Ayuh,.... Yer right, water flows downhill, no way 'round it,......
The problem I see with yer plan, is placement,....
Put the drain at the very bottom, in the soggyist spot, 'n pitch the drain to the culvert,.....
Ayuh,.... Yer right, water flows downhill, no way 'round it,......I was thinking of putting in a 3-4 ft deep french drain filled with gravel (pipe then gravel all the way up with the last 6 inches being soil for grass) a few feet uphill of the portion of the yard that gets soggy. I'm thinking that this will catch most of the surface and subsurface water that is making its way downhill and this will get rid of my soggy backyard problem. I would daylight the drain into a culvert on the side of the property and also potential a deep dry well