Many biblical stories often depicts parting of water most famously by Moses at the red/reeds sea. I have considered using present day science to explain Moses's feat but that proved impossible, my question is what kind of technology in the future would be required in order to part water? (I also remember that kind of power was used to drown many Egyptian soldiers in one swept.)
The future ACME Water Parter
Water is a diamagnetic material. That means you can use magnetic fields to part water. Frogs have been levitated using the water in their bodies, so we can already control water using magnetic waves to some extent.
In the future, larger, stronger magnetic fields could allow us to acheive exactly what you speak of.
Like a rogue wave, only a trough. Set up various resonators and different places, ahead of time. Allow the waves to spread with constant input of energy to distribute the motion throughout the body of water. At a pre-determined time and place, (nearly) all the water rushes away from the spot.
Sheets of strong material extend out of the bottom of the body of water, either rising out from a stowed position, or self-assembling to rapidly grow in place. This forms a robust barrier which forms a coffer dam.
A couple of black holes should it. One on either side and their gravity pulls the water apart.
You don't specify the direction of the parting. A downburst is a strong ground-level wind system that emanates from a single source above and blows radially, that is, in a straight line in all directions, from the point of contact at ground level. This would make a circular island that was lower than the water around it. Along an extended weather front, the downburst could be more linear, forming an inverted causeway.
the cheapest and most reliable way to do that is just outright lying.
Make sure someone tells you had that kind of power. Use some extra knowledge to make sure the group of people you want to lead through the gap is not where they were before. And make sure your enemies don't see the trick (and neither the quicksand, or deathtraps, or whatever) when they come rushing behind.
Then, with carefully spread rumour and not many survivors on the enemy side, you are set.
The survivors might even be encouraged to help spread the story (and be set free for this purpose exactly).