how to draw contoures showing depth?

Answer 1

The closer your contour lines are, the steeper the depth will appear. Think of the contour lines on a map. Hope that helps.

Answer 2

Each line should mark one foot of elevation. At each point where the elevation is the same, draw a line connecting those. Then do that for the next foot in each direction. Repeat.

You can use five feet, but for golf, you'd want to use one foot.

You'll obviously have to estimate.