"水力计算" can be translated into English as "hydraulic calculation" or "hydraulic computation".
"Hydraulic" refers to the science or technology of fluids in motion, especially water.
"Calculation" and "computation" both mean the process of using mathematics to find out a result, though "calculation" is more commonly used in this context.
So, depending on the specific usage and context, either "hydraulic calculation" or "hydraulic computation" would be appropriate. In most engineering and technical contexts, "hydraulic calculation" is the more prevalent choice.