Brumby mares appear to trap themselves by a gate during a flood. They move to higher ground

The brumby mares seem to trap themselves by the gate to stand with the next door herd. The flood water is rising and I'm seriously concerned for them. I look back to check on them and they vanished, they made their way up the hillside!

Edit:
They can come and go from here freely! https://youtu.be/h3ABO_4p-mg