Melange wrote:

I dont suppose you'll find too many people who've built an aquaduct on
here!

yes an aquaduct is a good analogy - as for leaks, it wont be on all
the time and as the wall slope there wont be any water sitting on it,
unless the pump is turned on.
I found a product called flexcrete - a cementouse coating, supposed
to water proof damp basements and im told was used to waterproof a
wall that had water cascading down it so should work fine, this is not
an exact science

however what i need help with is, in deciding is "How" to build the
wall taking all the factors i mentioned into account.


I would suggest building the wall in concrete blockwork, remembering
to allow proper drainage for the ground that it retains. You will
need a properly designed wall with a concrete footing. You will also
need to provide expansion/contraction joints in such a long wall.

Then at the top, I would suggest casting the very top section using
in-situ concrete formed in plywood shuttering and incorporating a
U-shaped channel made from either vitrified clay or uPVC. It would be
wise to include an admixture in the concrete that would improve its
watertightness. Or you could try one of Flexcrete's epoxy/cement
products - but that doesn't sound cheap.

http://www.flexcrete.com/buildingciv...waterproof.htm