Estimating CUBIC FEET-PER-SECOND

Estimate the surface width of the stream or river.
Let's say it's about 40 feet.

Estimate the Average Depth...you know...eyeballing it all, and coming up with a "mean" for the total shallows, the magnitude of the "V"....just the whole deal:

Lets say YOUR CONVERSION makes if 5-feet-deep RIVERWIDE.   This would require a max river-depth out there in the center to be 8-9-10 feet, depending on the "V."

OK.....40*5.....that's 200 square feet.

Now look at the water's speed past a fixed point midstream.

If it's a foot-per-second.....that's 200 Cubic Feet Per Second.

If it's 10 feet-per-second...(six miles per hour...which is way-faster than just any fast walk---and which means that if you were pointed upstream paddling as hard as you possibly could, you'd lose downstream ground at about 2-miles per hour).....that's 2000 Cubic Feet Per Second.

Your GPS is a totally useful device.

Lets say, one day on flat water, you used the "Miles-Per-Hour" readout on your GPS to find out what speed your boat would "do" given some "standard output."

Now on any river you can "point upstream" and paddle at that standard output-level.......your GPS will tell you your speed-made-good-over-the-bottom.....which in turn will tell you the speed of the current.

Alright, you know the takeout is some given distance.   Now you know exactly the time of your arrival at the takeout, if you just drift.

Judd

Interesting, Judd, but I think the fundamental flaw in that thinking is that the river drifts at the same speed in all places, which it does not.

I'd factor it more like this:  when's it get dark and how much beer do I have?     OK, there are many more considerations, the primary one being, "have I been here before?"  Even in familiar waters though, varying flow rates will present varying new potential hazards or even just anomalies in flow that affect your drift (eddies, hydraulics...etc.).  A river is alive and dynamic, as is a good paddler!  Only a generalization can be made about how long a drift will take.  IMO!   

Eric

Judd do you still use an abacus? Why not just go here. 
http://cdec.water.ca.gov/riv_flows.html

Interesting, Judd, but I think the fundamental flaw in that thinking is that the river drifts at the same speed in all places, which it does not.

I think the flaw is confusing current speed with flow rate.  In the absence of tides, tributaries or even small feeder streams adding more water to a stretch of river, the flow in cubic feet per second should remain constant.  The linear speed of the current, however, may increase or decrease with topography (i.e. slow current in deep, wide, flat areas and fast current in shallow, narrow, steep areas).

Back to Judd's original example... a 1 ft/sec current crossing a 200 sq ft (40 ft wide * 5 ft deep) section of river calculates out to a 200 cubic ft/sec flow.   When that same water heads into a rapid downstream that is only 20 ft wide and only 2 ft deep or 40 sq ft, the flow will remain 200 cubic ft/sec but the current speed will become 200/40 = 5 ft/sec.

Brian

Calculating discharge is a pain in the a$$.  Velocity is inconsistent both laterally and vertically. Cross-section is can be a minor component, particularly when slopes diminish...BTDT.  I'll post some pics from the office.  Long and short of it...guessing accurately is close to impossible. 

Just Like Geese know where and when to fly and a deer can forecast an approaching storm, so can Man attune himself to the rythym of the river. No matter if you've  been there before or not. Scientific data is appeasing to the logical mind but getting in touch with intuition will help on a river far more.

Scientific data is appeasing to the logical mind but getting in touch with intuition will help on a river far more.

True but I always check the flows before making a drive.
Hawk my wife tells me only women have intuition

Why do all that when you can just see your drift speed on the GPS?  It would seem that water flow would be irrelevant in calculating speed. Or am I missing something?

Gandoderma......You're not missing anything.....
I was.

It's called hypercerebralization........

   :  )

Judd

Back in the day...WAY back....I floated the American River in a 2 person raft from Sunrise to Watt. My mom...we are talking 30 years ago...was to pick up my date and me and drive us back to Sunrise. I told her it would be about 3 hours total.
Unbenounced to me the river flow was cut WAY back for some kind of construction.
The flow was cut so bad that we were actually drifting backwards in some spots when there was the slightest breeze and I had to row my @ss off to make any headway at all.
SEVEN hours later I was calling my mom to pick us up.
I didn't mind the at all. Who wouldn't want to be stuck in a 2 person raft when the chick is hot??  But was my mom ever pissed! I was supposed to babysit and the huge delay caused me some huge personal grief.
Moral of the story; when in doubt, call to see what the flows will be.

caused me some huge personal grief.

 

Who wouldn't want to be stuck in a 2 person raft when the chick is hot??

Moral of the story; when in doubt, call to see what the flows will be.

But would you have done it again?

We used to do that drift what a huge party it was too fun.