Simone Lawson
Low-head dams are deceptive structures that pose significant hazards both above and below them. They are often loaded with debris and create dangerous currents that can trap and drown people, boats, or other objects that enter the turbulent water below the dam. These currents can also swamp vessels, pulling them under the water. Due to their relatively calm appearance, they have been known to cause numerous incidents of drowning.
| Characteristics | Values |
|---|---|
| Height | Typically less than 20 feet |
| Appearance | Deceptive, calm water above and dangerous currents below |
| Hazard | Both above and below the dam |
| Hazard type | Recirculating currents, turbulent waters, backwash, hydraulic jump, hydraulic roller effect |
| Safety | Warning signs, markers or buoys are usually present |
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What You'll Learn
- Low-head dams are hazardous both above and below the dam
- They are deceptive in nature due to calm water above and dangerous currents below
- They are often loaded with debris, such as tires and logs
- They can create a life-threatening situation, despite not looking dangerous
- Low-head dams are known as drowning machines
Low-head dams are hazardous both above and below the dam
Low-head dams are hazardous due to the strong currents and backwash they create, which can trap and drown people, boats, and other objects. These dangers exist both above and below the dam, and the dam's small size and drop can make it deceptively dangerous.
From upstream, low-head dams are difficult to detect and may not appear dangerous. However, they can create life-threatening situations due to the recirculating currents and turbulent waters they generate. These currents can trap boats and individuals, pulling them under the water and pushing them towards the face of the dam. The backwash or recirculating current is formed when water flows over the dam, creating a hydraulic jump or roller effect, which can trap objects and force them underwater. This cycle can be challenging to escape, even for experienced swimmers or rescuers with personal flotation devices.
The dangers of low-head dams are compounded by the presence of debris, such as tires, logs, rocks, and steel bars, which can pose additional risks to those trapped in the currents. During periods of high water and heavy rains, the backwash current's reach extends downstream, increasing the potential hazards. Even small low-head dams that may appear harmless at low water levels can become deadly when river levels rise.
From downstream, the dangers of a low-head dam may not be immediately apparent. The water around the dam may appear tranquil, but it can hide strong turbulence and currents that can pull victims underwater and towards the dam. It is important to be aware of potential hazards and take precautions when approaching low-head dams, such as paying attention to warning signs, markers, or buoys and maintaining a safe distance.
The design, depth, volume, and velocity of water flowing over a low-head dam all contribute to the risks posed to boaters and individuals. It is crucial to prioritize safety when navigating near low-head dams and to follow safety measures and guidelines to minimize the potential hazards associated with these structures.
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They are deceptive in nature due to calm water above and dangerous currents below
Low-head dams are deceptive in nature due to the calm water above and dangerous currents below. These dams are known for creating hazardous conditions both upstream and downstream. The water above the dam may appear tranquil, luring unsuspecting victims closer, but the water below is turbulent and can trap people, boats, and other objects in a continuous cycle of recirculation. This is known as a "hydraulic jump" or a "backroller/boil", and it poses a serious risk of drowning.
The deceptive nature of low-head dams can be attributed to the flow patterns they create. The structure of the dam allows water to flow over its crest, creating a vertical drop. This drop causes a hydraulic current, which is a backwash that can trap and re-circulate anything that floats, including boats and people. The backwash pulls victims towards the face of the dam, where they are washed down under the surface to a point downstream called the "boil". The cycle then repeats, making it extremely difficult to escape.
The dangers of low-head dams are not always obvious or well-marked. Warning signs, markers, or buoys may not always be present, and even experienced boaters can be caught off guard by the unpredictable water currents. The calm water above the dam can give a false sense of security, leading to a higher risk of drowning. It is crucial to approach low-head dams with caution and to be aware of the hazards they present.
Additionally, low-head dams can be hazardous for all types of boats, including inboard-powered and jet-powered boats. The strong currents and eddies created by the dam can cause boats to capsize or be pulled under the water. It is not safe to cross a low-head dam at any angle, especially not at a 45-degree angle to its face. The unpredictable nature of the currents can lead to a loss of control and accidents.
While low-head dams serve important purposes such as water management, irrigation, and flood control, it is crucial to prioritize safety when in their vicinity. Understanding the deceptive nature of these structures and the risks they pose can help prevent accidents and fatalities.
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They are often loaded with debris, such as tires and logs
Low-head dams are man-made structures that are built within a river or stream channel, spanning from bank to bank. They are designed to allow water to flow continuously over the top. They are typically between 1 and 15 feet tall, though taller ones exist. Despite their small size, low-head dams are extremely dangerous. They are often loaded with debris, such as tires and logs, which can pose additional risks to those who get trapped in the dam.
The recirculating currents and turbulent waters below these dams can swamp vessels and pull people and objects underwater. This can lead to drowning, even for strong swimmers. The backwash or boil, a strong circular current at the base of the dam, can trap boats, boards, and people, pulling them underwater. The continuous motion of water over the top of the dam creates a dangerous vortex at its base, earning low-head dams the nickname "drowning machines".
The presence of debris, such as tires and logs on the surface, and rocks and steel bars just below, can further complicate matters. These objects can pose additional dangers to those who get trapped in the dam's currents. During periods of high water and heavy rain, the backwash current becomes more powerful and extends further downstream, increasing the risk of accidents.
Low-head dams are often difficult to detect, especially from upstream. They may not appear dangerous, with the water around them looking tranquil and inviting. However, the strong currents and turbulence created by these dams can be life-threatening. It is crucial to pay attention to warning signs, markers, or buoys and maintain a safe distance from low-head dams.
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They can create a life-threatening situation, despite not looking dangerous
Low-head dams are often difficult to spot from upstream and are usually not marked by warning signs, markers, or buoys. They are also referred to as "drowning machines" due to the hazards they pose to swimmers, kayakers, and other water recreationists. Despite their small size and drop, they are considered the most dangerous type of dam.
Low-head dams create a backwash or recirculating current that can trap boats, boards, or individuals and pull them underwater. The backwash is a hydraulic current that forms below the dam when water flows over a drop, creating a hole or hydraulic at the base. This backwash can trap objects, including people, and force them underwater, pushing them away from the dam and then circulating them back to the face of the dam. The circulating motion repeats, creating a cycle that is nearly impossible to escape.
The recirculating currents and turbulent waters below low-head dams can swamp vessels and pose a serious risk of drowning to boaters and swimmers. These currents can be unpredictable and even deceive experienced boaters. The concrete walls at the sides of the dam face can further block exit routes for individuals attempting to escape. Additionally, the spillway and turbulent water above the dam can pose risks to boaters and individuals who may be swept over the dam.
During periods of high water and heavy rains, the backwash current's problems worsen, and its reach extends further downstream. Even small low-head dams that may appear harmless at low water levels can become deadly when river levels rise. It is crucial to exercise caution and follow safety measures when navigating near low-head dams. Approaching these dams at certain angles, such as a 45-degree angle, can be extremely dangerous, and it is not safe to cross them at any angle.
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Low-head dams are known as drowning machines
Low-head dams are small structures that impound a small amount of water and span the width of a river or stream. They are usually made of concrete and are designed to raise the water level upstream of a river. While they may not appear dangerous, they are in fact the most dangerous type of dam and are known as "drowning machines".
Low-head dams create a strong circular current, known as a backroller or the boil, at the base of the dam. This backroller can trap boats, boards, and people, pulling them under the water. The recirculating currents and turbulent waters below these dams can swamp vessels and cause people to drown. The turbulence of the hydraulic jump entrains a lot of air, reducing the buoyancy of a swimmer. The water is often cold, increasing the potential for hypothermia and further disorientation.
The presence of a low-head dam can lead to the formation of a hydraulic jump, which creates a recirculating current and a hydraulic roller effect just below the dam. These conditions can trap and drown people, boats, or other objects that enter the turbulent water below the dam. The spillway and turbulent water above the dam can also pose risks to boaters and individuals who may be swept over the dam. These dams are usually loaded with debris, such as tires and logs on the surface, and rocks and steel bars just below the surface, creating additional dangers for those trapped.
Low-head dams are often difficult to detect and do not appear dangerous. They pose significant hazards both above and below them due to dangerous currents and the potential for trapping individuals and boats. It is crucial to understand the dangers of low-head dams and to observe safety measures when navigating near them.
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Frequently asked questions
Yes, low-head dams pose significant hazards both above and below them. They create dangerous conditions for anyone near the dam.
The pooling of water above the dam can lead to drowning risks. Below the dam, the water creates a strong downstream current known as a hydraulic jump or recirculation zone, which can trap individuals, boats, or other objects.
Water flowing over a low-head dam creates a strong circular current, known as a backroller or the boil, at the base of the dam. This can trap boats and individuals and pull them under the water.
Low-head dams should be approached with caution and it is important to be aware of the hazards they present. Always pay attention to warning signs, markers, or buoys and keep a safe distance.
