River Tracing Safety
The Risks and Hazards of River Tracing
River tracing, also known as river trekking or sawanobori, involves hiking, climbing, and swimming to navigate upstream through a river's course. While it offers a unique way to experience Taiwan's beautiful landscapes, it's crucial to understand the risks, and hazards involved, and the techniques used to avoid them.
General Hazards
Hypothermia
Hypothermia usually occurs due to prolonged exposure to cold water, especially when combined with lack of movement, and high caloric expenditure. Rivers with long gorges, deep pools without sun exposure, or located at altitude increase overall risk.
Tips: In addition to bringing adequate cold protection with you, a full rain suit can help mitigate the effects of evaporative cooling. Find out about the best ways to keep warm by reading the river tracing gear guide.
Don’t be like Yachi who went canyoning with just a bikini top and had to borrow someone’s raincoat.
Flash Floods
Flash floods occur when there is prolonged heavy rainfall upstream of a narrow waterway. A large watershed, and earth that is already saturated from continuous rain increases the risk of a flash flood occurring. During a flash flood there is a sudden increase in water volume (flow), and speed. Flash floods manifest as a wave of water traveling downstream which can increase water height by 1-2 meters or more. In Taiwan, flash floods result in multiple rescues each year, most of which are successful.
Tips: Flash floods are the most dangerous when you are unprepared for them. If it’s raining while you are river tracing, or if you think there may be inclement weather upstream of where you are, be ready for the possibility of a flash flood occurring. Make sure you are always aware of where you are in the river in respect to potential exits from the watercourse. As you move, keep an easy-to-reach escape route in mind. Avoid traveling through gorges and long pools. In the case of a flash flood, unless you are directly underneath a waterfall or have your line of sight blocked, you may have 10 seconds or so before the wave reaches you once you see it. Reach the banks of a creek and climb up 1-2 meters above the current water level and wait for the water level to recede.
When the water color starts to change, assume a flash flood is imminent. (Photo provided by George aka Shrek)
Falling Rocks
Features like canyons, gorges, and eroded sidewalls are extremely common in Taiwan’s rivers. In general, you are more likely to witness a minor rock fall than you are to see certain wild animals.
Tips: Always wear a helmet. Do not travel directly beneath rock fall areas if it can be avoided. If travel through rock fall areas cannot be avoided, travel in a way so that rocks are likely to launch over you as they bounce down a wall. One way to do this would be to hug a wall as close as possible where the chance of a direct hit is comparatively less.
Walking over recently fallen rocks on the side of a river. I should have my helmet on.
Minor Injuries
Cuts and light bruises are relatively common. Wearing gloves, high-top river tracing boots and long sleeve river tracing clothing helps.
Tips: Always carry a first aid kit in a waterproof bag. Proactively sign up for training in wilderness first aid.
Walking over recently fallen rocks on the side of a river. I should have my helmet on.
Taiwan’s Giant Hornets
Hornets build their nests in river valleys and on mountainsides between 0-2500 meters above sea level. Essentially every river in Taiwan is likely to have hornets nests in the vicinity or directly above the waterway. The most territorial and most dangerous species is the comparatively smaller black-bellied hornet or Vespa basalis, which can fly at speeds over 30 km/h and will chase trespassers for up to 100 meters. This species is known to become aggressive once trespassers pass within 5 meters of their nest.
It’s best to always back away from any nest encountered, and take the longest path around it that is possible.
Tips for dealing with Taiwan’s giant hornets:
Wear light-colored clothing and a light-colored hat to cover your hair, and spray mosquito repellent containing DEET.
When you enter the warning range of hornets, scouts will first come to check. Upon encountering a scout, be calm and wait for it to leave on its own. If the scout does not fly away, immediately leave quickly in the opposite direction from which the bee arrived. Do not wave your hands or clothing in an attempt to drive away hornets, as this may be seen as provocative behavior and may trigger a chase by the swarm.
When attacked, leave quickly. Do not panic, pay attention to the area around you, and leave as quickly as possible.
Sources: https://tfc-taiwan.org.tw/articles/9688; https://news.pts.org.tw/article/555855
Whitewater Hazards
Rope Entanglement
There is always an entanglement risk when attached to a rope and in water. This risk increases with water flow and complex currents. If a person becomes entangled in a rope, even in a relatively shallow area, there is a danger of drowning. Once a person is entangled, it's extremely challenging for them to free themselves, especially when their movement is restricted and they are combatting strong currents.
Tip: If working with rope in water, always have an easily accessible water rescue knife and be trained in self-rescue.
If you will be using rope in water and you haven’t taken a water rescue course, or practiced self-rescue, now is the time. Check out Commission Internationale de Canyon (CIC) Taiwan’s Facebook Page for each year’s course dates.
Low-head Dams & Recirculating Current
Low-head dams are among the most dangerous structures in rivers and have earned the ominous nickname "drowning machines". The primary hazard of low-head dams is the powerful recirculating current they create at their base. The geometry of some waterfalls can also naturally create this same hazard.
Mechanism of Entrapment (The Boil Zone): In a recirculating current, there is an area known as the “boil zone” where water is highly aerated and buoyancy is reduced. This area of water pulls objects back towards the dam or waterfall. Objects (or people) are then forced down with the flow of the water, brought back to the surface inside the boil zone, and pulled back again. Without external forces or effort, this cycle repeats, creating a nearly inescapable trap.
Visibility: Massive structures that take up the entire watercourse; relatively visible
Escape difficulty: Even strong swimmers with life jackets struggle to break free. The aerated water reduces the effectiveness of swimming motions. The uniform nature of the dam often eliminates escape routes to the sides.
Strainers
A strainer is an obstacle in a river that allows water to pass through but traps larger objects, including people. They are often formed when fallen trees, branches, or man-made debris are brought into the flow due to erosion or floods.
Mechanism of Entrapment: Strainers can pin a person against the obstacle, holding them underwater with the force of the current. The combination of the current's pressure and the physical barrier makes escape extremely difficult.
Visibility: Located in or above the waterline; relatively visible
Escape Difficulty: The force of water pushing against the trapped person or object makes extraction challenging. Self-rescue is nearly impossible. Rescuers must be careful not to become victims themselves when attempting a rescue.
The waterfall pool shown above is a dangerous area with multiple hazards. In addition to escaping from the top and bottom of the photo (orange), some water is escaping around the log between the boulders (pink). The log forms a strainer and there is potentially a siphon underneath the rock as well. Finally, the center of the pool is a boil zone with low buoyancy (red).
Siphons
A siphon occurs when a part of the water in the river flows through a hole under rocks, boulders, or other obstacles in the river. These areas, which may be very difficult to identify, occur often in Taiwan’s rivers. Siphons are considered particularly dangerous due to their often hidden nature, high entrapment risk, and the extreme difficulty of escape or rescue.
Mechanism of Entrapment: A strong suction force pulls objects or people underwater and towards the opening of the siphon. These openings may be too narrow for people to pass through but powerful enough to trap a limb or an entire body at their entrance.
Visibility: Siphons can be particularly dangerous because they may not be obvious to river tracers. Unlike more visible hazards like waterfalls or large boulders, siphons can be hidden and appear in seemingly calm areas. Not intuitive or easily visible
Escape Difficulty: Escaping from a siphon can be extremely challenging, often more so than from other hazards like hydraulics or eddies. The suction effect and confined space make any kind of rescue, even assisted, very difficult.
Notice how the water on the left of the chockstone doesn’t flow over the rock but disappears underneath (pink). This is a potential siphon. Some water exits normally on the right side of the chockstone (orange).
Undercuts
Undercuts are dangerous river features where water flows beneath a boulder, gorge wall, or other obstacle into a hidden underwater cavity. Often created where water is most forceful, such as the outside of bends, waterfalls, and high ledges.
Mechanism of Entrapment: Water flowing into the cavity will push objects into the undercut area, often at or below the water's surface.
Visibility: Can be spotted with careful observation; relatively visible
Escape Difficulty: Rescuing someone trapped in an undercut is extremely difficult and dangerous. If it’s an open undercut where water is pushed out and escapes in a linear direction, entrapment is less likely.
Notice how Cloud disappears underneath the rock below me for several seconds. The undercut pushes against the rock and even pulls back to the left. Cloud was lucky to aim farther away from the rock face as he floated, or he could have been caught in a circular current underneath the rock face.
Further Reading
This article from Canyonmag on river hydrology and river hazards covers water flow in greater detail and delves into how to overcome the obstacles mentioned above while canyoning.
River Tracing Safety Related Best Practices:
Get The Right Gear!
Always carry a helmet and wear felt-bottom waders. Bring a PDF for high-flow rivers, for multi-day trips, or if you aren’t a confident swimmer. Get more information by visiting our river tracing gear guide.
Research the River Prior to Heading Out!
Most popular rivers will have plenty of information come up if you Google the river name. For unknown areas, get your head around it ahead of time and research it using online topography tools. Make note of nearby hiking trails or roads. Make use of this information to inform how you will plan to escape in case of a flash flood.
Get Preemptively Certified in First-Aid!
Take a Wilderness First Aid, Wilderness First Responder or Wilderness Advanced First Aid course. Several different mountaineering safety organizations offer these courses multiple times per year in Taiwan.
Possible options: ZA Adventure WFA; Taiwan Wilderness Medical Association WFA; MTTiger Taiwan WAFA