Manky Badger wrote:

I'm starting digging a pond today. the plan is that it's 4 metres long, 2
metres wide, and going down in steps to a maximum of 2 metres deep.
Anyone got any tips?

Some questions spring to mind - can I just dig the hole & line it - will
the sides cave in?
If I (as I hope to) use the soil from the hole to build up the sides of
the pond, how thick should the sides be?

I've somehow lost the most recent posts to this group, so I'll respond to
your later questions here :-)

For _show_ koi (please: not "koi carp" - that's so repetitively redundant),
deeper is supposedly better. If you have herons or other predators, deeper
is better. 2 meters is probably more than you need, but 1.5 is good.

Whether the soil will tend to collapse depends entirely on the soil. I went
down 5 feet in almost pure sand, and had very little trouble - but I think
it was perhaps reaching it's natural lifetime when I sold that place after
about 5 years. There was beginning to be some slippage. In clay, you
probably never need to worry. You also need to worry about drainage,
though - if your pond goes below, or even close, to the water table, you
will _always_ have trouble with subsidence, even in clay, because the
hydrostatic pressure outside will counter the pressure inside the pond.
--
derek