The equation for predicting the amount of power that comes out of hydroelectric generators is: 

 

• Pth = ρ * q * g * h where Pth = power theoretically available (W), ρ = density (kg/m3) (~ 1000 kg/m3 for water), q = water flow (m3/s), g = acceleration of gravity (9.81 m/s2), and h = falling height, head (m). (engineeringtoolbox.com)

 

   Using this equation we get that with a water flow of 4.89 * 10^-7 m^3/s, a head of 10.5 meters, and a 90% efficient generator (according to altenergy.com most hydroelectric power plants are 90% efficient) we can generate 4.53 watts.