I have been watching this, to see how it developed, before answering. ( and trying to keep a straight face) I am not sure if the policy of not having an argument or debate at Dan and Rosemarys dinner table is the best solution to give genuine advice for questions raised on this forum. For Dutch drains replace with French drains then Google and you have all the information that you need and then sum. However I am not sure this is the way to go and be able to use the land productively. French drains are normally associated with draining motorway embankments where it does not matter if the land is undulating for the drains to be successful. Very little drainage is carried out now mainly because the 100% grants that were available years ago are no longer available. Environmental issues also prevent drainage being done ( one of the reasons that the water ways in summerset was not carried out was due to water voles population the area). If you search wavincoil or wavinflow it should also help and assist with your problem.
Good luck
Casper&smudge