[MikeM]

Hello.

Does anyone have any good heuristics they like to use for estimating time for river travel? eg. When climbing a hill, there’s a heuristic which suggests in a group of reasonably fit (not necessarily really fit) people, the group could expect to travel about 300 metres an hour. Faster with a small group of fast people, slower for a large group with one or two people who’ve never clambered over a tree root before, etc etc.

We had a walk down the Makaroro River (in the Ruahine) over Easter. We took some general guesses about the distance from the map’s swirls, added a bit to compensate for how we’d probably not follow the exact same line as the middle of the river, factored in some more for possible gorginess. We generally did okay from intuition, but I still don’t know specifically what rules we were following, if any.

I’m just interested to know if anyone has any actual rules or heuristics that they like to use for estimating this type of thing. I’ll probably screw it up some time, and when that happens I’d like to be able to point a finger at the accepted procedure I was following, instead of taking the blame myself.

Cheers and thanks.
MikeM.

[Amanda]

Hi Mike

For me and Richard, we tend to estimate 1.5km an hour for ‘average’ river travel in terms of terrain difficulty (eg something like the Ohau’s upper sections). Faster in a more open river like the Makaroro. Obviously in a group situation, depends a lot on how fast the slowest person is – river travel is definitely a learned skill!

This is not received wisdom though – I’m sure other people wil have other interesting thoughts.

cheers
Amanda

[MikeM]

Thanks. I’d certainly be interested to know any more factors people take into account (conditions, group), and what aspects of a map anyone looks at to identify possible gorge sorts of areas in rivers that might lead to rough estimation rules. Probably things like steep contours on the edges and the nature and frequency of corners mean something, but they don’t always give it away.

I checked the GPS log for a 3 hour stretch of Easter Monday morning, between Upper Makaroro and Barlow which is reasonably gorgey even though the river was in low flow. I stopped checking the log before the last major bend, where the river opens out more.

It’s about 3.5km in a straight line. If I eyeball the LINZ map quickly along the route the river follows, I get about 5km with all the river deviations shown on the map, so 1.5 km/h might have worked in this case, and I’d assume slower if the river was in normal flow. At least for our group, which included me constantly trying to stare at a map and take photos.

Introspectively if I look at the map really hard and stare at every corner, I can imagine about 6km of actual distance on the map around all the squiggles. The GPS track, after we’d walked it, has measured 7.5km for that 3 hour stretch, so *it* reckons we averaged 2.5 km/h over the whole section.

I’m assuming that all that extra distance from the GPS track is a combination of extra criss-crossing of the river that we needed to do which doesn’t follow its direct path, river deviations that were too small for the map scale, GPS track over-estimation (which will tend to happen given how it works), and possibly my own map-reading inability causes me to under-estimate the real distance.

Interesting stuff anyway, for me at least. I guess I’m just trying to work out how to combine all of this to have a better idea of what to expect based on what’s perceived from a map, from conditions, and from the state of a group.

[spencer]

I’ve done a few gorge trips in the last year or two involving pack floating. My cautious estimate is to use 1km an hour for gorges, with a group. This can, in fact, be pretty accurate! But is too cautious for non-gorge sections or for more determined tramping. It is useful for risk assessment in terms of daylight hours and predicted weather. I would add that smaller, steeper, rivers that are not commonly travelled might be much much slower, as witnessed by a DOC colleague a few weeks ago attempting to descend plateau stream. Not recommended.

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