On 2016\01\07 17:58, wrote:
On Thu, 7 Jan 2016 15:54:19 +0000, Basil Jet
wrote:

On 2016\01\07 15:01, wrote:
On Thu, 7 Jan 2016 12:46:15 +0000, Basil Jet
wrote:
People usually say the Thames is tidal to Teddington Lock, even though
the lowest lock is at Richmond Weir.
As well as the lock there sluice gates which are lifted when the tide
has risen high enough and the tidal flow is unimpeded.
When those are open craft just proceed past without using the lock.

I can't see them in Google. Why don't they just open both lock gates and
let the boats through there?

When the google river boat went through it was obviously high tide,
https://goo.gl/maps/Zb65Ca54SD92

In the down position they look like this.
http://www.geograph.org.uk/photo/587456

The Lock would impede the flow of the incoming tide even with all the
gates open as it is a lot narrower than the width of the opened sluice
gates.

Wouldn't the rising tide just go over the weir?

Also using the lock means it would be a bottleneck, High tide often
means higher traffic as many boats prefer to move on the deeper water.
You would find it difficult to pass upstream and downstream traffic
through the lock at the same time.

Fair point.