Sewage discharge estimation from a flow-stick monitoring device

This paper reports laboratory studies into the use of a simple suspended `flow-stick' for sewer flow estimation. The experimental observations have been subjected to a theoretical modelling approach based on fluid drag principles and recently extended to deal with installation in both circular and non-circular sewers. This enables the translation of signals from an inclination transducer on the suspended flow-stick, and an associated water depth measurement, into an estimate of the instantaneous flow rate in the conduit at the monitoring section. The theoretical approach has been developed into a spreadsheet-based modelling `algorithm' suitable for incorporation within logger systems for routine data analysis, to support multi-station logging and telemetry of flows in critical sewers and outfalls in the Thames region of the UK. A principal objective of the laboratory study was to establish the prediction accuracy of the device and associated calibration requirements. With accuracies potentially within a range plus or minus 20%, the flow-stick offers a simple, cheap and operationally reliable method for estimating sewer flow magnitude which should be of considerable value to the water industry in the UK and abroad.