A common discussion across the Te Araroa groups is on the rivers that maybe encountered while doing this through-hike. In particular there are a couple of rivers in the Canterbury section of Te Araoa that are particularly hazardous and are often are pretty contentious. Overseas visitors have not always taken on board the knowledge and warnings of New Zealand locals and should it go wrong there is a real risk of death. My concern is that some people are not heeding the safety message, hence the reason for this post.
So what makes our rivers so deadly? The simple answer is our unique geology, topography and weather systems. These things themselves aren’t what kills people; but more often than not, it is people underestimating our rivers and making bad decisions is what makes our rivers killers.
New Zealand is basically a series of ridges that have uplifted in the South Pacific ocean. The islands have low-lying plains that suddenly turn into high ridges. We are surrounded by water, with 3 predominant weather systems that all crash into the country. The warm systems that blow from the West, that have usually come across Australia building in intensity as they cross the landmass, then those system pick up water as they come across the Tasman sea, then they hit the Western sides of the ranges, dumping the water. Warm, wet systems that come from the North East that have picked up a lot of water moving across the Pacific Ocean that dump water when they hit land and/or other systems that are moving through. Then we have the famous New Zealand “Southerly”, this is the cold, wet systems that blow up from Antarctica and across the Southern Ocean, often bringing rain and snow with them. When these systems are “lows” all of them bring some form of precipitation. Our mountains are steep and so are our valleys, water always heads the fastest way possible downhill. Due to these systems combining, the predominate system can slow down or speed up so at times people get caught out by relying on a weather report that they “saw a few days ago”.
Our geology and topography is because of land is uplifted from the ocean or volcanic (Rim of fire) so water tends to run off fast, and you only need to look at the Dec 2017 – Jan 2018 rainfall and drought that we are currently experiencing. The other side of this is that our rivers rise fast, and often our rivers have huge watersheds in areas that you may be no where near. Braided rivers also occur here, these often wide but multi-channeled rivers also have additional risks. Due to the uplifted nature of our topography weather systems roll off the sea and hit the high gradient hills and pretty much dump all the water they are carrying. With water always travelling downhill, and looking for the easiest path, as the erosion had produced most of our valleys and gorges there are often deep and gentile looking rivers that are in fact carrying huge volumes of water.
What makes water so dangerous? Although I generally held a healthy respect for water, just how dangerous really sunk in when I learnt that a 1 cubic meter of water is about 1 tonne (1000kg) of weight coming at you. I was chatting with a friend who said that an elephant (African) weighs about 2.7 tonne, the image of elephants charging down a river stuck.
So what does this actually mean?? I could bore you all to death with hydrodynamics and laminar flow, undercuts and eddies but I’ll put some of this in more practical terms. I also had a chat with Heather Grady. Heather is both the local Manawatu and the National Chair of Outdoor Training New Zealand, a Bush 1 and Risk Management Instructor. So I thought I would get her perspective as to why people underestimate our rivers. Heather has also been a long time supporter of what I have been doing in the outdoors and I am truly grateful for her support over the years.
|Heather Grady, OTNZ
(get that camera out of my face Antnz)
The rivers rise fast. In 2005 when I was doing “Swift Water Rescue” training as part of my Diploma of Adventure-Eco Tourism, Rafting unit, we were training in a local river. We were doing things like swimming across the river, swimming through strainers (logs etc caught in the river), tethered rescues, releasing foot entrapment; well the trainers ended up calling quits to the day at about lunch time. We knew it was raining both at the site and in the watersheds, but hey we were going to get wet anyway! Knowing that it was raining we had placed “markers” at the river’s edge, 2m out, and 5m out. We probably entered the river at about 10am, by the time it was 11.30am the 2m marker had disappeared, and the river was also quickly making it towards the 5m marker. Not only that but we had full sized logs coming down the river at us.
When I chatted with Heather she mentioned that she had seen a river go from the bottom of a farm fence to completely engulfing the fence within 20 minutes, while the sun was shining. Yes this means that the rivers also fall pretty quick too, so always be prepared to wait one out. Gorges, narrow valleys and canyons are something to be especially weary of if there is bad weather in watersheds, as the river rises there is simply no-where to go to try and get to higher ground. Another consideration if in these areas is that they will often end in a set of rapids or a waterfall, neither are where you want to be in a high-flow.
Braided Rivers add risk, a braided river is a river of many channels with lots of “islands” of (generally rounded) river stones, often if you have to ford these rivers you go from island to island through the channels. Although all New Zealand rivers change, these rivers and channels can change from day to day. Due to the often rounded nature of the rocks and shingle in these channels they can literally move under your feet in these rivers. These rivers also usually have large watersheds and you can be in a 30 deg C day, yet it is still raining in the watersheds and flooding will occur in the “main river”. So in context of the rivers mentioned, a recent Te Araroa group took the decision to cross the Rangitata River, it took them 2 hours and this river is known to be in full flood with no channels showing within an hour. So essentially you could be half way across the river, finding yourself on a shrinking island of shifting river bed.
I asked Heather why she thought both international tourists and “non-bush” people can get themselves into trouble in our rivers. It was an interesting conversation, which confirmed a lot of my thoughts.
|Rangitata River in “normal” flow
|Rakaia River in “normal” flow
|Rakaia River in flood
I asked Heather for her “Top 3 Pointers and her main message about New Zealand Rivers while out “in the field” the following is her response.
“When coming across rivers:
1. always assess the river – is it safe to cross? Depth, how deep is it at the deepest in the crossing point. Am I comfortable with that depth? Speed/flow, how fast is it going? Faster than walking pace is too fast. How much force will it be at its swiftest? Remember flow is a combination of speed and depth so a deep slow flow may be ok but deep and fast is not. Can you see the bottom? If not is it in flood? If not how can you pick the path or know depth? What is the run out? ie what will happen if lose your footing? Waterfall, rapids .. or shallows or a nice slow pool?
2. If it is safe to cross? Consider where to cross. This may not be at the official crossing point. Rivers change all the time and sometimes there is a better point, which may not be very far away. Even at a good crossing point. Take time to work out your line – how will you pass around big rocks for example. Understand hydrology eg the effects of rocks on water flow.
3. If the crossing is anything other than very easy then cross bind together as a group. If you are solo it is best to use a long strong stick to help you (taller than you, and strong enough to bear your full weight). Use this upstream as a third leg. Move only one of these 3 legs at a time.”
“Main message – if in doubt keep out. Remember there is no time you must cross a river. Wait it out if it is flooding or go back. Good planning means having shelter and enough food so you can wait it out. Have a torch so you can go back in the dark if necessary. Check the weather beforehand – maybe change your plans, different route, different time. Look at the map beforehand, what are your alternative routes if the rivers rise?”
|Land-based practice of “mutual support”|
Outdoor Training New Zealand offers River Safety courses (as well as other courses in outdoor safety), that cover both the theory and practical sessions on how to cross rivers and I highly recommend them to anyone planning to spend a significant time in the outdoors inNew Zealand. A full list of currently available courses and costs across the country can be found at: https://www.outdoortraining.nz/courses/courses.php
A huge thank you to Heather Grady for her time and expertise while I was researching for this blog!
Stay safe out there everyone! Remember to #thrivenotsurvive!