A recent Wilderness magazine had a strange article about a group tramping down the Arawhata River. The article was written in the cliquey in-group style you get in tramping club newsletters. It seemed a bit out of place in a commercial magazine as the style leaves the reader disconnected. I wondered about editor Colin Moore's reasons for using it .
But anyway that's not what I'm writing about here.
Bad example of rivercrossing
What caught my eye was a photo of this group crossing a river using quite a dodgy version of the 'mutual support' rivercrossing technique. I've drawn a sketch showing the group's method of linking up in the river
This method of linking for a river crossing makes for much weaker support.
I'll explain why.
Mutual Support Rivercrossing Technique
In the standard 'mutual support' method, as shown below, the object is to provide a rigid line of support to the person breaking the current. With increasing force of current the person at the top end gets pressed against the next, who is locked into the rest of the line.
Even if the person at the top loses their feet they're still solidly held in place by the next person, with the interlocking arms across their backs. Their body is still breaking the current, sheilding the 2nd person and the extra weight pulling down on the 2nd makes their footing more solid.
This does happen reasonably often to parties crossing serious rivers. Usually the top person regains their feet fairly quickly and they carry on or back out as appropriate.
Illusion of support
In the arrangement pictured above, being held at arms length with no support at body level would mean the person at the top would be knocked over very quickly as the current increased. This is because the high grasp makes their shoulder the pivot point while the river is applying pressure against the lower part of their body. When they go over they would drop fully into the water, pulling the second person's arm down. The current would carry them down and across the front of the party.
The next person would then be exposed to the full current. But they also would be holding the full weight of the first person pulling them forward and down river. Because these are lateral forces and not just extra weight over their feet, they would be pulled over too.
Hence the whole line would almost instantly collapse like a row of dominoes immediately following the first one going down.
In fact the method of linking illustrated above would probably result in people going over sooner than if they all crossed individually.
New Zealand Mountain Safety Council bushcraft
The method for linking for a river crossing shown below is from the Mountain Saftey Council's Bushcraft manual and is the one recommended and rehearsed in training throughout New Zealand.
 Above is the method of linking for a river crossing reccommended by NZ Mountain Safety |
 Grasp pack strap on far side of next person |
Put the two strongest people at the upstream end of the line.
Undo all chest straps and loosen shoulder straps on each pack. Leave the hip belts done up.
Each person puts their arms between the pack and the back of their neighbour, grasping either the hip belt or shoulder strap (low down) on the far side.
Research and experimentation continues to confirm this method as the most effective for dimishing the risk in serious rivercrossing. I haven't yet heard of any improvement on what I've outlined here.
So, I'm not sure why the group in the Arawhata opted for their way of linking. If they're going to an area like that one would think they had a bit of experience already and would've come across the recommended technique somewhere
Lucky this time
Whatever it was, they were lucky the river turned out to be easier than they expected and their idea wasn't tested. And I just hope inexperienced people don't see that photo and think it's the way it's done.
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