Sunday, December 19, 2010

Water Levels

Everybody has looked at a river that looks like it's crazy flooding thinking 'wow, that's insane!', then maybe come back another day and seen it low and tame and thought wow, what a difference! After looking at my post yesterday, it came to me that people who read it might have no idea what '1.4' means as a water level...I don't mean just non-paddlers, but people who gauge other rivers as well, as saying 'it's at 1.4' is pretty specific to The Chilliwack as well. I remember being a non-paddler looking up 'whitewater kayaking' on Wikipedia and having no idea what half the terms meant or how paddlers could even remember the names of all the different strokes, water levels were the same thing, they meant nothing to me until I actually needed to understand them! So today's entry might seem a bit like a boring math or science lesson...

The Chilliwack has it's own specific gauge reading (as do many rivers), and it reads in meters of height (1.2 is low, 1.5 is medium, 1.7 is high). 'High water' also depends who you ask, for example, to a beginner paddler or someone who's only paddled a level below 1 m, 1.5 m could seem like very high water. To an experience paddler, high water wouldn't be until it gets over 2 m. There are also more than one gauge, typically the gauge you hear referred to is in Chilliwack Canyon, there's also one at Vedder Bridge and one in Slesse Creek. Water volume obviously builds up downstream as tributaries join the main flow. As a correlation for what I've done so far on the Chilliwack, I consider 1-1.3 low (lower than 1 is painfully low), 1.3-1.6 medium, 1.7 plus high.

To correlate the height ratings on the Chilliwack with other rivers we need to establish a common measuring level since actual height of a river doesn't necessarily have anything to do with power (they can be really wide or narrow), the common denominator is cms (cubic meters per second of water, in the USA they use feet "cfs" which you've have to correct for as well), this is the amount of water displacing a cubic meter of area each second. The Chilliwack at low flow for example, is maybe around 12-20 cms, at medium is around 20-40 cms, and at high flows is obviously higher. A big water river like The Thompson can be up around 600 cms.

It's a different experience getting on the same river at different water levels. Low water is slower moving, has less of a pumping, pushing, grabbing feel to it. Rocks are largely exposed, as are big eddies, eddy lines are small and unobtrusive, holes are small and not as sticky (won't hold your boat or a swimmer as easily). If there are swims it's usually fairly easy to gather swimmers and gear and get them into an eddy.

High water pushes you down the river really fast, you have less time to think and make decisions, there are less eddies to stop in and gather yourself and consider what to do or scout, making you more committed to your run and individual lines. Many rocks and features get flushed out, but where there were rocks there could now be holes, and at really high levels big rocks can become massive river wide holes. Eddy lines can get high and hard to cross, whirlpools form. To me the water feels like it's constantly piling up on your boat and pulling you under, and this seems to directly relate to what kind of boat you have...a more buoyant, less edgy boat will have less trouble while smaller playboats with lots of edges will have a much more difficult time.

The first time I tried a tiny playboat not even as long as I am tall was in The Chilliwack when it was over 2 m, and it was pretty crazy...the one big advantage is that you don't have to worry as much about being able to roll as often nothing will stop you...also you have to worry about massive logs rolling downriver which act like icebergs and pop up when you least expect them...but that's a whole other tangent! I can't wait to get on something big like the Thompson, it'll be a blast!

1 comment:

  1. There sia good big water run 30 minutes from you on the nFraser, lots of flat but 2 really big volume rapids. Good winter run when everything else is low,