Diagnosing Pumping Instabilities in the Southern Delivery Raw Water System

The Southern Delivery System Project for Colorado Springs Utilities (Utilities) consists of three pumping stations that deliver raw water supply from the Pueblo Reservoir to the Colorado Springs Edward W. Bailey Water Treatment Plant through 50 m of 66-in. diameter pipeline. The Juniper Pump Station is located at the Pueblo Reservoir and takes supply from the joint use header connecting through the dam and pumps it north to the Williams Creek Pump Station located south of Security-Widefield. Water supply is then pumped north to the Bradley Pump Station located within Colorado Springs and, in turn, pumped north and west to the new water treatment plant. Shortly after going into service, the Williams Creek Pump Station began experiencing unexplained flow instabilities. The flow fluctuation was observed as continuous speed changes generated by the automatic control systems to maintain an average pumping rate during low flow operations. The fluctuations were unanticipated and of a cyclic and intermittent nature, not always present. They were also not observed at the adjacent pumping stations within the system making the problem difficult to diagnose and solve after the most obvious potential causes, such as erratic meter readings or stability adjustments to pump speed algorithms, were ruled out. The owner was concerned about potential long-term equipment impacts, the effect on energy efficiency and long-term operational costs, and possible larger issues that could develop in the future with increased flow demands. The design consultant was requested to assist utilities in resolving the issue which involved a multi-disciplinary team of individuals represented by the designer, general contractor and subcontractors, SDS management team, and utilities operations. Investigations are described below with discussion of the final conclusion, range of solutions explored, and the selected operational changes implemented.