River grading is a scale which allows canoeists and kayakers to rate the relative difficulty of a stretch of river, or of a specific feature like a white water rapid. Rivers in the UK are graded from one to six.
Most of the waterways in London are flat or Grade 1. Weirs and other features on these waterways cannot easily be graded, and some can be extremely dangerous. Fortunately such features can usually be easily avoided. If in doubt, always avoid.
The following river grading system is the one used on the UK Rivers Guide Book – the leading kayaking forum in the UK.
The UK river grading system
Moving water, unobstructed and without technical difficulties. There may be small waves and riffles to challenge the paddler.
Waves, small stoppers and other minor obstructions such as rocks to avoid. Eddies and cushion waves may be strong.
Waves, stoppers and technical difficulties are more severe. There may be drops and powerful constrictions. The main distinguishing factor of Grade 3 water is that the paddler will have to follow a recognisable route to avoid obstacles and hazards.
Severe waves, drops, stoppers and other obstructions. The route is not easily recognisable and will usually require careful inspection from the boat or bank. Grade 4 encompasses a wide range of rivers, from those with pool-drop rapids to those with extended continuous rapids; so there is a huge variation in difficulty. It is common to distinguish easier grade 4 rapids by grading them as 4- and harder rapids as 4+ (or in some cases, 3/4 or 4/5).
Extremely difficult rapids with precise and technically demanding routes to be followed. Stoppers, currents and waves will be powerful and inspection is essential.
All of the above carried to extremes. Grade 6 usually means unrunnable rapids, which may just be possible in certain conditions.
Image credits: G1,2 & 5 courtesy of Dan Tattersall, G3 courtesy of Bobby Chen and G4 courtesy of Marie Czajkowski.