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I've trawled the manual and I can't seem to find the answer to this - if it is in there please let me know!

If I have multiple grids listed in the .tgc via the Read GRID == command, where cells overlap, does Tuflow treat the first grid as 'truth' then the second and third etc, or does the last grid overwrite overlapping cells from grids in the lines of code immediately above?

I could merge them in Esri but that creates more files, uses more disk space etc.


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There's no need for you to merge the datasets in Esri. TUFLOW's data layering functionality will give precedence to the elevation commands lower in the TGC if the datasets overlap on the same cell.

We commonly use this feature to "build" topography within a TUFLOW model refining the topography as you progress down the TGC. For example, the order of the elevations commands below will progressively overwrite the topography in overlapping areas to achieve a desired end result.


Set Zpts == 100                                                                             ! Sets every 2D elevation to 100m for the entire model

Read GRID Zpts == grid\DEM_20m_Regional_01.asc                 ! Overwrites the 100m elevation value where a coarse regional DEM is available                                                  

Read GRID Zpts == grid\DEM_1m_Refined_01.asc                     ! Overwrites the above elevation using a refined DEM

Read GIS Z Shape == gis\2d_zsh_survey_breakline_004_R.shp | gis\2d_zsh_survey_breakline_004_P.shp   ! Updated elevation data for a levee breakline 


Remember to use your model check files to review the final modelled topography and confirm it is as you were intending. There's information about the check files on the Wiki: https://wiki.tuflow.com/index.php?title=TUFLOW_Check_Files 


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