Saturday, December 2, 2023

On-farm research helps water quality

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An innovative approach to improving environmental sustainability is proving its success in intercepting and treating storm water before it leaves the farm and trials indicate it could be a game-changer for water quality.
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A four-year trial has looked at intercepting and treating storm water before it leaves the farm – stopping the phosphorus, sediment and E coli from washing off into Lake Rotorua

The detainment bund science project manager John Paterson says while there is an increasing spotlight on farmers and the impact farming has on waterways, this is a project developed and led by farmers.

The results will be released at a public field day on October 30 at one of the research sites near Rotorua.

The Phosphorus Mitigation Project Incorporated was established in 2016 and this farmer-governed research group has focused on intercepting storm water with structures called detainment bunds. 

“It appears the initial effort and expense is about to be well justified with some exciting outcomes.” 

Phosphorus loss to Lake Rotorua from human land use is about 20 tonnes a year and most of it comes from storm water runoff.

The detainment bunds are low earth mounds built across gently sloping land in valley floors where storm water flow paths occur during intense rain. They temporarily hold storm water runoff in a large ponding area for up to three days, allowing time for the ponded water to reduce in volume by infiltration. The suspended sediment particles and attached phosphorus cannot infiltrate and settle back onto the flooded pasture rather than going into the lake.

The research has been done by Massey University doctoral student Brian Levine. 

Levine found the detainment bunds capture about 60% of the phosphorus load and 80% of the sediment in storm water, depending on soil drainage conditions. 

Project group chairman Lachlan McKenzie says the bunds could make a significant difference to lake water quality.

A key attraction is they do not unduly compromise farming activity or pasture production in the area they occupy with the grass in the ponding area remaining healthy and productive.

“This technology has the potential to intercept and treat storm water for multiple benefits on a whole catchment scale that previously had not been considered possible.” 

Massey University’s Lucy Burkitt says the project is unique and shows the value of partnerships.

“Our collaboration with the Phosphorus Mitigation Project has demonstrated the incredible potential of researchers working closely with farmers and industry groups to help find practical solutions to improve the sustainability of farming.” 


The detainment bund research field day is on October 30 from 12.30pm at J and C Paterson’s farm, 136B Stewart Road, Kaharoa, Rotorua. Register with

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