TLDR: Looking to build a Gold/Muck dredge using Venturi effect. I think I have the pump and nozzle set, looking for guidance on hosing sizes. Or at least confirm my thoughts.

I’ve been reading through the forum, trying to piece together the information I need, with a lot coming from Driver Cody’s posts.

This trash pump seems to have enough power and is affordable. Craistlist and FB marketplace didn’t seem to offer much better options.
https://www.harborfreight.com/3-in-212cc-gasoline-engine-semi-trash-water-pump-290-gpm-63406.html

Going to spend a little extra for a nozzle, I suspect I could make one cheaper, but I like these:
https://www.keene.store/mm5/merchant.mvc?Screen=PROD&Product_Code=SN3
or:
https://www.keene.store/mm5/merchant.mvc?Screen=PROD&Product_Code=SN32

Setup thoughts:
So, I’ll have a 3” trash pump that I’ll put on my floating dock so it can move with me as needed. I’ll probably only need a few feet of 3” intake hose. I’ll have a short 3” discharge hose from the pump that I’ll have to reduce to 1.5” or 2” to the suction nozzle. And then however long 3” hose I need to pump out over the pond bank. From the nozzle, I’ll probably have a 3 to 6 foot 3” pvc pipe to a T joint or something with a 1 to 2 foot pvc capped with about ¾ inch holes drilled for a sort of vacuum end.

Questions:
Does this setup sound feasible? Am I correct in reducing 3” to 1.5 or 2” to the nozzle. I’m guessing it won’t negatively impact the pump? Any difference between 1.5” vs 2” at the nozzle?

Pond details:
I have a little under a ½ acre pond. I’ve been aerating (two bottom diffused) the past 5 years since we bought the property and using bacteria, it has cleaned up a lot. We live in an area with a lot of flat rock, you can find it in all the nearby creeks, and in our ditch by the road. I think the pond has a flat rock bottom. It is very, very solid probing with a measure stick, and is pretty consistently 8 feet deep all way around the pond. It has about a foot or so of loose muck/silt that I think will suck up pretty nicely. I plan to do most of the work in spring/fall when we have excess water and just pump over the bank towards the woods. I’m planning for a several year project. Perhaps later I’ll look at some sort of de-watering. The pond is roughly a triangle shape, so I’ll start at the swimming area point and work my way out over a handful of years.

Kids love the pond, it is right near the house. Would love to clean it up more and get rid of the leeches.

Stocking Yellow Perch and Pumpkinseed Sunfish will help with the leech problem. I've never had any experience with a dredge.

Currently has a bunch of bass, about 7 koi, one grass crap, and three painted turtles. I was thinking about throwing some bluegill in there, I may get yellow perch instead if they will gobble up leeches.

Thanks

Do you know what the requirements of the venturi nozzle are? I ask because trash pumps do not make much pressure and the nozzle manufacturer calls the connection a "pressure hose" . I imagine that connection wants high flow backed by higher pressure. On top of that you are talking about reducing the discharge size further. This will reduce the water flow through your pump/system. If you have not contacted the nozzle supplier, I would ask them what kind of pump parameters are required for a functional venturi.

Great suggestion, I'll try contacting the manufacturer.

Thanks

I contacted the manufacturer and they just want to sell me a complete dredge system for ~ $4,300, designed around a 13hp pump. Not sure if I really do need that much pump, they are just over engineering it, or they just want me to spend a bunch of money on their stuff. Anyway I guess I'll have to put this on pause and rethink since I can only spend around $1000 on it at this time.

Is it just soft silt or are there leaves and sticks mixed in? If its just silt why not just run in through the pump? You'll draw less water out of the pond and have more suction. I've used the 301cc HF full trash pump. Works well but its slow, very slow. At 8' deep this is going to make it even more difficult.

its just soft silt and muck. I rake as much of the sticks and leaves from the fall out as possible, by mid summer after aeration and bacteria I don't see any leaves left. But I'm sure some remain. Not many sticks, but some are there I'm sure. I plan to make some sort of 'vacuum head' with 3/4 or 1" holes drilled to prevent large debris. So, this might be a better plan.

I don't mind the time, I plan to work away at it over the course of a few years. And In fall I don't mind lowering the water level up to 4 feet.

Thanks

If you do have any leaves they will clog up any sort of grating quite quickly. I thought the point of a venturi dredge was so you really didn't need to screen out that stuff?

There isn't anything visible, and if you pull up handfuls you won't find much. I'm sure there are the odd bits here and there.

I'll have to pump it about 80 feet at most. Do you think a short discharge and longer intake would work best, or the opposite?

thanks

They push much better than they suck so go as short of intake, and close to the water as you can, then run the discharge as far as you want. I have 300' of discharge.

I had some leaves in the shallows/edge but after a few feet deep it was just pure pudding like muck.

Just dont want to set the wrong expectations.

Perfect, I'll place the pump on my floating dock so it can follow me. Thank you.

Sounds like my pond has similar muck. I think I'll give this a try with that 301cc HF pump.
Thanks again

I'm not sure how to access the archives but I spent a lot of time sucking muck out of my pond with a trash pump. There are a couple of threads about doing it. I built a couple of devices to suck it up they all worked. One allows me to stand on the shore and pull it across the bottom of the pond and then pull it back and do it again. Works really good when the muck has been sitting undisturbed for a while after a couple of passes you get down to firmer muck. I use forty feet of intake hose that allows me to keep moving further across the pond without getting into the water and extending the intake pipe. If you can access the archives there is a picture of what I called a hydro dozer. It's what I would pull across the pond

3rd from the top. Common Pond Q&A (archives) https://forums.pondboss.com/ubbthreads.php?ubb=cfrm

Here is a link to one of cb100's threads on dredging muck.

Dredging Muck

I think cb100 also made some good comments in someone else's thread?

Here is the other thread I was trying to remember.

Pond Restoration

Good luck on your project!

Thanks for the help finding those other threads. If you need me to try to explain how it works I will give another explanation. It worked fairly well but you can make more headway by getting in the pond and using an intake that you hold in your hands and work down into the muck.

This is what I'm planning to do. A setup similar to what you have, but I would use it in the pond and in a similar way I would use a vacuum cleaner. A vacuum head similar to your design. Thanks to all for the help. Hopefully I actually get to try this out around Sept/Oct and can report back with good results.

Having spent some considerable time dredging using Keene and other equipment, vs trash pumps, I can tell you it is worthwhile to buy the Keene venturi and appropriately matched pump / suction hose / Nozzle... They just work very well, better pressure and volume from that pump design. We would modify our nozzles with handles to stand up with, and fire nozzles run from a second pump to break up hardpack material.. Would recommend a settling run with return back to the pond to recycle water if you have the space available to slow the flow enough to settle out your silt, youll be amazed just how much water youll run outta the pond.