Joshua 4, the Memorial Twelve Stones

Believe it or not, this is not a debate thread, but asking for help in Joshua 4, and it is a minor point, concerning the twelve stones the marked the crossing of the Jordan. In verse 8, it basically says that each man from each of the twelve tribes picked up one stone and brought it to where the Israelites were lodged. It then says, and this may be the problem, that Joshua took the stones to the mist of the River Jordan, where the feet of the priests stood, and set them up as a memorial marker. It goes on to say this is where they are to this day.

At some point after that the waters return to normal. Then, in verse 20, it says Joshua took the same twelve stones and set the up at Gilgal for the same purpose, to remember the crossing of the Jordan.

This is my questions. How did the stones survive after the water in the Jordan was returned? How did Joshua retrieve them? Why does the Bible say they are there to this day when the book was written after all these events? Why did he move them to Gilgal?

Any help is appreciated, maybe someone who knows Hebrew or has studied this chapter before?