Personally I see no problem with 2m deep. However 2m deep and only 2m
wide, with shelves, is going to make for an awkward lining with sheet
liner, I speak with the experience of lining my 4ft deep 10ft wide,
shelved pond. Try making up a shelved cardboard box and try lining that
with plastic sheet to see what I mean. Given your dimensions I'd suggest
either digging straight down to depth and building concrete block walls
or if you want built in shelves reduce the depth or preferably increase
the width significantly.

Personally straight down and concrete walls would be my choice, its
simpler to line and greatly increases the water volume, plant shelves
can them be made of benchs sat on the pond floor or plants can be hung
in baskets from the sides. Make sure you or visitors could, unaided,
get out of 6ft deep water should they fall in

That said I would do some research before going any further, look into
filtration, pumps, access, wiring and plumbing etc

A good UK site to browse is http://www.koicymru.co.uk/construct.htm
http://www.yorkshirekoi.co.uk/ may also be useful

useful american board is
http://208.67.224.245/forums/
the latter is for ideas, not techniques, their building methods differ
from ours.

Re a minimum thickness for soil levees, I dont know numeric values but
I think they are a good idea because, IMO, they allow the pond level to
be above the surrounding ground level which avoids runoff and liner
ballooning issues. Mine is about 2ft wide at the top, ie wide enough
for a path, for ease of access reasons not structural.




--
sean mckinney