At least as to river heights, the Flood of 2011 may be second or third largest Mississippi River Flood in modern times. Total volume of the flood is hard to compare because the river and the tributaries are more constrained than in the past. Water in a leveed river will be much higher than in a river without levees where it can spread out horizontally.
Projected flood heights – NOAA – Corps’ Morganza floodway projections
Satellite images of the floods