This is just one country boys opinion that has spent his life chasing the papermouths on oxbows and bar-ditches.
Crappie will spawn as shallow as they can and as far back in the brush as they can get. As long as your lake or ditch is at normal level, the crappie will spawn in that shallow water you refer to. But Crappie as I know them have a tendency to only spawn on "normal" or natural banks. I mean, if the bar-pit is 3 foot high creating "new" banks, I tend to fish the old bank line and find most of the spawners there. However, high water can produce new feeding areas and crappie tend to move to this fresh area to feed only.
Some of the biggest crappie I have ever caught has come from water less than a foot deep during the spawn. Black crappie are famous for laying behing cypress trees in less than a FOW.
Be careful though, crappie are extremely spooky in water this shallow and you may have to extend your pole reach to 11 or 12 foot and fish the lightest line you can( typically 4 or 6lb test).
But again, I'm no expert and this works for me!
