Initial Trip Report: Dakawa Pump Station

The initial focus of the project will be on rehabilitating the pump station at the Dakawa Irrigation Scheme, including the pump, electrical supply, and building itself. This report summarizes first impressions of electrical, mechanical, and civil engineers who participated in short-term assessment consultancies. The pump station draws water from the Wami River and discharges into an irrigation canal system for the irrigation of rice fields. A regulating weir in the river controls the water surface elevation at the intake to the pumping station. The bed width of the pump channel is 5.0 m, and side slopes are V:H=1:1 to 1:1.2. The channel is lined with 5.0 m x 5.0 m plain concrete panels. Sedimentation is uneven in the pump channel due to a bend, which induces transverse flow and causes most sediments to settle in the inner bend. The diversion weir has four openings that are closed with wooden flaps. It should be kept open during high flow stages of the Wami River to prevent sediment from settling in the pump channel and being sucked up by the pump. The proposed area extension of 1,000 ha will result in stronger transverse flow in the pump channel, causing uneven water flow to the inlet. The pump station structure consists of three components: a cast-in-place concrete wet well, a cast-in-place concrete pump room, and a concrete-framed superstructure covering the entire pump room and extending beyond each end. The superstructure supports a bridge crane runway for the length of the pump room and one additional bay on each end. The building roof is a steel-framed peaked construction with metal decking. The intake structure must be checked for hydraulic instabilities when installing 1,500-mm diameter pipes that discharge 1.5 times the current discharge. A steel trash rack is needed to replace the present one, and openings should be 16 mm. The deck supporting the sluice gate operators is in poor condition, and the slab needs to be completely rebuilt. The pump room substructure appears to be in good condition, with no cracking or displacement observed. However, the superstructure above the pump room is supported by the pump room foundation, and some portion of the superstructure is supported by a slab-on-grade foundation. The foundation for both ends of the superstructure has severely settled, resulting in severe settlement of the superstructure walls and a downslope of the bridge crane runway at each end. The bridge crane needs access to one end bay to safely move equipment components in and out of the pump room.