okay. i have some questions but out of what i gather,
1. yes i would put a reed bed at the top if you think the water wont flush the whole system away (depends on the kind of rain and how fast the water flows down from the road)
2. Swales swales and more swales was the first thing i thought, trying to divert that red water flow line so it doesn't go to the house
3. the reed bed and all those pretty plants would filter the water for you, you could add a bit o charcoal in the reed bed system like you would use in a greywater treatment. but i don't think it's a problem after for the garden plants, unless you live in a very polluted area.
how would it be if trees are on the top and reed bed closer to the bottom? i think trees profit from better drainage and i suppose its more clayey at the bottom..but you might have to make bigger swales to divert water in the right direction and slow it down to go into the reed bed. (not sure if im getting everything right)
