Principal Financial Group Inc. leaders will join Des Moines Mayor Frank Cownie and sponsors and guests on Oct. 7 to celebrate the completion of the Principal Riverwalk.  A formal program will be held at 6:30 p.m. Monday at the HubSpot, 215 Water St. The Iowa Women of Achievement Bridge, one of the Riverwalk's features, also will be dedicated, and the names of the first Iowa Women of Achievement honorees will be announced.