The national gauging station number is a unique six digit reference number which serves as the primary identifier of the station record on the NRFA.
The first digit is a regional identifier being 0 for mainland Britain, 1 for the islands around Britain and 2 for Ireland. This is followed by the Hydrometric Area number given in the second and third digits, further details and a map of which can be found here. The fourth, fifth and sixth digits comprise the number, usually allocated chronologically, of the gauging station within the Hydrometric Area.
