I've been using sinuosity as a way to determine the percentage of streams that have been altered or straightened.
I did this by splitting rivers at each junction, and then dividing them into segments of no less than 250 meters (which we determined to be the minimum meander length for streams of our size). I then calculated sinuosity for each segment and applied a threshold value to determine whether it was deemed "natural" or "straightened".
Doesn't have a moving window or anything like that, but it works for a large area