Oh, and another quick one ; If there is loose weed or algae on the bottom, blow it away with your fins or hand, then search these areas. The algae is heavier than water and therefore sinks to the bottom and will accumulate in the lowest spots just like water does. I often use this method to find channels , vortices, and areas where the current has moved sand from. Of course if you don't have any algae you have to rely on other methods.
I have also noticed over the years, that stingrays are a good indicator that sand has moved, they feed on crabs and molluscs that live under the sand. When there is a big sand movement the stingrays come to get an easy feed on the shellfish that take a little longer to bury themselves again, so lots of stingrays might mean lots of gold. It has worked for me.