A specific flow will be drawn by a water turbine operating at a specific speed. The turbine may begin to drain the river if there is insufficient river flow to meet this requirement, which would cause a rapid decline in performance. As a result, it must either regulate itself or change the internal geometry of the system. Regulated turbines can change the amount of flow they draw by moving the runner blades and/or intake guiding vanes. The various turbines’ efficiency will eventually drop as they draw less flow. The novelty of the present work given in the complete specification by adopting the tail race water level at minimum threshold level of 659 m EL at design load of 4 MW will yield saving of 2.27 m3/sec or yield 0.472 MW input hydraulic power. The work will hold the key in novelty during the design and excavation of tail race channel or for renovation, modernization, and uprating (RMU) of the existing old hydropower plants. The design in selecting suitable width, depth and by adopting flow regulating means will yield and improve the net head substantially and thereby saving of discharge to an extent.