  • Other related activities

A hydrographic survey is used to ascertain:

  • Minimum depth
  • Under keel clearance
  • 3D bottom model
  • Capacities

Mariners need to know precise water depths and be aware of dangers to navigation. Knowing what is on the sea floor assists with anchoring, dredging, structure construction and fisheries habitat management. Total Hydrographic’s marine mapping & GIS specialists turn raw hydrographic data into a product which our clients can use efficiently. The final product is accurate, clean, efficient and appropriately presented.

Total Hydrographic are a respected hydrographic survey company. Our clients are assured that surveys are conducted by hydrographic experts backed by certification, experience and knowledge. Total Hydrographic are certified, experienced specialists in this niche field. 

For further information contact us  or read more.

Multi Beam and Single Beam Surveys

Hydrographic Surveys are generally undertaken using either a Multibeam Echo Sounder (MBES) or a Single Beam Echo Sounder (SBES). Your requirements will determine which one of these echo sounder principles will be used.

SBES utilises a single sonar beam to measure the depth of water and is a highly efficient solution for shallow water surveys. 

MBES uses an array of sonar beams in the shape of a fan to scan the bottom of the waterbody. An MBES system achieves its best results in deeper water and provides 100% seafloor coverage. In deeper water an MBES system is extremely efficient at covering large survey areas.

Did you know?

Sonar surveys conducted using the echo sounder principle work by calculating the water depth by measuring the time it takes for an acoustic signal to return from the bottom of the waterbody. Where the water is shallow the echo returns quickly but takes longer in deeper water.

Pre and Post Dredge Surveys

What is dredging?

Simply put dredging is an underwater excavation process.

It is necessary to carry out this process to clear out sediment such as mud, weeds and rubbish from the bottom of rivers, harbours or other bodies of water.

How is this relevant to hydrographic survey?

To ensure that you get the best from your dredging contractor any dredging work should involve:

  • A pre-dredge survey
  • A post-dredge survey
  • Some volume computations

To protect the integrity of your data these surveys should be undertaken by a certified hydrographic surveyor. 

A pre and post dredge survey is an essential tool for effective project management as it provides:

  • A surface from which to base all calculations
  • An accurate estimation of material to be removed to achieve design depth. This is vital for:
    1. Accurate budgeting
    2. Tender documentation
    3. Permit applications
  • An accurate computation of the volume of material that has been removed during the dredging campaign
  • Progress surveys can be undertaken during the dredging process to ensure the project is on track and on running on time

Hazard Clearance Surveys

If you are responsible for the management of an area of water, then it is your obligation to know what’s happening beneath the surface of the water. 

Both open water and shallow water hazards are everywhere but locating them can be impossible without the right tools. However, the right tools in experienced hands can create a detailed picture of the bottom and potential hazards or features can be identified. 

Side Scan Sonar (SSS) and Multibeam Echo Sounders (MBES) are great tools for scanning large areas for hazards or features. 

SSS has the capability of scanning sideways through the water column to identify features that are protruding from the bottom. 

MBES scans and measures the entire bottom surface so that any hazards or features can be identified in the 3D point cloud data or surface model. MBES also enables accurate dimensions and heights of the hazard to be observed.

Under Keel Clearance Surveys

Under keel clearance is critical for safe navigation and movement of vessels; this applies to commercial shipping and recreational boating. 

Under keel clearance refers to the minimum clearance available between the deepest point on a vessel and the bottom of the water body. The consequences of running a vessel aground can be catastrophic; therefore, safe under keel clearance is vital.

To maintain a safe under keel clearance you need an accurate model of the bottom of the water. This can only be achieved by working with a certified hydrographic surveyor performing a MBES survey.

Habitat Mapping

To effectively manage our marine environments, we need to understand the distribution, structure and extent of seafloor habitats. Habitat mapping aims to accurately identify and describe the characteristics of different benthic habitats. We create a comprehensive picture of the underwater habitat using varied and integrated data sets.

The habitat map, the final product from this service, reveals the diversity and distribution of a variety of marine habitats. This map serves as a useful tool in biological valuation and marine management.

Total Hydrographic’s state of the art Multibeam Echo Sounder (MBES) is used for habitat mapping. By commissioning Total Hydrographic to conduct your habitat mapping you will additionally receive a certified hydrographic survey that can be used for navigation or other engineering purposes.

Side Scan Sonar Surveys

Side Scan Sonar (SSS) interpretation is the process of emitting a sonar beam and recording the strength of the return echo. We use this echo to tell us what we need to know about the depth of the water. 

SSS is a great tool for searching large areas for hazards or features protruding from the bottom and for seabed classification on a broad scale. It scans the bottom with a wide swath and from a side on perspective. 

SSS works best when the device is operating 2-4m above the bottom. Therefore, in deeper water we tow the unit behind the vessel to ensure the best possible result. Generally, SSS is coupled with bathymetry to improve the overall product. 

In shallow water (less than 4m) a SSS coupled with a Single Beam Echo Sounder (SBES) can be a method of detecting hazards and features. SSS is also used for seabed classification as the tool can be integrated into a marine habitat mapping system.

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