Hello Hamish,
Some good advice there already esp. from @benno573 on water layers. My son and I crabbed quite a bit (before we got a boat that's painted!) in your neck of the woods, we found rocky ground was productive - or just off rocky ground. There'll be a heap of debris in the river after the rain - regular checking is a good idea as they tend to move if light. The Seventeen Mile Rocks rock bar and a bit further up - just downstream of the Jindalee bridge on the northern side, is a rocky area that's produced, as well, the river side of Hazelmere Parade is also worth a try - but keep your eye on your pots there as the current can be strong.
Good luck!
Rusty