Scientists worked for three years to test inflows and outflows from the site and the Pomahaka Water Care Group has collaborated with the Phosphorus Mitigation Project to run several field days throughout this time.
The preliminary results show about 80% of sediment was being trapped by the bund including about 70% of phosphorus and 60% of nitrogen.
You can read a great write up about this work here.
The Phosphours Mitigaiton Project have developed a Detainment Bund guide, where they describe what a detainment bund is:
A Detainment BundPS120 (DB) is a low earth berm placed across an ephemeral storm water flow path on a farm to temporarily detain storm water run-off for water quality objectives. DBs are usually located on valuable and productive pasture paddocks as these areas are often where ponding opportunities can be optimised with the least earthwork requirements. They are generally not located on permanently flowing waterways.
You can find out more about Detainment Bunds here, and see a video of the Pomahaka trial site working in this time lapse video:
Detainment Bund PS120
The Phosphorus Mitigation Project Inc. (PMP) has been undertaking a trial on a Pomahaka property to assess how effective effective Detainment Bunds PS120 are at mitigating contaminant movement on our heavier clay soils.
PMP Inc. is a farmer governed group instigating and directing NZ researchers to help find new ways of addressing water quality issues. PMP’s efforts have been primarily funded by MPI’s Sustainable Land Management and Climate Change Fund (SLMACC) however over the last 10 years all the NZ ag sectors and several Regional Councils have also been helping to fund the applied research work on DBs.
There has been a large amount of work illustrating the effectiveness of detainment bunds in other parts of the country, however there was a limited amount of trialing done on heavier soil types. The Pomahaka Water Care Group was approached by the PMP Inc. to see if we could help find a farmer who would be willing to have trial site on their property.
We managed to help them find a farmer and after extensive searching using specialist GIS techniques, they found a suitable site that meets the DB specification for adequate storage i.e. Ponding that achieves ≥120m³ of stormwater runoff storage per hectare of catchment serviced by the DB.
