How can they tell that leaving a lock gate open will drain a waterway?

I JUST cannot understand how Canal & River Trust can tell that leaving a lock gate open will drain a waterway, writes T. Lang.

Even to telling the BBC the same thing, that it of course published trusting the information it is given to be accurate.

Not accurate

But it certainly is not accurate [Sorry, but we do not use capital letters—Editor.] as everyone of us many thousands of boaters who use, or have used the waterways locks well know. The only way you can actually open a gate is if the remaining gate is firmly closed, holding back the water.

Isn't there anyone at Canal & River Trust who knows about the workings of the locks on its waterways?  And knows full well that opening a gate cannot drain a canal, otherwise every boaters on the waterways will be emptying them when he or she opens a bottom gate to either bring a boat in or take one out.

This really is stupidity at its worst.

And from Dom Grant:

If, as Canal & River Trust want everyone to believe, leaving a lock gate open drains the waterway, how come we can cruise them? 

For if we drain the pound, as Canal & River Trust tell when opening the bottom gate that sometimes is open for quite a while, how can we proceed, if the canal is then drained? For there will be no water!

And there are lock gates where you are asked to leave open, yet the water is still there!  It's Crackers!

There are other emails in the same vein but their language is not publishable!—Editor.