: You must have both Spatial Analyst and 3D Analyst enabled.
Technically, official support from the USACE Hydrologic Engineering Center (HEC) for GeoRAS ended after version 10.2. However, later versions have been made available via the Esri FTP site to support subsequent ArcGIS Desktop releases: hec georas for arcgis 10.8
HEC-GeoRAS acts as a bridge between the GIS environment and the hydraulic engine: : You must have both Spatial Analyst and 3D Analyst enabled
Using HEC-GeoRAS for ArcGIS 10.8: Compatibility and Best Practices hec georas for arcgis 10.8
: Users digitize river centerlines, banks, and cross-section cut lines from a Digital Terrain Model (DTM) or TIN.