Devices to Measure the Speed of Flowing Water?

"riverman" (nospam@sorry.com) writes:

 > I use this 4mph estimate when planning longer trips. If I have, say 10 days
 > and want to paddle about 6 hours a day, I'll expect to cover (without
 > portages or lots of scouting) about 240 river miles. If there are lots of
 > little rapids, I lower my estimate to 3mph, and would expect to cover about
 > 180 miles.

I'm familiar with a 4 mph still water paddling speed, but isn't the
current usually added to that? For example, on a river such as the
Mississippi where the flow is a pretty consistent 4.5 mph the resulting
downstream speed is about 9 mph. The upstream paddling speed would be nil.
I suspect you are including more than river current and paddling speed into
your estimate.


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 >> Stay informed about: Devices to Measure the Speed of Flowing Water? 

"William R. Watt" wrote in message

 >

 >
  >> I use this 4mph estimate when planning longer trips. If I have, say 10
  >> days
  >> and want to paddle about 6 hours a day, I'll expect to cover (without
  >> portages or lots of scouting) about 240 river miles. If there are lots of
  >> little rapids, I lower my estimate to 3mph, and would expect to cover
  >> about
  >> 180 miles.
 >
 > I'm familiar with a 4 mph still water paddling speed, but isn't the
 > current usually added to that? For example, on a river such as the
 > Mississippi where the flow is a pretty consistent 4.5 mph the resulting
 > downstream speed is about 9 mph. The upstream paddling speed would be nil.
 > I suspect you are including more than river current and paddling speed
 > into
 > your estimate.

Valid point, and I suspect that my rule of thumb probably takes into account
several errors cancelling themselves out.

For the Canadian rivers, I found that I spent a lot more time leaning on a
brace than paddling, and almost no time scouting, so my overall speed was
very close to the overall river velocity. However, for shorter 'lower-48'
trips, you're correct that you have to add paddling speed into the formula.
However, if you also add in the time spent on scouting, leg-stretching, etc,
it comes back to 4 mph again. The fact that this is close to average river
velocities is probably as much coincidence as it is from some 'rhythm of
nature'. The velocity that you <drift> in your boat is going to be less than
the average stream velocity, as the surface waters are slower, you tend to
snag eddys, etc. Paddling will increase that velocity beyond stream
velocity, but stops decreases it again.

How many times have you spent several days running a river, playing tag with
a recognizable log or peice of flotsam that just drifted along on its own
pace, until it got hung up on a rock or sweeper or something? I think this
observation is what got me thinking about this in the first place.

You know who might have some interesting input into this is someone
experienved with river S&R, or environmental hydrologist. If a dead body,
some pollutants or something is washed into the water, what is the average
rate that they plan on seeing it moving downstream?

--riverman
 >> Stay informed about: Devices to Measure the Speed of Flowing Water? 

Randy Hodges wrote:
 >
 > I worked with the Desert Reserch Institute on a flow study on the
 > Truckee river last year. We had a device (not likes simple or cheap)
 > that we could use to measure the velocity of the water at different
 > depths. I have seen the USGS people use a similar device when they
 > are calibrating the flow gauges. You might give DRI a call.

This thread has devolved into a guy-type discussion of GPS gadgetry
so I wanted to go back and ask about Randy's post.

Randy, must this device be used both in the center of the river
and on the sides?

Laminar flow theory says that water flows fastest in the center,
more slowly at the surface, much more slowly near the bottom,
and perhaps doesn't move at all near the banks.

I don't understand how any mathematical formula could expect to
accurately estimage CFS (or cumecs) from mere stage information,
especially at different flow levels. The riverbed could cause
laminar flows to vary unpredictably at high water.
 >> Stay informed about: Devices to Measure the Speed of Flowing Water? 

On 29-Sep-2004, "riverman" wrote:

 > Like the voyageurs, I could
 > see starting in Grand Portage to skip the St Lawrence and the Lakes, but
 > from GP to Alaska would be exquisite.

Start from Montreal and you'd skip the St. Laurence - the route was up the
Ottawa and then down the Mattawa to the French. From the French along the
North Shore of Georgian Bay is some of the best Great Lakes paddling there
is! Pukaskwa on Superior is one of the other great paddling destinations
in the Great Lakes. Don't short change yourself!

Mike
 >> Stay informed about: Devices to Measure the Speed of Flowing Water? 

On 28-Sep-2004, "John R Weiss" wrote:

 > ...and that is why many of the errors ARE eliminated!

And I'm referring to the errors that are still there _after_ these corrections
are applied.

 > "most GPS errors vary slowly and are very strongly correlated within short
 > distances."

A statement made without any reference to a source. How short is a short
distance?

 > At <a rel="nofollow" style='text-decoration: none;' href="http://www.edu-observatory.org/gps/gps_accuracy.html" target="_blank">http://www.edu-observatory.org/gps/gps_accuracy.html</a> you will also find that
 > the significant sources of GPS error are predictable and correctable.

I went to one of the links and the _measured_ error data was dated two days into
the future. This is reliable?

Mike
 >> Stay informed about: Devices to Measure the Speed of Flowing Water? 

On 28-Sep-2004, "John R Weiss" wrote:

 > Modern consumer-grade GPS receivers provide velocities accurate to within 0.1
 > knot

Leave your GPS sitting in one spot and watch the velocity change. You'll
see velocities much larger than 0.1 kt. I'm not talking about specs here,
I'm talking about turning the unit on and watching what happens.

Mike
 >> Stay informed about: Devices to Measure the Speed of Flowing Water? 

Michael Daly wrote:


 >
 >
  >>Modern consumer-grade GPS receivers provide velocities accurate to within 0.1
  >>knot
 >
 >
 > Leave your GPS sitting in one spot and watch the velocity change.

It gets pretty boring watching the display that just says 0.0 knots
for long periods of time with a few sporadic blips up to a few tenths.
And when walking at a steady pace the displayed speed is also almost
always constant within 0.1 or 0.2 mph.

 > You'll
 > see velocities much larger than 0.1 kt.

Some, which is not surprising since the spec is for 95% of the readings,
so once every 20 seconds or so one might expect a reading that's higher
than the spec.

 > I'm not talking about specs here,
 > I'm talking about turning the unit on and watching what happens.

When I've connected mine to my PC and recorded the readings over
extended periods of time the results have been in agreement with
the specifications.
 >> Stay informed about: Devices to Measure the Speed of Flowing Water? 

"Michael Daly" wrote:
 >
  >> Modern consumer-grade GPS receivers provide velocities accurate to within 0.1
  >> knot
 >
 > Leave your GPS sitting in one spot and watch the velocity change. You'll
 > see velocities much larger than 0.1 kt. I'm not talking about specs here,
 > I'm talking about turning the unit on and watching what happens.

OK...

Garmin GPS 3+, no WAAS or DGPS.

Inside, at the desk: 3 sats, DOP 5.8. Distance from a nearby waypoint
initialized at 76' and varied from 68 to 82 over 5 minutes. Distance stayed
between 70 and 75 most of the time. Velocity never came off 0.0.

Outside on patio: 6 sats, DOP 2.1. Distance initialized at 74' and varied
from 67 to 77; most of the time between 70 and 73. Velocity always 0.0.

Walking up and down the street over a span of less than 200' the velocity
started reading after 11 steps and steadied at 3.4 - 3.5 mph. Speed varied
proportionate to my slowing, turning, etc. Since I have previously measured my
brisk walking pace at 17-19 minutes per mile, the GPS results are consistent.

Looks accurate enough to me to me...
 >> Stay informed about: Devices to Measure the Speed of Flowing Water? 

On 29-Sep-2004, Peter wrote:

  > > Leave your GPS sitting in one spot and watch the velocity change.
 >
 > It gets pretty boring watching the display that just says 0.0 knots
 > for long periods of time with a few sporadic blips up to a few tenths

And I've seen mine wander around 3-7 kph for a while before settling down
to a smaller number lots of times. YMMV. Garmin 12XL.

 > Some, which is not surprising since the spec is for 95% of the readings,
 > so once every 20 seconds or so one might expect a reading that's higher
 > than the spec.

Not random, consistent. Again - YMMV.

It's funny, ever since they turned off SA, so many people claim their
GPS readings are perfectly accurate. Turning off SA only increased the
accuracy by a factor of 6.

 > When I've connected mine to my PC and recorded the readings over
 > extended periods of time the results have been in agreement with
 > the specifications.

Of course - averaging kicks in. Duh...

Mike
 >> Stay informed about: Devices to Measure the Speed of Flowing Water? 

Michael Daly wrote:

 >
 >
   >>>Leave your GPS sitting in one spot and watch the velocity change.
  >>
  >>It gets pretty boring watching the display that just says 0.0 knots
  >>for long periods of time with a few sporadic blips up to a few tenths
 >
 >
 > And I've seen mine wander around 3-7 kph for a while before settling down
 > to a smaller number lots of times. YMMV. Garmin 12XL.

It would be nice to have some reasonable statistics to see how
significant your "many" times are. When I've recorded data from
my GPS receivers over thousands of samples such outliers occur
only a few percent (and usually under 1%) of the time and are
pretty obvious and easily discarded in practice.
The existence of such occasional outliers is recognized in the
accuracy specifications being given as holding for 95% or more
of the samples.

Another thing to note is that the 12XL is a pretty old design
which was introduced in 1997 when expectations were that
SA was going to be with us for the foreseeable future.
As a result, I wouldn't be at all surprised if the firmware
design wasn't quite as concerned with avoiding such small
'glitches' given that the effects of SA would frequently
produce them anyway. But my experience with the Garmin 12
is still that such outlier values are rather rare.

 >
 >
  >>Some, which is not surprising since the spec is for 95% of the readings,
  >>so once every 20 seconds or so one might expect a reading that's higher
  >>than the spec.
 >
 >
 > Not random, consistent. Again - YMMV.
 >
 > It's funny, ever since they turned off SA, so many people claim their
 > GPS readings are perfectly accurate. Turning off SA only increased the
 > accuracy by a factor of 6.
 >
 >
  >>When I've connected mine to my PC and recorded the readings over
  >>extended periods of time the results have been in agreement with
  >>the specifications.
 >
 >
 > Of course - averaging kicks in. Duh...

No, I record each of the samples. The thousandth sample has no more
averaging than did the tenth. [BTW, this is not the case for
Magellan units which unfortunately do report internally averaged data.]

By having a large group of samples I can then see what the variation is
for 50% of the samples, 95% of the samples, 98% etc.

But the main thing that you've been claiming is that GPS can't be used
to measure fairly low velocities and that is simply not what I
observe every day when I go walking. The reading is very stable with
variations of only around +/- 0.1 mph when walking at a steady pace and
are consistent with my actual speed as determined by how long it takes
me to walk the 3.65 mile path. I also see that if I speed up a little
the GPS display goes up by a few tenths of a mph just as expected.
AFAICT, the same behavior occurs when using my GPS receiver on my
kayak deck where it gives me indications of my actual ground speed and
when I drift I get readings that are generally very consistent with the
expected tidal flow rates.

Sure I occasionally have seen glitches where the GPS displays an
incorrect value, probably due to multipath errors and switching of
which satellites are being used for the calculations. But such
glitches happen rarely, are short-lived, and are generally easy to
recognize and ignore.
 >> Stay informed about: Devices to Measure the Speed of Flowing Water? 

rhopley.DeleteThis@earthlink.net (Oci-One Kanubi) wrote

 > OK, assuming good health and physical fitness, and no particular time
 > constraints, I'd go Washington to Washington; ocean to ocean.

Richard, I hope to someday follow along vicariously as you undertake
that trip, maybe even accompany you for some small portion of the
upriver Potomac portion.

Yer not getting any younger you know...

I guess my last trip would be a reprise of my 1988-89 trip - take off
in my truck with my boat and gear and no firm plan, just following my
nose where whim and weather takes me for a year or two.
 >> Stay informed about: Devices to Measure the Speed of Flowing Water? 

"Mike McCrea" wrote in message


  >> Maybe a nice long float on the West Branch from Lobster Lake on
  >> down to Ambejejus...
 >
 > Riverman, isn't that what your will stipulates we do with your ashes?
 > Pour them loose into a scale model tripper and launch you onto the
 > West Branch from Lobster Trip on a crisp fall morning?

I'm not sure if I should be asking my lawyer to investigate the leak or not,
but actually (all BS aside) that is almost <exactly> what my will
stipulates!! Half my ashes to be sent down the Grand Canyon and (illegally)
dumped in Marble Canyon, the other half sent down the Penobscot.
Specifically, I said off the bridge above Cribworks, but I think I'll modify
it and have myself sent down in a scale model tripper. I can spend some time
building the model myself...

--riverman
(spooky...)
 >> Stay informed about: Devices to Measure the Speed of Flowing Water? 

"riverman" wrote

 > I'm not sure if I should be asking my lawyer to investigate the leak or not,
 > but actually (all BS aside) that is almost <exactly> what my will
 > stipulates!! Half my ashes to be sent down the Grand Canyon and (illegally)
 > dumped in Marble Canyon, the other half sent down the Penobscot.
 > Specifically, I said off the bridge above Cribworks, but I think I'll modify
 > it and have myself sent down in a scale model tripper. I can spend some time
 > building the model myself...
 >
 > --riverman
 > (spooky...)

What's really spooky is that I knew it would be a crisp fall day. I
really shouldn't have let that slip out. At least I didn't mention the
year

(Seriously, I think that would be a wonderfully fitting way to go,
ashes launched downstream in a scale model canoe, one last adventure
on the river. I'll have to amend my own will acordingly too)
 >> Stay informed about: Devices to Measure the Speed of Flowing Water?