Civil Engineering July 2021 | Vol 29 No 6

Civil Engineering July 2021 37 inside. The upper two levels are con- fined by the front flood wall and the shafts to the fine screen filters in the lower channels. The fine screen filters catch particles that could damage the pumps and can be retracted up their respective shafts to the top deck platform for cleaning. The 18 m long upper channels flow from the fine screen shaft wall down to the front flood wall, turn 180° and flow back up to the other fine screen shaft wall. Sluice gates in the flood wall allow for periodic flushing of the channels. The flow in the top channel discharges into the middle channel over a 3 m high weir before the fine screen shaft. Flow from the middle channel discharges through a chute under the top gallery into the reservoir. The bottom channels and pump wells operate in duty-standby mode and are isolated from each other up to just below top deck level, but otherwise will reflect the prevailing upstream water level in the river. Water is pumped via a pipeline in the upper gallery to four 350 mm hydro-cyclones located at the head of the top sedimentation box channel. Waste from the hydro-cyclones flows back down the upper gallery to discharge to the river. Bypass valves allow flow from the pumps to bypass the hydro-cyclones either into the top channel or directly to the reservoir which overflows to the upper gallery. The weirs in the top and middle channels ensure a minimum 3 m depth of water in the channels. The water level in the reservoir can drown the chan- nels but this would not decrease their efficiency. With the reservoir at the “front” of the structure, high lift pump station No.1 is now contained in a pump room at the “back” of the structure. The three high-lift multistage pumps are located on a platform 5 m above riverbed level and have access to approximately 1.8 Mℓ of water in the reservoir when full. The switchgear, drives and standby generator are located at top deck level. About 3 m of bottom space in the res- ervoir allows for additional settlement of Inside the structure are three levels of 2 m wide sedimentation channels and a three-level gallery The settled water reservoir and the first high-lift pump station fit in the space between the riverbank and the sedimentation channels