Sunken garden and pond

[Simon B]

Hello,
I have taken it upon myself to excavate a sunken garden and pond (remember Blue Peter garden ??) in my townhouse garden - and I am a novice at these things (too ambitious maybe!). The area is in the centre of the garden and away from the house. I have dug a trench around the area to be paved to build a retaining wall but I am a little unsure wether i should incorporate an element of drainage (maybe a gulley all around the area to hold standing water ?) How would you tackle this situation and would you incorporate some kind of land drain ??

i would very much appreciate your help

[84-1093879891]

With a sunken garden, unless you're on very free-draining ground, you need some sort of drainage at the lowest point to prevent it flooding. This drainage will need to be connected to the SW system, a ditch/stream, or to a reliable, working soakaway.

However, with a pond within the sunken garden, then the drainage point should be an overflow system, that prevents the water in the pond rising above a certain level. Again, you need to consider the outfall point.

Is the pond at the lowest point within the sunken garden, or is it, effectively, a raised pond in a sunken garden?

[Simon B]

thanks for responding so quickly. The pond is sunken within the sunken area.
I am thinking of making a gulley around the sunken area which would be filled with shingle/hardcore. I agree with you about a drain away/ overflow from the pond and I could install an overflow pipe out to the gulley area
The soil is heavy (clay-ish) but from last two days downpours it didn't seem to be retaining water (even in the lowest part of the pond)

I welcome your thoughts and advice

[84-1093879891]

Would the base of this gravel-filled gully be lower than the the base of the sunken garden, though?

[Simon B]

yes, the gulley will be as deep as the centre of the pond although it will be fill with shingle. the gulley also forms part of a trench for the laying of foundation for the retaining wall

[84-1093879891]

So where will this gully drain to?

[Simon B]

I was hoping just into the ground - is that a bad idea ?

[84-1093879891]

Mmmm...depends on the porosity of the ground. I know you mentioned it's not particularly prone to flooding or waterlogging, so it should be ok.

Have you dug a trial pit to see if you can find the water table? If you can get down to, say, 500mm below the lowest point of the planned sunken garden and there's no sign of the water table, I'd take that as a good sign.