On 2014\05\03 18:43, Robin wrote:
I'm not convinced... no matter how narrow a stream is, it won't
normally be built over unless it's a high density urban area. And I
don't see the benefit in anything much being over the waterwheel..
axles of arbitrary length can transfer the torque to a river bank
site, although I suppose some energy would be lost.
FWIW account at one tidal mill was:
a. water mills tend not to be built on solid rock[1]
b. so pretty hefty foundations tend to be needed for the wheel which
exerts a fair old force with vibration and all
c. having built those foundations it'd be waste not to use them for
the mill itself, the more so as
d. when you have to make everything out of wood and what the local
smith can fettle you want to keep everything in the power chain as short
and simple as you can
[1] obviously there are exceptions and you may be lucky enough to have a
stream running through stone. Of course that may not be near good land
for corn 
Thanks! Really glad I asked now!