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Old 10-17-2005   #11
Join Date: Jun 2005
Posts: 103
Check out this USGS fact sheet

It's got an very scientific sounding title, but basically it's about side-canyon debris fans and how they evolve through time. The example they present is lava falls.

Figure 2 is side-by-side aerial photos taken in March and April of 1996, before and after the experimental flood.

Figure 4 shows a plot of elevation versus distance for the fastest moving water (the thalweg - more geology speak). Anyway, the plot shows a 4 meter drop through lava, almost all of it occurring in the first 100 meters of the rapid. I imagine that the tail waves will pretty much double that distance, but don't add much to the drop. So much for 37 feet!

It still doesn't answer how fast the water is moving, though.

I haven't tried, but has anyone taken a look with Google Earth? I've looked before and very clearly seen rafts tied up on a beach somewhere (Nankoweap?)


back again:
Hydraulic map of Lava Falls Rapids, Grand Canyon, Arizona
scroll to the botoom. either view as images or download the dejavu plug-in.
The highest velocity is about 7 meters/second, which equals about 14 knots, or 15-16 mph. These measurements were taken at 10,000 cfs (see the notes on the right side of the map) sometime in the mid-eighties.

Ain't the web amazing?

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Old 10-17-2005   #12
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Join Date: Nov 2003
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very cool

thanks. very cool info.i'll check out that site. i did find the maps through the online index of usgs. i'll post more as i find stuff. that's interesting about the four meter drop and the 16 mph flow.

as for the demon....well, he did reach up and snatch my spare oar.


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Old 10-18-2005   #13
Avon, Colorado
Paddling Since: 1997
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Posts: 471
Equation for River Velocity

Not sure why you need the velocity, but it can be computed very easliy with a few assumptions. Use Mannings Equation (computes open channel flow). You need the Flowrate (any flow you want) the channel slope (which you have 37ft over 250 yards), the cross sectional area (you can get width from google earth, but depth may be hard---ask some of the hole swimmers how deep it is!!) and a coefficient of friction for the channel bottom.

Google Mannings Eqn and have at it!! (yes, i'm an engi-nerd)
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Old 10-18-2005   #14
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Bham, Washington
Paddling Since: 1997
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Dude, manning's eqn. is a load of crapola. you'd be better watching a orange/watermelon floating through and timing it than using manning's. all it will give you is an average cross sectional velocity but the results are highly variable on the assumptions used.
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Old 10-18-2005   #15
Avon, Colorado
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Einstein is that you??? It is the ONLY equation to compute open water flow. Just trying to help the guy out (ball park figure). But go with Einstein and the watermelon case study.
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Old 10-18-2005   #16
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Systems & Process Design, Colorado
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See for yourself...

There are two pictures of Lava on under Paddling - Stills - Colorado River - Grand Canyon. Pictures 95 and 129.
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Old 10-18-2005   #17
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i'm getting a headache. thanks. no need for the melons. lets just say it's fast. i like the 20 seconds whether you're in your boat or not equation.

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Old 10-19-2005   #18
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Summit, Colorado
Paddling Since: 1996
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I'm just posting this because it doesn't seem to go along with what you were saying earlier:

"A River" in John McPhee's Encounters with the Archdruid describes the trip down the Grand where Floyd E. Dominy, the guy basically responsible for Glen Canyon Dam, goes down the river with David Brower, the guy basically responsible for preventing all of the other dams from going in on the Grand Canyon. Definately a good read with a lot of interesting stuff I didn't know. Anyways, he talks about the water speed being 15-20mph at the fastest (don't know how reliable this is) and when he talks about Lava, he says it's a 26 foot drop over 100 yards. Again, I'm not sure how reliable these specific numbers are but I do know that McPhee put a lot of research into some the other topics he writes about in the book.

"The world would be a better place if everyone kayaked."-Brad Ludden (Valhalla)
"You only get one chance to run a drop blind."-DD
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Old 10-19-2005   #19
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i've read the book and you're right, it's a good read. i know he's a good researcher....but if nobody in the grand canyon can come up with the numbers, nobody in the usgs office can verify it, and nobody else really seems to know, where did he get his facts. it seems all to common to me that, especially when it concerns numbers, we just take other peoples words for granted and it builds and builds. people just source one another.

i can't tell you how many places i've read the guiness book of records thing or heard lava is the fastest stretch of whitewater.....but i'm just wondering where that came from, especially if the book of records thing doesn't really exsist, and i've searched that site and contacted them.

i'm not out to debunk anyone. just finished my first canyon trip and am writing a piece about it. but when an editor asks where the "facts" come from it made me curious.

i don't take any of it seriously; i mean who really cares. just a little fun.


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Old 05-11-2012   #20
Boulder, Colorado
Join Date: Sep 2009
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Bump. So what's the final answer on the total drop?

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