I use Nays2D Flood to simulation area with 800 km2 of surface. The mesh is about 1 millions points.
The initial Elevation (imported file) in my interest point is equal to 100,41 m (this is not bathymetric point but surface point)
In result of the simulation, i found the following elements for the same point:

Elevation = 103.62m
Water surface elevation = 109.2 m
Depth = 5.58 m

I know that the elevations are not the same (problem of interpolation between center of element and around points),
so my question is: Can we say in reality, that the Water surface elevation = initial elevation + Depth ?
In other word, to avoid interpolation problem, i use initial elevation and calculated depth to estimate Water surface elevation?

Thank you for your response