Modern Rules of Hydrographic Surveying
- What Is Hydrographic Surveying
- Why Hydrographic Surveys Are Important
- How Hydrographic Surveying Is Applied
- Hydrographic Survey Equipment
- The Key Methods of Hydrographic Surveying
- Modern Surveying
- Multi-beam vs Single-beam Echo Sounders
- Wire-drag Surveying
- Lead Lines and Sounding Poles
- Difference Between Hydrographic and Bathymetric Surveys
01. What Is Hydrographic Surveying
Hydrographic surveying is used to map bodies of water. It’s important because it provides data on the depth and shape of waterways, which helps people know what kinds of vessels to use in different areas. Hydrographic surveys take place on land and boats, and they use a variety of tools, such as multi-beam echo sounders.
Primary Uses of Hydrographic Surveying
Hydrographic surveying techniques are used to create maps of bodies of water and to measure various properties, such as depth, temperature, and salinity. They also help maintain navigation channels and can be used for search-and-rescue operations or oil exploration.
Hydrographers use an array of tools depending on what they want to accomplish. For example, if you’re measuring depth in a river with a handheld depth sounder, you’ll need to move slowly so that your measurements are accurate enough for navigation. This usually requires measurements within less than one tenth of a foot. If you’re creating a bathymetric map on land or at sea with sonar equipment mounted on board a ship or vessel, sometimes called “echo sounding”, then your survey area will probably not be too large. In that instance, only one type of instrument would be suited for this job: sonar equipment mounted on board ships or vessels.
The following are some key things you should know about hydrographic surveying:
Surveyors need to know the depth of water in order to do their job effectively. The depth measurements are taken at different points along a route so that they can create maps that show all areas where there may be shallow water or submerged objects like rocks that could damage boats or ships passing through them at high speeds over long distances, such as those used by military submarines.
Surveyors also need information about whether there is any kind of obstacle in certain areas along these routes—like trees growing on islands instead of sand bars because they have been planted there intentionally by local residents just for this purpose.
Hydrographic surveying is an important way to measure the undersea environment can be used for a variety of purposes, from detecting potential hazards to mapping out paths for ships. The tools and techniques used in hydrographic surveying are constantly evolving, making it easier than ever before to collect this kind of data.
02. Why Hydrographic Surveys Are Important
Hydrographic surveys are an essential part of the shipping industry. These surveys provide detailed information about the structure and geography of the waterway, which is used in planning and creating a safe passage for commercial shipping vessels.
Without hydrographic surveys, it would be impossible to plan safe routes through waters that are filled with hazards. A properly conducted hydrographic survey will map the type of terrain, depth of the water, any local currents, potential hazards such as reefs, and even the location of potential fishing grounds.
The data from a hydrographic survey typically also includes the location of any potential underwater hazards, such as wrecks or pipelines. Without accurate charts, commercial vessels would face a much higher risk of running aground or colliding with underwater obstacles.
Benefits of Hydrographic Surveys for Shipping
While there are a many of surveyance options on the market, hydrographic surveys offer a wealth of benefits:
- Safety: Survey data will help to create routes that are free of hazards, such as shallow waters, underwater hazards, and areas that are too narrow for ships to pass through. This will help to reduce the risk of shipwrecks, especially in areas that experience high levels of traffic.
- Efficient routing: The most direct route often isn’t the most efficient. Along with avoiding hazards, a hydrographic survey will also look for areas where ships can save time by taking advantage of the current.
- Reduce transit time: Every minute that a cargo vessel is at sea is a minute that the ship isn’t earning money. By using a more efficient route, the ship can reduce transit time and increase its profit margin.
- Cost savings: It may come as a surprise, but hydrographic surveyance actually is one of the more cost-effective. A shorter route, avoidance of hazards, and the ability to take advantage of currents will all lead to lower operation and transit costs.
Limitations of Hydrographic Surveys
Hydrographic surveys can provide detailed information about the bottom topography with high resolution and accuracy. However, certain limitations may limit the amount of information obtained during a hydrographic survey. These limitations include shallow waters, adverse weather conditions, complexity of the coastline, rough seas, and operational costs.
As with many surveys, hydrographic surveys are only as accurate as the person who is taking the measurements. If the person doing the survey is careless or inattentive to detail, they may misread the data or make a mistake in the measurements, which could lead to dangerous routing decisions.
The most important thing to remember about hydrographic surveys is that they’re a snapshot in time. If the water level is too shallow during the collection window or we encounter rough seas, it could affect the project.
Changes in the water, such as shifting currents or seasonal changes in the water level, can alter the accuracy of the data got from a survey. If bad weather is forecasted, the survey may need to be postponed until the weather clears up.
Hydrographic Data Collection
In order to be accurate, hydrographic surveys must be conducted under the best possible conditions. This means the surveyor must wait for the weather to be clear and calm, with little to no current, in order to get the most accurate data possible.
At Triad Drones, we’ve built a system to ensure you have the highest quality data possible. Our expert hydrographic surveyors employ autonomous hydrographic data collection techniques for optimum results.
03. How Hydrographic Surveying Is Applied
Hydrographic surveying has several applications, including marine navigation and as a source of data for cartography. If you’re thinking about getting into hydrographic surveying or adding it to your business as an auxiliary company, this chapter will help you understand its benefits and applications in the real world.
If you’re looking to navigate a river or lake, then you’ll want to know the water depth and any changes in the water level that might require you to change your course. In addition, you will also want to know the location of any hazards that might be in the water, including rocks, sandbars, logs, or even other boats or ships. Hydrographic surveying collects data about the waterway and then uses the data to create a map of the waterway. In addition, those maps can then create a chart for the waterway. Nautical charts are like road atlas maps in that they provide lots of information about a particular location. Nautical charts are especially helpful for fishermen, boaters, or anyone else who might travel near or on the water.
Navigating by GPS
Modern hydrographic surveys rely on GPS technology for navigation. GPS (Global Positioning System) is satellite navigation that allows surveyors to pinpoint their latitude and longitude at the time of the survey. This is crucially important for hydrographic surveys, where the location of the surveyor is critical for the accuracy of the data collected. GPS technology is also useful for surveying on the open water, as it is sometimes difficult to pinpoint the location of a surveyor in the middle of a lake or river. GPS also allows surveyors to create a digital record of the survey as they are conducting it.
Maritime Safety and Security
Hydrographic surveying is also a key part of keeping waterways secure. For example, the U.S. Coast Guard conducts hydrographic surveys to maintain nautical charts. These charts display information about waterways, markers, and other important landmarks that are critical for safe boating.
Assessing Environmental Damage
The information gathered from hydrographic surveys is also used to track human-caused damage to the environment. For example, if an oil spill has contaminated an area, surveyors can use their data to see exactly where the spill occurred. This information can help officials determine the extent of the damage and decide how best to clean it up.
Determining the Cause of Stream Discontinuity
Stream discontinuities are a real problem that can cause issues for people living along a stream. A discontinuity is a break in the flow of water that causes the stream to dry up. Hydrographic surveying can track changes in the flow of water in a stream. If the flow slows or even stops at any point, then the surveyor can return to the location to see what is causing the change. Surveyors will typically look for the cause of the problem, mark it with flags, and then return at a later date with special equipment in order to record the exact location of the break in the stream.
Flood Risk Analysis
Flooding impacted over 34.2 million people around the globe in 2020, according to a Statista report. Floods can cause devastating to property damage, disrupt transportation, and even threaten human life.
If an area experiences flooding, hydrographic surveys are used to investigate the cause of the flooding. The surveyors will mark any obstructions to the flow of water (such as a sunken tree or bridge), which can be helpful when trying to locate the source of the flooding.
Moreover, hydrographic surveys are instrumental in flood prevention. It helps determine the risk of flooding in a particular area by mapping out the elevation and water depth.
Additionally, hydrographic surveying can track changes in the water level after a flood has occurred. The data from the survey is then used to create a computer model that shows how water flows through the area. This model can help determine the reasons for the flooding and what experts can do to prevent it from happening again.
Marine Construction and Development
Are you planning a new port or shipping channel? Or maybe you’re looking to build on a piece of land near a body of water. In either case, hydrographic surveying can be extremely helpful. Nautical maps and charts can determine the best location for marine construction and development. It can also track changes in the water level in real time that might reveal a need for adjustments to the construction.
Finding Objects Underwater
Another application of hydrographic surveyance is locating buried objects such as submerged pipelines or shipwrecks. If you’re looking to find something that is submerged under water, then hydrographic surveying can be very helpful. For example, hydrographic surveying can find something as large as an aircraft or something as tiny as a specific mineral. Hydrographic surveying can be a large-scale operation involving the use of sonar or other equipment that can locate an object even if it is buried under sand or mud. Alternatively, it can also be a smaller-scale operation in which surveyors use markers that indicate the position of an object.
Benefits of Hydrographic Surveying
Hydrographic surveying has many benefits for those who use it. It makes it easier for people to navigate different bodies of water and identify hazards such as strong currents or shallow spots. It also helps with construction projects involving lakes or rivers such as dams, bridges and canals. Let’s dive into some of the benefits of hydrographic surveying.
Commercial and recreational sailors alike use navigation charts. These charts collect information about the water and its features, such as rocks and sandbars, which are constantly changing. These include normal changes in water flow, as well as human activity, such as dredging and construction. Regular hydrographic surveying is used to keep these charts as accurate as possible.
Improved Resource Management
River management is a crucial part of hydrographic surveying. By tracking the flow of water to determine where it’s slowing down, or even stopping, researchers can predict floods and drought. In addition, they can also track the movement of sand and silt, which can affect the construction of bridges and other man-made structures.
04. Hydrographic Survey Equipment
Today, hydrographic surveying has evolved into an advanced process using sonar, laser scanning, and other technologies that are more accurate and require less physical effort on behalf of the surveyor.
With advancements in technology continuing to take place at a rapid pace, businesses of all sizes have begun adopting new strategies to remain competitive within their respective industries. As a result, there has been a spike in the number of companies investing in automated surveying software with a special focus on hydrographic surveying services. Here’s an overview of the most common equipment in hydrography.
Marking devices are essential for any hydrographic survey. Surveyors use markers to indicate the location of survey points, set endpoints for GPS measurements, and mark hazards such as rocks, wrecks, reefs, and channels.
In the past, surveyors used a variety of items for marking, including colored yarn, cable, plastic bottles, and paint. Today, however, surveyors use highly visible low-tack (also referred to as low-adhesion) marking tape. This tape is easy to remove when the survey is finished, so it doesn’t leave a lasting mark on the waterway.
Marking tape comes in a variety of colors, including
- Orange. Orange is the standard color for marking hazards such as submerged rocks, wrecks, channels, and other obstructions.
- Yellow. Yellow is often used to mark endpoints for GPS measurements.
- Red. Red marking tape can be used to mark any feature, including hazards and channels.
- White. White marking tape can be used to mark any feature, including hazards and channels.
GPS and Optical Measuring Devices
GPS units allow hydrographers to record survey points with accurate GPS coordinates. GPS units mark the location of a hydrographic survey in real time, so surveyors don’t have to mark survey points with markers or other devices. Many GPS units also have built-in inclinometers that allow surveyors to determine the elevation at each point along the survey. GPS units take advantage of satellites in orbit around the Earth. They record the location of a surveyor and the orientation of the device (i.e., the device’s “heading” and “tilt”).
The GPS unit then uses these recorded details to calculate the surveyor’s current location and the distance to other points in the survey area. Some surveyors also use surveying instruments for measuring the distance and angle between two points. These include theodolites, alidades, and levels.
Theodolites are the most accurate instruments, but they’re also very large and difficult to transport. Alidades are smaller and easier to transport but less accurate than theodolites. Levels are even less accurate than alidades, but they’re still useful for some hydrographic surveys.
Hydrographic surveyors can use sonar equipment to survey extensive areas of water, identify underwater obstructions, and determine water depths.
Surveyors can use different types of sonar, including
- Side-scan sonar. Side-scan sonar is best for surveying large areas that are close to shore.
- Echo sounders. Echo sounders are best for surveying shallow water.
- Multi-beam sonar. Multi-beam sonar is best for surveying large areas that are farther from shore.
Multi-beam sonar is the most accurate sonar tool available for hydrographic surveying. It transmits sound pulses in all directions and then uses a computer to interpret the echoes reflected by submerged objects. This allows surveyors to see a detailed image of the water floor and locate hazards such as rocks and wrecks.
Video equipment can be useful for recording images of underwater features and monitoring other crew members while visibility is low. Some surveyors also use video equipment to document the progress of the survey, allowing them to review their work after they finish the survey and make any necessary adjustments.
Surveyors often use specialized camera equipment to record images of underwater features during the survey. Commonly used camera gear includes video cameras, digital still cameras, and GoPros. When choosing a camera, surveyors should look for a model that is waterproof and can withstand movement and vibrations.
Electronic Navigation Tools
Electronic navigation tools are helpful for hydrographic surveys. These tools provide current and tidal information, weather forecasts, and marine traffic alerts. Some electronic navigation tools feature mapping software that allows hydrographers to create surveys and overlay existing charts. They’re also often equipped with GPS technology that works in tandem with the mapping software. Some electronic navigation tools also feature sonar functionality. These tools are referred to as Electronic Navigation with Sonar (ENSON). They’re helpful for identifying hazards, charting the progress of the survey, and conducting hydrographic surveys in low visibility conditions.
Rotating Beams and Strainers
Rotating beams and strainers are helpful for measuring water depths. Hydrographers use rotating beams to determine depths directly below a stationary location. They use strainers to determine the average water depth over an area measuring 10 to 30 meters.
Strainers comprise a weighted line with a bucket or basket at the end. Surveyors lower the strainer into the water and then measure from the water’s surface to the bottom where the weighted line rests. They can then use that measurement to estimate the average depth of the water in the area.
Rotating beams and strainers are highly accurate, but they can also be tricky to use. It’s important to do the measurements in a pre-defined order to ensure accuracy. It’s also important to use the right equipment for the right application.
Bottom Profiling Equipment
Bottom profiling equipment is useful for surveying shallow areas and identifying hazards such as rocks and wrecks. Bottom profiling tools include side-scan sonar, multi-beam sonar, and echo sounders. They’re also often equipped with video cameras and rotating beams and strainers. Bottom profiling equipment transmits sound pulses in all directions, like multi-beam sonar. Submerged objects reflect the pulses, and the equipment uses a computer to interpret the echoes. Bottom profiling equipment is useful for surveying shallow areas where multi-beam sonar might not be effective. It’s also useful for surveying areas with poor visibility, such as near shore or around underwater obstructions.
05. The Key Methods of Hydrographic Surveying
Hydrographic surveyors are the navigators of the modern world. Through hydrographic surveying, you can learn about the exact location and size of features like sunken ships or natural springs. You’ll also get information about tides, currents, and other relevant factors in an area so that you can more safely travel there again in the future. This chapter will explore three key methods of hydrographic surveying: boat-based surveys, fixed sensor surveys, and remote sensing techniques.
Recording the Water’s Surface Shape
The surface of the water can reveal a lot of information about the surrounding area. To make sense of it, hydrographic surveyors use laser scanners, sonar, and other types of remote sensing equipment. Their tools employ various technologies, such as
- Laser: This is used to determine the depth of water. The surveyor locks the laser onto a surface and then records the time it takes for the light to return to the instrument.
- Sonar: It is used to map the water’s surface by sending out pulses or sound waves and then measuring their return. The equipment can also be used to measure the depth of water.
Measuring Near-Shore Areas
A hydrographic surveyor can take measurements at various depths in the water and then calculate the surface area of near-shore areas. This process, known as swath mapping, can be done by taking measurements directly on the water’s surface or with a boat-mounted instrument called a hydrographic winch. The hydrographic winch is usually mounted on a small boat and is used to lower an instrument called a swath-meter into the water.
Bathymetric surveying is measuring the depth of a body of water, usually with a sonar instrument. The surveyor can use a single beam, multi-beam, or side-scan sonar to collect data, which is then processed to create a bathymetric map. This type of map shows the underwater topography in great detail and is used by hydrographic surveyors to determine the depth of the water. At Triad Drones, our team uses multi-beam sonar technology.
Assessing Water Quality
Finally, hydrographic surveyors look for evidence of water pollution, such as oil, sewage, or other contaminants. If harmful substances are present, the surveyor uses photogrammetry, a type of remote sensing, to create images to help authorities identify the sources of contamination. Photogrammetry uses aerial or satellite photos or digital images to create three-dimensional models that can identify and prioritise pollution sources.
06. Modern Surveying
In the last decade, hydrographic surveying has transformed. When compared with traditional methods using paper charts and plotting tables, modern hydrographic surveying is almost unrecognizable.
What Is Modern Hydrographic Surveying?
Modern hydrographic surveying is a method of recording the water column with an array of sensors to create a high-resolution bathymetric survey (underwater topographical survey). The sensors to record hydrographic and topographical data. These sensors may include sonars, synchronised echo sounders, still cameras, video cameras, and LiDARs.
In earlier survey methods, hydrographic data was recorded by hand on paper, or mechanically on paper or film that was later digitised. Using computers and sensors to record hydrographic data has many advantages over manual and mechanical recording methods, including the ability to record data faster, more accurately, and with a higher repeatability.
New Technology in Modern Surveying
Hydrographic surveying has seen a revolution in the last decade, with new technologies that have transformed the way hydrographic surveys are conducted.
The first major change in hydrographic surveying came with the emergence of modern multi-beam sonar technology. Modern multi-beam sonar systems are digital instruments that use sound to create a detailed picture of the water column. The multi-beam sonar transmits a fan-shaped beam of sound through the water column, which is reflected to the instrument. The time taken for the sound to travel through the water and be reflected back is used to calculate the distance from the instrument to every point in the water column. With two or more beams, it can mathematically combine these distances to create a bathymetric survey.
Why Are Modern Surveys Faster and Cheaper?
The ability to record hydrographic data faster and more accurately allows survey vessels to complete more surveys per day than traditional methods, which means fewer days at sea per survey. This has several benefits in terms of reduced personnel costs and reduced operational and support costs.
Fewer days at sea per survey means that survey vessels and crews spend less time at sea and so have lower costs associated with crewing, consumables (food, fuel, and other supplies), and other operational costs such as maintenance, vessel wear and tear, and insurance premiums.
Modern surveying techniques are also far more efficient than traditional survey techniques, meaning that less time is spent on administrative tasks such as data quality control and data processing, which again allows survey vessels to complete more surveys per day.
The Future of Hydrographic Surveying
New technologies like autonomous underwater vehicles (AUVs), synthetic aperture sonar (SAS), and unmanned surface vessels (USVs) will transform hydrographic surveying in the coming years. Conducting surveys using AUVs and SAS systems has the potential to allow hydrographic surveys to be conducted 24/7, 365 days a year, regardless of weather. This would allow surveys to be conducted in more challenging environments, such as in ice-covered waters, and would allow surveys to be conducted all year round, regardless of seasonal weather. Using AUVs and SAS systems would also allow hydrographic surveys to be conducted in areas of high marine traffic, such as at major ports, or in areas of high commercial fishing activity, where the use of manned survey vessels would be dangerous or impractical.
07. Multi-beam vs Single-beam Echo Sounders
When you’re navigating a busy channel, there are many things to keep track of. There are other vessels, structures and even your own anchor cables all within the same small area. It’s not uncommon for smaller vessels to strike an unmovable object on a congested channel. For this reason, every vessel needs reliable echo-sounder technology that can detect objects in the surrounding water.
Echo sounders are electronic devices used on board ships to measure the distance of objects in proximity to the boat using sound waves produced by underwater sonar transducers.
Avoiding collisions is always the top priority on board any vessel, and successful captains know how to use their surroundings to their advantage. The captain of a ship must be able to see where they are going so they can plan accordingly and pick the best path through any waters.
What Is a Single-beam Echo Sounder?
A single-beam echo sounder is the most common type of underwater sonar transducer and is ideal for most commercial vessels. It uses a single downward-facing transducer to produce a single fan-shaped acoustic beam that can only detect objects in a single line. This means it cannot detect objects at a distance on either side of the vessel, which makes it a poor choice for waters where there are lots of other vessels and stationary objects such as bridges and piers. Single-beam echo sounders are ideal for waters that are less congested, as they only detect objects in a single line straight below the boat. People commonly find them on recreational boats as they are less expensive and easier to install than multi-beam units.
What Is a Multi-beam Echo Sounder?
A multi-beam echo sounder is a type of underwater sonar transducer that projects several acoustic beams. Someone typically mounts these at different angles on either side of the vessel, which allows it to detect objects off both sides of the boat.
Multi-beam echo sounders are often installed on commercial vessels in areas with heavy traffic, such as rivers, as they can detect and avoid vessels on either side. However, they are not as effective in shallow waters and are not recommended for use on recreational boats. Multi-beam echo sounders are more expensive than single-beam units and require more complex installation.
Which Is Better: Single-beam or Multi-beam?
The best choice between a single-beam and multi-beam echo sounder depends on your specific situation and the waters you will be navigating. If you are navigating in a heavily trafficked area or near any stationary obstacles, a multi-beam echo sounder is the better option. Single-beam echo sounders are ideal for waters that are less congested, as they only detect objects in a single line straight below the boat. Surveyors commonly found them on recreational boats as they are less expensive and easier to install than multi-beam units.
How To Use an Echo Sounder?
To correctly use an echo sounder, you must first know the difference between transmission and reception. Transmission is when the echo sounder sends out sound waves, while reception is when it receives the sound waves reflected off of objects in the water.
In order to read the depth of the water, you need to know the difference between a single-beam and multi-beam echo sounder as each one has different settings.
A single-beam echo sounder is designed to read depths in a single line along the center of the boat. A multi-beam echo sounder reads depths of objects at a 90° angle to either side of the boat. If you want to know the depth at the center of your boat, you need to set the echo sounder to single-beam mode. If you want to read the depths of objects on either side of the boat, you need to set it to multi-beam mode.
08. Wire-drag Surveying
Wire-drag surveying is an indirect measurement technique that uses the properties of a wire to measure the length, width, and volume of a feature. The wire-drag method was developed as an alternative to tape and chain surveys in areas, like oceans, where vegetation and terrain made other methods impractical.
The wire-drag method uses wires with a high coefficient of friction to move over the ground; it is dragged behind a moving survey marker, which sees when the wire slips or catches on protrusions. The additional length of the wire from one point to another determines if any dips or peaks exist, which may indicate changes in elevation.
Wire-drag surveying requires specialized equipment and experienced operators, but has proven effective in locating new water wells or monitoring changes in stream beds during flooding events.
How Does Wire-drag Surveying Work?
A surveyor will pull a tensioned wire behind a survey marker that is mounted on a vehicle. The wire will drag across the ground and will pick up any changes in the ground’s elevation. Next, the surveyor will use a computer to record the distance between the survey marker and the portion of the wire that is in contact with the ground. The computer calculates the elevation of the ground by referring to the length of the wire that is in contact with the ground and the tension of the wire. This method of surveying works best in flat, open areas with little vegetation.
The wire-drag method is based on the relationship between the length of the wire between two survey markers and the amount of wire that is in contact with the ground at anyone time. Changes in the location or length of wire in contact with the ground show a change in elevation. Most surveyors use a wire that is 1/16-inch to 1/8-inch thick.
Equipment Required for Wire-drag Surveying
The following are the basic components of a surveyor’s field kit used for wire-drag surveying:
- Tension meter: A field strength meter can be used to measure the electrical resistance in the wire. The computer takes the reading from the field strength meter and uses it to calculate the amount of tension in the wire.
- Drag wire spool: The wire spool is made of fiberglass or plastic and is designed to hold large spools of wire. Surveyors use a compact car or boat that is towed behind the survey marker to drag the large spool of wire.
- Drag wire: The wire is normally made of stainless steel, monel, or other low-copper-content materials. The drag wire comes in different diameters and is several thousand feet.
- Vehicle: Most surveyors use 4-wheel drive vehicles that have a towing hitch to tow the survey markers and the car that is attached to the back of the vehicle to pull the drag wire.
Steps for Wire-drag Surveying
The following are the steps for wire-drag surveying:
- Set up the Wire: Surveyors attach the drag wire to the survey marker and let the wire unroll off the spool. Surveyors measure the amount of cable between the two survey markers and let out just enough cable to ensure the wire is dabbing the ground.
- Drag the Wire: The vehicle with the survey markers attached to it and the drag wire attached to the back of the vehicle will begin to move forward, dragging the wire across the ground.
- Calculate the Difference in Length of Wire: As the vehicle moves forward, a computer records the amount of cable that is between the two survey markers. The computer records the amount of cable as the length of the wire that is in contact with the ground.
- Estimate Volume of Shifting Material: The surveyor will use the difference in length of wire from one point to another to estimate the amount of soil that has been moved and determine the volume of earth that has been displaced.
- Estimate Change in Elevation of Surface Material: The surveyor compares the difference of wire from one point to another to locate areas of dips or swells on the ground surface.
Step 1: Set up the Wire
The first step in wire-drag surveying is to set up the wire. Two wires are often used in wire-drag surveying, each being 5 to 10 times longer than the distance between the survey markers. The wires should be 1/16- to 1/8-inch diameter, as smaller wires may break easily and larger wires are more difficult to handle. Stainless steel alloy is the best wire material for surveying because it has excellent corrosion resistance and high coefficients of friction. The ends of the wire can be smooth or crimped to prevent fraying and facilitate attachment.
Step 2: Drag the Wire
Drag the wire is the second step in wire-drag surveying. The wire is attached to the survey marker with a clip-on device to allow the wire to swing. The wire should be dragged behind the survey marker at a rate of 3 to 5 feet per second to prevent the wire from being broken by rocks or tree roots.
Step 3: Calculate the Difference in Length of Wire
The third step in wire-drag surveying is to calculate the difference of the wire. The surveyor records the starting and ending points for the wire. Next, she determines the difference between the beginning and end of the wire with a tape measure. The difference of the wire indicates any dips or peaks in the ground that changes in elevation or changes in the volume of soil may cause.
Step 4: Estimate Volume of Shifting Material
The fourth step in wire-drag surveying is to estimate the volume of shifting material. If there is a change in the wire’s length, the surveyor can estimate the volume of the ground that has shifted by multiplying the difference in the length of the wire by the cross-sectional area of the wire.
Step 5: Estimate Change in Elevation of Surface Material
The fifth step in wire-drag surveying is to estimate the change in elevation of surface material. If changes in elevation are indicated by a dip in the wire, the surveyor can estimate the amount of elevation change by measuring the distance of the dip in the wire.
Limitations of Wire-Drag Surveying
The wire-drag method works best in open areas with few obstructions. The wire must be in contact with the ground at all times for the method to work.
Ideal Soil Conditions
For the wire-drag method to be effective, the soil must have a low clay content. Most soils have some clay content, which makes them unsuitable for the wire-drag method.
The wire-drag method works best in dry, non-clay soils. Heavy rains or wet conditions reduce the effectiveness of the wire-drag method.
The wire-drag method works best in areas with little or no vegetation. The method cannot work when the ground is covered with grass or other vegetation because the wire will not be in contact with the ground.
The wire-drag survey can be used in many types of terrain, but it works best in areas with loose, sandy soils that are free of large rocks or tree roots and low-precision surveys of surface features, such as changes in water levels in a river or a new water well.
09. Lead Lines and Sounding Poles
Lead lines and sounding poles are tools that were historically used to measure the depth of water. Lead lines were typically used in shallower waters, while sounding poles were used in deeper waters.
Lead lines consisted of a length of rope with a lead weight attached to one end. The lead weight would be dropped into the water and the depth would be marked on the rope at the point where the lead weight hit the bottom.
Sounding poles were similar to lead lines, but they comprised a longer pole with the lead weight attached to the end. The sounding pole would be lowered into the water and the depth would be marked on the pole at the point where the lead weight hit the bottom.
A Brief History of Lead Lines
Lead lines and sounding poles are no longer used today, as modern technology has made more accurate depth-measuring tools available.
The use of lead lines and sounding poles has declined since the 19th century with the advent of echo sounding. Echo sounding uses sound waves to determine the depth of water. It is a more accurate method of measuring depth than lead lines or sounding poles and does not require the use of a physical object, such as a lead weight, to be lowered into the water.
Echo sounding is now the preferred method of measuring water depth and is used by recreational and commercial vessels.
How Lead Lines Measure Depth
Lead lines were used to measure the depth of water by lowering a lead weight into the water and marking the depth at the point where the lead weight hit the bottom. The lead weight would be allowed to sink to the bottom and then pulled up until it was level with the surface of the water. The depth would then be marked on the lead line at the point where the lead weight was level with the surface.
The lead weight would be lowered again and the process would be repeated until the entire length of the lead line had been marked with depth readings.
How Echo Sounding Works
Echo sounding works by sending a sound wave down into the water and measuring the time it takes for the sound wave to bounce back to the surface. The depth of the water can then be calculated based on the time it takes for the sound wave to bounce back.
What Is the Difference Between Lead Lines and Sounding Poles?
Lead lines were typically used in more shallow waters, while sounding poles were used in deeper waters. This is because lead lines were only able to measure depths of up to about 100 feet, while sounding poles could measure depths of up to 1,000 feet.
Lead lines were also shorter than sounding poles, which made them more convenient to use in shallower waters. Sounding poles were typically used in deeper waters because they were able to reach depths that lead lines could not.
How Do You Determine the Placement of these Tools on Your Project Site?
There are a few factors to consider when determining the placement of lead lines and sounding poles on your project site.
- Water Depth: If the water is shallow, lead lines will be sufficient. If the water is deeper, sounding poles will be necessary.
- Project Site Size: Lead lines and sounding poles can be placed at intervals around the perimeter of the project site. The interval will depend on the size of the project site.
- Bottom Type: If the bottom is soft, lead lines may be the better option. If the bottom is hard, sounding poles may be the better option.
Lead lines are typically used in shallower waters with soft bottoms. Sounding poles are typically used in deeper waters with hard bottoms.
10. Difference Between Hydrographic and Bathymetric Surveys
Hydrographic and bathymetric surveys are two different marine survey methods. Both help to determine the depth or elevation of a body of water. However, they are used for different purposes and have different measurement scales. Understanding the differences between hydrographic and bathymetric surveys is essential for anyone who works as a marine engineer, captain, pilot, or any other job that requires working with boats on water.
When it comes to surveying the ocean floor, there are two main types of surveys: hydrographic and bathymetric. Both have their own unique benefits, but which one is right for your needs? Here’s a quick rundown of the difference between hydrographic and bathymetric surveys.
Hydrographic vs. Bathymetric Surveys
Hydrographic surveys are typically conducted from the deck of a boat, using specialised equipment to measure the depth of the water. This type of survey is typically used for navigation, as it can provide detailed information about the shape and depth of the ocean floor.
Bathymetric surveys are conducted using sonar technology, which can map the ocean floor in greater detail than a hydrographic survey. This type of survey is often used for scientific purposes, as it can provide information about the topography of the ocean floor.
How Do Bathymetric Surveys Work?
Bathymetric surveys are conducted using sonar technology, which works by sending sound waves into the water and measuring the time it takes for the waves to bounce back. This information is then used to create a map of the ocean floor.
Bathymetric surveys are typically conducted using a boat-mounted sonar system, which comprises a transducer that emits sound waves and a receiver that listens for the waves that bounce back. For example, the multi-beam echo sounder is a type of sonar system that is commonly used for bathymetric surveys.
The data collected by the sonar system is then processed and used to create a map of the ocean floor. This map can be used for a variety of purposes, such as navigation or scientific research.
What Are the Benefits of Bathymetric Surveys?
Bathymetric surveys have a number of benefits, including:
- They can provide detailed information about the topography of the ocean floor.
- They can study the effects of waves and currents on the ocean floor.
- They can be used to find new areas for fishing, oil and gas exploration, and other commercial activities.
Which Survey Is Ideal for You?
So, which type of survey is right for you? If you need detailed information about the shape and depth of the ocean floor, a bathymetric survey is the way to go. If you’re just looking for general information about the ocean floor, a hydrographic survey will suffice.
Autonomous Hydrographic Data Collection
If you’re looking for a more efficient way to collect hydrographic data, consider using an autonomous data collection system. Autonomous data collection systems are designed to collect data without the need for a human operator. This can be a great way to save time and money while still getting the data you need.
Benefits of autonomous hydrographic data collection include:
- Reduced operational costs: Autonomous systems may be used to conduct surveys at a fraction of the cost of traditional methods.
- Increased efficiency: Autonomous systems can frequently gather data more rapidly and efficiently than traditional surveys.
- Improved safety: Autonomous systems can reduce the risk of injuries associated with traditional surveys.
- Enhanced data accuracy: Autonomous systems can give more accurate information than conventional surveys.
If you’re interested in using an autonomous data collection system for your next hydrographic survey, contact us today. We’ll be happy to discuss your options and help you find the right solution for your needs.
Contact us today to learn more about our hydrographic surveying services.