Top level
The stuff you can see is the uppermost layer in my composited scene. Don't know what that means? Then click here.

That grey and white checker board pattern tells me that I haven't got anything in that region yet.

The tide's out
I've got the beginning of my background layer showing now. That layer is sitting underneath the foreground layer, so the eye interprets it as being behind the boat. It looks like the sand continues on forever, which is just the impression I want to make. But I'll flood it with water next.

The tide's in
Here's the water. It shows sky reflections and boat reflections but you can't see through it. So it's time to use some of the power of Photoshop...

Transparency
Here you can see what I've done to the water. I've made it transparent at the bottom of the picture going up to not transparent at the top of the picture. You can judge the amount of transparency by how much of that grey checker board pattern you can see through it.

In the next step we won't be seeing grey checker board through the water. We'll be seeing the sand.

Instant water
... And here's the sand being seen through that semi-transparent water. This was really quick - only a few seconds work - to get this effect. That's why I chose this method instead of setting it all up in the 3D program. As much as I love 3D, I love my time even more!