The primary reference at water-level recording stations is a set of stable bench-marks, installed in locations where their level should not change. Upon initial set-up of a station, the levels of the
relevant parts of the installation are established and recorded by means of accurate leveling.
At least every two years, the levels of the staff gauges, sensor level, internal gauge, tower structure and benchmarks should be measured relative to each other as a check that records are not in error due to bank subsidence or other movement.
Accurate levelling is thus a particularly important part of site establishment, installation and quality assurance. All staff shall be thoroughly familiar with its theory and practice. Level