JUST read the 'Farmers water abstraction article' guess understanding its permitted minds at narrowboatworld already whirring, writes Dave Godfrey.
But in case not might be a worthwhile exercise to a Freedom of Information Canal & river Trust permitted water abstractions by third parties.
Some are plain and simple, for example the Notts Beeston heat exchanger which is fed from the Trent and is returned after cooling usage.
Though others are as per the farmer article and are a straight loss of navigational water to lower lying land, couldn't say how many but thoughts crossed my mind as to how many on navigations closed or under current restrictions.
You may also want to ask how much the trust receives for the abstractions, could make an interesting review.