‘And Yahweh discomfited Sisera and all his chariots, and all his host, with the edge of the sword before Barak.'
It was a total rout. Without iron accoutrements to hinder them, and more lightly armed, and fired by the belief that Yahweh had done this, the Israelites could cope with the conditions much better. And the Canaanites were already in disarray. So while there would undoubtedly be some resistance, they were totally unprepared. And not knowing how many of these dreadful barbarians were coming against them, and being without their main officers, who were caught up in their chariots, to rally them, they panicked and eventually turned and fled. And a fleeing army is easily beaten, especially by the more lightly clad.
‘And Sisera lighted down from his chariot, and fled away on his feet.'
This is the only indication we have in Judges 4 of the flooding of the plain. Sisera must have left his chariot because it was unusable. Only flooding could have done that, and caused him to panic in this way. Possibly his officers were the ones who told him to save himself while they fought a rearguard action, or perhaps he got away in the confusion, but it emphasises the panic that had seized hold of the Canaanite army, and Sisera as well. They had heard about the activities of Yahweh, God of Israel, and now they were seeing Him in action. They did not like the odds.