How best to fit overflow and pump pipes?

[Lisa555]

Hi everyone. This is my first post and I am looking for some advice please!

We have built a small raised pond (~500litres) from hollow concrete blocks. It's on a slope so deeper at the front than the back but level around the top of the walls.

I left a gap in the blocks so can put some kind of overflow in and also a pipe for the water feature pump.

The pond will just have plants in and hopefully the frogs will return.

I have attached photos. The blocks are 23cm deep. The gap I've left at the back of the pond is about 25cm wide and 7cm high.

I've bought epdm pond liner and a fleece underlay. The wall will be topped with coping stones. I don't mind leaving one loose coping stone above this gap for future maintenance (or would it be better to mortar it in position?)

I was thinking the best thing would be to fit two bulkheads (one for overflow and one for pump) with the overflow as close to the bottom of the coping stone as possible but I really don't know what the best method would be and am open to options. And I don't know how to go about fitting a bulkhead. Or if the liner would support this without it sagging down?

What would you do? Anything I might have missed that I need to think about?

 

[Mmathis]

Hello and welcome! Honestly, when I did my pond, I had an area similar to what you have, and just smushed the liner down into the cavity. Never had any problems. Basically, it was just a low spot where water could overflow. I don’t remember how I I did it (sorry), but I did include a grate (from the PVC section at Home Depot) so that the fish wouldn’t wash out with the water. It wasn’t anything fancy or technical.

Be sure you use some good underlayment over those blocks (sharp, coarse surfaces) to protect your liner. I ended up using an angle grinder to smooth out all the sharp edges.

 

[combatwombat]

Was going to make all the same suggestions as @Mmathis.

 

[j.w]

@Lisa555

 

[poconojoe]

I wouldn't use a bulkhead in a flexible liner. I wouldn't cut any holes in a flexible liner, but that's me.
Go over the top for any piping or hoses. Hide it under your coping stones. Make a notch in the concrete block, lay the liner and set the pipe/hose on top of that. Then cover with your coping stone.

Do the same thing for an overflow. Just an open pipe. You can put a drain cap on the pond side to prevent fish from entering. If you can't find some kind of cap with a grill, use a plain blank cap and drill holes in it.

 

[Lisa555]

Thanks for your speedy replies! That sounds so much simpler and less likely to go wrong. You have saved me a lot of time having to think about bulkheads! I think I was worrying too much about overflowing water just going out the back of the pond instead of being fully directed away but it would actually be ok if it just went out the back. I didn't notice the previous (sunken) pond ever overflowing.

 

[combatwombat]

Thanks for your speedy replies! That sounds so much simpler and less likely to go wrong. You have saved me a lot of time having to think about bulkheads! I think I was worrying too much about overflowing water just going out the back of the pond instead of being fully directed away but it would actually be ok if it just went out the back. I didn't notice the previous (sunken) pond ever overflowing.

You can always add a piece of scrap liner outside the pond to direct the overflow away. Or place a catch basin for the overflow to spill into and direct away with a pipe.

Placing something to keep fish from being swept out with the overflow might be a good idea, but it can also backfire if your pond will have a lot of leaf litter or wind swept debris because it can clog a grate during an overflow event and cause the water to overflow somewhere else.

 

[poconojoe]

My pond just overflows naturally wherever the low spot is. I don't know exactly where that is nor do I care. I never notice any puddles around the perimeter after a heavy rain.