What is the meaning of "bi'Ketzei ha'Mayim"?
Alshich: [Before they reached the Yarden, their feet entered] water that spilled over the Yarden's banks.
Metzudas David: It is the eastern edge [of the Yarden].
What are "Gedosav"?
Rashi: They are high banks.
Why does it say "all the days of harvest"?
Radak #1: Even though they crossed [after winter ended,] in days of harvest (Nisan 10), the Yarden was full.
Radak #2: The Yarden is normally full all the days of harvest, for snow on the mountains melts and fills rivers (that empty into the Yarden).