Sub-surface drainage put simply is under ground drainage that directs excess water away from below the ground. You need a trench that has ‘fall’ in it, a socket agiline, gravel and this is wrapped in Geofabric for silt retention.
Good planning and supervision makes a hard job easy especially if you have mobile plant and helpful labour on hand.
There are two main types of drainage
Swales: Swales are shallow, elongated depressions in the land that collect and move water. They are visible in the landscape and often highlight the movement of water through their material choices and layout. Swales move water, but they also slow it down and allow it to percolate back into the ground to improve water quality.
Subdrainage: Subdrainage consists of underground constructed drainage systems, including drainpipes and drain inlets, that collect and move water. Because it is buried in the landscape, subdrainage is often invisible to us. Buried drainage moves water quickly and efficiently across the landscape.