gravity dredge ?

Yup, that is true.
If you are super worried you can call Fish and Game, Mark is the guy I talked to about that and using water pressure to blow overburden away.

You can get into a 100' 4" tube and make a nozzle for it for under $75 dollars.

Just remember at least 7' of drop is needed, 10+ is optimal.
 

(1) Suction dredging. For purposes of Section 228 and
228.5, the use of vacuum or suction dredge equipment (i.e.
suction dredging) is defined as the use of a motorized
suction system to vacuum material from the bottom of a
river, stream or lake and to return all or some portion of
that material to the same river, stream or lake for the
extraction of minerals. A person is suction dredging as
defined when all of the following components are operating
together:
(A) A hose which vacuums sediment from a river, stream
or lake; and
(B) A motorized pump; and
(C) A sluice box.
(2) Motorized. For purposes of these regulations,
“motorized” means a mechanical device powered by
electricity or an internal combustion engine.
Click to expand...
...
 

no motorized means good to go,if you try it let us know how it worked out.
 

Well I drug 50' of 4" necked down to 1" out to the river. Set up the big end in a pool, about 12' up, but tried to run a 2" power jet. Didn't quit have the power to get the suction. I'm on the right track, I just need to do some off season experiments. I'm working on a small suction nozzle right now.
 

I think you have to draw your water from quite a ways upstream to get enough pressure to do the job, right? It seems to me from readings I've done on the subject that you have to have a lot of pipe a long way upstream, and taking advantage of slope and gravity to develop the water power you need.

All the best,

Lanny
 

Lanny in AB said:
I think you have to draw your water from quite a ways upstream to get enough pressure to do the job, right? It seems to me from readings I've done on the subject that you have to have a lot of pipe a long way upstream, and taking advantage of slope and gravity to develop the water power you need.

All the best,

Lanny
Click to expand...
Rabbit hole --> Gravity Dredge Plans
 

General rule of thumb, 10' of drop for 4"

I have read others doing it with 6-7' drop over 100' with 4" though.

If you build a damn where you are working you also help.

I am no expert though, thats just what I have read.
 

The way I understand gravity dredging is that you lay out your hose downstream of where you want to suck. You can run it into a crash box mounted on a sluice. In the youtube video that I saw i don't remember how long his hose was but at the up stream end he had pretty good suction. His only problem was that his hose was corrigated so final clean up was a bear. If you are wanting to run a nozzle at the bottom end I would think you would need a rather large opening in some really fast running water to generate the pressure you'd need. I agree 50' wouldn't be long enough and you would want it to be as straight a run as possible.

Gramps
 

My mind has been all over this for a while. I'm glad you brought it up. I'm thinking I could make a decent venturi nozzle out of pvc (fill with sand, heat and bend). Then attach it to the end of a 20', 2'' hose and run the other end into the sluice. The problem is that when there is material in the hose, the flow slows. So, you can't rely on siphon alone. So, feed the venturi with water from a garden hose with a funnel at the other end from upstream to give the material some back pressure to aid the siphon when it bogs down. And you put the venturi at the input end rather than the usual sluice end. Does that make sense? Wrong question. I'm going to try it, so have any suggestions?
 

Rik,

I'm no expert, but I think having the venturi on the out put end of the hose makes the most sense.

Running your material through a long run of hose is asking for trouble. Sounds like you're gonna try it anyway, so let us know what happens.

It's very interesting that suction dredging is ok without a motor....just a loop hole, or is it the noise of an engine that is causing all the fuss?
 

Gold Maven said:
Rik,

I'm no expert, but I think having the venturi on the out put end of the hose makes the most sense.

Running your material through a long run of hose is asking for trouble. Sounds like you're gonna try it anyway, so let us know what happens.

It's very interesting that suction dredging is ok without a motor....just a loop hole, or is it the noise of an engine that is causing all the fuss?
Click to expand...

Yeah, trying to suck material through a long hose clogs up. I tried with 50'. I think 20' might work. But that's not long enough to get a good drop...I'll let you know what I find out.

The last draft of the law that I read very specifically mentioned motors in every sentence about dredging. It seemed to me they intentionally left the door open for gravity. One BLM site mentioned that gravity dredging was allowed. They pretty well close down the river for the salmon spawn, up to the first dam on the Merced. Leaves me to think it is just about noise. But speculating on the intentions of bureaucrats could have it's own thread...

The "Gravity Dredge Plans" link is great. Lots of good info. Under those conditions, it looks like it would work.
 

Last edited:
I did the raised suction pool type with 60' to sluice and SOMEONE STOLE MY PIPE!!!!
But it did work with about half the suction of a standard 4" dredge.
I though up a new type that uses a standard venturi. When I can spend a $100.00
I'll put it together and shulp it up to SGEFR
Let me know your thoughts.
Gravity Suction multiplier 1.0.png
 

I thought I try a variant on this idea, and to get to the point .... it did not work. I have drained my pool (for winterization) over the hill using the 1 1/2 inch pool vacuum hose. It will flow thousands of gallons in a very short ammount of time, I generally have to keep an eye on it not to loose the entire 25000 gallons (big pool .... it came with the house) if I have the hose in too deep. I thought it would work in the river mounting the downstream end to my A52, and the upstream end doing the vacuuming. It sounded simple enough, just keep the upstream end submerged and once the siphon started ... I should be able to gently vacuum up along the exposed bedrock. I had plenty of water to accomplish this, but it did not go as planned. The pool hose floated when not full of water. I was never able to rid the hose of air, and get the full water flow I desired. I had two sections of hose together, so there was 100 feet (remember, ...I said it was a big pool) of hose lying in the stream, most of it floating. THere was a good ammount of water flow in the brook, and this made for quite a wrestling match to simply hold the hose upstream. I did not really see this coming, but with that much hose in the current, it took a great deal of effort just to hold the upstream end in the water. The hose is ribbed and the water friction was quite powerful. Although never ridding the hose of air and thus getting a adaquate flow of water to test how much suction I would gather, I do not think it would have been enough. I was only looking at a verticle drop of 5+/- feet. When I emptied my pool it was in excess of 10. Even if all else had been sucessful, I think I simply would have filled the hose with sand (or gold) and stopped it up. After arriving and letting this 100 foot snake beat the heck out of me for 1 1/2 hours, I thankfully gave up on the idea and wrestled the hose back into the truck. The rest of the day was much more relaxing.

Most of you above are doing this on a different scale, and probably a smarter one. I just throw this story out there for those who may read it and be temped to try. It may have worked if I could have A) had a greater vertical drop B) the ability to lay the hose out of the water flow C) found a smoother (inside and out) type of hose (although I am not sure if ther is such an animal remaining flexible and portable).
 

Trial and Error are how we get things done. :)

Next time tie sections of the hose off to rocks, stumps or stakes to keep from having to fight it so much.
It also helps to have a valve at the low end to shut the water in, this way you can work water in and remove all of the air from your hose before pinning it down with a rock underwater and going back down to open the valve and start the flow.

1.5" is pretty small, 5' over 100' is probably not enough for that size.
I would also reduce that size down to .75" to keep from clogging the hose and to increase suction.

Next time if you can find something like 15' over 100' I think you could have something working.
Also, you could probably get away with 4"x100' with a 2.5" or 3" reducer with 5' drop but 10' over 100' is better.

:)
 

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