Shallow drainage is the preferred option for land improvement where soils are impermeable, where water is unable to flow down from the surface or sidewards within the soil. It usually involves installing relatively shallow carrier pipes and then ripping open cuts in the soil above to allow rainwater flow down into the pipes. The main rationale behind shallow drainage is cost. Making openings in soil with a machine like a subsoiler or mole plough is cheaper than installing stoned drainage pipes at close intervals.
Stone must be used over collector pipes for the system to be effective. The teeth of the ripping machine must be able to cut into the stone layer – without coming too close to the plastic pipes. If you have collector pipes installed in your land, be sure to record how deep they are placed and what cover of stone is put over them.