Just used a mini tiller on my lawn as I have recently had drains inserted which left the top uneven, I am planning on laying turf down in a few days. However the current surface after tilling is a mixture of shredded grass and topsoil roughly 3-5inch deep. I was unable to go any deeper with the tilling as this would have destroyed the new drainage system. I have added a picture below. will this surface be ok to lay turf on top of? once I have used a plank to flatten it.