Calculating power requirements for AC Motor?

I am trying to determine the power requirements for an AC Motor for 2 types of wavemakers; Plunger and Flap.Here is the layout of the plunger and tank

I think you need: F= Discharge (in m^3/s) * Speed Speed can be calculated according to you data. Discharge would the amount of water displaced every second, in m^3/s. Use P=F*V, should get you the power.