October 6, 2021
What is Hydrographic Surveying?
Hydrographic surveying is an important civil engineering service that determines the physical features of an underwater area. Like topographic or land surveys, these surveys use special equipment to measure and define a body of water to support marine construction.
Do you know the types of projects that require a hydrographic survey? Continue reading to discover why and how surveyors detail the floors of rivers, lakes, oceans, and other water bodies.
Purposes of Hydrographic Surveys
Hydrographic surveys are often needed whenever someone wants to make a significant change to an area of water. This includes projects such as:
- Building docks or marinas
- Waterway planning
- Diversion of water sources
- Removing soils
- Wreck location
Teams working on these projects need to know the exact site layout. Imagine starting to build a house on a piece of land only to discover a massive ditch in the middle of your site. That is what it would be like to start a water-based project without a hydrographic survey.
Water Depth Estimation
The primary reason hydrographic surveys are used is to determine the depth of a body of water. It is necessary on every construction project for the parties involved to know how deep their building area is.
Additionally, water depth is a key point of knowledge for maritime navigation. Bodies of water are full of irregular soil deposits, coral reefs, and hidden obstructions that threaten traveling ships. Many times, surveys are utilized in port planning and construction to determine where the water depth needs to be adjusted for the maximum size of ship that can fit. This is especially important for shipping safety — 80% of the United State’s international trade is conducted through the marine transportation system. With that many ships coming in and out of port, it is paramount to know where a vessel can and cannot navigate through.
Another common practice is to have an area surveyed before and after a project is completed. For example, if a river needed dredging, the team would bring in a survey crew to give them an exact picture of the river bed and any obstacles or sunken objects lying there. Once they completed their dredging, the team would then bring the survey crew back to show them the results of their work.
Completing an Underwater Survey
The beginning of hydrographic surveys can be traced back to fishers tying a weight to a rope and seeing how far it took to get to the bottom. Thankfully, technology has improved so that factors such as water movement do not affect a survey’s accuracy.
The primary resource survey crews use is sonar, which is a system of detection that uses sound waves to bounce or “ping” off of objects to determine their distance when they reflect back.
Two of the most commonly used types of sonar in surveying are:
- Single-beam sonar uses a single transducer to transmit and receive pings from a specific location in the area.
- Multi-beam sonar uses multiple single-beam transducers to cover a wide area rather than focusing on a single point.
A good way to understand the purposes of each sonar is to consider them as a flashlight and a floodlight. A flashlight enables you to focus a large amount of light on a very specific point, while a floodlight enables you to see a wider area, but with less specificity than the flashlight. In the same way, a multi-beam will give you a general picture of a large area, and a single-beam allows you to hone in and get the details of a single spot.
The JBPro Process
Every hydrographic survey is completed onboard a boat. Once we have our equipment aboard, our surveyors use GPS techniques to establish a control for the area. Next, each piece of equipment is calibrated to ensure perfect accuracy. Using a combination of single and multi-beam sonar, we then determine the layout of the waterbody.
After the initial survey is complete, we compare our findings with the GPS control from the beginning of the day. If everything seems in order, our crew brings the results back into the office to create an exact drawing of the water body layout.
JBPro for Your Hydrographic Survey Needs
Underwater surveys have a complicated and detailed process that must be done correctly to ensure the safety and success of any project. Our team has experienced hydrographic surveyors to provide your project with the seamless detail it needs. Let us help you with your next marine construction or hydrographic surveying project today!