Detainment Bund visit prompts action by Ngongotaha group

(Published on 16th January 2018)

A recent field trip to a Detainment Bund study site by a group of Rotorua landowners has started conversations and plans for similar Bunds to be established in their catchment. John Paterson lead the field trip with the Upper Ngongotaha Catchment Group to the Kaharoa farm site where he manages a project trialling detainment Bunds for a farmer lead group supported by farming industry and MPI’s Sustainable Farming Fund.

Landowners in the Upper Ngongotaha Catchment have experienced a particularly wet year with  many properties still dealing with the disastrous effects of multiple heavy rain events on their land. A desire to find solutions for the area has brought about the establishment of a Catchment Group, supported by NZ Landcare Trust, where landowners and community can work together to improve water issues. After the November meeting of the Catchment Group, a field trip was planned to look at Detainment Bunds as a possible option to slow the flow of water across the land.

"Detainment Bunds have been proven as an effective means to collect storm water, and enables settlement of sediment and phosphorus," Paterson explains. "This current study by the Phosphorus Mitigation Project is about understanding and quantifying the beneficial  effects  for water quality and how to optimise the process."

A Detainment Bund can be built where storm water naturally flows across the land to a collection point and these Bunds are often located on highly productive pasture paddocks. Unlike a dam, a Detainment Bund has a riser at the out flow point that means the cleaner surface water is skimmed off and flows out when the pool reaches a certain level. A restricted outlet culvert pipe at the bottom of the Bund slowly disperses the water from the Bund so the valuable paddock is back in action within approximately three days.

Paterson has identified areas in the Upper Ngongotaha catchment that would make viable detainment Bund sites to mitigate flooding issues and to reduce  phosphorus and sediment reaching the Ngongotaha Stream which flows into Lake Rotorua. After the recent field trip, two landowners have expressed an immediate desire to work with Paterson on establishing a Bund on their properties. Currently, Detainment Bund construction  on farmland  is subsidised by the Bay of Plenty Regional Council as part of their Riparian Management Programme  support for landowners.

"We can see how these Detainment Bunds will help with flooding issues for the whole catchment alongside improving stream water quality,"  commented Sarah Thomson, spokesperson for the Upper Ngongotaha Catchment Group. "It's a win-win."

For more information about the Phosphorus Mitigation Project and Detainment Bunds, please contact John Paterson by email at or phone 0272496114. For more information about the Upper Ngongotaha Catchment Group, contact Sarah Thomson on or phone 022 0624 986/07 343 6407.



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