We have some raised beds which border on to a lawn. The raised beds are
watered each night through an automatic irrigation system.

The grass at the side of the beds has become very, very wet - and really never
dries out: it is particularly noticeable in the morning after the night
watering session. The raised beds drain very, very well.

We have removed a strip of the lawn adjacent to the raised beds - about a foot
wide (and thrown the sods away: not particularly good quality grass) - we have
dug a trench - about a foot deep today - and going to deepen it another foot
tomorrow to make a soakaway.

It is our intention to fill the trench with aggregate(?) - put a permeable
membrane over the top and then top with a mix suitable for growing a fresh
strip of lawn.

Questions:

Is aggregate the correct thing to fill the trench with - or do I use course
gravel - or something else?

What mix (peat/sand/topsoil/???) should I top the trench off with prior to
sowing lawn seed?

How deep the "soil" layer?


Any other pointers please.