How to pipe bottom drain to raised waterfall via filtration unit

[Klute]

Hi, I'm in the process of building a smallish (12,500 litre) pond to host some Koi and other fish. The pond will be part below ground (1m-1.2m) and part above ground (70-80cm). I'm installing an aerated bottom drain with a 4" pipe to get the dirty water to the filter units - currently looking at the Oase Screenmatic2 60000 unit (which I know from specs is oversized, but I'm erring on side of caution with manufacturer figures on filtration efficiency). So getting the pipework from drain to filter is all good and gravity flow works. But the clean water coming out the filter I want to then get up a 1.5m rise to the top of a waterfall - just not sure how I achieve this? Clearly I need a pump after the filtration unit, but how do I ensure correct flow rates such that pump does not run dry (if piped directly to filtration unit outlet) or do I need some sort of connecting pump chamber such that as the pump pushes water out and up to waterfall, gravity ensures that water rate incoming from bottom drain maintains the water level in the pump chamber? Or am I missing something and/or overcomplicating things!!

 

[j.w]

and welcome @Klute
So that's about 3000 gallons. So how many koi do you plan on adding? I only have goldfish as koi need a ton of room.

 

[Klute]

Hiya J.W - thank you for the welcome!
I'm actually inheriting 3 Koi (around 8 -10 inches) from a workmate who is selling house and the new owners have said they will fill in the pond he has. I'm not expecting to add to this (unless they get frisky!) - just planning on goldfish otherwise also!
I have been told that it may be worth just running the filtered water back to the pond and use a separate pump for the waterfall, which I guess could work, but I definitely don't want the pump in the pond - so the extra piping effort... meh!

 

[GBBUDD]

I'm erring on side of caution with manufacturer figures on filtration efficiency)

Wise.

Sorry I do not know any of the oase line up but any gravity fed filter like a sieve works by dropping onto a micron filter. The pump goes below and as the water returns to the pond it rises thus falling over the sieve again.

if it's a foam filter of some sort beware as it starts to clog the water can over flow.

A bead filter can be a gravity fed as well as could a shower. And those to would need the pump on the out flow. As it pushes water up to the top of the falls it simply drops back to the pond and round and round she goes. Now water in. Motion is also a player here if you have a small waterfall then it's not much to consider but if it is say 20 fet long there has to be an area when the power goes out to catch that water. So it doesn't overflow and when the pump does start again that it doesn't run dry because it lost water.

 

[Klute]

Thanks GBBUD and J.W > so i've been having a think and trying to sketch out what I want to do - and I think my thinking had started to look at flow rates - given that I want to return the clear water via a waterfall that is somewhat more dramatic than trickle... I hope the attached picture shows what my current thinking is - going to a local pond / aquatic company at weekend to discuss further.
As mentioned before looking at part submerged pond, utilising a bottom drain to supply sufficient flow to a Cetus Sieve and then pumping out to 2xpressure filters (Oase Filtoclear or Hozelock Bioforce revolution) through to waterfall. I think the bottom drain will supply sufficient waterflow! Thoughts/comments?

 

[Klute]

 

[GBBUDD]

I know you folks on the other side of the pond like your raised rectangular ponds. But I can't believe you have energy water being pumped and not having a waterfall. I'd look at bead filters to go with the cetus. That's a good combination. I don't know what your looking at I'm not familiar with those filters

 

[Klute]

Hey GBBUDD - thanks for the response. I understand the products are probably not familiar to you. Not sure why you think I don't want a waterfall - that is exactly what I DO want!!
Hence my key concern is the flow rate I can achieve from a 110mm / 4" bottom drain - will I get sufficient flow from the drain to maintain a good flow over a 24inch wide waterfall at 1bout 1.5m head? I'm calculating I need around 13,200 litres/hr for this - but if the bottom drain can only supply say 8,000l/hr then clearly I need to supplement this with either a second bottom drain or another source if water. Hope that makes sense!?

 

[GBBUDD]

wasn't shown in your drawing was all.

the simple answer to your 4" pipe question is yes it will give you more much more than you'll need. 1000 gph is needed per foot of spill way or waterfall for a minimum. so even with 4 feet of head pressure you can still get 260 gpm or 15,600 gph now that may sound like crazy water flow but i push 12000 two return jets and on feed up to the bog.

Water Flow Capacity in Steel Pipes (sch 40)​

Pipe Size	Maximum Flow (gal/min)	Velocity (ft/s)	Head Loss (ft/100 ft)
2"	45	4.3	3.9
2-1/2"	75	5.0	4.1
3"	130	5.6	3.9
4"	260	6.6	4.0