Drainage! Ah, I know it well. I have land that hasn't been drained for 40 years and we could lose bodies in it.
We are draining field by field, but deep draining. Our problem isn't surface water going down, but spring water coming up and then not being able to get back down. Which have you got?
Deep drainage is the following - dig down until you hit the spring line (at least 5 feet) and lay your pipe north-south (all springs go east to west - don't ask me why) with outfall to ditches, tanks or streams. Rod your pipes every month for the first year, knock back the piles of earth over the pipes and then mole plough.
It's working for us. We are getting 2500 litres a day minimum from 3 1/2 acres and now have stock on those fields.