Crappie aren't that particular about spawning locations. They will use mud banks just a readily as gravelled banks in our lakes. A stump or laydown tree works too. I do best on steep mud banks in one of my lakes that has gravel areas too. Black crappie will spawn on the edges of flooded vegetation as well. Generally the muddier the water, the shallower they'll spawn. I've found them in less than a foot of water in turbid lakes. Water temperature does influence the time to hatch for the eggs. The warmer the water, the less time to hatch. Hope this helps.