I also found the H.Avon very hard going last season. After the weed cutters had gone through some stretches were like a desert. On parts of the Severals it was gravel from bank to bank. Hopfully things will improve this season with a ban on weed cutting.
I dont know about trying the Stour, that was just as hard you only have to look at the river reports on this site with only 5 pages to the end of the season, and very little of that was about Barbel. Most of the posts were talking about Bream, Chub, & Carp.
The Upper Benyons also did not fish that well during the day, however the guys who night fish did very well which just goes to show that the fish are still there!
It is a matter of trying different tactics and baits, and getting back to basics.