On Tue, 17 Nov 2009 08:33:59 -0000, Bob Hobden wrote:

That is the way most modern Koi ponds are built although they often line
it
with Butyl Rubber to make doubly sure it's watertight and they also
include
bottom drains so the can remove the sludge at the turn of a tap/pull of
the
drain. I've seen them 9ft deep built that way.
One thing, if you build it deep enough with straight sides you won't
have a
Heron problem as they won't be able to wade in it. Ours is a metre deep
at
the sides and although Herons have looked they always fly off empty
beaked.


I'll answer the mechanical bit, no doubt Spider will reply on the other
queries.
The blocks were fixed with a strong 3:1 mortar mix using ordinary cement.
They are built on a very substantial solid concrete bed, and I don't
expect any leakage.
There is no drain. Since the pond is raised above ground level we can
siphon it off onto the garden with a few feet of hose, and because the
bottom is flat and smooth we can easily scrape up the muck with a plastic
dust-pan.
One reason for making it raised was that if it ever got too much to look
after as a pond, we could fill it with earth and turn it into a nice
raised bed. Another crucial requirement was that the sides should be at a
convenient height for sitting and drinking tea whilst watching the bees on
the summer border.
There is a sump cast into the lower pond to house the circulating pump.
Copper pipes for water and cable conduits were laid inside the concrete
base.
There is an underwater light in the upper pond which has two functions -
it can illuminate the fountain, and in very cold spells we can run it at a
much lower level so that it gives off just enough heat to stop the pond
freezing solid. The pump and light are both wired from dimmers inside the
garden room so that we can remotely adjust the levels.