What is Hydrographic Surveying? Importance of Hydrographic Surveying

What is Hydrographic Surveying?

A Hydrographic Survey is a  survey that uses sound waves to produce detailed data about the water column, such as the depth of the water and its contents, including layers of sand, clay, and rock formation.

It is the science of identifying and describing elements that influence marine navigation, marine construction, dredging, offshore oil exploration/offshore oil drilling, and associated operations.

This information can be used for navigation and to assess the environmental impact on marine life.

History of Hydrographic Survey

The practice of hydrographic surveying can be traced back to the ancient Egyptians and Greeks who used it to map the Nile and the Mediterranean Sea.

The development of the modern hydrographic survey began in the 18th century with the commissioning of the Royal Navy’s first survey ships.

These vessels were equipped with the latest technology, including echo-sounding devices, to map the coastal waters of the British Isles. Hydrographic surveying has since evolved into a sophisticated science that is used to chart the world’s oceans and waterways.

In 1807 President Thomas Jefferson approved a mandate requiring a survey of developing nation’s coast.

So started the history of the Survey of the Coast. This agency would alter its name and structure but not its essential objective of supplying nautical charts to the maritime community for safe passage into American ports and along 95,000 miles of U.S. coastline.

Today, as it did in Jefferson’s day, the Office of Coast Survey performs hydrographic surveys, which are a critical component of nautical charts.

NOAA surveys the sea bottom using two types of sonar, depending on the charting requirement: multibeam and side-scan sonar.

Hydrographic Survey Instruments

A hydrographic survey instrument is a device used to measure the depth of water and is an important tool for navigation and survey work.

There are many different types of hydrographic survey instruments, including sonar devices, depth gauges, and compasses.

Hydrographic survey instruments are used to measure the depth of water in both coastal and inland waterways and are essential for navigation and surveying work.

The main instruments include;

1. Hydrographic Echo Sounder – this is a device used to measure depth and provides readings of the water column.
2. Sonar – this device uses sound waves to locate objects on land or in water and can be either active or passive. Active sonar sends out pulses of sound waves which bounce back off an object in the water column when it reaches that object, whereas a passive sonar listens for any noise made by ships.
3. Depth Measurement Sounder – this instrument was designed to measure depth in a continuous manner and provides information such as water temperature and salinity.
4. Multibeam Sounder – this is a special type of electronic navigation system that records the depth, water column, and seafloor.
5. Real-Time Kinematic Global Positioning System – (RTK-GPS) – this is a system used to determine the position on land or at sea in real-time and with high accuracy.
6. Hydrophone – This device detects vibrations in the water caused by either ships or whales.
7. Sonobuoy – this is a device that floats in water and measures horizontal and vertical gradients of sound waves as they travel through the water column.
8. Acoustic Doppler Current Profiler – these instruments produce maps of ocean currents using electromagnetic pulses, which are transmitted to sensors on the ocean floor.
9. Bottom-mounted Acoustic Sensor – this sensor is designed to measure the bottom topography and sea floor without causing damage to the structure of the seabed
10. Magnetometer – this instrument measures the strength of magnetic fields present in the water.

Hydrographic Survey Applications

•  Irrigation– this uses Hydrographic Survey data on the seabed to determine water depth, the condition of the seabed, and to calculate any necessary adjustments in levels for irrigation purposes.
• Geological survey– this applies the sounds produced by a hydrographic echo sounder to map out and explore seabed formations.
• Oil and gas exploration – by collecting data from the sea floor and measuring changes in water depth as drill sites are drilled, it is possible to evaluate where oil deposits are most likely to be found.
• Water Power-based irrigation or sprinkler system is based on the hydrographic survey. Hydrographic surveying is commonly used to determine the layout of pipeline routes and may also be used to identify optimum pumping stations, water intakes and outfalls, and other facilities associated with a water supply network.
• Land reclamation-hydrographic surveying is usually the first step taken to determine the possibility of land reclamation, and then to assess the potential marine and coastal environments that may be affected.
• Flood control- the hydrographic survey is used to measure the depth of rivers, streams, and lakes before flood control measures are implemented.
• Sewage disposal- the depth of the water column and the sea floor is measured to determine where sewage and waste may be successfully discharged.
• Dock and Harbor Engineering– the depth of the water column and the shape of the sea floor is used to create accurate plans for the construction of docks, piers, and boat launching facilities.
• River works- the hydrographic survey is used to determine the best location and method of constructing river works such as bridges and dams.

Types of Hydrographic Survey

• Harbor Survey– where a boat surveys the depths in a harbor or port area, with the use of an echo sounder to determine water depth, sea floor and shoreline.
• Passage Survey– where a boat is taken through a passage, with the use of an echo sounder to determine water depth and sea floor.
• Coastline Survey– where the water column along a coastline or island chain is measured using an echo sounder in order to create a profile of the depth of the water column, seafloor, and any underwater features such as reefs. These profiles can be produced as cross-sections, or stacked on top of each other horizontally to create approximate three-dimensional profiles.
• Survey for Correlation- where the depth of a water column is measured using an echo sounder, and then the depth of the sea floor is also measured using a sonar. Both depths are known, a line can then be drawn on land from reference points on shore to show the depth at which each side of the line intersects.
• Overhead Survey – where surface measurements are taken by an individual, who steers a boat while holding an echo sounder, or who flies overhead with a depth measurement sounder.
• Track Line Survey – where a boat travels along a line, at set intervals taking surface measurements from the track line.

Methods of Hydrographic Survey

1. Single Beam Echo Sounder- where the echo sounder sends out sound waves that bounce back off an object in the water column when it reaches that object.

The echo sounder records the time delay before receiving the reflected waves and then converts this into a depth which is displayed on a linear graph.

2. Dual Beam Echo Sounder- where the echo sounder sends out two different frequencies of the sound wave, one low frequency, and one high frequency.

The frequency at which the sound waves bounce back depends on the depth of water. The reflected waves are received and then converted into a depth which is displayed on a linear graph.

This depth can be measured in meters, or it can be converted to miles and fathoms for use in navigation.

3. Improved Sonar/Sounding Device- is equipment that sends out high-frequency sound waves in the form of pulses, which travel to the bottom of the sea and bounce off any objects there.

4.MultiBeam Echo Sounders- where multiple echo sounders are used in series, and the transmitted sound waves are bounced back at different angles to different sensors on the surface of the sea.

5. Modern Surveying- where satellite positioning devices are used to determine the location of a vessel, combined with engine and GPS data to track the speed and location of the vessel.

6. Wire-drag Surveying- where a wire is deployed behind the vessel, which drags along the sea floor. A float on the end of the wire collects debris but also snags itself on any obstructions that may be present.

The strain gauges attached to the wire and float record changes in tension and pressure, indicating obstructions under the water.

The main advantage of a Wire-drag Survey is that it allows for continuous survey work in deep water areas, without having to deploy anchors or send down divers for measurements.

Process of Hydrographic Survey

1. Reconnaissance Survey- The first step in the hydrographic survey is to obtain an overview of the area being surveyed. The results of this reconnaissance survey are utilized to help determine the method that best suits the area.
2. Exploratory Survey– This is where a hydrographic sounding device, echo sounder or sonar, is used in order to collect data about the sea floor, water depths, and shallows along a proposed route for a pipeline or dredging project.
3. Hydrographic Survey– This is the step where all of the data collected from the previous steps are used to create charts and maps for navigation, flood control, or marine safety.
4. Adjustment Survey – this is done as a re-survey after a period has elapsed, to ensure that no changes have occurred in regards to sea levels, sea currents, and new obstructions under the water. This type of survey may be conducted using a modern surveying device or a wire drag.
5. Re-plotting Survey – this is a re-survey after a period of time has elapsed, to ensure that none of the magnetic fields in the area have moved or been disturbed. This type of survey may be conducted using a modern surveying device or a wire drag.
6. Dedicated Survey – This is where a survey team is sent out to dedicated areas that have received no previous survey attention. This type of survey may be conducted using modern surveying equipment and a wire drag.
7. Dredging and Construction Survey – where a vessel conducts a survey to establish the depth of water required for dredging or construction equipment. This type of survey may be conducted using a modern surveying device or a wire drag.
8. Post Hydrographic Survey – This is where a survey team returns to the area that was surveyed previously, in order to determine any changes that have occurred and take further measurements if required.
9. Post-Reconnaissance Survey – This is where the data from previous surveys are input into a modern surveying system in order to generate charts, navigation maps and other navigation aids. This may be conducted using a modern surveying device or a wire drag.
10. Offshore Survey– This is where a vessel is used to create charts and navigation aids for offshore locations such as oil rigs. This may be conducted using a modern surveying device or a wire drag.

Uses of Hydrographic Survey

1. Shore lines can be determined- The depth of water at low tide can be ascertained and marked using the information from the hydrographic survey.

This is used to determine the location of proposed new structures such as boat harbors and marinas.

2. Depth of the bed can be determined- The depth of water at low tide can be determined, along with any obstructions beneath the water, using a wire-drag survey. This can be used to determine the requirements for dredging a new harbor or shipping lane.

3. Shore lines can be determined- The depth of water at low tide can be ascertained and marked using the information from the hydrographic survey.

This is used to determine the location of proposed new structures such as boat harbors and marinas.

4. Locate sewer fall by measuring direct currents- The depth of water at low tide can be measured, along with any obstructions beneath the water, using a wire-drag survey.

This is used to determine where existing sewer lines lay within ocean floor sediments.

5. Tide measurement- The depth of water at low tide can be measured, along with any obstructions beneath the water, using a wire-drag survey.

This is used to determine the tidal range for an area, allowing for the prediction of tides and current velocities.

6.Massive structures like bridges, dams’ harbors are planned- The depth of water at low tide can be measured, along with any obstructions beneath the water, using a wire-drag survey.

This is used to determine where major structures would lie within the sea floor, providing a point of reference for charting and navigation.

7. River and stream discharge measurement- The depth of water at low tide can be measured, along with any obstructions beneath the water, using a wire-drag survey.

This is used to determine the amount of water flowing into and out of an area in a given time period, which is then used to predict future land development.

8. Scouring, silting and irregularities of the bed can be identified- The depth of water at low tide can be measured, along with any obstructions beneath the water, using a wire-drag survey.

This is used to identify areas where sediments have been scoured bare by waves or currents.

FAQs

What is the difference between hydrographic and bathymetric surveys?

Hydrographic surveys make use of the science of measuring and describing characteristics that impact maritime navigation, marine building, and so on.

Bathymetric surveys also provide marine depths, but they often offer a more precise topology of the bottom surface.

What data does a hydrographic survey provide?

Bathymetric surveys allow us to estimate the depth of a body of water as well as map its underwater features

What is sextant in the hydrographic survey?

This Sounding sextant is an essential marine/hydrographic device that is primarily used for measuring angles between coastal objects in order to locate the position of a boat relative to the coastline. It is distinguished by its unusually big aperture telescope and lack of filters.

What is the main purpose of a hydrographic survey?

The primary goal of hydrographic surveying is to collect data for nautical charts, which indicate water depths, navigation channels, constructions (such as piers), breakwaters, and so on and are utilized by seafarers.

What are the advantages of using a hydrographic survey?

1. Hydrographic surveys produce more precise and detailed data than do bathymetric surveys.

2. Hydrographic survey can be done at different times of the year and in different seasons, as to how frequently bathymetry must be conducted in order to provide an adequate sample.

3. It provides a basis for creating charts, navigation maps, and other navigation aids.

4. Hydrographic survey is more affordable than the bathymetric survey.

What is the main challenge in Hydrographic Survey?

Hydrographic survey is very complex and the main challenge for Hydrographic Surveyor is to make sure that the measurements are accurate.

What are the recent developments in hydrographic surveys?

There has been a lot of development recently in this field. For example, GPS and also other automation instruments have been used to decrease the complexity of survey work and increase the accuracy of data collection.

What should a Hydrographic Surveyor do?

A hydrographic surveyor primarily uses the information from bathymetric surveys to produce nautical charts, allowing seafarers to more accurately locate the position of their boat.

How does a Hydrographic Surveyor prepare for the work?

A Hydrographic Surveyor should always be ready with the relevant equipment, such as echo sounder, sextant, GPS, and so on to minimize the time spent on preparation before any start of the survey.

How long is Hydrographic Surveyor expected to work?

The duration of a survey will vary depending on all possible factors. Generally speaking, it will last approximately 2 to 5 days.

How much does a Hydrographic Surveyor earn?

In the United States, the national average compensation for a Hydrographic Surveyor is $67,629 per year

What is the career growth of a Hydrographic Surveyor?

A Hydrographic Surveyor can generally take up senior survey positions, such as head of surveys or staff hydrographer after gaining enough experience and also expertise in the field.

What are the common tasks in Hydrographic Survey?

The main task of a hydrographic surveyor is to survey the exact depth and position of constituents. This is done by using an echo-sounder or other hydrography tools.

What is Hydrographic Survey Software?

Hydrographic Survey Software is software that allows hydrographic surveyors to automatically draw the data for bathymetric and hydrographic surveys.

Example;

1.SeaDAT, a multi-platform and multi-purpose database software allows hydrographic surveyors to easily and manually create a database of the collected data in relatively short time spans.

2. Hydroviewer is a program that automatically draws bathymetric maps using hydrographic survey data.

3.SurveyNET can be used to communicate and share bathymetric survey data with other hydrographic surveyors and is mainly used for multi-user survey operations.

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