Abstract: This paper derives a mathematical model of hydraulic transients for a system with bifurcated
pipes converging behind a tailrace surge tank based on the method of characteristics (MOC). A
corresponding numerical model has been developed using the data of a real hydropower station with the
same configuration of pipe bifurcation and surge tank, and a simulation of the probable transient process in
this system is conducted, focusing on the influence of throttle orifices on the transient behaviors. The results
show that in steady flow condition, the bidirectional flows passing through the orifices are significant in
volume and a greater cross-sectional area of the orifice results in a larger discharges of the bidirectional
flows but little effect on the tank level and the water head of generator unit. In unsteady flow condition, if
the cross-sectional area of an individual orifice is different, then it produces different refection to water
hammer but the surge process occurring in the tank would be the same as long as the sum of cross-sectional
areas of all the orifices is fixed. The conclusion is helpful to design and operation of similar hydraulic
transient systems.