Dakawa Irrigation Scheme: Pump Station Design Criteria Report

The report is a result of a contract between CDM International Inc. and the U.S. Agency for International Development (USAID) to evaluate the existing pump station, develop designs and construction contract documents, and oversee procurement of equipment and construction. The pump station provides water from the Wami River to irrigate approximately 2,000 hectares of farmland at the Dakawa Rice Farm, which is owned and operated by the farmers' cooperative, the Dakawa Irrigators Cooperative Union (UWAWAKUDA Ltd.). The irrigation supply infrastructure comprises a pump station and a 7.3-km main canal that provides water to six secondary canals. The existing pump station was constructed in 1981 and includes six horizontal centrifugal pumps and motors, piping system, electric switchgear, and transformers. However, only four of the six pumps are currently operable, and the pumps deliver an estimated 1.0 to 1.4 m3/sec per pump. The recommended option for the Dakawa pump station is to completely replace the existing end suction centrifugal pumps and motors with axial flow pumps with integral submersible motors, installed directly into the intake well, and with new electrical motor control centers (MCCs) and switchgear, electrical transformers, and power cabling. The proposed axial flow submersible pumps will be started manually by the operator, and design conditions allow for the operation of five pumps continuously with the sixth pump as standby. Duty time on all pumps should be balanced so that all pumps see approximately the same number of running hours per month. Pumps will normally be stopped manually depending on the demands of the irrigation scheme, but a low water level shutoff will be provided to stop all pumps when the intake well water level drops to a predetermined level. The report also outlines the civil/site works, including site excavation, backfilling, and grading, access road rehabilitation, perimeter security fence and access gates, and site security lighting. The operations building will be designed to house the new pumps, electrical equipment, and control systems, and will include a design concept, concrete and reinforcing steel, windows and doors, finishes, and building utilities. The mechanical/electrical works will include pumping criteria, pumping equipment, electrical equipment, and a monorail and overhead traveling hoist. The report also includes a list of acronyms and abbreviations used in the document. The recommended option for the Dakawa pump station is to completely replace the existing end suction centrifugal pumps and motors with axial flow pumps with integral submersible motors, installed directly into the intake well, and with new electrical motor control centers (MCCs) and switchgear, electrical transformers, and power cabling. This option would entail complete removal of the existing pumps, motors, suction piping and valves, electrical switchgear, and transformers, and would require structural and piping changes to the station. The existing pump house superstructure would be removed and disposed of properly, and existing mechanical and electrical equipment would be removed and turned over to UWAWAKUDA. TANESCO will provide power to the new transformers via the existing 33-kV transmission line.