I'm creating a report on the possible implementation of a sub hydro system and need some help. I've attached the image of what I'm proposing, where I've essentially created a head via a riser B with a water inlet just below sea level, which will then flow down into the hydraulic turbine and fill up the pipeline and Riser A to create electrical energy.
In it's initial state, the entire system is full of water. When power isn't in demand I've incorporated an ESP to then evacuate the pipeline and Riser A back out of Riser B (Riser B is still filled after). Initially I calculated the required energy needed to evacuate Riser A and the pipeline which would act as potential energy using the simple energy equation E=mgh. That potential energy would then be converted into electrical energy upon subsequent flooding of the system again.
I'm having trouble in determining the ideal size of the turbine though because I'm not sure how to calculate the flow rate that will be coming into Riser B and subsequently into the turbine itself since Riser B is never completely empty. I assume that I won't need that large a one due to the the large head, but I'm not sure of the appropriate governing equations or if they're even needed given my potential energy calculations.
I'll be testing multiple values of pipe diameter and pipeline length but original values were:
Riser A = 500m
Riser B = 50m
Pipeline L = 10000m
Pipeline, Riser A/B Diameter = 500mm
Any help would be appreciated, because I'm stuck in a bit of a rut finding the connection between the two as I'm using two different ideas and joining them.
Also for reference the ESP will be powered using excess energy from a wind turbine (not shown).