Not sure what you mean by adjust the map depths
The SH4 terrain is in the files contained in this folder
C:\Program Files\Ubisoft\Silent Hunter 4 Wolves of the Pacific\Data\Terrain\Data
TerrainData.BFD and TerrainData.BFI
The terrain governs the depth etc of the sea and maps the terrain
There was a terrain editor made for SH3 which added the canals of Kiel\Panama and Suez
As well as alterations to Heligoland and Scapa
I dont think that editor works in SH4 though
http://files.filefront.com/SH3Terrai.../fileinfo.html
The terrain ed is dicussed here in great length
May help
May not
http://www.subsim.com/radioroom/showthread.php?t=89658