I've been using Arc Hydro for the last 7 years to determine catchment characteristics. I'm currently setting up a new model to determine structure locations along a proposed railway alignment. This is the largest study area I've ever had to process and currently its failing when I try to generate the Flow Accumulation Grid. My Flow Direction Grid for the study area has 863 398 034 cells.
I'm looking for advice in how to successfully generate my Flow Accumulation Grid. If ArcGIS can't handle such large DEM's will GRASS be able to process such a large DEM and generate a ArcGIS GRID as an output that I could use for further processing of catchment characteristics.