Lake Rotorua Groundwater Boundary

Lake Rotorua Groundwater Boundary

Meeting notes from 11 December 2014

These notes are based on a meeting held in Ngongotaha Hall, 11 December 2014. About 25 landowners from 13 properties within the additional groundwater area attended, plus other farmers, Bay of Plenty Regional Council staff and scientists from GNS (Geological and Nuclear Sciences) and NIWA. A basic agenda and invitation was pre-circulated with links to groundwater maps and a recent report by GNS.

The meeting took place because Bay of Plenty Regional Council (BOPRC) is developing new rules to reduce nitrogen loss to Lake Rotorua to protect water quality. The current “Rule 11” is limited to the surface runoff catchment within BOPRC’s jurisdiction. Most nitrogen is transported to the lake by groundwater and the groundwater catchment is partially outside of the surface water catchment boundary.  Council intends that new nitrogen rules target the entire groundwater catchment. The new rules are scheduled to be notified in May 2015.

Landowners from the additional groundwater area were invited to meet with the scientists who helped define the groundwater boundary. Landowner contact details were obtained from Bay of Plenty Regional Council’s rating database and sent out by the Lake Rotorua Primary Producers Collective.

Presentations at the meeting were given by:

  • Paul White – Senior Groundwater Scientist, GNS
  • Kit Rutherford – Principal Scientist Catchment Processes, NIWA
  • Rob Donald – Science Manager, Bay of Plenty Regional Council
  • Sarah Omundsen – Water Policy Programme Manager, Bay of Plenty Regional Council.

Landowner concerns and questions (as recorded at 11 December meeting)

  1. We don’t know what will happen on the Waikato portion of the groundwater catchment and that makes farm investment decisions more difficult.
  2. How will the level of science uncertainty around the Ohau channel outflow and the related additional groundwater area be reflected in nitrogen rules?
  3. What will be the basis for allocating nitrogen in the additional groundwater area given there is no Rule 11 reference point? [Meeting postscript: BOPRC will discuss some options with the Stakeholder Advisory Group in early 2015].
  4. More clarity is needed on what Waikato Regional Council will do about regulating nitrogen in its part of the groundwater catchment. This depends on Waikato Regional Council’s policy and catchment priorities across their whole region. Any such regulations need to go through formal RMA processes, including consultation, and are likely to be several years away. Federated Farmers will help keep the affected farmers informed.
  5. What is the total additional nitrogen coming from the additional groundwater area, and how long does it take to get to the lake?
  6. Runoff on Mamaku podzol soils is greater than indicated by the Kaharoa lysimeter site which is on a more permeable pumice soil.
  7. Mamaku locals often observe surface storm runoff which drains towards Waikato and therefore their contribution to groundwater flowing to Lake Rotorua may be less than assumed by BOPRWhat is the impact of dry years on groundwater drainage?
  8. How does the spread and intensity of storm events affect runoff and groundwater drainage?
  9. What is the impact of dry years on groundwater drainage?
  10. Some farmers do not agree that the nitrogen focus is justified given the alum dosing has improved the lake by controlling phosphorus.
  11. Could monitoring of local bores improve groundwater understanding?
  12. Is it possible that there are other non-Mamaku groundwater sources for the Hamurana and Awahou springs, and is there any documentation on that?
  13. Additional effort is needed to engage with the newly impacted landowners who are only now hearing about the likely nitrogen loss limits. The next meeting should also explain the draft rules, including how Nitrogen Discharge Allowances will be calculated given there are no 2001-2004 benchmarks for the additional groundwater area.

Some catchment facts and figures

The catchment areas involved (excluding the lake surface area of 8068 ha) are:

Lake Rotorua catchment descriptionArea, hectares
Groundwater (GNS 2014)45,721
Surface runoff (total)42,258
Surface runoff Rule 11 (within BOP region only)40,758
Groundwater additional to surface3,463
Groundwater additional to Rule 114,963
Groundwater additional to surface in BOP region2,406
Surface runoff in Waikato region1,500
Groundwater in Waikato region (includes surface)2,557

Nearly all of the additional 3,463 ha of groundwater catchment is near Mamaku area and is divided between BOPRC and Waikato RC jurisdictions. There are also two Waikato areas to the south-west and south-east of Rotorua which are surface and groundwater catchment. These areas are shown in the map below.