By John Paterson & Lachlan McKenzie,

torm water runoff events cause around 12 tonnes of phosphorus to end up in Lake Rotorua every year. Detainment bunds can reduce this flow of nutrients to the lake by temporarily detaining storm water run-off, allowing phosphorus laden particles to settle out.

A project plan to improve knowledge on detainment bunds was submitted to the Sustainable Farming Fund (SFF) last year by John Paterson on behalf of a farmer group that includes the Collective to progress. We are pleased to report that MPI has now advised that this project has been shortlisted through the very competitive SFF process.

The project is titled “The P Project – Advancing on-farm phosphorus loss mitigation in conjunction with applied research on a new mitigation tool – the Detainment Bund.”

The research will build on the validation work undertaken in 2012 on three detainment bund sites in the Rotorua Catchment. This study was part of a University of Waikato student thesis that provided ‘proof of concept’ but was severely limited by the number of storm events that could be sampled at its three trial sites within the constraint of a one year sampling period. While this student research provided valuable ‘qualitative’ evidence, the new SFF project will provide the much needed ‘quantitative’ performance data.

Developing the knowledge and skills needed to maximise the performance of detainment bunds will be a key aspect of the project – or in other words “We now know they work, but how well do they work and what is the best way to drive them.”

Fieldwork will run for three years, analysing data from six detainment bund sites and their farming catchments in various locations in the wider lakes area including Lake Rotorua.

The new P Project intends to conscript a PhD student to help complete this work. Additional supporters include BOPRC, Beef and Lamb NZ and Deer Industry NZ as well as the farmers who have invested in building the storm water treatment detainment bunds that the project will be focused on. Talks are continuing with other interested groups.

A start date for the project is dependent on final confirmation of full funding by SFF which is expected by April this year. We’ll keep you posted on our progress.

You can find out more about detainment bunds here