Seriously Mort I have taken enough of the barbel's cousins in other countries of the world to know that fly fishing for barbel is probably deadly.
Barbel eat vast numbers of nymphs, especially caddis and damselfly nymphs. They probably also take lots of midge pupa.
The best method would be an adaptation of the very popular "Czech Nymphing" style on beefed up tackle, say a 8 weight 10 foot rod with 8lbs leader.
Fish one nymph tied on say a size 10 hook below a strike indicator. Fish upstream and across and when the indicator sinks, hit him.
Have no mistake, a powerful fly rod with a disc drag reel will soon master the biggest barbel. I have caught Vaal River Smallmouth Yellowfish (Barbus holibi) up to 8 lbs on size 12 flies and those fish fight even harder than barbel.