Water and Effluent Treatment Magazine
Issue link: https://fhpublishing.uberflip.com/i/742656
November 2016 WET NEWS 15 Flow and level measurement has been a crucial part of operating a water network for generations. Yet, while solutions have moved with the times the problems they address remain the same. i2o's Keith Hilson explains. Balancing the water network INSIGHT Flow & level monitoring • W ater companies face the constant chal- lenges of ensuring there is sufficient potable water in the network to meet demand. It is a delicate balancing act that cannot simply be addressed by holding excess amounts of water. Ensuring that just the right level of water is made available is important for a number of reasons, not least water quality. Chlorine, used to disinfect water, evaporates over time so storing water for longer than necessary in service reservoirs can result in water quality issues. Measuring water into supply flow rates also helps water companies to know precisely what level of chlorine dosing to apply. There is also the risk of much more catastrophic failures. Too much water at this point in the distribution system can result in a service reservoir overflowing, creating flooding and increasing non-revenue water levels. Too little enhances the risk of service reservoirs running dry, devastating customer service and generating remediation bills from the extensive work required to bring them back into service. 'Inherently leaky' Leakage is another significant issue that is, at least in part, addressed through accurate measurement of water flow and levels. Water pumped to service reservoirs passes through transmission mains, which are inherently leaky. Water companies that pump more water than they need lose more through leakage here and waste huge amounts of energy. At the customer end of the supply network, flow measurement ensures that customers only pay for what they use. Aggregating this information assists with demand forecasting and assessing non-revenue water levels. Beyond operational consid- erations, effective flow and level measurement is a major part of compliance. From telling the Environment Agency (EA) how much water is being extracted from the environment, to meet- ing Ofwat's requirements around leakage and security of supply, water companies must provide accurate figures and make precise calculations to sat- isfy their regulatory obligations. The way in which level measurement is done has gradually evolved over recent decades. Historically, these vital measurements were taken manually from boreholes and service reservoirs by engineers using a dipping stick or a weighted tape measure. These spot readings were noted on pieces of paper and driven back to the office. Some water companies still record levels this way on rare occasions where permanent level measurements do not exist or to check transducer measurements. Such approaches were advanced through the use of pressure transducers that could measure levels and transmit the readings electronically to a chart recorder. These same transducers continue to be used, but now the data is typically fed into SCADA systems and transmitted automatically to head office for analysis. Digital storage The measurement of flow has a slightly more complicated history. Initially there were no measurements for extraction flow or distribution input flow, although this changed in the latter part of the 20th century with the introduction of either differential pressure or mechanical flow meters. As with level measurement, Several water companies have deployed loggers across their entire networks to provide a constant, reliable feed of data THE CONCEPT • Loggers implemented across entire networks provide a constant, reliable feed of data • Data is fed into intelligent software and used to remotely control and automatically optimise network pressure • Pressure reducing valves (Prvs) and variable- speed drive pumps can be adjusted to ensure smooth pressure changes NEED TO KNOW 1 The evolution from manual, paper-based processes to automated data collection, transmission and analysis has taken 25 years 2 effective flow and level measurement is a major part of compliance 3 most water companies worldwide are using smart software and algorithms to ensure that water pumped into distribution is correctly treated THE VERDICT "Water companies can now gain the same kind of understanding and control of water flow and levels throughout their distribution networks as they achieved in water treatment plants when they began using PLCs" Keith Hilson, i2O