Their Golden Bay farm a few kilometres from Takaka is bordered by the Anatoki and Takaka rivers that meet in sometimes dramatic fashion when heavy rain in the mountainous country to the rear fills their banks and flows over the surrounding land.
In a flood, they can access only 20% of their 90ha farm for the 300-cow crossbred herd and in the aftermath they are refencing and removing debris, but the trade-off is the “good dirt” underneath that produces 1500kg milksolids/ha.
In the past, their traditional small effluent pond had storage for only a couple of days before being spread through a travelling irrigator onto the paddocks and in a climate where it’s not unusual to be doused with 15cm or more overnight and 2.5m through the year, something needed to be done.
“I was going to get my hand smacked sooner or later, so I started going down the track of building a pond and having a weeping wall,” John said.
“But I kept saying to our engineer that there had to be a way of doing this without catching the rain.”
Then out of the blue, a Tasman Tanks representative turned up at the farm and offered a possible solution with a 1mm thick polypropylene cover, the same material as the liner which comes with a 20-year guarantee.
“Without a cover I was looking at a pond measuring 40m by 40m which is 1600m2 of productive land. And groundwater was going to be a huge issue. This tank is 25m in diameter which covers 490m2, so I’ve given up less land and I honestly think that if I’d dug a 40m by 40m pond and built the sides up, it would have cost me more than this tank.”
All up, installing the covered galvanised steel tank, liner and a GEA slope screen separator that he opted for so the effluent could be pumped through 2.5mm nozzles of the K-line, has cost about $150,000, with the actual tank about $59,000.
“If you’re putting a cover on it, you can’t agitate it, so we needed to separate the solids.”
Solids head to a concrete storage bunker, which he estimates will store 12 months of solids. They will be spread back on the paddocks and down the track might be turned into compost to sell to the public, though that’s just an idea at this stage.
Predictably, he’s had a few teething problems and spent about three months working through the connection of the tank with the slope screen separator as they were bought from separate companies.
“I concentrated on building the tank and storage bunker and then connected the screen, so I was working it out stage by stage,” John said.
“I really enjoyed it though because it was a challenge and I’d wake up in the night thinking about how something would work.”
A hole at the centre of the cover takes the collected rainwater down through a pipe and out to the river, though John said the cover always needs a little water sitting in it to stop it catching the wind, even though it is tied down around the edge.
“I wonder whether a better cover design would be a bladder.”
From the tank, the effluent is spread via K-line to the paddocks as power lines and the numerous creeks dissecting the property make it impossible for a centre pivot. He can spread effluent over 86ha of the farm compared with 40ha with the travelling irrigator from a small pond.
“It’s going to paddocks that haven’t seen effluent before.”
Though still early days, the system has impressed a neighbour enough to install their own smaller covered tank, along with a slope screen separator.
Tasman Tanks business development manager, Greg Lilly, said the company had sold 170 above-ground tanks to dairy farmers throughout the country in the past two years and several of those had added a cover, including areas not considered high rainfall.
“The cover means you have a smaller footprint which is a big thing for farmers when you’re building on a prime piece of land. It reduces your capacity.”
