There are two options: Either you create a point shape file from the raster in GIS and use this as the basis for interpolation in FEFLOW, or you export the FEFLOW mesh nodes to a shape file, transfer the elevation from the raster to the points in ArcGIS and import the points again in FEFLOW, using an inverse distance weighting interpolation with only one neighbor. We usually prefer the latter option as it does not require the import of the huge point shape file generated from the raster in ArcGIS into FEFLOW.
