Salinity modelling of the Avon-Heathcote Estuary Ihutai

This salinity study received support from the Brian Mason Scientific & Technical Trust to engage in a collaborative project with NIWA. The work involved the development of a scenario modelling method to assess effects of the earthquakes on the estuarine salinity environment.

This information will assist in developing effective policy and planning approaches for earthquake recovery, and for the longer term protection of habitats and ecosystems that must include appropriate responses to climate change.

In upper estuarine ecosystems, sea level rise will cause a shift in the position of the freshwater-saltwater interface. Species and habitats that are adapted to brackish conditions will need to migrate to the future location of the interface as it changes through time. Inanga spawning habitat and saltmarsh ecosystems are examples of important areas for conservation that are strongly influenced by salinity. These areas will be undoubtedly affected by sea level rise. For these reasons, methodologies for assessing the potential impacts of sea level rise on these area are urgently needed to underpin conservation actions. 

One way in which the information from such assessments can be particularly useful is for understanding the future impacts of contemporary land use and development decisions. 

In our initial round of modelling we achieved an excellent calibration result in the lower estuary and in the Avon / Ōtākaro. We also made an unexpected finding with the discovery of a leak in the Woolston Tidal Barrage. This caused a strong  anomaly between the modelled versus observed salinity datasets for the Heathcote / Ōpāwaho catchment. The leak was brought to the attention of Christchurch City Council who have since discovered and removed debris jammed in the tidal gate structure. It is now important assess the impact of the repair on salinity levels in the upstream reach which are likely to have been elevated for a considerable period due the leakage. 

Read more about it here in the Brian Mason Trust report on 'Development of a fine-scale salinity model for the Avon Heathcote Estuary Ihutai'.

Report available as a free download here.

The Resilient Shorelines team would like to thank the Brian Mason Scientific & Technical Trust and also NIWA for bringing their support to this exciting research.


We are currently completing a follow-up project with support from Christchurch City Council


Please feel welcome to make contact if you are interested in any aspect.





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