Installing a Field Drain

Installing a Field Drain

The rain has finally come to Auckland in bucket loads—great for the dams but not so great if your garden lacks good drainage. Installing a simple field drain beneath lawn areas can help eliminate excess water on your property and minimise those boggy patches.

Central Landscapes stock everything you need for a DIY drainage project, including:

Step 1 – Identify where to lay the field drain

You’ll want to run the drain from the area that is prone to flooding -  to a lower point on your property. You need at least a one per cent slope on the drain coil for the water to flow sufficiently. Ideally, you should aim for a straight trench that avoids obstacles such as tree roots or concrete paths. (If you are laying new paving, this is an ideal opportunity to install drainage below the paving).

Drainage spade

Step 2 - Digging the trench

A trench is typically 200mm wide and between 200 to 400mm in depth. Centrals stock a handy trench spade for this very purpose. This type spade allows for ‘levering’ even the most compacted soil, which is an easy way to excavate the area.  Cut the top layer of turf carefully into square sections so that you can re-lay the lawn later. Use a spirit level and a string line to check that you have sufficient fall in your trench, to ensure the water will flow in the right direction.

Step 3 – Line the trench

You can add Geo-textile fabric to the floor and sides of the trench to stop soil and grit seeping into the drain coil. Without this barrier, the coil with clog up over time.

Drainage metal

Step 4 - Add Drainage Metal or Scoria

You can use drainage metal or scoria to fill the trench; either material will work well. To begin, add a layer to the bottom of the trench as a bed for the drain coil.

Filter SockDrain coil

Step 5 – Lay the drain coil

Central Landscapes stock two sizes in Novaflo drain coil – 65mm and 110mm. ‘Punched’ coil is an option for the sections that require drainage. This coil has slots in it that allow the groundwater to seep in. Use non-punched coil when you simply want to transport water through the pipe. The exterior of the drain coil should be covered with a filter sock, which stops soil and sediment seeping into the pipe. Central Landscapes sell filter sock that is preloaded with coil – ready to install.

Step 6 – Fill the trench with metal or scoria

Cover the drain coil and fill in the trench with drainage metal or scoria. Don’t fill the channel completely - leave enough space to re-lay the sections of turf.