Monday 27 June, 2022
A 3D model of groundwater under the Poverty Bay Flats can predict long-term fluctuations in aquifer levels from now until 2090.
The information gained will help determine sustainable water allocations, which incorporate climate and drought predictions and give effect to Te Mana o te Wai – the vital importance of managing fresh water.
Senior groundwater scientist Joanne Ferry says Council would like to formally thank all parties who played a part in creating this truly remarkable risk analysis tool.
Gisborne District Council along with Wallbridge Gilbert Aztec (WGA) and Aquasoil Consultants collaborated to develop this groundwater model of the Poverty Bay Flats.
"Ultimately the development of the groundwater model was based on a combination of a 3D geological model and a conceptual hydrogeological model."
Mrs Ferry says the objective of this project was to work with Treaty Partners, Councillors and stakeholders to develop a robust groundwater model that could simulate the geology, hydraulic behaviour and effects of the consented groundwater allocations of the five aquifers beneath the Poverty Bay Flats.
“The groundwater model uses computer simulations to predict long-term fluctuations in aquifer groundwater levels. This allows scientists to run different groundwater management scenarios and climate change predictions.”
In late 2021 Council held community workshops for Treaty Partners, Councillors and stakeholders to raise questions that the groundwater model could potentially answer and highlight the risks with future climate change predictions, land-use changes and groundwater allocations.
Council’s science team then translated those risks into numerical scenarios that could be run in the groundwater model to simulate groundwater changes from now until 2090.
The scenario settings from community questions and concerns are shown in the table at the bottom.
In early 2022, prior to running the scenarios, calibration of the groundwater model was completed using historic groundwater level data, which has been monitored and recorded across the Poverty Bay Flats since the 1980’s.
“This calibration was successful and presented a good match for the model to represent the five different aquifers and their seasonal fluctuations,” says Mrs Ferry.
In April 2022 community workshops were held to present the outcomes of the first draft run of the groundwater model scenarios. The presentation showed how climate change, sea-level rise and repeated droughts, in combination with current water allocations would degrade the aquifers.
Mrs Ferry says the decision was then made to re-run all scenarios to incorporate all of the significant climate change risks.
“The information gained will help Council determine sustainable water allocations.
“Whilst we wait for the scenarios to be re-run, elements of groundwater chemistry will also be incorporated to further highlight groundwater quality risks, such as increasing aquifer salinity.”
All findings from this groundwater modelling process will be reported by WGA and Aquasoil in the second half of 2022.
Click to watch the video on the creation of the Poverty Bay Flats Groundwater Model.
Baseline + Climate Change
Current Allocation Limit
Managed Groundwater Replenishment
Extreme events (RCP 8.5)
Climate Change (RCP 4.5)