I am designing a pitchback waterwheel for a head of 1m and flow rate of 20l/min. I've calculated that the theoretical power available to me is 3.27W and I know that the mechanical power I can extract is the product of torque and angular velocity but I'm struggling to find information on optimum torques/angular velocities. I've read online that overshot wheeels have an optimum rotational speed of 21/√D (where does this come from?) but would that be the same for pitchback too since I've heard they're quite similar? Is higher torque better for waterwheels? Also, I want to maximise the efficiency of the waterwheel so could anyone link me to an article that lists how to calculate losses in the various components and analyzes the forces acting on it? Thanks for the help.