From my builder "In W.A to get building approval council require a engineer certification with drawings".
got to give the council employees something to do - and its all about liability - if your house falls down your slope, councils dont want to get involved.
one tree - phoning the council is the best bet - everything goes by them, so you may as well play the game. and ask them every question you can think of over the phone. The advice will be free, so take it and write it down.