I'm trying to figure out when land reclamation happened, mostly in the Low Countries
Digging through wikipedia and the internet doesn't yield much in the way of draining of marches and fens, most results relate to the draining of Flevoland (which date is readily available.)
At what point in history did the technology to drain land get discovered and how was it expanded, and when did the Dutch start using it widespread?
Holy Roman Emperor, and the lord over the still very much divided Netherlands, Charles V gave permission for land reclamation near Alkmaar through the use of windmills in 1533. There was significant activity in the early half of the 17th century, when the (now united) Republic of the Seven Provinces was at the height of its (financial) power and the war against Spain was a relatively done deal.
I am currently quoting from memory. I wrote an undergraduate paper on, and had a lecture/seminar/course on more or less this issue. I am pretty certain that Willem van der Ham, probably the authority on the history of Dutch water management, will confirm what I said in his recent book Hollandse Polders (2009). I'll have a look later today.
At what point in history did the technology to drain land get discovered
Suetonius records the Romans draining land for farming. in particular, the Fucine Lake and Lake Kopais were large scale projects, although the technology involved was mainly digging drainage canals. This would require skill at surveying, and lots of labourers.
Rivers and the Power of Ancient Rome by J.W. Campbell, University of North Carolina Press 2012