overflows all its banks all the days of harvest

Question

In Joshua 3:14-16 (NASB)

14 So when the people set out from their tents to cross the Jordan, with the priests carrying the ark of the covenant before the people, 15 and when those who were carrying the ark came up to the Jordan and the feet of the priests carrying the ark stepped down into the edge of the water (for the Jordan overflows all its banks all the days of harvest), 16 then the waters which were flowing down from above stood and rose up in one heap, a great distance away at Adam, the city that is beside Zarethan; and those which were flowing down toward the sea of the Arabah, the Salt Sea, were completely cut off. So the people crossed opposite Jericho.

What causes the Jordan to overflow "all its banks all the days of harvest"? Also, harvest of what?

Answer 1

Ellicott offers this neat summary -

Jordan overfloweth all the time of harvest — This is meant, not of wheat-harvest, but of the barley-harvest, as is manifest from their keeping the passover at their first entrance, (Joshua 5:10,) which was kept on the fourteenth day of the first month, when they were to bring a sheaf of their first-fruits, which were of barley. So that this harvest, in those hot countries, fell very early in the spring, when rivers used to swell most; partly because of the rains which had fallen all the winter, partly because of the snows which melted and came into the rivers. And this time God chose that the miracle might be more glorious, more amazing and terrible to the Canaanites; and that the Israelites might be entertained at their first entrance with plentiful and comfortable provisions.

Matthew Poole offers similar comments:

This is meant not of the wheat harvest, but of the barley harvest, (which was before it, Ruth 1:22 2 Samuel 21:9) as is manifest from their keeping of the passover at their first entrance, Joshua 5:10, which feast was kept on the fourteenth day of their first month, when they were to bring a sheaf of their first-fruits, Leviticus 23:10 Deu 16:9,10, which were of barley, as Josephus affirms, and is evident from the thing itself. So that this harvest in those hot countries fell very early in the spring, when rivers used to swell most, partly because of the rains which have fallen all the winter, and partly because of the snows, which then melt into water and come into the rivers; for which reasons the same overflowing of water which is here ascribed to Jordan, is by other authors ascribed to Euphrates, and Tigris, and the Rhine, and Maine, &c.