Vasil, there are many good ...

Vasil, there are many good ways to measure riverbank erosion. We've used historical aerial photographs (see attached paper) as well as 'erosion pins,' i.e., long pieces of rebar steel rods pounded horizontally into the river bank, and then measuring the erosion from the tip of the exposed rod.  However, I'm sure that others can suggest ways of using satellite imagery measurements as well, which may be the only way to get good measurements in remote areas that have not been photographed from airplanes over time.