The Tidewater was a short-lived train that went from Newport News, Virginia to New York City only on Fridays and Sundays. Leaving Newport News at 4 pm, the train complemented the Colonial, which departed Newport News daily at 7 am. Left unexplained is how the cars that made up the Tidewater made it back to Newport News, but they probably were made a part of the southbound Colonial.
I’m not certain, but I think the train was inaugurated in 1977 and only ran for a year or two. Someone who has collected all of Amtrak’s timetables could tell, but I only have a few.