how do you calculate water displacement?

[Whycantinamemyself]

lets say a character dove into the water and displaced it quite a large amount(by displace i mean throw into the air because the impact was enough to knock the water away), how would you calculate this? would this be speed or ap?

 

[FinePoint]

Three dimensional fluid dynamics are extremely complicated, but for a very rough estimate you can calculate this with conservation of energy assuming the impact stops their movement to a near halt.
If you know the volume of the water and how high it rose you can use Ep = M*g*h.
M is the mass in kilograms (volume of the water times its density), g is the acceleration due to gravity (9.81ms^-2 on Earth.), and h is the height it rises in meters.
This would give you the potential energy put into the water, and by extension the kinetic energy they had before impact.

If the impact does not stop their movement, then you must also add the kinetic energy they maintain through the water using their mass and speed.

 

[Whycantinamemyself]

i appeared to have goofed up in what i meant, heres the panel to show what i mean

he actually started in the water instead, this changes things because its in water instead of air