OPINION: Recent total or partial failures of earth walls around effluent ponds with compacted clay bottoms and sides have highlighted the risks of not having a more carefully engineered storage facility.
In the past six months, Waikato Regional Council’s farming services team has been aware of at least four total wall failures and several partial ones.
Not only does this cause environmental risks but failures can lead to the loss of valuable nutrients and end up costing farmers more overall than having installed a sounder pond in the first place.
“The bottom line is that farmers need to ensure they have well-constructed and sited storage facilities,” resource officer Hamish Walker said.
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“While well-constructed and managed clay-lined ponds can work, a bit of additional investment in a solid storage system using such things as synthetic liners can save farmer headaches and better protect our waterways.”
Sound pond construction methodology is well-established, including recommended materials, and the best places to locate ponds.
“The ponds that are being lost have not been built to these standards and this has increased the risk of something going wrong. The amount of time they have been in the ground, often with very little in the ways of repairs and maintenance, increases the risk further.”
There are a number of things farmers can do to help avoid pond failures, whatever their construction, sustainable agriculture advisor Mark Gasquoine said.
“Keep an eye of the foot of ponds to ensure they aren’t showing signs of slumping and get advice quickly if they are. Also, keep an eye on pond walls for signs of erosion or soft spots where liquid can potentially seep through.”
Testing ponds to see if they had an unseen leak somewhere also helped identify situations where a failure may potentially be ready to occur, he said.
“Basically what we are asking of farmers is for vigilance and for them to understand that having a pond sitting in the same place for 30-plus years does not necessarily mean it is completely safe and low risk.
“Ongoing monitoring and management of existing storage facilities is essential.”
The farming services team notes that while pond failures can occur due to an adverse event, such as an earthquake or flood, those that have occurred recently have been under relatively normal circumstances.
Farmers generally should be looking to upgrade storage facilities to meet industry standards and regional council rules where required.
“Our recommendation to farmers is to do it once, and do it right,” Walker said.
“It’s important to select the right professional advisors and ensure that all of the potential risks are adequately mitigated.”
This includes getting the size right to deal with adverse weather conditions, getting the building material correct and the pond sited properly, getting good contractors building it, and managing the storage well.
“Farmers who are not upgrading their systems will be expected over time to prove to the council that any existing facility they continue to make use of is not leaking, and that it has little risk of failing overnight,” Gasquoine said.