There are regular questions in the forums (OzCanyons on Facebook, Australian Canyoners) around whether to go canyoning, or to do a certain canyon after rain, or when rain is forecast.

This page aims to give some pointers around that decision. Note that a significant number of the deaths in canyons around Sydney have been due to high water. See the accident reports at: https://ozultimate.com/canyoning/canyoning_deaths.htm if you need any confirmation of this. The canyons will be there tomorrow. If you make poor choices, you might not be.

Also note that the NPWS Adventure Sports Safety page says:

"Avoid canyoning, climbing, caving and abseiling after heavy rain or if rain is forecast. Surfaces can be slippery and rocks may be dislodged. High water flows are dangerous and can create unexpected hazardous conditions."

The first thing to note is that this information relates to the sandstone canyons of the Greater Blue Mountains. It's not for other areas - Kanangra, Bungonia, Macquarie Pass, North Coast. Different areas have different rock types, elevation profiles and rainfall patterns, and guidelines for one area are unlikely to be applicable elsewhere. For example, Kanangra has higher flows for many days longer.

The second thing to note is that Blue Mountains sandstone canyons are not moving water canyons. Blue Mountains canyons are low flow canyons. High flow conditions in low flow canyons creates risks that are not present in canyons that are normally high flow. I would strongly advise against even experienced whitewater canyoners attempting to enter a Blue Mountains sandstone canyon during a flood event. Keep in mind that track notes for Blue Mountains canyons have been written with low flow in mind, so hazards from higher flow, like dangerous hydraulics, are generally not known and not listed.

A northern Blue Mountains canyon in higher flow

Canyoning after rain

Before you go

  • Water levels in sandstone canyons generally go up and down quite quickly. If no further rain is forecast, as a rule of thumb:
    • small catchment canyons (say 3 km2 or less) will probably be OK by around 24 hours after heavy rain
    • medium catchments (say up to around 10 km2) by 48 hours
    • larger catchments, such as the Wollangambe, may take 72 hours - or more - to go down
  • Be wary doing canyons like Hole-in-the-Wall, which drains into the Bungleboori, or the various canyons entering the Wollangambe after rain. You will have to negotiate a much larger canyon on the exit.
  • Mt Tomah and to a lesser extent, Mt Wilson, are basalt topped mountains, so the canyons draining off those areas will have higher flows for longer than those that are just in the sandstone areas.
  • Each rain event is different - if there has already been rain prior to the heavy rain event, then levels will take longer to drop than if it has been very dry

Once you've started

  • There is no shame in walking in and having a look, while being prepared to cancel the trip and walk out again. Checking the actual water level is an excellent learning opportunity
  • If you walk into the start of the canyon, keep in mind that there will probably be more water flow at the end. Make sure any decision to continue considers this. Also keep in mind that narrow sections will channel the flow, so it helps to know the canyon and be aware of possible pinch points in advance.
  • The volume of water that it is safe to wade or swim through can be much higher than the volume of water that it is safe to descend a waterfall under, or a cascade through boulders. Again, being familiar with the canyon and its obstacles at lower water levels can help make good decisions at higher levels.
  • If you do decide to venture into a canyon after rain and find that you get to a dangerous point that you can't easily exit from, consider waiting. Water levels will likely continue to drop and may get to a safe level. Unless you cannot get dry/warm, this is likely to be a better option than trying to negotiate a dangerous obstacle.
  • Also remember that if you are in a canyon after heavy rain has fallen, other risks will be elevated. These include logs and boulders having shifted, anchors damaged, and increased chance of rockfall and landslip

Canyoning when rain is forecast

Understanding the forecast

A band of thunderstorms across the Blue Mountains
  • Make sure you understand rainfall forecasts. Rain spread out over an entire day is typically much less dangerous than heavy rain in a short space of time. Check the 3-hourly forecasts (or hourly where available) to get an idea of this. 10mm of rain in a day will make water levels go up a little, 10mm of rain in half an hour may well cause flash flooding.
  • First and foremost, keep in mind that a forecast is just that - a forecast. If the forecast rainfall from the BoM says 5-10mm, this means that there is a 75% chance of more than 5mm and a 25% chance of more than 10mm. It does not tell you what the maximum rainfall might be. Depending on the weather pattern, it could be 12mm, it could be 20mm, or it could be 50mm! Make sure you're prepared for higher than forecast rainfall.
  • Less than 5mm of rain over a day will make minimal difference to most sandstone canyons, beyond everything being wet. Even 10mm of rain won't do much unless the rain falls in a very short space of time, or the catchment is saturated already. Beyond 10mm, you'd want to start being careful.
  • Consider the type of rain forecast:
    • If the forecast is for possible thunderstorms, these often start building around the middle of the day, and hit in the early to mid-afternoon. Consider doing a short canyon that you can be out of the constriction by lunchtime - while remembering that storms can come at any time! Remember also that even if you are out of the canyon when a storm hits, being outside at all in a thunderstorm can be very scary and dangerous. I've been caught outside three times in a thunderstorm, with no protection, and each time was absolutely terrifying. Sometimes there is nowhere to hide.
    • If the forecast is for steady rain, consider a canyon with a very small catchment. Jugglers, Better Offer (Magnifying Glass) and Tiger Snake are a few canyons which have very small catchments and which won't flood in light rain.
    • Go north and west - for coastal type weather patterns, the Blue Mountains often gets drier the further north and west you go. Often, Newnes will be dry when it is still raining at Mt Tomah (=Claustral).

Before you go

  • Ensure you know the canyon well:
    • Where are the standard exits, and any other possible escape spots?
    • Do these exits get you out, or are you just in another canyon?
    • Are there any very narrow bits that could cause problems?
    • Are there wide sections that you will be safe in even if water levels rise?
    • How long are the constricted sections?
    • How long will it take you to get through the constriction?
    • Will the abseils cause problems in high water?
    • If you don't know the answers to these questions, then you should reconsider your canyon. Don't do a canyon for the first time in bad weather.
  • Consider your party:
    • Keep your group small
    • Take experienced canyoners that can move quickly and efficiently
  • Keep in mind that any canyon - even tiny catchment canyons - can flash flood given enough rain.
  • Keep your options open. Forecasts generally get more accurate the closer you get. Check and re-check forecasts the morning of the trip and be prepared to have a fallback plan if the forecast has deteriorated.

Once you've started

  • Be prepared to turn back before a point of no return if the weather is worse than forecast.
  • If you know or suspect there are other parties ahead of you:
    • Factor additional time in for waiting at obstacles
    • Consider turning back if the extra time adds unacceptable risk
  • Once in the canyon, keep your eye on the ball. Watch for bail-out points as well as storm activity. Have a plan ready in your head at all times for what to do if rain or a storm hits.
  • Keep an eye out for changes in the water conditions. Debris floating in the water, or brown cloudy water can be advance indicators of a flood. Look to make for higher ground, or for escape options.
  • If you have committed to a canyon and you are confronted with rapidly rising water, you need to make decisions quickly. Do you go forward, go back, or try to climb to higher ground where you are. This is where your pre-existing knowledge of the canyon becomes critical. Often it is best to try to find higher ground and shelter and sit out flooding. Water levels can go up and down very quickly.

In general

  • Remember that injuries or incidents can occur at any time, and the impact of these will be magnified if there it is raining, or storms are forecast. An injured party member will make moving at speed difficult or impossible - possibly even moving at all.

Specific Canyons

Empress Canyon

Despite a relatively small catchment, Empress is a risky canyon when rain is forecast. The catchment runs off the streets and gardens of Wentworth Falls, and as a result, flash floods easily. It also has a dangerous hydraulic at the final pool.

Claustral

Claustral in slightly higher water is reasonably safe. You can largely stay out of the flow on the three main abseils, as well as most of the problems in the lower section. The main challenge in high water is the boulder pile just before the first abseil in the lower section.

Serendipity/Why Don't We Do It In The Road?

A relatively popular canyon when rain is forecast, Why Don't We Do It In The Road? has a fairly small catchment. You can escape just before the lower constriction if weather is closing in or water rising, and at the end, you can traverse along a narrow ledge to exit, avoiding entering the much larger Wollangambe.

Upper South Bowens

While Upper South Bowens has a reasonably large catchment by the time you reach the exit, the canyon has no really narrow sections, and the obstacles can largely be avoided out of the flow. A fairly good one after rain.

Dalpura

Dalpura has short canyon sections separated by more open sections of creek. The canyon sections are not particularly constricted and it is easy to escape the narrow bits, so reasonably safe in wet weather or after rain.

Jugglers / Better Offer (Magnifying Glass) / Tiger Snake

As noted above, Jugglers, Better Offer and Tiger Snake are all good ones in light to moderate rain, due to very small catchments.

Canyons like Hole-in-the-Wall and ones on the northern side of the Wollangambe (Whungee Wheengee, Water Dragon, Geronimo) empty into larger canyons and are best avoided in/after rain. Likewise with Breakfast Creek emptying into Rocky Creek - there is a section going upstream in Rocky that is difficult in higher water.

Wrap Up

Canyoning in the rain can be fun. It can also be dangerous. The pointers on this page are just that - pointers. They are no substitute for experience. You won't drown or get washed away in a flash flood sitting at home! (Well probably not!)