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Depth of Water by Timing the Bubbles

09/30/2021 9:25 AM

A friend of mine,an avid hunter since he could crawl, told me that he could tell the approximate depth of the water in a lake by throwing in a rock and timing how long it took for the bubbles to break the surface.

Is there any scientific basis for this method?

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#1

Re: Depth of water by timing the bubbles

09/30/2021 9:50 AM

Well depending on the depth of the water and the size of the stone, one still cannot be assured that the bubbles are traveling from the actual bottom...so even if one possessed the knowledge that bubbles rise 1-2 feet per second depending on shape, I wouldn't believe this information to be dependably accurate....

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#2

Re: Depth of Water by Timing the Bubbles

09/30/2021 10:56 AM

I guess there will be some air entrained with the rock but, if the rock is tumbling on the way down, wouldn't that separate before the rock hit the bottom?

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#3
In reply to #2

Re: Depth of Water by Timing the Bubbles

09/30/2021 12:31 PM

He said he timed the last bubble.

He said that gas is always trapped at the bottom,and will bubble up if disturbed.

But I wonder:Do bubbles in water rise at a certain fixed rate,depending on temperature and salinity and other impurities?

Will large bubbles rise faster than small ones?

Will the rate of rise vary with atmospheric pressure?

Will bubbles rise in water if in zero gravity?

What if the drop of water in zero gravity is rotating?

Would the bubble go to the outside edge or toward the center?

I think I need a government grant to study this!

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#5
In reply to #3

Re: Depth of Water by Timing the Bubbles

09/30/2021 2:03 PM

Well, the rise of a bubble is dependent on 2 forces, drag and buoyancy. The buoyancy force is proportional to the volume of the bubble, or radius cubed, whereas drag is proportional to the cross-sectional area, or radius squared.

On rising bubbles, the forces are equal, so the speed of ascent should be proportional to the size (radius) of the bubble.

You have to figure the time it takes for the rock to sink to the bottom. Like the bubbles, the rock has weight and drag, and the rate that the rock sinks would be proportional to both the size and density (and maybe shape).

I can see how your friend could get a feel for estimating the depth from the size and heft of the rock and the size of the bubbles.

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#7
In reply to #5

Re: Depth of Water by Timing the Bubbles

09/30/2021 4:58 PM

It is hard to beat what we call "Kentucky Windage",that is,using experience and instinct to make a judgement call.

He has done this many times,so he probably has an instinct about the depth.

Like catching a ball,you don't calculate ,you just know where to put the glove and when to do it.

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#15
In reply to #7

Re: Depth of Water by Timing the Bubbles

10/02/2021 12:06 PM

Another thing occurred to me. Water waves have a defined depth called the wave base, which is half the wavelength. The water rotates in a circular pattern of diameter decreasing with depth vanishing at the wave base as shown in the diagram below.

The speed of water waves in deep water (deeper than the wave base) is proportional to the square root of the wavelength. In water depth much smaller than the wave base, the speed is proportional to the square root of depth. There is a transition between shallow and deep where the wave speed is determined by both depth and wavelength.

"When the water below a wave is deeper than the wave base (deeper than half of the wavelength), those waves are called deep water waves. Most open ocean waves are deep water waves. Since the water is deeper than the wave base, deep water waves experience no interference from the bottom, so their speed only depends on the wavelength:

where g is gravity and L is wavelength in meters. Since g and π are constants, this can be simplified to:

Shallow water waves occur when the depth is less than 1/20 of the wavelength. In these cases, the wave is said to “touch bottom” because the depth is shallower than the wave base so the orbital motion is affected by the seafloor. Due to the shallow depth, the orbits are flattened, and eventually the water movement becomes horizontal rather than circular just above the bottom. The speed of shallow water waves depends only on the depth:

where g is gravity and d is depth in meters. This can be simplified to:

Intermediate or transitional waves are found in depths between ½ and 1/20 of the wavelength. Their behavior is a bit more complex, as their speed is influenced by both wavelength and depth. The speed of an intermediate wave is calculated as:

which contains both depth and wavelength variables."

10.1 Wave Basics – Introduction to Oceanography (pressbooks.pub)

It occurred to me that your friend might subconsciously be estimating depth from the behavior of the splash wave from the stone.

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#16
In reply to #15

Re: Depth of Water by Timing the Bubbles

10/02/2021 12:35 PM

I'd just use a portable depth sounder....or a fish finder in this case...

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#4

Re: Depth of Water by Timing the Bubbles

09/30/2021 12:36 PM

A hunter is probably interested in whether he can wade across. The timing of bubbles will be a good indicator of shallow vs. deep water. In shallow water the bubbles will stop sooner than in deep water. With a little practice you could develop a go-no go strategy based on bubble timing since you are interested in finding:

1. up to 2 ft. deep - go ahead and wade

2. up to 4 ft. deep - wade, but suffer somewhat

3. 4 ft.+ - swim across

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#6
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Re: Depth of Water by Timing the Bubbles

09/30/2021 4:53 PM

He is a regular Daniel Boon.

He hunts,fishes,and traps as well.

He uses the rock test to determine how deep to set his hook,he said.

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#8
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Re: Depth of Water by Timing the Bubbles

09/30/2021 10:58 PM

I think he got a bite.

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#9

Re: Depth of Water by Timing the Bubbles

10/01/2021 8:03 AM

Tying a light string onto the rock, lowering slowly it into the <...lake...> until it struck bottom and released the tension in the string, and measuring the wetted length of string, would be an order of magnitude more accurate....

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#10
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Re: Depth of Water by Timing the Bubbles

10/01/2021 9:35 AM

Which is why a method similar to what you describe was used on 19th century Mississippi riverboats when navigating shallow water. A leadsman would cast a sounding line - a line with knots at regular intervals fastened to a weight - and call out the depth to the helmsman. The knots could be felt by hand so that even by night the water depth could be measured. There are two stories I have heard about the leadsman's call. One is that he called out "mark on the twine" followed by the depth in fathoms, and with repetition, the words became slurred and sounded like "mark twain". The other story is that "mark twain" was used to indicate two fathoms - 12 feet - which was a safe depth for the riverboats. Whichever the case, Samuel Clemens worked on the riverboats for a time, was familiar with the leadsman's call, and consequently took "Mark Twain" as his pen name.

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#11
In reply to #10

Re: Depth of Water by Timing the Bubbles

10/02/2021 4:41 AM

Also the origin of the phrase "swinging the lead".

Swinging the lead - A person pretending to work (or claiming to be ill) when he is not.
Pre-modern days, seamen would check the depth of water by dropping
a lead weight, attached to a thin marked rope, to the bottom of a
waterway. Some lazy sailors would take as long as possible about it.
They would swing the lead to and fro several times instead of just
dropping it straight into the water.

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#14
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Re: Depth of Water by Timing the Bubbles

10/02/2021 9:36 AM

Never heard that expression here in Canada, but "get the lead out" means the same thing, and maybe has the same origin. Many expressions have a nautical origin.

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#12
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Re: Depth of Water by Timing the Bubbles

10/02/2021 4:42 AM

I think HTRNs friend was fishing from the bank.

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#13
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Re: Depth of Water by Timing the Bubbles

10/02/2021 7:38 AM

Yes.It is impossible to carry a canoe or boat through thick woods and undergrowth where this guy goes.

He has a trap line about 10 miles long that he checks every day.

It is hard to follow him sometimes carrying nothing.

I am getting too old to keep up.

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#17
In reply to #13

Re: Depth of Water by Timing the Bubbles

10/02/2021 8:54 PM

Probably could go with an inflatable...just 30lbs

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#20
In reply to #9

Re: Depth of Water by Timing the Bubbles

10/04/2021 3:44 AM

...also, throwing a rock in will reduce the available depth at that spot.

In the limit, one is building a dam/outcrop/island.

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#21
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Re: Depth of Water by Timing the Bubbles

10/04/2021 4:02 AM

"PWSlack's Uncertainty Principle": carrying out such a measurement, by throwing a rock in, affects the result of the measurement. Or something...

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#18

Re: Depth of Water by Timing the Bubbles

10/02/2021 9:49 PM

Outside of making very coarse qualitative depth measurements (wading, or swimming deep water), I doubt your friend can judge the depth of a lake from a tossed rock.

I find it even less likely your friend independently measures the depth of a lake he tossed a rock into. Why bother, he convinced you he can do this.

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#19

Re: Depth of Water by Timing the Bubbles

10/03/2021 6:20 AM

I'm not fisherman myself, but I did accompany my father on a few occasions; his insistence on being quiet and keeping out of site leads me to believe that hurling a rock in would not be a good move.

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