The Portobello Pump Station forms a key component of the stormwater drainage network for the residential stormwater catchment of South Dunedin. Upstream of the pump station is a silt well and bar screen aimed at reducing the volumes of sediment and gross pollutants entering the pump station.
The area has recently been subjected to severe stormwater flooding. Blockages at the bar screen was identified by Dunedin City Council (DCC) to be a key contributor, with DCC’s operations staff expressing concerns relating to elevated risks of blockage during high flow conditions, and a lack of suitable access to clear blockages during such flow conditions.
This paper describes the considerations for developing a new bar screen design (and rearrangement of the silt well) to maximise hydraulic efficiency, reduce risks of blockage, improve accessibility for operations staff, and reduce health and safety risks associated with working at heights above water, during severe weather. The paper also describes the range of design options considered (including automated and manual screen cleaning/ screen withdrawal arrangements) and the decision making process involved in arriving at the final solution.
The selected design offered a cost-effective and constructible design, with improved operability, and a ‘worst-case’ screen withdrawal option that can be enacted from the surface, via a basic pulley system.