At a particular port the level of the water is expressed as a height above a local datum which is also the datum used for the depths of the sea on nautical charts (chart datum).
This datum is defined with reference to permanent benchmarks ashore and the zero of the tide gauge. The datum adopted usually approximates Lowest Astronomical Tide (LAT) which is the lowest level the tide can be predicted to occur under normal meteorological conditions.
Zero points used in tide predictions
Auckland 5.233m below B.M. 98-21 SO 69501 (LINZ code DD1N), a bronze plaque set in concrete into the road at the entrance to Captain Cook Wharf.
Bluff 8.620m below Bluff Fundamental B.M. (LINZ code ABCC), a stainless steel pin set in concrete under an iron cover, south eastern corner of Lee and Barrow Streets.
Dunedin 3.728m below B.M. WW 83 (LINZ code AFEQ), a stainless steel pin set into the concrete base at the north western corner of G Shed, Birch Street Wharf.
Gisbourne 4.091m below B.M. GB 01 (LINZ code ACVP), a stainless steel pin set in concrete at the east end of No. 6 Wharf.
Lyttleton Has been retained at its pre-earthquake level which has been determined to be 4.508m below the position of B.M. UD 40 (LINZ code B40V) as at April 2012, a stainless steel pin set in a concrete block adjacent to the main pier of the overbridge to the main wharves.
Marsden Point 4.816m below the RNZN benchmark (LINZ code DJM9), an iron bolt set in concrete near the base of the light standard on the inshore east end of the Northport Ltd. pier near the launch steps.
Napier 4.837m below B.M. H 40 (LINZ code B3XM), a stainless steel pin set in a concrete block under an iron cover near the south western corner of the Port of Napier Ltd. office at the railway crossing.
Nelson 5.772m below B.M. N 1 (LINZ code AC4T), a stainless steel pin set in the front steps to the old brick building in Wakefield Quay, known as Anchor House.
Onehunga 5.593m below B.M. CC 65 (LINZ code ADLT), a stainless steel pin set in a concrete block near the easternmost corner of Shed B, Onehunga Wharf.
Picton 2.771m below Elaine Cairn (LINZ code BQFK), a cairn of cement 0.61m in height, 250m south east of the Ferry Terminal Building.
Port Chalmers 3.816m below Pin 1 SO 17533 (LINZ code DR0F), a stainless steel pin set in concrete under an asphalt and white tile cover immediately to the left of the steps to the Port Chalmers Museum (ex Post Office building).
Port Taranaki 6.721m below New Plymouth Fundamental B.M. (LINZ code AGMH), a stainless steel pin set in a concrete block, 0.305m under a concrete cover and iron cap on the east side of Rigger Shed, Port Taranaki.
Tauranga 4.103m below B.M. BC 84 (LINZ code B309), a stainless steel pin set in the concrete foundation at the north eastern corner of the Port of Tauranga Ltd. administration building.
Timaru 5.767m below B.M. UD 42 (LINZ code B2Y9), a stainless steel pin set in the concrete base of the light tower at the south end of No. 2 Wharf.
Wellington 3.551m below B.M. K80/2 (LINZ code ABPC), a stainless steel pin set in concrete under an iron cover, at the southern end of Lambton Quay, 35m from Willis Street.
Westport 7.327m below B.M. Harbourmasters Office (LINZ code DJMC), a stainless pin set in concrete, immediately above the steps to the pilot boat, adjacent to the Harbourmaster’s Office on the main wharf.