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Max cfs for wading?

Started by trout_boyII, December 17, 2008, 08:27:43 am

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fleming13

Quote from: wvyou on December 19, 2008, 14:10:26 pm

After a close call on the Raven Fork last weekend, I'm taking the better safe than sorry approach.  If you don't drown,  plan on the water temps killing you.

I would not want to be caught up in the park with the water coming up.  Any stream that can put big hemlocks on top of SUV size boulders is scary!  Now with the water normal.... ;D

Everybody quiet, the Christian is in the room. 

I have been smited for the name of the Lord.

TROUTMASTER3000

Just wear a belt.  Its fun to then jump in to a big plunge pool at the end of the day (In the summer to cool off).  Plus your waders keep the air in them and its hilarious, sometimes they float and you are floating upside down!  Its great to take underwater pictures!

Anything is possible with will, determination, and an endless supply of expendable labor.
AMERICA RULES

Silver Creek

Quote from: troutphisher on December 17, 2008, 09:40:39 am

Deuce,

Another trick you can employ, is to only stand on one foot. This decreases the surface area on witch the force of the water can act upon. It's like cheating physics!

A simple calculation shows that P is a product of F/A, so by reducing A, you also reduce P.

P= Pressure

F=Force

A= Area

Unless I am misinterpreting what you are saying, I've got to respectfully disagree for fast water. I believe having only one foot on the river bottom is generally less safe than having two.

Your formulas are correct but I think you have applied them incorrectly. P (pressure) is force per unit area and is not the most important factor. The physical property holding to the bottom is actual Force (body weight) acting through friction between your feet and the river bottom. Pressure is how that force is distributed, and not the force itself.

I think you are confusing the force pushing you down the river vs the force holding you to the bottom.

The force pushing you downriver is not related to the area that your foot has on the bottom of the river but the total body area in cross section to the direction of the flow of the river. Standing sideways to the flow is the way to minimize cross sectional area and reduce the total force pushing you downstream. The PSI or pressure per area actually stays same, but you decrease the total force by minimizing the area.

The force holding you to the river bottom is your body weight. Lifting up one foot will shift some additional force or your weight to the remaining foot. So the pressure per area increases but the total force does not and most of the time actually decreases. How does this happen? By lifting up one foot, your center of gravity shifts. To compensate in fast flows, you need to lean more forward into the river flow to remain in balance. When you lift up one foot, your center of gravity is no longer centered over your remaining foot so you actually have less total weight on that single foot than you had on both. The vector force of your weight centered over your remaining foot is less than your total weight or force when centered over both your feet.

That is why a wading staff helps. When you use a wading staff, it is possible to keep your weight centered over the staff and remaining foot even with one foot off the river bottom.

Stand sideways to the river flow and use a wading staff. Keeping both feet on the river bottom or a staff and one foot keeps your weight centered over the attachment points. Always cross the river below a deep section rather than above.

Regards,

Silver

http://tinyurl.com/kkctayx


"Discovery consists of seeing what everybody has seen and thinking what nobody has thought"..........Szent-Gyorgy

troutphisher

LOL....you missed the jest of it.

But since you brought pressure, I think you misunderstood. The pressure you are referring to, is a result of the persons weight. That weight in-turn acts upon   the surface area of the person shoe print or sole size, as is not necessarily an even distribution. It also greatly depends on the surface of the sole, what is the coefficient of friction, since it is friction and pressure holding the foot firm. Another way to look at this as an example would be to study the fiction between a hard rubber sole and the felt sole. Felt has the ability to grip based on the long fibers of the felt and rubber has a much smoother surface, resulting in lower coefficient, thus would slip more if a force acting on it was perpendicular to the friction surface.

Pressure is a result of force, and the unit in this case is area. If the person wading had fat chubby legs, it is entirely possible, that the surface area and resulting force, would overcome the friction and pressure of the sole resting on freestone rocks. And it that case, reducing the surface area subjected to the force, in this case water flowing against the leg area, one could reduce the resulting pressure, by reducing the exposed area.

It is a balancing or equilibrium of these pressures, based on coefficient of friction, water flow in cfs, and weather your a fucking fat ass or not, that determines weather you are stand against the force on one leg, or take a drink.

of course assuming the force vectors are perpendicular witch results in higher values.

The object of life is not to be on the side of the majority, but to escape finding oneself in the ranks of the insane.

fishhunterphil

Quote from: troutphisher on February 02, 2009, 19:25:19 pm

LOL....you missed the jest of it.

But since you brought pressure, I think you misunderstood. The pressure you are referring to, is a result of the persons weight. That weight in-turn acts upon   the surface area of the person shoe print or sole size, as is not necessarily an even distribution. It also greatly depends on the surface of the sole, what is the coefficient of friction, since it is friction and pressure holding the foot firm. Another way to look at this as an example would be to study the fiction between a hard rubber sole and the felt sole. Felt has the ability to grip based on the long fibers of the felt and rubber has a much smoother surface, resulting in lower coefficient, thus would slip more if a force acting on it was perpendicular to the friction surface.

Pressure is a result of force, and the unit in this case is area. If the person wading had fat chubby legs, it is entirely possible, that the surface area and resulting force, would overcome the friction and pressure of the sole resting on freestone rocks. And it that case, reducing the surface area subjected to the force, in this case water flowing against the leg area, one could reduce the resulting pressure, by reducing the exposed area.

It is a balancing or equilibrium of these pressures, based on coefficient of friction, water flow in cfs, and weather your a fucking fat ass or not, that determines weather you are stand against the force on one leg, or take a drink.

of course assuming the force vectors are perpendicular witch results in higher values.

Epic, applaud worthy, response.


overbrook

The Congaree....

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DCBuckeyeguy77

Quote from: wvyou on December 19, 2008, 14:10:26 pm

After a close call on the Raven Fork last weekend, I'm taking the better safe than sorry approach.  If you don't drown,  plan on the water temps killing you.

I gotta say that Raven's Fork is one of the last places that you want to get caught at when its rainy. I believe that it's one of the fastest rising rivers in the park... and out of the park.


hillbilly327

Generation schedules on Tailwaters are a good guide for safe wading.  CFS means little if you do not know the stream.  1000 cfs is a flood on a small stream and a drought on a large stream.  200 cfs will have an average instantaneus depth for a linear foot of water of 2 ft on a 100' wide stream and 20' on a 10' wide stream.

I will opine on 3 rivers that I wade and hopefully others can fill in the more information on other tailwaters so that we can create a safe wading guide (all streams will have deep holes and drop-offs even in drought conditions):

SoHo--easy to wade with no generation and hard to impossible when generating.  Because of the Wier, it appears that the water has a slow rise until the wier is full and a quick drop after the wier overflow stops--very nice.
Hiwassee--easy to wade with no generation, difficult but wadeable on one generator, unsafe to wade with two generators.  Water takes about 30 minutes to get about 2 miles and rises fairly fast.  Our rule is reel in and walk off the river as soon as the water starts rising if your are in the first mile or so from the power house.
Blue Ridge--easy to wade with just the by-pass generator and impossible when generating.  River takes about 4 hours to rise as far down as Curtis Swich.  It comes up dangerously quickly if you are near the dam and the high, muddy, banks--stay alert.
Clinch ?
Watuga?
others ?

Please add your observations.


Jeffrey7302

Folks, I am new to fly fishing, but am an experienced angler and an environmental scientist, and you need to appreciate how streamflow is computed. It's the cross-sectional area at any particular stream location, generally a sum of polygon approximations, multiplied by the avg stream velocity. This means that you could have a very big river, but with a low current, and still compute a huge cfs. But, as long as the depth is wadable, that flow is not gonna be a problem. Or, you could have a small mountain stream with a really fast current w/whitewater, that, because of the small cross sectional area, will compute as a low cfs, but which could easily knock you down.

So, it's really the stream velocity that you want to focus on. You can back this out of the cfs by estimating the cross sectional area, in square feet, and dividing the cfs by this area,

As to what's a safe velocity, off the top of my head I'd say anything within about six fps of current, which is about 4 mph. A more experienced wader could no doubt handle more.

Of course, the water depth is important too. It's one thing fighting a 4 mph current thats around your shins, and quite another when its up to your waist.


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