Deriving PS Discharge Volume: A Case Study in Tauranga
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| The key objective of this study is to gain a better understanding on the limitations of the discharge volume derived using differing data sources at pump station sites. Flow monitoring is typically undertaken to understand the performance of the existing network, in particular Inflow and Infiltration conditions. This flow data is often used to calibrate a hydrological and hydraulic model, which can be utilised to assess network performance and plan capital works needs. A potential source of flow data for model calibration is pump station operational records, this presentation sets out the differing methodologies to derive pump station discharge volumes, limitations, and advantages of each approach. Three methodologies were assessed to derive the discharge volumes at pump station sites, and they are Q(fill), Q(run) and Q(out). Q(fill) and Q(run) were calculated at a pump cycle level using the logged pump start/stops, wetwell level or pump station capacities and were then aggregated up to hourly volumes. The third approach Q(out) is a straightforward volumetric based calculation whereby it uses the total pump run time over an hour and pump station capacities to derive the hourly volumes. Further, the council’s Kingfisher control unit has a flow integration system to derive the inflow to the pump station using wetwell dimensions and water level. Errors were quantified by comparing the hourly volumes derived from the above methods for a typical dry weather flow period and a wet weather flow period against the volumes derived from independent source of measurement such as HVQ or council’s owned Magflow meter. Our presentation describes the case study that was undertaken for several key pump stations of varying complexity in Tauranga including understanding the variability of the inputs and associated efforts required to derive the discharge volumes for each of the above-described methods. The results were used to help Tauranga City Council inform the preferred approach for the key pump station sites, prioritised programme for pump station inspections and drawdowns, required SCADA improvements and permanent flow monitoring sites. |