David A Stocks wrote:
"Basil Jet" wrote in message
news

http://maps.google.co.uk/maps?hl=en&...03433&t=h&z=19

If you track the combined brook southwards, it nearly meet the Lea at
Stonebridge Locks, but has its own channel alongside it to just past
Tottenham Locks. Why is the brook deliberately kept apart from the
Lea Navigation?

The plumbing in this area is very complicated; you can get an idea
from the diagram on this page:

http://en.wikipedia.org/wiki/River_Lee_Navigation

Presumably there isn't any need for water from the brook to feed the
Lea Navigation between Stonebridge and Tottenham Locks. If the brook
is ever at a lower level than the Navigation then that's your answer.

Oh, I hadn't considered levels. Now, the obvious answer is that the banks of
the combined brook are lower than the water level in the Navigation until
you get below Tottenham Locks. I had no idea that the Lea Navigation was so
high (two locks worth) above the surrounding ground above Stonebridge Locks.
It suggests that the Lea Navigation was not so much dug as erected.... or
maybe a bit of both, i.e. it was deliberately built at a level such that the
earth removed from the shallow trench would exactly match the earth required
to build the low banks.