H = the available fall after deducting loss of head in pipes and
channels from the gross fall;
Q = the supply of water in cubic feet per second; and
[eta] = the efficiency of the turbine.
The work done per second is [eta]GQH, and the horse-power of the
turbine is h.p. = [eta]GQH/550. If [eta] is taken at 0.75, an
allowance will be made for the frictional losses in the turbine, the
leakage and the friction of the turbine shaft. Then h.p. = 0.085QH.
The velocity of flow through the turbine (uncorrected for the space
occupied by the vanes and guide-blades) may be taken
u_i = u_i = 0.125 [root](2gH),
in which case about (1/64)th of the energy of the fall is carried away
by the water discharged.