The problem is still unsolved.
I think it's not a fail DEM problem.
Fig. 1. DEM
[ATTACH=CONFIG]23440[/ATTACH]
Fig. 2. Total curvature grid layer
[ATTACH=CONFIG]23441[/ATTACH]
Fig. 3. Topographic Wetness Index (TWI) / Compound Topographic Index (CTI) / Catchment Wetness Index (CWI) (DEM derivative) - the same problem with pixels with extreme values which looking like chess board.
[ATTACH=CONFIG]23442[/ATTACH]
maybe there is an intelligent way to smooth the grids? any ideas?