Managing stormwater

Reducing wastewater volumes results in:

  • Reduced costs when applying wastewater to land.
  • Less risk of wastewater being applied to land during unsuitable conditions.

Stormwater flowing into the wastewater treatment system decreases its efficiency by:

  • Reducing the retention time of wastewater within the system – it flushes the effluent through.
  • Lowering the pond's temperature; affecting the essential bacteria and algae that thrive at warmer temperatures.
  • Flushing poorly treated wastewater through the system into the receiving waters.

Roof water

It is strongly recommended that all roof water is permanently diverted away from both the yard and wastewater system. The addition of clean water is an unnecessary cost (financially and environmentally). In most cases, this extra volume can be easily – and cheaply – excluded from the system.

Catchment stormwater

Drains or bunds can be used to divert stormwater from the surrounding land away from the wastewater system.

Stormwater diversions

The ability to divert stormwater from the yard is crucial, particularly in Northland where high intensity rainfall events are common. Stormwater diversions need to be simple and visual so they are routinely used and checked.

The diversion system must be sited before any gravel trap to prevent accidental wastewater discharge to water.

Operation of stormwater diversion systems

It is essential to follow good management practice to avoid any accidental discharge of untreated wastewater down the stormwater drain.

Signs, coloured boards or flags – that are visible from a distance – can be used to indicate the position of the diversion system.

The images below show an innovative way to signal wastewater/stormwater mode.

Stormwater Stop sign.  Stormwater Go sign.

Many methods are used to divert stormwater from the buildings and yards away from the treatment system, after the yard is cleaned.

Some examples are outlined below.

Sump and up-stand

Sump and up-stand water diversion method.A pipe up-stand is moved to channel stormwater to a drain, or wastewater to the ponds. This image shows the diverter in stormwater mode.





"Y" with spade

"Y" with spade water diversion method.The spade is moved to select either "stormwater" or "wastewater" mode.








Automatic water diversion method.Solenoid-actuated diversion valves operate remotely from the dairy. As they are some distance away and below ground, a position indicator is advised. Regular checks must be made to ensure the diversion is working.





Feedpad water diversion method.Feed pad diverter: the board is removed to channel wastewater to the pond when the pad is in use.






Simple stormwater diversion system

  • Can be seen and operated from the yard.
  • Red flag indicates stormwater diversion mode.
  • A green flag could also be used to indicate when wastewater is going to the pond.
  • A simple barrier such as a bungee cord across the pit entrance can be used as a reminder when the system is in diversion mode.
  • Low cost.

Simple stormwater diversion system.