Hec Ras 5.0.7 wil not merge terrains

[Dazzler]

I am trying to merge two (ideally3) TIFF files to produce one 2d grid for use in my model.

Effectively there is Background Lidar, the Channel and and a site survey. I add terrain – having set a suitable projection and then select each of the three files to import as a terrain for the 2d model. I select merge inputs to single raster. Each time I try this I end up ONLY with the topmost item in the list actually being imported.

Has anyone got any idea what’s going on ?

[Luis Partida]

I never have issues with this but I also never select “merge inputs to single raster”. RAS will automatically create an .hdf of the terrain that will be merged but will keep its individual .tiffs as independent terrains.

Unselect that option and it should work. Also remember the order must be in order of burn to base. Meaning if your base surface is the channel and your other surface is just a burned tributary, the burned tributary must be on top in the order

[Lonnie A]

the merge terrain in mapper is intended for mostly non overlapping terrain files as there is no control as to the order it merges them.
If you let RAS just build the surface and then export it to a resampled surface be warned that it will likely adjust the background Lidar elevations through its reporcessing.
The best way I’ve found is to bring the individual surfaces into GIS and mosic them there…be sure to set the environment to snap to the background lidar. If you do that it won’t modify the lidar outside of the area of the channel and site survey surfaces.

[Author]

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