How deep should I dig this trench?

Question:On the side of my house, there is about 7 ft of flatland between the house and the trees. The trees are pine trees that are on a small hill which lead up to the neighbors house. Every winter when the snow melts, it all goes down the small hill and just sits in the flat part, I am digging a long trench aroudn the bottom of the trees and will be filling that with riverrock to help the water drain better because this area does not recieve sunlight. How deep should i dig the trench to fill with the riverrock? 4 in. 6 in, 8 in, a ft?

Answers:
I am currently RE-digging a trench around my pond and pretty much doing the same thing to funnel the water away from the walkway. The only advice I have is it is better to dig it too deep than not deep enough - it is hard to redo a trench. Make sure you use large enough rock so that it will not clog up easily and that weeds will not grow in it easily. If you dig it too deep you might run into the tree roots too. If you do I would not dig them up but just dig around them and fill it with rock. The roots are also helping in soaking up the water that sits there too. If it is winter thaw you are having problems with the trench if filled with frozen water might not do much good but it is a step in the right direction. Good luck!