My interpretation: 100 years ago, dig a ditch and put a few clay tile mains in, drained the slough. 50 years ago, branches were put in of the mains, drained the sloughs off the sides of the previous sloughs. 30 years ago, pull a line in the wet spot, but not too far uphill (save money) 20 years ago pull that SOB ALL THE WAY till it starts going down the other side of the hill. 10- 15 years ago, put one every 30-50 feet! | 
Tile question
