Add4.845m to data values 1992-1996 to refer to RLR (1997)
Add 4.823m to data values 1997-1998 to refer to RLR (1997)
Add 4.831m to data values 1999 onwards to refer to RLR (1997)
RLR (1997) is 9.7m below BM Pier no. 2
