NEW research shows the main aquifer used to irrigate crops on the Poverty Bay Flats might be in decline.
Modelling research on the Makauri aquifer by GNS Science predicts a decline in its water level of two centimetres a year, on average, for the next 50 years.
It predicts 0.01 litres, or two teaspoons, per second is being lost from the aquifer — which might eventually result in a level where there is insufficient artesian pressure for the aquifer to replenish.
This information was presented at the first round of public consultation meetings on Gisborne District Council’s draft vision for its freshwater plan.
The GNS report makes several key assumptions about the aquifer, says GDC water conservation team leader Dennis Crone.
It appears to be a blind aquifer and is not discharging into the sea. The recharge trigger for replenishment is the removal of water by users and the assumed uptake of water is 30 percent of current permitted takes.
The report suggests the aquifer is not as robust as previously thought. It is a key source of water for Gisborne’s horticultural producers.
Mr Crone says the assumptions in the draft report require some sensitivity analysis, using a range of values to model the impact on predicted water levels.
Over a recent two-week dry period, actual water extracted was 27 percent of the permitted take.
“There are 30 consents for water takes from the Makauri aquifer and data from these bores has been monitored for a number of years,” he says.
Early on it had appeared to be declining but then seemed to replenish in the 1980s.
This new study provides a better understanding of the inter-relationship between underground aquifers and the Waipaoa and Te Arai rivers.
Water in the Makauri aquifer is as old as 8000 years and the Matokitoki aquifer is even older, says Mr Crone.
Both aquifers are used by LeaderBrand and other producers.
Guidelines to help councils develop freshwater plans have been set by the National Policy Statement for Freshwater Management, produced with input from the National Land and Water Forum.
The process involves identifying freshwater values — ecological, economic and cultural — then developing water quality standards and allocation limits on water use.
“We need to develop a vision that takes into account the views of all water users,” says GDC natural resources policy team leader Yvette Kinsella.
The council formed a Fresh Water Advisory Group (FWAG) 18 months ago, to develop the plan and represent the views of all stakeholders with an interest in the district’s fresh water.
The group represents a balance of freshwater interests — river and groundwater users, farming and forestry interests, iwi representatives, recreational and environmental users, government departments and council staff.
Horticultural industry representation includes Stuart Davis from LeaderBrand Produce, the region’s largest irrigator.
“The various reports commissioned by GDC and other parties have lifted the available knowledge on our water resources to a whole new level,” says Dr Davis.
“It will enable our community to make much better informed decisions about conservation of waterways, sustainable water use and economic development.”
Land and Water Forum chairman Alastair Bisley highlighted the work happening in Gisborne at a conference in Wellington this week, saying it was an example of good practice and innovation in developing a water plan.
How water is allocated, the quantity available for allocation and the potential limits on how much water can be taken — and still ensure the values of others using the water are met — are all part of the discussion.
Because of the size of the district, it has been broken down into several catchments.
The initial focus has been Waipaoa catchment, which includes the Te Arai River, because the use is higher and some data on the catchment was already available.
It is the source of the city’s water supply and of water for irrigation, and has strong tangata whenua values, says Ms Kinsella.
FWAG chairwoman Pat Seymour says the process is about respect for the competing interests of cultural and recreational users, while still allowing sufficient water for the district’s continued economic development.
“We will then move to other catchments such as the Uawa and Waiapu.”
Envirolink, The Ministry of Science and Innovation, NIWA and GNS have provided funding for a series of research projects to help understand the dynamics of the aquifers beneath the Poverty Bay Flats and their inter-relationship with the river systems.
“We have a greater level of knowledge on how these systems operate now and more confidence to make decisions on the taking of water” says Mrs Seymour.
“We would encourage all interested parties to attend the public consultation meetings.”
■ A key meeting for the group and the district’s horticulturalists will be held on July 5 at the Bushmere Arms from 3pm.