Differences between ArcHydro and Hydrology spatial analyst

[OmarVargas_Suarez]

What are the main differences between these tools and which would be the most recommended for the field of hydrology? and why?

[DanPatterson_Retired]

• Compare their docs.
• Both.
• Neither fully covers the other.

And 'hydrology'? from an engineering or a geomorphological perspective would probably dictate the needs.