Tide levels have been recorded Ferrymead Bridge since 1974 and at the Styx tide gates (Brooklands) since 1990, Sumner Head since 1994, and on the Avon at Bridge Street since 1997. Tide levels are also recorded at Lyttelton.
Historical trends in mean sea level rise
The Ministry for the Environment in their document, Coastal Hazards and Climate Change - Guidance for Local Government, note that records from the four main port gauges indicate “there has been a doubling of mean sea level rise from an average of 1mm/year earlier last century to nearly 2mm/year from 1961”. The Ministry also note satellite estimates of mean sea level rise of 4.4mm/year around New Zealand in the period 1993 to 2015.
NASA have assessed the rate of sea level rise on a global scale based on 25 years of American and European satellite data. They note the rate of sea level rise has increased from about 2.5mm/year in the 1990s to about 3.4mm/year today.