Please note that HEC-PACK is no longer offered or supported by Bentley Systems. It consisted of a collection of flood modeling applications, almost all of which are now available for download from the Hydrologic Engineering Center (HEC) of the US Army Corps of Engineers.
If you are interested in river or flood plain modeling, please refer to HEC-RAS and other HEC applications from the above link, or consider Bentley OpenFlows FLOOD. See also: Difference between OpenFlows FLOOD and HEC-RAS
If you are interested in watershed and pond modeling, please refer to Bentley PondPack.