A Type of Hydrographic Survey
A bathymetric survey, sometimes referred to as a fathometric survey, is a type of hydrographic (water-based) survey that maps the depths and shapes of underwater terrain to illustrate the land that lies below.
Bathymetric surveyors work to obtain an exact representative image of the seabed and identify specific elevations, anomalies, and the presence of any scour around submerged structures. They also analyze and define the surrounding shorelines, tides, currents, and waves to create a better model of the area features overall.
When performing bathymetric surveys in deep bodies of water (like seas and oceans) for marine construction projects like dredging or offshore energy, multi-beam survey technology aboard a custom vessel is typically utilized. A multi-beam echo sounder attaches to a boat sends out a wide array of beams across a “swath” of the waterbody floor. The multi-beam system pings sound waves in a fan shape of narrow adjacent beams that bounce off the seabed and return to calculate the distance to the seafloor. As the beams are bounced back from the waterbody floor, the data is collected and can be processed in real time on the vessel during the survey.
On the other hand, for smaller bodies of water a single-beam beam survey is often used. Single-beam bathymetry measures the water depth directly under the boat.
Acoustic Doppler Current Profilers (ADCP) are used to measure water velocity by transmitting sound waves reflected off sediment and structure in the water, The streamflow data is used to aid in bathymetric mapping.
Many bathymetric surveys for projects like shoreline stabilization, engineering design, or infrastructure remediation, require bathymetric surveys to be performed in very shallow waters inaccessible by traditional vessels.
Conducting these surveys in shallow water can be extremely difficult in terms of accessibility, space, fast-flowing currents, submerged debris, navigational hazards, or environmentally sensitive habitats. To mitigate these effects, our surveyors use cutting edge tools like remote-control Unmanned Surface Vessel (USV) technology. This state-of-the-art equipment conducts precise bathymetric surveys in shallow water safely and efficiently.
For these shallow water surveys, hydrographic crews use high-tech equipment including Teledyne Z-boats and HyDrone Unmanned Surface Vessels (USV) combined with either a multi-beam or single-beam echosounder, positioned with RTK-GNSS.
For projects such as the survey of bridges and nearshore embankments, topographic mapping is often needed in addition to a bathymetric survey. For this, custom solutions tailored to each project may include the use of small Unmanned Aerial Systems (sUAS) / Drones, mobile lidar, or terrestrial 3D laser scanners.
McLaren’s bathymetric survey work has been an integral part of the development of many bridge and marine projects like Domino Park, Weehawken Pier, Westchester Bundled Bridges, NYC Ferry system and the development of Off-shore Wind facilities in the United States.
Hydrographic surveys are one of the first steps to determine if a project in or near water is conceptually and physically feasible. In addition to large offshore or near-shore construction projects, these surveys can also be used as analysis for flood inundation, scour and stabilization, water-quality studies, waterfront facility inspections, habitat mapping, dam removals and environmental spills.