In the time before modern, intensive farming techniques there were a number of ways to keep soil fertile. In many places in the world people living on flood plains learned to live with the annual floods, taking the good with the bad. The bad being possibly unpredictable flood levels or the need to evacuate the land for part of the year, the good being that flood-fed, alluvial soils are renewed with every flood cycle.
I'm not sure if parts of Poland might fit into this category but I suspect they will. When the dams are no longer functioning or are gone, the annual floods might make a return in many parts of war-torn T2K Europe (and many other parts of the world).
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 "It is better to be feared than loved" - Nicolo Machiavelli
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