Undesired flows in lateral-intake multiple forebays and their hydraulic implications: case study for Asia’s largest urban water supply pumping station

Urban pumping stations often adopt the design of lateral-intake multiple forebays to accommodate multiple pump units in a limited space and to reduce interaction between the operating units. However, a full understanding of the undesired flows and hydraulic characteristics of lateral-intake multiple forebays remains limited, resulting in the design of flow-regulating measures relying on trial and error. This study numerically investigated the undesired flows in lateral-intake multiple forebays and their hydraulic implications, using Asia's largest urban water supply pumping station as a case study. The results show that the undesired flows, including flow recirculation, helical mainstream and vortex strip, are the main reasons for the deterioration of hydraulic characteristics in the forebays. The undesired flows are more pronounced at higher inflow Froude numbers or for the forebay closer to the diversion channel inlet, resulting in lower flow uniformity and higher hydraulic loss. Further discussion shows that the flow-regulating measures improve the hydraulic characteristics by limiting the generation and development of undesired flows within the forebays. This provides references for the design of flow-regulating measures for similar forebays to reduce the cost of trial and error, which is of general value for the lateral-intake multiple forebays required for urban pumping stations.