The GU is mostly around 4ft deep down the boat track I.E the middle.
Then it shallows gradually to the far bank to as little as 9"
The best and normal way to fish the canal is an outright squatt! approach with carefull plumbing to find where the far shelf starts!. When the match starts begin by feeding via pole pot 1 ball off your fav light crumb on this line and loose feed squatt over the top
( about 10 squatts a time!) the key is to do this ALL THE TIME!!!
As the match progresses you will find the fish drift further up the shelf and it is a matter of keeping them by following them across and gradually shallowing your rig for as long as you can.
It is also worth on every peg feeding a few casters at the start on the far side or at anything that looks like a feature.
Another good tip is to also feed a near shelf line at bottom of nearside shelf with a couple of balls of your fav mix and drop a big maggott or worm and pinkie etc over the top often can snare some big perch this way.
There are also so many other approaches using hemp etc if the roach are havin a go! however the above will hopefully get you a few!
Finally if you geta chance grab a couple of DVD by MARK POLLARD ON THE GRAND UNION The guys and absolute legend on the place and you will also pick up some good tips via him
Don't force the fish over to the far bank too soon, as there's only one way for them to go then and that's right or left and you'll lose them. You want to keep them on that slope as much as possible and that's where the constant feeding comes in.