Bass swim in every inch of the water column, but most of mine come off the bottom using sinking lures that are hopped.
Different times of the year will see them favouring different depths. In the winter I get bass in deep water using metal slugs cast as far as I can from the bank. Most of these bass are schooled up and sitting very close to the bottom.
Bass don't like sunlight too much so generally in the morning they'll be closer to the edges of the dam. As the sun comes up they'll head out deeper. In the arvo they'll come back in again to have a sniff around. That's how they behave in Samsonvale...not sure about Borumba or Baroon as I haven't fished them yet.
When I use spinnerbaits I usually let them sink to the bottom. I work mine very slowly so they drag along the bottom. Sometimes I'll give them a little flick but most times just a very very slow retrieve is all you'll need. So slow that the blades just spin.
Use pauses on the spinnerbaits, bass will follow them but sometimes a pause is all that is need to make them hit. And use stinger hooks.
Dragging lures along the bottom will mean more snags but it will also mean more fish.
Jackalls are usually hopped along the bottom, if they are dragged too slowly they'll all snag. Work them as slow as you dare.
Try different retrieves as there's no set way to use these lures. Sometimes I'll rip the hell out them to get vibrations and noise to travel through the water.
Most times just a slow steady hop is what the bass want.
Good luck.