Minimum depth for land drain

[aadvark]

Hello, I intend to lay a 100mm flexible land drain along a gravel path that will only have light foot traffic. Does anyone know the minimum depth I can put it at. The fall to the surface water drain is minimal so ideally I'd like to lay it as shallow as possible. I'm hoping I can lay it at 300mm. If this is not feasible is there a protective mesh or other I could lay on top of it to prevent damage from under foot.
thanks

[seanandruby]

that will be fine at that depth, keep the trench width tight as poss