Water does not throw creatures but it can push them, but pressure does not push them. Creatures are only pushed by flowing water less than 7/7 depth. At 7/7 pressure takes over, which involves teleportation of water from the top of the water column to the bottom. This has nothing to do with the high velocity of the water a la minecarts, but is just a programming trick to allow large bodies of water to not be too much of a resource hog. The body of water is treated as one continuous unit, and 1/7 pieces of water are freely teleported from the top to the bottom without worrying about pathing in between. Meaning it never touches a creature in the way.
So if you want to push enemies and elves off your entrance, use shallow water. The easiest way to do this is to put pressurized water (from a pump or water source on a higher level) through a "grate" of diagonals (pressure is only N S E W Up Down, no diagonals) to produce constant flowing water.
Again, this only pushes, it does not throw. You can push them off a cliff to their splattery doom, or onto cage traps, or spikes, or into a pit for later rinsing with magma to wash away all things that aren't iron.
If you want to throw your enemies so they splatter against a wall, you need blunt impact. Minecarts work well for the purpose, and can be made more potent by loading them with dense or sharp things.
The diagonal pressure reducing grate trick has many other uses, like keeping cisterns filled from a water source on a higher level without complex plumbing or risk of flooding, or making dwarf permeable flood control screening (diagonal checkerboards of columns forming screens also allow invaders to approach your dwarves without having line of sight to use crossbows).