The other day we had some overnight rain, with some falling in the headwaters of the Rangitikei River.

The next morning we had a rafting trip, and a decision had to be made on whether the trip would proceed or be cancelled.

Over the years we have adopted a number of indicators that foretell the likely effect of upstream rain on river levels, particularly on the Grade 5 section. We don’t want a trip to be on the water if the river is likely to lift above our maximum safe rafting level.
I was not involved directly in the process of deciding whether the trip should go ahead or not as this is the responsibility of the Trip Leader and other senior guides on the trip. I did however monitor the conversation by radio.

What we have noticed over the years is that this decision making has become more complicated.

The reason for this complication is that much of our forecasting has been based on correlations with other river systems. In other words if a certain river, in this case the Waipakihi has a lift to say 50 cumecs, we would anticipate a lift to about 100 cumecs on the Rangitikei at the Lodge in 6 hours time.

What we are increasingly finding is that while the time of a lift on the Rangitikei at the Lodge is still around 6 hours after the lift on the Waipakihi, the size of that lift does not correspond anywhere as well.

We as yet don’t know why this is so.

So what happened this particular morning?

What happened was a discussion around the anticipated lift, it’s timing, rainfall density per hour and so on. At the end of the discussion, a decision was made not to go, based on gut instinct probably as much as anything. This proved to be the correct decision.

Is it possible to write all these variables down?

Other than a general outline I don’t think it is. What formed the final decision was based on experience as well as written guidelines. It was if you like a form of institutional knowledge that cannot be replicated quickly or easily.

The team of guides at River Valley have years of experience on the Rangitikei River. This is especially so amongst the senior guides. It is a great feeling to have as a company owner, to know how professional and thoughtful that decision making is.

Brian Megaw

Being on the river when it is doing this is NOT fun