I really appreciate the wisdom on this forum. There is truly nothing like it in the pond world. I was hoping to get your help on a diffuser placement question that I haven't been able to find much info or discussion on.

I am planning a dugout pond 360 feet in diameter with a 200 foot diameter island right in the middle, giving it a "donut" shape. The pond would have 3:1 sloping sides, a depth of 12 feet, and an 8 foot wide "flat section" at the bottom. Total volume would be 3.5 million gallons. The pond is in the North East, so a good amount of cold weather and snow.

I know this shape isn't ideal from a fish production perspective or from an aeration perspective, but my primary goal is to give the kids something to boat and swim "around". I would like the water to be as clear as possible and as effective as possible at breaking down organic debris, so I am planning on putting several diffusers around the pond.

My question is how many diffusers should I put in and with what air flow?

The length of the "center line" of the pond bottom is 880 feet, so if I put one every 100 feet that would be 9 diffusers. Is that too much? Or too little?

Your thoughts are greatly appreciated.

Ted

Ted I don't know anything about diffusers, but thought you might like to look at this:

https://www.ecohome.net/guides/2237/natural-ponds-and-natural-swimming-pools/

Thanks Zep. I’ve actually been on quite the research journey with NSPs over the last few years. Originally I was planning to put an NSP “marsh” in the center of the donut, and use a pump to pull water from the top of the donut, into the marsh, and have it flow out at the bottom of the donut, where the water would then circulate back around each side of the donut to the beginning of the marsh again. My thinking was this would create filtration and horizontal flow.

As I researched it more it seemed that these marshes can get “clogged” quite quickly. I was also worried that the water circulating horizontally wouldn’t be enough to get oxygen to the mud/water interface at the bottom of the pond where it’s needed to decompose organics. So I decided to scrap the central marsh and use the pump in the middle of the donut to circulate the water horizontally (2000 gpm with a series of “air lift” pumps) and put the “marsh” around the outside of the pond where water would flow through it at the edges.

At this point I thought I should probably have bottom diffusers to circulate the water vertically as well. But if I’m going to have vertical circulation it seems that horizontal circulation is redundant.

So I’m coming full circle a bit. I’d like the water to be clear, maintenance to be minimal, and operation and construction costs to be minimal. A big wishlist for sure. Right now I’m thinking I have a series of bottom diffusers to create vertical circulation and leave it at that for now. But I’m not sure if that’s right or best.

I'm wondering what people think about vertical circulation vs horizontal circulation. Vertical circulation via bottom diffusers vs horizontal circulation via a donut shape pond + a pump.

Vertical circulation seems like a must, as it seems like the only way to bring up bad water from the bottom of the pond.

Given that vertical circulation will create some "local horizontal circulation" as the boil hits the surface, it feels like "global horizontal circulation" of water continuously circulating around the donut is unnecessary. I'm wondering what you all think about this?

Here is a sketch of the proposed pond to help you visualize the donut and how we could create horizontal circulation by pumping water across the "wall" in the river area.

Btw Bill Cody, I was just re reading this thread from a year ago: http://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=501349 At the time I was thinking of doing a horseshoe instead of a donut. At the bottom of the thread you suggested maybe putting a stream across an island. I missed the comment at the time. Seems like you were a few steps ahead, as that's now what I'm considering (one horseshoe turned into two horseshoes connected together). I'm wondering if you think a stream would be "worth it" or if I should just doing normal bottom diffusers spread around the pond. The challenge of the stream on the island would be getting there to do maintenance and repairs.

The two pictures of the pond are different. Are you reshaping and rebuilding the pond? The water movement from the airlift stream outlet (down stream) will basically circulate a shallow band of water horizontally due to water density; warm being lighter than cooler water. To get deeper water at the stream inlet you will have to extend the air lift tube at an angle deeper into the pond with the air injection at the bottom of the tube. I'm not sure how all the fluid mechanics of this would work. The guy that I know who built a U shaped stream using air lift has died so I can't ask him questions. The water that circulates in the pond according to your arrows would I think be mostly surface oriented moving water maybe only 2 to 4 ft deep and not a full water depth column type of circulation assuming most of the pond is 7-9ft deep.

Hey Bill. The pond is not yet built. I have a flat field of clay that holds water well (tested in a few spots). We dug a 70x70 foot pond a few years ago that we really enjoy. I’ve been working on a plan to expand the pond. Given that it is a dug out we have somewhat of a “blank canvas”, so I’m thinking about how we can get it just right.

I think you are right that only the top couple of feet will circulate. Given this I’m thinking we’ll need to do bottom aeration all around the donut as well. But once we add bottom aeration I’m not sure if we’ll get any benefit from having horizontal circulation as well.

What do you think Bill? Do you think bottom aeration is a must? If so, do you see any advantage to including horizontal circulation as well, especially as it pertains to water quality? Any thoughts from others are appreciated as well.

Ted

With bottom aeration I do not see a significant benefit to the horizontal circulation unless you want a stream spawning fish such as walleye, suckers, trout, or shiners to reproduce in the stream like conditions. The more a pond shape deviates from the circular shape the more bottom aeration diffusers it takes to get good mixing throughout the whole pond. A bottom diffuser works most efficiently in a bowl shape. Also the more a pond shape deviates from the circular the more shoreline there is and the more space or area there is for weeds filamentous algae(FA) to grow. Weeds and FA are always a problem in shallow shoreline water not in the deep parts of the pond. Pond design can minimize weed problems. Your Canadian pond is likely to be very clear so a large percentage of deeper water will reduce your weed problems.

That’s a good point Bill about the shoreline weeds. I haven’t seen many weeds in our 70x70 pond, but it is only 3 years old so perhaps there hasn’t been enough time yet. Perhaps I could help add pond dye if needed?

If we were to go with this donut shape, what spacing on the diffusers would you recommend?

If I do 5 diffusers that would put the diffusers 175’ apart from each other, with each one responsible for turning 700,000 gallons. What do you think about this?

Diffuser spacing at 175' would in my opinion be the maximum separation distance. This assumes that each diffuser receives at least 2cfm of air. The less air a diffuser receives the fewer bubbles it makes and the less water it moves. If you are delivering only 1 cfm per diffuser then closer spacing would IMO be needed. 2cfm x 5 diffsr = 10cfm. 0.75 hp compressor delivers about 10cfm. The island is deflector of water movement; thus the shape requires more diffusers. I do not like islands in a pond due to water circulation problems plus it adds more shallow water weed problems, but some like the look of islands.

I agree. My thinking is that a large island might make the pond “feel bigger” by obfuscating “how much further the pond might go”. I’m also thinking it will keep the kids more engaged by giving them something to “go around”. We will see if I regret that.

If 5 diffusers is the minimum, what would you do if it was your pond? I have time to plan all this out, so I want to get it right vs saving a few dollars on a few extra diffusers.

For the compressor, what depth would the 10 cfm be at? Any particular model you’re thinking of?

The 10cfm compressor would be a 3/4 hp rotary vane that produces good air volume down to 17 maybe 18ft, but better air flow is at >17ft. Best diffuser placement will be dependent on final shape of the pond. IMO is you use the air lift stream feature a separate compressor should be used for powering the air lift so you get maximum water flow through the stream.

I was thinking the same thing Bill, with one compressor for bottom diffusers and one compressor for what I am calling "the bubble wall" at the start of the stream.

For the bubble wall I am thinking of pouring a concrete wall at the start of the stream with a series of 4" PVC pipes going through the bottom of it. I would then attach this to a pipe PVC to create the airlift pump. I would pump in air at the bottom. Here is a rough sketch:



I've done quite a bit of research on Airlifts over the years. According to (this study) you get the best efficiency by using a regenerative blower and splitting the air across multiple pipes and injecting it at a fairly shallow depth. This study suggests that I might use the Sweetwater S45 1.2 kw regenerative blower to power 27 4" diameter airlift pumps, each getting 3 cfm at a water depth of 50 inches. It is suggested that under these conditions that each air lift could move 4,365 GPH, for a total flow of across the bubble wall of 117,000 GPH. This would give a stream with a 6.7 square foot cross section a flow of 0.66 feet per second, if my math is correct.

Balancing the airflow across 27 outlets seems a bit daunting, but I'm thinking it could be doable. One other interesting thing I found in this study suggested that flow rates only increased by 5 to 10% when injecting air through a diffuser vs just an open pipe. This should make it a bit simpler to build 27 airlift pumps, vs needing a diffuser for each one.

What do you think of this?

Hey Bill. Wondering if you or others see any "gotchas" with this.

While I think I will still need bottom aeration, I do wonder if 100k GPH stream could also help act as a "skimmer" of sorts, allowing leaves and debris to be pulled into one spot where I can easily remove them.

I think this is all pretty new in common pond management. You are probably going to actually do this to prove its effectiveness. In theory and on paper it should work. However you know what they say about the best laid plans of mice and men.