Transient analysis of multi-branched pipeline systems is generalized by the development of an impedance method. Both open and closed boundaries of branched pipeline elements were implemented in the analytical development of a reservoir pipeline multi-branched pipeline valve systems, in which the performances of the impedance and transient responses were compared with those of conventional approaches. To address realistic boundary conditions along the branched element, a partially-opened boundary condition was implemented in the impedance expression of the branched pipeline system. The performance of the generalized multi-branch impedance was tested on a large water supply system with 10 minor branches from an actual system. The impact of the designated branches was evaluated using the rootmean-square error (RMSE)of the pressure and the difference in the energy spectral density between the original and skeletonized systems. Combinations of multiple branches for certain flow conditions was identified based on the holistic response for both the frequency and time domains. The proposed method can be a useful alternative to effectively address the skeletonization issue for pipeline systems with multi-branched pipeline elements.