Just an update, it's now been a good few months without any rain, thing are really very hot & dry over here, this whole week has been around 38-41C (+100F).
Went out again today with my wires to see what results I might get, as I was hoping the wires reacted the same at the two possible underground stream locations, that my brother and I located some months ago.
All I need now is to drill a hole to find out for sure!!