Bathymetric Surveys: Purposes and Methods

Did you know that over 70% of water bodies cover the planet?

Humans have been exploring underwater for thousands of years, called seafloor mapping or bathymetric survey. Early techniques used cable or heavy rope lowered over a ship’s side until it made contact with the sea bed, making it time-intensive and inaccurate. As technology progresses, experts now use modern devices, such as multibeam sonar equipment that analyzes echo sounders’ data in their vessels. 

What Is a Bathymetric Survey?

Bathymetry is the study of beds or floors of water bodies, including rivers, streams, oceans, and lakes. The term “bathymetric” originally came from two Greek words: “bathys,” which means “deep,” and “metrike,” which means “to measure.” 

Sometimes referred to as a fathometric survey, a bathymetric survey allows experts to study and map the depth and shape of a body of water. It shows an exact representation of the seabed, including its elevations, any scour around submerged structures, and irregularities. It also examines the surrounding tides, shorelines, currents, and waves to create a better model of the overall area.

Methods of Bathymetric Surveys

• Multi-beam surveying. Engineers use a multibeam echo sounder attached to a boat, which maps a swath of the seafloor under the ship. The device sends out multiple, simultaneous sound waves at once in a fan-shaped pattern. Experts can read the processed data in real-time on the boat. This method is usually used in larger bodies of water.
• Single-beam surveying. This method measures the water depth directly under the boat, typically used for smaller bodies of water.
• Sub-bottom profilers. Sub-bottom profilers are commonly used to view the layers of rocks and sediments under the floor of a water body. A transducer is utilized to penetrate and send a sound wave to the water body floor. Experts then map the returned sound waves to show the layers underneath the floor of the water body.
• Acoustic Doppler Current Profiler (ADCP). It is an instrument to measure how fast water moves across an entire water column. It is anchored to the seafloor to measure the current speed of the bottom, as well as the equal intervals until the surface.
• Ecomapper Autonomous Underwater Vehicle. Ecomappers can collect detailed bathymetric data in places that are difficult to reach by boat. They use side-scan sonar and a Doppler velocity log. 

Purposes of Bathymetric Surveys

1. Planning and Construction of Dams, Docks, and Harbors

Experts need to ensure that the depth of the water in and around ports is enough for ships to enter and berth safely. In addition, the sea beds that support floating structures must have a strong foundation. 

On the other hand, when constructing dams or other marine structures, engineers need adequate knowledge of the surrounding terrain to ensure the structure’s strength, using sonar for marine construction.

2. Helps in Flood Control Systems

Bathymetric surveying helps experts predict potential flooding zones so they can suggest safety measures that prevent disasters. They will study how the ocean floor changes around the coastline and correlate it to historical records of flooding and tsunamis.

3. Studies and Research

Through surveying, the government can determine the shorelines that extend around a coast. They use these shoreline charts to conduct studies on the effect of water bodies on land and identify the actual maritime border of countries. This data also helps countries in launching space shuttles and rockets.

4. Ship Navigation

Bathymetric survey results are used to help identify the possible paths that a vessel can safely take since some ocean routes may have rocks and coral deposits or low depths that pose a danger to ships. 

5. Dredging

Dredging means the removal of sediments, debris, and rocks at the seabed of lakes, harbors, rivers, and other water bodies. Because sedimentation (gradual filling of channels and ports with sand and silt) naturally occurs, the shipping industry needs to maintain or increase the depth of navigation channels, berthing areas, or anchorages for the safe passage of boats and ships. Bathymetric survey results are the basis for this process.

6. Pipeline System Installation and Maintenance

Underwater surveying ensures that pipe tracks are constructed correctly when laying seabed pipelines. Experts use sonar pipeline inspection equipment to survey the surroundings where the pipes will be installed, the pipe itself, and the pipe surface.