Aye – would depend on the garden really. Is it on a fall? ie higher at one end then the other, or mainly flat?
If it’s mainly flat then would need to install a snake like loop of the landrain throughout the garden to catch a lot of rainfall.
Always amazed me how effective this stuff is when installed properly.
you don’t need to be that deep – enough to acheive a fall from one end of the landdrain to the other. lay the drain in the bottom of the trench and surround with a 10mm clean stone to approx 75 – 100mm shy of the surface. top of with a free draining grit sand ( river sand ) then finish with a sod of turf to level. Everything needs to be free draining otherwise water won’t reach the pipe. The end of the drain needs to be connected to your surface water drainage via a silt trap.
alternatively strip all your existing turf – aerate the subsoil with a fork then replace the turf with an amenity type sod from Rowlawn (or similar). instant good lawn