I would use the pointed angle iron fencing posts, backed by good chain link
fencing, then back filled with rocks. For this, you might find a demolition
taking place where large manageable chucks of concrete could be obtained.
They would last longer with regards to erosion and the limited power even a
torrent would have in trying to dislodge them.

Wooden stakes and boarding will as you realise rot and then the backfill
would be exposed and again washed away


I have noticed on another river the 'council' have used coir rolls ( a
bit like long sausages) resting upon willow faggot rolls. All with
wood posts at intervals, to hold it all back.

I would have thought that that would have only lasted 2 or 3 years,
and washed away.

Whereas I am being told if you use vaccum tanalised timber they could
last over 10 year.

How long would steel last in water ??? unless it was heavily painted
or stainless, in which case it would proably get knicked round here.
And what size crosssection for the steel

Just a few thoughts. Water is funny stuff AND powerful