There was a download of RiverCAD 16.0 on the developer's website when we last checked. We cannot confirm if there is a free download of this software available. The RiverCAD installer is commonly called acad.exe. The most popular version among RiverCAD users is 16.0. The software lies within Photo & Graphics Tools, more precisely 3D Design. We recommend checking the downloaded files with any free antivirus. The actual developer of the program is BOSS International, Inc.
From the developer:
RiverCAD® is a sophisticated river modeling software that completely supports HEC-RAS and HEC-2 within AutoCAD. RiverCAD makes it extremely easy to compute water surface profiles for modeling bridges, culverts, spillways, levees, bridge scour, floodway delineation, flood plain reclamation, stream diversions, stream restorations, stream realignments, channel improvements, and split flows.
You may want to check out more software, such as P-CAD 2004 Viewer, Baldor Electronic Catalog or AutoCAD OwnerGuard, which might be related to RiverCAD.