Even after a normal storm, its possible for canyons to change, but after a major storm event, the first groups through a canyon need to be prepared for significant changes. Its up to you to make sure you’ve got sufficient experience, skill and equipment to deal with those changes and to let the community know if there’s anything significantly different.
Changes to pools
The most common change to a canyon after a big storm is in the pools. Sometimes, a flood will completely remove all the gravel/boulders in a pool, leaving behind a deep, clean bedrock pool. Sometimes you’ll even find new jumps that were previously impossible.
Other times, you’ll find pools that were super deep are now ankle deep, or boulders have shifted underwater, or trees have fallen in. This reminds us why it is important to check every pool with a mask before jumping, especially after any kind of rain event.
Part of the though process for situating an anchor is for it to be protected from damage during a flood, but in a major storm event, the water can get so high that anything is possible. The action of the flow can loosen nuts on bolts, and eventually remove the hangers. Also, debris such as rocks or log can smash bolts, leaving them completely unusable.
If it’s a committing canyon, then you’d need to assume that all of the anchors could have been ruined and take enough gear, skills and time to replace anchors enough to get you down safely.
Changes to log jams
As well as high water, major storms usually have high winds, so there’s potential for trees to fall in, creating new log jams. These new log jams will be less stable than ones which have been there for some time, so treat them with extreme caution.
Only one person at a time should be near or on the log jam, and should move slowly and carefully. These log jams can often create a dam, where gravel and other debris piles up, creating a false floor. The ‘danger zone’ of unstable floor can extend many meters up-canyon from the obvious log jam. Some are so unstable that nudging one key log could collapse the dam with dire consequences.
As well as new log jams, old ones can shift, become more or less stable or even disappear completely. Treat any log jam with the greatests of respect, as they are one of the most dangerous hazards in a canyon.
Slips, landslides and dams
It is not uncommon for heavy rain to create slips or landslides, which have the potential to partially and/or temporarily dam a river. This could be within the canyon, or more commonly above the canyon. These temporary dams could burst during the storm, or afterwards, sending a wall of water down the canyon. If you ever see a sudden water level rise, or a sudden discolouration of the water, then seek a high refuge point or escape the canyon immeadiately.
Like happened in Camp Creek near Wanaka, the whole canyon wall could even collapse during a storm, or even from an earthquake, leaving a dangerous, unstable rock pile to negotiate.
The key message is that canyons change, and they can change dramatically after a major storm event. The first group through after a storm needs to be well prepared for those changes, and should let the community know of those changes (or that its still the same!).
Guidebooks become out of date the second they are printed, so check online at the canyon page of the trip you’re planning on www.KiwiCanyons.org to see if there has been any updated information.