What is Hydrographic Surveying and How Does it Work?

Navigating the underwater landscape is not as easy unless you have a type of guidance to follow. It is where land and hydrographic surveying come into play and make a great difference, helping us map out both the underwater region as well as the coastline surrounding any body of water.

Hydrographic surveying is closely tied to land surveying, with the main difference of course being doing it is done underwater. Creating a detailed underwater map is crucial for us to understand the submerged world beneath us. Knowing the depths, underwater contours, and potential hazards can help us safely navigate the area, plan infrastructure in a correct way, and manage valuable marine resources.

The same to topographic surveying and any type of land surveying, hydrographic surveying uses specialized equipment to get things done. Today, we will explain the types of projects that require hydrographic surveys, the main type of equipment used, and explain the steps behind every survey. 

Hydrographic Surveying Definition

Hydrographic surveying is a civil engineering service that helps to determine the physical features of an underwater area. Basically, it works like an underwater X-ray machine that helps to map out the physical characteristics of oceans, seas, lakes, or any other body of water. The gathered information that we get from these surveys includes water depth, seafloor composition, potential hazards, and water properties.

The data is usually presented in nautical charts, except that its purpose goes well beyond mere navigation. The applications of hydrographic surveying and the data collected can be used for environmental research, managing marine resources, civil engineering projects, and even understanding marine ecosystems. 

How Does Hydrographic Surveying Work?

The process of hydrographic surveying involves various steps that have to be deployed as meticulously as possible. The stages involved are there to make the results as accurate as possible and make the data collected as reliable as it gets.

In most situations, surveyors act in accordance with the following agenda:

1. Planning and Preparation: Involves meticulous planning, where a clear objective has to be established first. Surveyors also need to determine the scope of the project and the area that needs to be looked at. It is also important to address potential challenges in the planning stage.

2. Data Collection: Survey vessels will collect data with the help of sonar systems, GPS, and other necessary equipment. They will navigate only the predetermined routes set in the previous stage. 

3. Data Processing: Raw data is processed and analyzed after being collected. It needs to be converted into a format that can be interpreted and then used to create accurate maps of the surveyed area.

4. Charting and Reporting: The final stage involves creating detailed charts or maps of the surveyed area. This should provide a visual representation of the surveyed underwater area, including details such as water depth, potential hazards, and important seabed features.  

Why is Hydrographic Surveying Important?

Hydrographic surveying activities are important because they provide us with a detailed map for underwater teams so they don’t navigate blind. This way, potential hazards like rocks or uneven seabed topography can be safely avoided. It helps to safeguard lives as well as protect valuable equipment used for underwater exploration and building.

Some of the main uses of hydrographic surveying are whenever someone wants to make a drastic change to a water area. Some potential projects include: 

• Dredging

• Building docks or marinas

• Diversion of water sources

• Waterway planning

• Wreck location  

• Removing soils

Knowing the exact site layout helps underwater teams to meticulously plan routes and complete each task with minimal risks. Just imagine starting a project and then only later finding out that there is a ditch preventing you from continuing. It is the same with underwater projects, where you are going to want to have the exact layout of the area where you are planning to build something.

Types of Hydrographic Surveys

Hydrographic survey application can be divided into several main types. There are actually five main ones, with a few subcategories also available. But the ones that you are mainly be concentrating on are the following:

• General Hydrographic Surveys: The most common type of hydrographic surveying, used to collect data involving water depth, coastline contours, mean sea level, and seabed features. With the help of these types of data nautical charts are created, which help in safe water navigation.

• Harbor Surveys: These types of surveys are naturally conducted in harbors or ports in order to collect data on water depth and the seabed and prevent any potential hazards. The data collected also helps ensure safe seafaring for all vessels and helps plan dredging and various maintenance activities.

• Coastal Surveys: This type of surveying is closely connected with land surveying, except that the data collected concentrates mainly on the shoreline. The information collected can be used for port development, coastal erosion studies, and habitat mapping.

• Wreckage Surveys: Wreckage surveys help out in mapping shipwrecks. The data collected here can help with salvage operations, archeological studies, and hazard identification. 

• Passage Surveys: A passage survey is conducted in areas where there are shipping lanes or in places where there is a lot of maritime traffic. The survey helps collect data on water depth and various hazards that may affect navigation. 

Hydrographic Surveying Equipment

In the past, there was a lot of guesswork involved when conducting these types of surveys. People used primitive equipment, and it even required a lot of manual labor to get the desired data. Luckily, hydrographic survey requirements have evolved and so has the equipment that we use today, making it immensely easier to collect precise data.

Sonar

The emergence of sonar technology helped to revolutionize hydrographic surveying, making it not only easier but also more precise for us. It uses sound waves to help us measure the water depth and get various information located beneath the water level. There are actually different types of sonar scanners that cater to different needs. 

For instance, a side-scan sonar is ideal for scanning large, near-shore areas. It can create a detailed image of the seabed and also reveal underwater obstructions. On the other hand, echo sounders are perfect for measuring depth in shallow areas. 

Finally, a multi-beam sonar is the most accurate piece of sonar equipment that you can have. A multi-beam sonar helps to transmit sound pulses in all directions, creating a clear picture of the entire underwater terrain.

Marking Equipment

A proper hydrographic survey should always start with good marking. In order to designate survey points, surveyors would often use high-visibility, low-tack marking tape, GPS measurement endpoints, and even underwater rocks, shipwrecks, and reefs. 

However, you still need to use proper equipment as each color comes with its own meaning. For instance, orange is used for marking underwater danger. Yellow is used for GPS measurement endpoints, while red and white are flexible and can be used for marking various features.

GPS and Optical Devices

Like in so many other types of surveying, GPS equipment serves as a cornerstone for hydrographic surveying. These devices can provide us with real-time, accurate coordinates for each point that we are working on, eliminating the need for physical markers. Not only that, but a lot of advanced GPS units come with a built-in inclinometer that helps to determine the exact elevation of every point. 

However, there are still situations where even advanced GPS equipment isn’t possible to use. In such cases, surveyors can still turn to traditional surveying equipment like theodolites, alidades, and levels. Theodolites are the most accurate type of alternative that can be used here, while alidades are much easier to carry.   

Electronic Navigation Tools

Electronic navigation tools are one of the most essential types of tools for professional surveyors. When it comes to hydrographic surveying, they can provide you with important data on tidal data, weather forecasts, and marine traffic alerts. Some models even have mapping software that helps in overlaying existing charts. 

Most importantly, many of them already come with GPS technology and sonar functionality, also called Electronic Navigation with Sonar (ENSON). These systems can be valuable in hazard identification, charting survey progress, and conducting surveys in low-visibility environments.

Video Equipment

Video cameras help to capture valuable footage of underwater features, which is especially important in low-visibility conditions. The type of video equipment that you will be using here are video cameras, digital still cameras, and GoPros. Be sure to pick a camera that is water-resistant and has the ability to withstand movement and vibrations. 

Depth Measurement Tools

Besides sonars, there are additional specialized types of surveying tools that can help with precise underwater measurements. These depth measurement tools involve rotating beams that can determine the depth below a stationary position. On the other hand, strainers can estimate average depths over a designated area. However, these tools may be highly accurate but do require meticulous execution if you want to get the most accurate results. 

Bottom Profiling Equipment

Bottom profiling equipment is best suited for shallow areas or hazard identification. This type of technology usually includes a multi-beam sonar, a side-scan sonar, echo sounders, video cameras, rotating beams, and strainers. Bottom profiling equipment usually emits sound pulses and uses echoes to create a detailed picture of the seabed. This could be especially valuable in areas with limited visibility.

Deployment Platforms Used in Hydrographic Survey

While a hydrographic surveying boat is the most obvious deployment platform that surveyors usually use, there are many ways to start off a survey. Depending on the situation and individual needs, each one of them has its own advantages and disadvantages. 

• Manned vessels: Survey ships are traditionally the most stable platforms that are used for hydrographic surveys. They are stable enough and can carry a wider range of equipment than any other method.

• Unmanned surface vehicles (USVs): USVs represent a cost-effective way of surveying a larger area. They use acoustic technology that allows them to make underwater measurements with ease. 

• Unmanned underwater vehicles (UUVs): These pieces of surveying equipment are excellent for going deep beyond the vessel you are on. UUVs possess acoustic equipment that helps them navigate autonomously and that way collect underwater data.

• Unmanned aerial vehicles (UAVs): UAVs are excellent for hydrographic surveys in shallow waters. LiDAR drones are excellent for these sorts of situations and can be effective in capturing water depth measurements.

Purposes of Hydrographic Surveys

Hydrographic survey services are needed in various sorts of situations. More so, they are important for various sorts of facets, allowing professionals to get to the data they need. 

Safeguarding Navigation

At the core of hydrographic surveying are bathymetric surveys, which help to measure water depth at centimeter-level accuracy. The data collected here is used to create accurate nautical charts that help ship captains on their routes. That way, safe passage of precise cargo is ensured, as well as the safety of individuals on board.  

Civil Engineering

Engineers who are tasked with various harbour construction or dam building projects rely heavily on hydrographic surveys. The critical information gathered from these surveys, namely water depth, the composition of the seafloor, and the underwater terrain in general, allow engineers to create structures that are strong enough to withstand the forces of nature and ensure the longevity of the structures.

Land Reclamation Projects

Any land reclamation project depends on a precise hydrographic survey. Engineers are able to identify suitable locations for land expansion by knowing the composition and seabed topography. That way, they can assess the possibility of the project they are attempting to do. Only with the help of precise data will they be able to make informed decisions and shape the coastline for further development.

Flood Control System Design

Flood control systems can only be created with a perfect understanding of the underwater landscape. With the help of a hydrographic survey, professionals will be able to learn about potential flooding zones with centimeter-level accuracy. Precise data allows them to pinpoint exactly where levees need to be reinforced or where natural drainage channels can be restored.

Resource Management

Hydrographic surveys are not only helpful in water areas, they can aid in mapping alluvial and silt deposits near water bodies, helping to identify fertile land with high agricultural potential. Not only that, but knowing river discharge patterns allows us to understand potential erosion risks better. With the help of this type of data, land management strategies can be secured to reach sustainable agricultural practices.

Offshore Industries

Industries like the offshore oil and gas industry rely heavily on hydrographic surveys. With their help, oil rigs and underwater pipelines can be inspected, allowing for the determination of potential water damage or any tears that might occur. This can help maximize preventive maintenance and diminish any risks or environmental disasters.   

Hydrographic Surveying vs Bathymetric Surveying vs Marine Surveying

In certain situations, terms hydrographic surveying, bathymetric surveying, and even marine surveying are sometimes mixed up. While people often mistakenly use hydrographic and bathymetric as synonyms, they are definitely not.

A bathymetric survey focuses only on a single aspect of underwater surveying, and that is determining the water depth. On the other hand, a hydrographic survey is something that goes beyond water depth, as it offers us a comprehensive understanding of everything found down below the water line.

As far as marine surveying goes, this is a term that focuses on ships and not really the situation beneath them. A marine surveyor is a person who determines the aptitude of vessels and their ability to sail the waters safely. They are certified specialists who survey entire boats, deeming them worthy of traversing different waters. 

FAQ

Here are a few additional answers to a few questions in regards to hydrographic surveys. 

Who conducts hydrographic surveys?

Hydrographic surveys are conducted either by government agencies or the private sector. National hydrographic offices and the coast guard are usually the ones to do it, but there are specialized survey companies that possess a hydrographic surveying certification, allowing them to do so.

What data does a hydrographic survey provide?

The type of data gathered through a hydropgraphic survey includes water depth, the shape of the seafloor and coastline, physical features of water bodies, and the location of possible obstructions.

What instrument is used in a hydrographic survey?

The type of instruments used in hydrographic surveys includes sonars, GPS and optical devices, USVs or UUVs, video equipment, and various vessels.