What has changed?

1 second 2 seconds 3 seconds 4 seconds 5 seconds 6 seconds 7 seconds 8 seconds 9 seconds 10 seconds 11 seconds 12 seconds 13 seconds 14 seconds 15 seconds 20 seconds delay, loading photo...          Downstream of the previous pair of photographs in 1999  Author: Chiltern Society,          Noting the absence of any water flow in 1997  Author: Chiltern Society,