Before the introduction of GPS (Global Positioning System) it was nearly impossible to create a national height system. Instead, we relied on approximate mean sea-level measurements from various points. This led to many local datums being established as required, including 13 local vertical datums (LVD) and secondary city and drainage vertical datums.
New Zealand Vertical Datum 2016 (NZVD2016) established a unified reference surface for height, depth and elevation data. Introduced in June 2016, it is now well established and will remain New Zealand’s national vertical datum for the foreseeable future. The use of NZVD2016 reduces costs and risks, while increasing resilience and the ability to support our communities.
New Zealand Vertical Datum 2016
Continuing to use an LVD has significant disadvantages. For instance, there are limited LVD benchmarks available, mostly situated on state highways and the centre of towns and cities. The benchmark networks established by Toitū Te Whenua have not been maintained since installation, which occurred mainly from 1960 to 1980. Many benchmarks have been relocated or damaged over time, or errors in their height have been recorded and their accuracy cannot be verified. LVD heights should not be used to predict sea levels as they are referenced to an approximate sea level from the past, not a current mean sea level.
Nelson City and Tasman District Councils were the first to adopt NZVD2016 on 1 July 2017. Many councils have adopted NZVD2016 since then and others are committed to adopting it in the next few years.
Case study: Inconsistencies in the local vertical datum
When working with heights for planning and risk monitoring, the primary focus is usually on relative values. These projects typically rely on the reduced level (RL) or published height of a small group of benchmarks. For example, when assessing the condition of a flood embankment, a control benchmark near the river mouth can serve as a reference. We can monitor any changes in the flood bank's height in relation to this benchmark.
However, benchmarks can move over time or being washed away. It can also be difficult to compare this data with regional information that is not based on the reference benchmark (such as LiDAR survey data or data from neighbouring rivers). Replicating or combining these height measurements is problematic.
Unlike a uniquely identified benchmark, NZVD2016 heights can be established anywhere and are easily recoverable if reference marks are moved or destroyed. NZVD2016 is also nationally consistent, so NZVD2016 RL values can be combined across projects.
Engagement with councils
Implementing New Zealand Vertical Datum 2016 may present challenges for councils, given that height and elevation data is the cornerstone of databases, decisions and processes across multiple disciplines. Between November 2018 and March 2020 LINZ, in collaboration with Survey and Spatial New Zealand (S+SNZ), held a series of meetings with local and regional authorities. These covered the advantages of NZVD2016, highlighted the limitations of LVDs, and addressed the obstacles councils may be facing.
Survey and Spatial New Zealand
The presentation slides from the first meeting with councils and the subsequent technical meeting can be found in the materials below.
Toitū Te Whenua is committed to helping any council that needs further information or support. Contact us at crm_geodetic@linz.govt.nz