so how has that castle flooded with out a major modern civil engoneeribg project? all youve done by posting that pic, is show it doesnt require, 21 century engineeribg to cause a flood of a castle
il give you a clue, floods happen when the water is ariving faster than it is leaving, you dont have to hold back the total extent of the water, that would take some doing, rather just reduce its flow marginally , so it starts to back up
its common here for floods to happen as there is a bend in the river or or a bridge that marginaly obstructs the flow
you can test this yourself, by running your kitchen tap full and then droping a few peas in to the sink hole and the sink will slowly start to fill, ergo a flood, i know this as iive just had to remove three peas from my sink hole