Overseer review

Overseer background

It is widely accepted that the water quality of many New Zealand rivers is degraded, and changes need to be made.

One of the main causes of poor water quality is excessive nitrogen.

Discharges of nutrients, including nitrogen, are managed through the use of the tool, Overseer.

Overseer helps estimate nitrogen loss on a farm and in so doing can help with the management of nutrient loss.

We, alongside other regional councils, have used Overseer to gather modelled output data on different farm systems via this online interface.

We are required to use Overseer as a regulatory tool in our operative Tukituki Plan to understand nutrient loss on farms and at a catchment level.

Industry groups have for some time debated the use of Overseer as a tool for regional council’s planning and consent process.

Government review

In late 2018, the Ministry for the Environment and the Ministry for Primary Industries commissioned a review of Overseer by a Science Advisory Panel. Eight independent experts were appointed to the panel.

The panel considered Overseer’s ability to estimate nitrogen loss across a range of conditions found in New Zealand.

The panel concluded that they wouldn’t have confidence in Overseer to estimate the volume of nutrient loss and whether nitrogen was being increased or reduced as a result of on-farm actions

The Government is committed to test, upgrade or supplement Overseer over the next 12 months and will support the use of Overseer over this time to enable regulatory requirements to be met.

You can access the full report here

You can access Government's response here

What this means for the Tukituki community?

In view of the SAP review of Overseer and the Government, the Council is unable to continue with implementation of the Tukituki Catchment plan as it is currently proposed in the Tukituki Catchment Plan (PC6) Procedural Guidelines (version 3, published March 2021).

We have determined that we will be unable to reliably assess whether individual high leachers are exceeding their LUC N allowance, based on Table 5.9.1D, without the use of Overseer. Enforcement of this rule based on Overseer outputs would also be unlikely to succeed. Therefore, we do not believe that we will be able to require applications for individual high leachers that are located outside a DIN exceeding sub-catchment.

We will still require applications for properties located within sub-catchments which are exceeding their DIN target. These farms require consent regardless of their Overseer estimated N loss. However, we will not be able to determine the ‘activity class’, which is based upon the amount of N leaching modelled in an Overseer nutrient budget, as currently required by the rules in the plan. Instead, we propose to apply a single ‘activity class’, of Restricted Discretionary, under Rule TT2 across all the DIN exceeding sub-catchments using other provisions in Rule TT1 (namely Rule TT1(j))4).

Farmers have been implementing good management practices and we expect that to continue.

Consents and farm plans still need to be submitted, and Overseer can still be used to collect farm data.