Filling in an old Koi pond (drainage)

[Cam1210]

I'm filling in an old Koi pond. It was constructed by the previous owner of my house. He dug about a 1.5 metre deep hole and lined the bottom with concrete. Prior to backfilling it, I thought I'd better break the conrete bottom up to make sure I don't end up with an area of the garden susceptible to water logging. I used an SDS Plus drill to dig into the base and found that he used a lot of concrete! The base is about 1 foot thick. Underneath the base the soil seems wet and clay-like. After a day or so, the hole I made has filled with water from underneath and we've had no rain. We live reasonably close to a brook (within 200m) - is it likely I've reached the water table?

My thinking now is, if I continue to break up the base by hiring a concrete breaker, is this a pointless exercise? Am I best just to fill the hole with hardcore in the expectation that any water will drain sideways into the surrounding ground?

I attach images - you'll see the sides are dry, ground level is approximately the level of the first sleeper which sits above a lintel of concrete, then the hole is about 90cm below surface level.

 

Pond and surrounds:

 

Inside of the pond/profile of sides. The hole I broke through the base is just above the centre drain pipe of the pond:

 

Close up of the hole in the base, with water that has come upwards:

[saveasteading]

5 minutes ago, Cam1210 said:

any water will drain sideways into the surrounding ground

That. 

Seasonally by the sounds of things.

A few holes in the bottom is good.

Perhaps put a layer of rubble on the bottom as a void for any extreme rain. I'm guessing you will knock in the sides to some extent.

Presumably the pond sides used to be lined with rubber liner..that stuff in the foreground. 

[Cam1210]

On 08/07/2023 at 13:49, saveasteading said:

That. 

Seasonally by the sounds of things.

A few holes in the bottom is good.

Perhaps put a layer of rubble on the bottom as a void for any extreme rain. I'm guessing you will knock in the sides to some extent.

Presumably the pond sides used to be lined with rubber liner..that stuff in the foreground. 

 

Thanks for that…yes, he had a rubber liner in the pond that I removed to reveal the sides and base.