Tidal level information for surveyors

Determination of MHWS

There is no definitive method for establishing mean high-water springs (MHWS) boundaries – it requires a tailored approach that considers factors like hydraulic gradient, land type and the survey accuracy that is required. For example, the definition of the coastal boundary of a large rural class III or IV survey is often based on physical evidence and will not require the same degree of rigour as a high-value beachfront subdivision.

Baker and Watkins (1991, referenced below) suggest several methods for establishing MHWS boundaries, with greater accuracy tending to require more work by the surveyor. Direct levelling can only be used near a standard port tide gauge, so the most common methods for high accuracy definition are the education and range-ratio methods. Both involve the transformation of a MHWS level from a standard port tide gauge to the survey location using a local tide gauge and sea level observations (with a gauge established for the duration of the survey if required).

Using MHWS levels from the Nautical Almanac is no longer recommend for cadastral or administrative boundaries due to their navigation-oriented nature and annual variability. The Nautical Almanac only represents tidal levels for the next 12-month period, and these change from year to year by up to 15 centimetres over the course of the 18.6 year tidal cycle.

Predicted tidal levels for surveyors

The following tidal levels are average predicted values over the 18.6-year tidal cycle. These are suitable for MHWS determination in cadastral surveys, but this is only one way to determine MHWS – the most appropriate method should be determined by a cadastral surveyor.

See guidance for tidal boundaries

Tidal levels at New Zealand standard ports for cadastral and engineering purposes

Warning

These values must not be used for navigation purposes.

The values provided in this table are the expected tidal levels at the New Zealand standard ports, which serve as primary reference points for tidal measurements. The values are reference to 'chart datum’, a level representing the lowest anticipated water level under normal tidal conditions, and which is also used as the zero-prediction value for data. For each standard port, values are listed for the average heights of the specific tidal levels: mean high water springs (MHWS), mean high water neaps (MHWN), mean low water neaps (MLWN), and mean low water springs (MLWS). These averages are calculated from both high and low tides occurring during normal weather conditions, using data from between 1 January 2000 and 31 December 2018.
Standard Port	MHWS (m)	MHWN (m)	MLWN (m)	MLWS (m)	Definition of Chart Datum	Harmonic Constituent Set
Auckland	3.30	2.78	0.95	0.41	5.233m below BM 98-21 SO 69501 (DD1N)	2 Jul 1996
Bluff	2.82	2.43	1.04	0.57	8.620m below Bluff Fundamental BM (ABCC)	1 Jan 2002
Dunedin	2.18	1.80	0.39	0.07	3.728m below BM WW 83 (AFEQ)	1 Jul 2002
Gisborne	2.02	1.76	0.70	0.44	4.091m below BM GB 01 (ACVP)	15 Feb 2005
Lyttelton	2.49	2.05	0.65	0.27	4.478m below BM UD 40 (B40V)	1 Jul 2000
Marsden Point	2.72	2.29	0.86	0.42	4.816m below RNZN BM (DJM9)	2 Jul 1996
Napier	1.84	1.46	0.40	0.06	4.837m below BM H40 (B3XM)	1 July 1997
Nelson	4.26	3.24	1.41	0.46	5.733m below BM N1 (AC4T)	1 Feb 2001
Onehunga	4.19	3.39	1.38	0.51	5.593m below BM CC 65 (ADLT)	1 Jul 2003
Picton	1.62	1.12	0.58	0.13	2.716m below Elaine Cairn (BQFK)	24 Aug 2005
Port Chalmers	2.14	1.77	0.47	0.16	3.816m below Pin 1 SO 17533 (DR0F)	1 Jan 2003
Port Taranaki	3.58	2.78	1.14	0.34	6.709m below New Plymouth Fundamental BM (AGMH)	1 Jan 1996
Tauranga	1.88	1.60	0.44	0.13	4.103m below BM BC 84 (B309)	1 July 1996
Timaru	2.42	2.05	0.77	0.45	5.759m below BM UD 42 (B2Y9)	1 Jan 2004
Wellington	1.77	1.45	0.70	0.45	3.565m below BM K80/2 (ABPC)	2 Jan 1996
Westport	3.25	2.57	0.94	0.25	7.351m below BM Harbour Masters Office (DJMC)	1 Aug 2000
Whangarei	3.12	2.64	1.02	0.52	5.182m below BM DD99/23 (A2Q9)	2 Jan 2003

Reference

Baker and Watkins (1991) "Guidance notes for the determination of Mean High Water Mark for land title surveys" NZIS Professional Development Committee; published in Kearns, Kerr and Smith (1997) Chapter 5 Law for Surveyors - Boundaries and boundary definition, Dept of Surveying University of Otago/NZIS available from School of Surveying, University of Otago.