If I want to measure the flow at the bottom of a rain water pipe, then want to add a nozzle... how can I calculate the flow at the nozzle? will it be the same? I have experimentally measured Q at the big pipe. I want to design a Pelton turbine so I have to know how to calculate the flow and how the flow in affected as I decrease the area of the nozzle. and how can I calculated the power of the system if the efficiency of the turbine is 80% and the height of the tube is 15ms. will the jet velocity increase as we decrease the nozzle size? and if it increases to what limit... thanks a lot!!