How far would an average river's shoreline move in 140 years?

Answer 1

There is no easy answer to your question.
River channels usually migrate alot in only certain parts of their reaches--and there are many physical factors that control how much room or leeway they have to move.
Here's a slide show that discusses some basics with graphics--but doesn't give numbers on movement. http://www.dnr.wa.gov/sflo/frep/watertyping/
And here's a site that discusses technical definitions of channel migration zones and regulatory considerations--if that's the need for your question:
http://www.ecy.wa.gov/programs/sea/sma/st_guide/jurisdiction/CMZ.html
http://www.ecy.wa.gov/biblio/0306027.html

If really important to you: link to site for ordering TRB's National Cooperative Highway Research Program (NCHRP) Report 533: Handbook for Predicting Stream Meander Migration describes the application of a stream prediction methodology and provides illustrated examples for applying the methodology. http://trb.org/news/blurb_detail.asp?id=4416