Most of the Netherlands only exists due to sheer bloodymindedness. Nearly 20% of it is actually below sea level.
Thing is, if the land wasn't sinking to begin with, exactly why were you considering levees in the first place? ;-)
Whatever the case may be, if you're building levees, you need to factor in the sink rate of the land around you, among the many factors. And you need to factor in the cost to maintain them indefinitely.
It's an expensive proposition; but by the simple fact that you're alive, standing there, and considering it already, chances are the ROI is worth it.