Written by Wild Asia on 30 Mar 2005
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Each river is a highly complex, dynamic individual. Some are friendly. Some less so. Sitting in a raft or kayak and cascading down the rapids is only part of the fun. The real thrill comes from utilising one's experience and skill to read and figure out the best course to tackle the river. Since the white water rafter must work with the current rather than fighting it, understanding water flow is essential to having a successful, safe and enjoyable ride.
The International River Grading System
The first and basic step in understanding a river is knowing what previous rafters have said. This is why the International River Grading System was introduced. The system is a quick and simple guide which rates the difficulty of a particular stretch of river. However, it is just that - a guide. It is the responsibility of each rafter or group leader to decide on the day whether or not a section is appropriate for their personal experience and skill level.
Grade I: Easy
Rivers with long, flat stretches of slowly moving water with occasional simple rapids, or ripples. Waves are low, with obstructions obvious and easy to steer. No technical training needed and self-rescue is easy.
Grade II: Novice
Fairly frequent rapids, usually with moderate regular waves or easy eddies, which are evident without scouting. Manoeuvring may be required but obstructions easily avoided with some training. Swimmers are seldom injured and group assistance, while helpful, is not needed.
Grade III: Intermediate
The proficient white water rafter will seek out this grade of water. The main distinguishing factor of Grade 3 water is that the paddler will have to follow a recognisable route to avoid major obstacles and hazards. Rapids numerous with fairly high irregular waves, broken water, and eddies. Often a series of steps with a steep gradient. Course not always easily recognisable. Inspection from the bank advisable for inexperienced parties. Large waves can be avoided and tight and complex manoeuvring is required. .
Grade IV: Advanced
Very difficult, long extended stretches of rapids with high irregular waves, difficult broken water, eddies and holes - course often difficult to recognise. Much of the grade will be because of waterfalls or drops up to 3m high. Channels often narrow and steep sided. Scouting necessary the first time down. May have high unavoidable waves and some rapids may require 'must' moves to avoid dangerous hazards. Rescue requires group skills.
Grade V: Expert
Water features are similar to Grade IV but they are larger, more violent, and less predictable. Drops may contain holes or steep, congested chutes. Course always complex and very difficult to choose and will involve significant risk to the canoeist and equipment. Scouting is mandatory but often difficult. There will always be a need for bank support for safety and rescue is difficult even for experts.
Grade VI: Extreme
This is at the extreme limit of white water. Definite risk to life. Rescue may be impossible. This does not include suicidal unrunnable drops (eg. Niagara Falls) but may include drops only occasionally run at favourable water levels, after close inspection, with a team of experts as bank support.
Drawbacks to the Guide
Naturally, rivers do not fit easily into a single category, and individual interpretations can vary. For a more accurate assessment of a river's danger and difficulty it is important to learn details about the nature of that particular river's rapids, its hazards and potential consequences. Take into account the river's volume, velocity and depth - a river's difficulty often rises with its water level. Also, rafters should note the potential danger or likely consequences involved to both themselves and equipment if something goes wrong. Danger increases dramatically if for example, the river is remote, rocks are sharp, there are trees or obstructions in the water, or the water is extremely cold. A Grade V rapid may be far less dangerous than a Grade I river full of crocodiles.
Reading Rapid Features
To truly assess a river's friendliness, experienced white water rafters read its basic features by looking for visible signs on the river. This is done both while rafting, concentrating on where to go, and while scouting ahead overland to gauge a run. The signs to look for include visible rocks, water features and hazards. Of course, reading a river isn't simply as easy as reading this article. It takes proper training, experience and practice. However, here is a short introduction to some of the things experienced rafters look for.
Visible Rocks
Experienced rafters know that rocks rarely pose a significant threat. They can be spotted easily and avoided. If they are hit, the river current pushing against the rock creates a cushioning effect that slows the boat. Then, with a little paddle work, it is simply a matter of pushing the boat back into the current. What rocks can do is indicate which way the current is headed. Figuring out why the current is deflected and which way it goes is the key to reading a rapid.
Chutes
Chutes are features of smooth water flowing through a channel, characterised by V-shaped ripples pointing downstream. They indicate good course. On the other hand, a course where the V-ripples point upstream is not a chute, but a rock, and should be avoided.
Eddies
An eddy results from water curling to fill the void behind a rock or other obstacle. Often the current in an eddy is very calm and sometimes even flows upstream. It provides a peaceful rest stop before preparing for the next rapid.
Holes
Submerged rocks can be recognised by either the smooth dome of water flowing over them, or if they're deeper, the turbulent water created just downstream. This turbulence is called hydraulics or holes. The friendliest shallow holes create waves in front of the rock. However, there are numerous different types and names of hydraulics, some very dangerous, depending on the gradient, volume of water, and size of the rock. Common names include: ledge hole, souse hole, wave, stoppers, reversals, keepers, and pour-overs
If the water pouring over the rock has only a horizon line and little frothy waves, chances are it is a deep ledge hole or souse hole. With these holes water pores in from all sides and also back on itself, creating a backwave. In large ledge holes, the backwave can be very powerful and hard to escape. These holes are dangerous and should be avoided.
Hazards
Anything in the water is dangerous: trees, branches, old cars, bridge pylons. The experienced rafter continually scans the river, watching for anything unusual. A strainer is an obstruction, usually a tree branch, that is lodged in the river but allows water to flow past. These are among the most serious trapping hazards for rafters.