River having dried up on the banks, used a digger (9)

'used a digger' is the definition.
The definition and answer can be both to do with contact as well as being past participle verbs.
Perhaps you can see an association between them that I can't see?

'river having dried up on the banks' is the wordplay.
I cannot quite see how this works, but
'river' could be 'r' (abbreviation for river) and 'r' is present in the answer.
'on' could be 'to' and 'to' is found in the remaining letters.
The remaining letters 'welled' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...

Can you help me to learn more?