Management Techniques and Technologies for Leak Detection and Control in the Water Industry. Final report

Transcription

1 Management Techniques and Technologies for Leak Detection and Control in the Water Industry Final report WRc Ref: G

2 WRc is an Independent Centre of Excellence for Innovation and Growth. We bring a shared purpose of discovering and delivering new and exciting solutions that enable our clients to meet the challenges of the future. We operate across the Water, Environment, Gas, Waste and Resources sectors. RESTRICTION: This report has the following limited distribution: External: WWU and NGN Any enquiries relating to this report should be referred to the Project Manager at the following address: WRc plc, Frankland Road, Blagrove, Swindon, Wiltshire, SN5 8YF Telephone: + 44 (0) Website: Follow Us:

3 Management Techniques and Technologies for Leak Detection and Control in the Water Industry Authors: David Beckett Date: Report Reference: G Anthony Bond Project Manager: Project No.: Sarah Homewood Stuart Trow Client: WWU and NGN Killian Spain Document History Version number Purpose Issued by Quality Checks Approved by Date G10278 Final report issued to client. Sarah Homewood, Project Manager Sarah Homewood 26/03/2015 WRc plc 2015 The contents of this document are subject to copyright and all rights are reserved. No part of this document may be reproduced, stored in a retrieval system or transmitted, in any form or by any means electronic, mechanical, photocopying, recording or otherwise, without the prior written consent of WRc plc. This document has been produced by WRc plc.

4 Contents 1. Executive summary Key findings from research review Conclusions Introduction Aims of this report Scope of this report Background to water leakage in the UK Factors contributing to water leakage in the UK Real and apparent losses Customer supply pipe leakage Driving Factors For Leak Management in the Water Industry Introduction Socio-political drivers Regulatory drivers Economic drivers Environmental drivers Conclusion Leakage Management Policy and Practice Introduction Active leakage control and Passive leakage control District Metered Areas Calculating total loss of water due to leaks Leak location Conclusion Active Leakage Control Technologies Leak Localisation Leak location and pinpointing on small pipes Leak location and pin pointing on large pipes Experimental technology for leak detection and location Pressure Management Theories behind Pressure Control Transient pressure Pressure control in practice... 45

5 6.4 Pressure Requirements and Regulation Pressure management control systems Technologies for Pressure Management Pressure Reducing Valves (PRVs) Pressure Modulation Flow and Pressure Monitoring Introduction Transferability of water industry practice Methodology Matrix tables Conclusions... 1 References... 2 List of Tables Table 2.1 Average English and Welsh company statistics (2010/11)... 5 Table 4.1 Annual water balance Table 4.2 Night flow analysis balance Table 9.1 Table 9.2 Full list of transferable pressure and leakage practices from water to gas... 1 Shortlist of transferable pressure and leakage practices from water to gas... 4 List of Figures Figure 2.1 Water company reported and forecast leakage from Figure 2.2 Leakage profiles from reported mains, reported service connection and unreported service connection bursts Figure 3.1 Graph of leakage control and financial investment Figure 4.1 Methods of leakage control and cost analysis Figure 4.2 Diagram of a typical Water Resource Zone with DMA subsections Figure 5.1 Schematic of leak noise correlator Figure 5.2 Operation of a ferret Figure 5.3 Sahara leak detection system Figure 5.4 Free swimming detection device... 39

6 Figure 5.5 Diagram of TDR leak detection Figure Figure 7.1 Globe type valve fitted with a hydraulic pilot rail and an i20 system Figure 7.2 A diaphragm valve fitted with additional hydraulic modulation Figure 7.3 i20 system components List of Photographs Photograph 2.1 Reported leaks are noticed and reported by the public... 8 Photograph 2.2 Unreported leaks are discovered by active leakage operations and not the general public... 9 Photograph 5.1 Tri-parameter system in operation Photograph 5.2 Acoustic listening sticks Photograph 5.3 Ground microphone in operation Photograph 5.4 Leak noise correlator Photograph 5.5 Magic carpet device Photograph 5.6 Gas tracing equipment Photograph 5.7 Ferret equipment Photograph 7.1 Butterfly PRV Photograph 7.2 Spring loaded diaphragm valve Photograph 7.3 Retrofitted bias chambers to allow local control... 53

7 1. Executive summary 1.1 Key findings from research review The water industry differs from the gas industry in that economic, environmental and customer demands, rather than safety, are the overriding concerns. Public concern has resulted in regulatory targets aimed at reducing leakage. Over the last two decades, regulation has been the driving force behind leak reduction. The results have resulted in the water industry developing a more complex and proactive approach to managing their water networks. The water industry calculates water loss across the network at both macro scale and the local scale allowing for effective planning of the leak management strategy of a company, despite the inaccuracies that often appear in such calculations. By estimating leakage from a top down water balance across the whole company, and a bottom up analysis of night flows into individual districts, a maximum likelihood estimation technique (MLE) removes most of the uncertainty in the KPI reported to Ofwat. Both night flow analysis and annual water balances have accuracies greater than 95% and improvements are continually being made as a result of increasing meter penetration and improving instrumentation. The most common methods of reducing leakage are to respond to reported leaks as swiftly as possible, embrace Active Leak Control (ALC) techniques and technology to find and fix unreported leaks and, introduce pressure management (both fixed pressure reduction and flow or time modulation), and replacement of mains and service connections. Water companies use a combination of all of the above. Active leak detection is universally adopted in the UK water industry. It has been demonstrated in the water industry that relying on reports from the public leads to a steady increase in the backlog of unreported leakages leading to ever greater water loss in the long term. As part of an active leak detection system, methods have been developed to both localise and pin point the position of a water leak. Localisation methods are used to judge whether a sub section of the network has a leak. Pin pointing a leak covers the different methods by which the exact locations of any leaks are traced. Localisation is vital in ensuring that resources for more accurate leak detection are allocated to where they are needed. It is often impractical to inspect the length of the pipe using pin pointing technologies. Localisation techniques are cheaper and quicker per length of network they survey. Sounding, pressure testing correlating and step testing are used to localise leaks. The division of larger networks into smaller district metering areas (DMAs) has been highly successful in aiding the detection and location of leaks allowing for district flow rate monitoring and night flow analysis. It is possible that DMAs will become less important with the advent of WRc plc

8 new noise loggers (with a communication capability to detect leaks from the sound they emit as soon as they occur). Nevertheless, the division of the network into DMAs provides the facility for more efficient pressure control with pressure management areas (PMAs) often matching DMAs. As such, DMAs should continue to be a key part of future network management. There are a number of technologies available to the water industry for leak localisation: Noise loggers; Step testing; Pressure testing; and Computer modelling. There also a number of tools to pin point leaks: Acoustic devices cover a wide array of equipment including listening sticks, ground microphones and magic carpets; Correlating noise loggers; Accelerometer and hydrophone; In pipe sounding including Sahara, Smartball and Urchin; Physical measurement of in-pipe pressure changes with the Ferret; Gas detection; Aerial surveying. Other technologies are in development but are not currently used or have limited use in the water industry. These include ground penetration radar, thermography and time domain reflectrometry. Aerial imaging has recently been introduced to hunt down leaks in rural areas and is highly effective at pin pointing leaks over a wide area. However there is considerable technical skill involved. WRc plc

9 Pressure reduction to reduce leaks can be highly effective in the long term as it reduces the level of leakage and the rate of failure. Pressure control is extremely effective in the water industry due to the fact that the high pressures traditionally used leave considerable room for reduction. Pressure management makes use of static control, timed and modulated flow control systems. Smart pressure control to stabilise pressures across the course of the day is becoming the norm in the water industry. Other techniques to control pressure include booster pumps, pump control and ensuring that PMA (pressure management areas) all have a similar pressure. Break pressure tanks and service reservoirs are also used to control excess static pressures. 1.2 Conclusions For this study there were four main areas where there is either technology or best practice knowledge that could be taken forward for testing/evaluation as part of Task 4, these included: Modelling of relationships between PRE/pressure and pressure/failures Pressure management practices and implementation Acoustic sensing for leak location Sensing for water ingress The project steering group agreed to take forward three out of four of the areas identified for further investigation based on the project resources available. Water ingress was excluded as it was deemed to be too large a subject to be covered in this project in sufficient detail. Proposals for bespoke research into acute and chronic water ingress are under development by WRc. The results from the assessment of these technologies can be found in individual reports (WRc Report G10772, WRc Report G10781, WRc report G10785 and WRc report G10810). WRc plc

10 2. Introduction 2.1 Aims of this report Over recent years, the UK water industry has made much progress in reducing leakage to an economic level by strategic analysis at a DMA (District Metering Area) level. This has included the pro-active use of leakage detection, pipe repair/renovation/replacement and pressure management, for example the use of flow modulated reducing valves (PRVs). Within the water industry, leak detection technologies (e.g. acoustic logging and pressure transient detection etc.) have been used to identify the precise location of defects and, in some cases, provide an indication of the defect size/leakage rate. The accurate leakage data has allowed the network operator to target investment by selecting the most appropriate and cost-effective intervention option ranging from localised report to fully structural renovation replacement. The first objective of this project was to review and demonstrate water network practice to the GDNs for leakage and pressure management. This reports summaries water industry practice and concludes with what technology or best practice could be taken forward for testing/evaluation as part of this project. 2.2 Scope of this report As part of an examination into the potential strategies and technologies that the gas industry could implement to reduce leakage expenditure and address water ingress, an examination of the practices in the water industry to reduce leakage has been undertaken. This report examines the driving factors for leak reduction, management systems, methods and technologies associated with leak detection and reduction in the water industry. This report is divided into five sections: Driving Factors for Leakage Reduction covers the regulatory, economic, socio-political environmental pressures driving water companies to reduce leakage. The section explains how these factors interlink with one another. Leakage Management Policy and Practice examines the different methods for estimating, reporting and auditing leakage levels across a network and highlights difficulties encountered. It also looks at the different processes and procedures water companies undertake to identify and localise leaks. Active Leakage Control Technologies covers the range of technologies and tools used in the field by repair teams to detect and pin point leaks. WRc plc

11 Pressure Management focuses on the methods used to reduce system wide pressure. It outlines the theory and practice of pressure including pressure reduction techniques and control systems. Technologies for Pressure Control focuses on the selection of pressure control technologies. It presents the different types of pressure reducing valves (PRV), pressure sensors and flow rate instruments used. 2.3 Background to water leakage in the UK In England and Wales there are 10 regional water and sewerage companies and 11 water only companies. To give a guide to the network size the statistics for the average company are shown in Table 2.1. Table 2.1 Average English and Welsh company statistics (2010/11) Average England and Wales Company Property count Length of main Total leakage (Ml/d) Leakage per property (millions) (km) (l/prop/d) , Leakage has been a major issue in the UK since privatisation of the water industry in A historic lack of investment in network infrastructure and management strategies saw a large increase in the volume of water lost from the system. Leakage peaked in the mid-90s coinciding with water supply restrictions during a national drought. As a consequence, mandatory leakage targets were introduced by Ofwat for all companies, with severe financial penalties for non-compliance. As a result of targeting leakage, substantial progress has been made with a decrease in leakage volumes of 35% since This 35% reduction is equivalent to 15,000 Ml/d, or the daily needs of ten million domestic customers (Ofwat, 2003). This reduction was brought about by a 90 billion investment in leak detection, repair and replacement of water and wastewater networks. Furthermore, pressure management became universal across the industry and increasingly sophisticated, contributing to the reduction in leakage volumes. The greatest gains were made during the late 90s with water lost through leakage being reduced by 30% over a 5 year period from its peak in WRc plc

12 Figure 2.1 Water company reported and forecast leakage from 1994 Source: (Environmental Agency, 2009) Data from the 2009 water resource management plans were published by the Environment Agency showing the forecast trend for leakage up to 2034/35 (see Figure 2.1). Since then a review has been undertaken of the factors affecting the companies targets and the business plans submitted for PR14 are projecting stable or modest future reductions in leakage Expressing leakage rates The media often talks about water lost as percentage of distribution input when reporting on leakage. Leakage is usually reported as a volume lost per time period in mega litres per day (Ml/d). It can also be normalised by the size of the network by number of properties or length of mains. These scaled values can be misleading in terms of comparative performance and so a measure which takes account of network size, pressure, and network configuration, known as the infrastructure leakage index (ILI) was developed by the International Water Association (IWA). While this measure is used internationally, and has been used to compare zones within the same company it is not used for inter-company comparisons in the UK. 2.4 Factors contributing to water leakage in the UK The rate of water leakage is influenced by: Parameter Age Effect Pipes from different eras fail at different rates WRc plc

13 Parameter Material Corrosion Maintenance of fittings Joint failure Mechanical loading Pressure transients (water hammer) Temperature variation Ground movement Water pressure Leakage management activity Effect Different materials age in different ways leading to different types of failure and leak Influenced by inadequate or compromised corrosion protection and corrosive soils Poorly maintained fittings such as line valves, air valves or hydrants may leak at seals Ageing or poor initial installation Creates strain on the pipe or joints Mechanical strain from water hammer (pressure transients) and pressure variations which can cause premature ageing or failure of pipes that have suffered from other degradation (such as corrosion) Expansion and contraction putting strain on the pipe Changing moisture content in the surrounding ground or variable surface loading Higher pressure will result in greater leakage from the same sized hole The leakage management practice employed to detect and rectify leaks will affect the overall leakage rate by changing the length of time that leaks run for before being repaired Leak types The leaks in the water industry can be divided into three broad categories based on the way they are detected. Reported leaks Reported leaks come to the surface and are noticed by the public and reported to the water operator. These leaks have a high flow rate and account for the majority of the number of leaks repaired by the utility. Typically, larger reported leaks will be isolated and fixed within a period of 48 hours (Farley & Trow, 2003). WRc plc

14 Photograph 2.1 Reported leaks are noticed and reported by the public Source: (BBC, 2006) Whilst the larger bursts are detected almost immediately, smaller leaks can take days, weeks or even months to be noticed, reported and dealt with. This leads to higher volumes of water loss in the long term. Generally, whilst reported leaks account for the majority of repairs, they account for only 10 to 20% of the water loss from the water networks. Unreported leaks Unreported leaks are not noticed or reported by the public and are instead discovered by active leakage control operations by the water companies (see Section 4.2). These leaks account for approximately 30 to 40% (by volume) of all leakage across the network. Water companies focus the majority of their efforts in reducing unreported leakage. There has been significant increase in investment in leak detection operations since industry privatisation to achieve a reduction in unreported leakage. Detecting and eliminating the backlog of unreported leaks, the result of underinvestment over previous decades, was the primary cause for the reduction in leakage in the late 1990s and early 2000s. WRc plc

15 Photograph 2.2 Unreported leaks are discovered by active leakage operations and not the general public Source: (Drips and Drains, 2010) Background leakage The third type of leakage is background leakage. This is an aggregation of small leaks which are individually too small to be detected using current technology and are therefore not repaired unless the water company decides to renovate the pipe. The extent of background leakage is an estimate based on the water balance calculation (see Section 4.4). It includes all remaining unaccounted water loss after reported and unreported leaks. New detection technology can potentially increase the number of leaks that can be detected, thereby reducing the level of background leaks. Background leakage in the UK typically accounts for 50 to 70% of the water loss from a network (Beal, Trow, & Haywood Smith, 2012). It should be noted though that due to the way water loss is accounted for across the network (Section 4.4), not all water loss assigned to background leakage will be from leaks. Some water loss will be due to illegal and unknown connections or water overspill from service reservoirs but these are minor contributors to the overall level of leakage. Unavoidable annual real losses (UARL) The concept of unavoidable annual real losses (UARL) derives from the fact that it is impossible to completely eliminate all leakage in a system. The UARL is therefore the lowest level to which leakage can be theoretically reduced. A formula based on the length of mains, the number of connections, the length of service connections and the average operating pressure is used to estimate the UARL for any section of the network. The value is calculated using a formula developed by the IWA Water Loss Task Force. The formula is given below. WRc plc

16 Equation 2.1 Unavoidable annual real losses (UARL) formula ( ) Where: UARL is in litres/day L m is length of mains (in km) L p is length of private pipes (in km) N c is number of connections. P is pressure. Note: P is typically assumed to be 2.5 bar (this is a typical pressure in pressurereduced urban areas). The calculation is used as a benchmark for maximum achievable leakage reduction if economics were not an issue Leak Run Time The key to managing leakage is to minimise leak run time, which comprises an awareness time (A) from the leak occurring to the water company being notified of its existence, the location time (L) from being aware of the leak to pinpointing it, and the repair time (R) taken to effect the physical repair. As smaller, unreported leaks on pipes run for the longest time, they tend to make the largest contribution to leakage. WRc plc

17 m 3 / day m 3 / day m 3 / day WWU and NGN Figure 2.2 Leakage profiles from reported mains, reported service connection and unreported service connection bursts 1.1 days 75 Reported mains burst 82 m 3 16 days Reported service connection burst 400 m 3 25 A L R 25 6 months? A L R Unreported service connection burst >4500 m 3 Source: (Original) 2.5 Real and apparent losses Water losses are usually divided into real and apparent losses depending on the nature of the loss. Real losses include leakage and overflow from storage reservoirs while apparent losses result from meter inaccuracies, unmeasured or inaccurately assessed consumption and illegal connection. 2.6 Customer supply pipe leakage Ownership of the water network by the water companies stops at the customer s property boundary where there is a stop tap that allows the company to isolate the supply if necessary. The customer owns, and is responsible for repairing leaks on, the pipework within the boundary of their property although the water company is tasked with reducing leakage on the entire network, including that from customer supply pipes. This presents the water companies with challenges related to enforcement of repairs, and there has been considerable debate with the industry over the potential to adopt the supply pipe until it enters the customer s building. Defra has yet to publish its consultation response on this issue but WRc is working with a small group of companies to improve the evidence for the business case for supply pipe adoption. WRc plc

18 It is worth noting at this stage that there is not yet universal metering of customers supplies and that the location of meters has a significant impact on customer side leakage. Water meters are often sited in the curtilage at the property boundary in this case the customer is charged for any water lost through leakage on their pipework providing a pressure for them to make repairs. Leaks are often spotted through unusually high meter reading. However, in certain circumstances, it is preferable to fit a meter at the point where the supply enters the building. In this case leakage within the property boundary, but before the meter, is not billed for and also more difficult to detect. Water companies have a variety of approaches that they adopt in dealing with supply pipe leakage with some offering free repairs through to implementing enforcement notices to require repair. WRc plc

19 3. Driving Factors For Leak Management in the Water Industry 3.1 Introduction There are several important factors that drive water companies to reduce leakage. These are regulation, social and political pressures, the economic cost of water lost, environmental considerations and the desire to demonstrate good practice. Regulation is the primary driver influencing water companies leakage management, followed by consumer preferences/willingness to pay and economics. The largest motivator for leak reduction in England and Wales following privatisation was the regulatory targets set by Ofwat and increased pressure by the Environment Agency to reduce abstraction in the companies water resource management plans. More recently, as leakage has fallen to the regulatory required levels a desire to demonstrate good management practice provides a continued drive to improve performance. Similar mechanisms have applied in Scotland and Northern Ireland with the relevant national regulators. 3.2 Socio-political drivers High levels of water leakage can result in poor customer relations and increased complaints. This can become particularly acute in times of water stress and when prices are being increased. The comparison between the leakage performance of companies can be a powerful motivator in its own right as companies strive to demonstrate they are they are outperforming each other. Public perception of water leakage is significant with the accountability for water shortages usually being laid at the feet of water companies, especially during periods of prolonged drought. The public outcry about the performance of water companies in tackling long running leaks during the 1995 drought and the very high media profile given to leakage during the period had a direct impact on water companies and was a major driver in the introduction of mandatory targets for leakage reduction. In this case social pressure drove political (regulatory) action. Tellingly, 78% of people surveyed in the 2013 heat wave blamed poor maintenance by the water companies for the need for hosepipe bans. This was despite the water companies involved going beyond their statutory requirements. Good leakage management and communication is therefore vital in reducing customer complaints and ensuring compliance with water saving measures. Most water companies will therefore advertise their success on leakage reduction as part of their communication with their customers. Equally important, leakage reduction boosts confidence with shareholders that they are investing in an efficient and profitable enterprise. WRc plc

20 Where there is an abundant supply of cheap water (such as in the north east of England), regulatory pressure can be the biggest influence on leak reduction as high levels of leakage could otherwise be economically tolerated (Butler & Memon, 2006). In these cases good practice is also a driver for water companies. 3.3 Regulatory drivers The regulator for England and Wales, Ofwat, requires water companies to meet an economic level of leakage, see Section 3.4. Companies must meet their individual targets, based on their Sustainable Economic Level of Leakage (SELL, Section 3.4.2) or face legal and financial penalties. Water companies are obligated to repair reported leaks on their pipelines. Most water companies will also offer free or subsidised leak detection on domestic supplies (after the water meter and within the property boundary) but they are not obligated to do so. Water supply and distribution in Scotland is managed by Scottish Water which is government owned and regulated by the Water Industry Commission for Scotland (WICS). The body is primarily focused on price regulation and fostering competition for business customers but also regulates the level of leakage using an approach similar to that of Ofwat. Since 2006 WICS has required Scottish Water to meet ELL targets. Most companies meet their leakage targets. Exceptions in the last decade include Southern Water, which missed their targets: United Utilities, in and , Severn Trent, in and , Thames in and Portsmouth Water in In all these cases, Ofwat has forgone its power to impose fines on the offending companies and has instead sought legal binding agreements with the companies to spend additional money on appropriate additional leakage control activity. Thames water for example was required to invest an extra 150m to replace aging Victorian era pipework (Consumer Council for Water, 2013). Target-driven regulation has disadvantages as fixation on the target may discourage companies from pushing further to reduce leakage. Ofwat predicts that there will be no change in the levels of leakage over the next five years as most companies are now achieving their leakage targets. Many companies have actually pushed below the SELL as a result of consumer engagement and reputation risk arising from not being seen to take action on this politicised issue. Further information on the water industry regulatory landscape can be found in a report produced for GDNs in March 2014 (WRc, 2014). 3.4 Economic drivers Water has an economic worth based on the capital investment costs (capex) and operating costs (opex) of the company. Data gathered on water companies finances by Ofwat for the WRc plc

21 Cost ( /yr) WWU and NGN period, showed operational costs for water production and distribution ranges between 34p/m 3 and 73p/m 3 (Ofwat, 2009). Different methods of calculating the cost of water can be used depending on the level of detail available. The complexity of these calculations range from assuming linear relationships between total production and overall operating costs to comprehensive calculations designed to reflect the costs of supplying water from different sources. Metered customers are based on measured consumption. The majority of non-household customers are metered. An increasing percentage of domestic customers are also on a metered supply. Households that do not have a meter fitted pay a fixed rate based on the house s (historic) rateable value Economic Level of Leakage (ELL) The money saved by reducing leakage volumes can be compared to the cost of carrying out leakage reduction activities. This can be displayed in graphical form, see Figure 3.1. With no leakage management, the company loses an ever increasing volume of water from burst pipes until they are unable to meet demand. At the other extreme leakage, reduction activities have increasingly diminishing returns - the easy to detect or cheap to repair leaks are all addressed - until the cost to locate and repair leaks would far outweigh the value of the water saved. Figure 3.1 Graph of leakage control and financial investment B D A D C C B A Leakage (Ml/d) Cost of survey Cost of water lost Total Cost Policy Minimum Source: (UKWIR, 2010) WRc plc

22 There is an optimal point known as the economic level of leakage where the level of leakage is such that it would cost more to make further reductions than to produce water from another source. This is known as the Economic Level of Leakage (ELL), and the policy minimum is defined as the asymptote (Figure 3.1). Operating at the ELL means that the total cost to the customer of supplying water is minimal and companies are operating efficiently under the conditions that exist at that time; there is no financial incentive to reduce leakage further. A variation in the cost of water or improvement in leak detection or repair capability and efficiency could change the ELL. With the investments made since privatisation the UK water companies have reached their individual ELL, however more recently Ofwat has set targets for companies based on their SELL (see Section 3.4.2) Sustainable Economic Level of Leakage (SELL) Concerns that there would be little incentive to continue to reduce leakage once the ELL has been reached resulted in the introduction of the Sustainable Economic Level of Leakage (SELL). This is currently used by Ofwat to determine the target leakage level a water company should achieve. It is a calculation that takes into account both the internal economic cost of the water and the social and environmental benefits incurred through water resource management and leakage reduction. The calculation assigns an economic value to the benefits and weighs it against the cost to reduce the level of leakage. The value of SELL will be lower than the traditional economic level of leakage due to it taking into account factors not normally included in an ELL calculation, and typically the external unit costs added to the value of water are higher than those associated with leakage reduction. This lower level is designed to encourage water companies to seek better methods of leak detection and repair and produce downward pressure on leakage levels. A number of companies are now successfully operating at, or below, their SELL. 3.5 Environmental drivers Environmental regulation and good management practice related to reducing impact on climate change provide drivers for the water companies to reduce abstraction and delivery costs (energy). Headroom is an important concept in the water industry whereby the network operator ensures there is a buffer zone between the supply of water and the extraction rate. This is adopted to prepare for uncertainties such as drought, water pollution or other events. Reducing leakage is an effective method of increasing the headroom without increasing supply, investing in alternative sources or restricting the water usage of customers (all of which would be considered unpopular). Successfully demonstrating leak reduction is useful in persuading customers to reduce water consumption, further increasing the head room. WRc plc

23 Pumping large volumes of water at high pressure has a considerable impact on the water companies energy demand. The UK water industry currently produces 3% of the UK s CO 2 emissions. Reducing the level of leakage reduces the volume of water that needs to be pumped, resulting in reduced energy consumption. Certain leak reduction management techniques reduce the pressure across the network further reducing energy demands as a side effect. A water company keen to develop its green credentials will focus on achieving a leakage rate below its SELL target. 3.6 Conclusion Regulatory, economic, environmental, political and social factors are becoming increasingly interlinked. The development of sustainable economic level of leakage takes into account the finite supply of clean water from the environment. Political and environmental factors often overlap with environmental groups lobbying the government to conserve water. Finally, customers can be expected to pressure media and government channels if they believe water companies are not providing the service they feel they deserve for their money. It should be noted that the driving forces differ from region to region. In areas were the cost of supplying clean water is high, economic factors dominate while in regions that have suffered from a drought public pressure can be enormous. Regulation can be the driving factor for a region where there is plenty of cheap water available. Water companies now need to weigh social, political and economic factors in a dynamic analysis with the level of acceptable leakage often guided by the most pressing factor. WRc plc

24 4. Leakage Management Policy and Practice 4.1 Introduction There are several components to leakage management in the water industry; this section outlines the various processes used to control leakage. Leakage is addressed through a mixture of responding to reported leaks, active leakage control to detect and repair unreported leaks (i.e. actively searching for leaks, see Section 4.2), pressure management and mains replacement. 4.2 Active leakage control and Passive leakage control Traditionally in the UK, there were two approaches to leakage management; passive (reactive) leakage control and Active Leakage Control (ALC). Passive control relies on the public reporting leaks and repairing those leaks as and when they arise. This strategy is clearly a lower cost option in terms of operating expenditure on leakage control and investment in leakage management equipment and facilities. However, it results in a higher level of leakage due to the volume of water lost from smaller leaks which run for a long period of time (see Section 2.4). Active leakage control involves a company putting resources into detecting, localising, pinpointing and repairing unreported leaks (Pearson & Trow, 2005). This method of leak control requires careful planning due to the high cost of staff resources. Overall, the total cost of water lost and leakage control is found to be higher with a passive strategy than with an active strategy. Therefore, the UK water industry had already moved towards a more active control based approach between the publication of the influential Leakage Control Policy and Practice (UK Water Authorities Association, 1980) which outlined the two approaches in detail, and the setting of mandatory targets in the 1990 s. Prior to 1980, the approach adopted by most water companies was to employ a policy of regular sounding on all mains fittings (valves, hydrants, stop cocks etc.) to listen for leaks. Each area would be surveyed typically every year or two. However, the rate of rise of leakage (i.e. the rate at which new unreported leaks occur) would vary considerably from one part of the network to another, as would the effort involved in undertaking the survey; it is more difficult in heavily trafficked urban areas than it is in suburban housing estates for example. All water companies in the UK now implement active leakage control. The following sections outline the processes used to in this approach. Each leakage reduction activity will follow the diminishing rate of return as shown in Figure 4.1; the more each activity is undertaken, the less cost effective it becomes. Therefore, the challenge is to find the optimum mix of activities and the optimum extent of each. This will WRc plc

25 vary from region to region depending on the nature of the network, the level of leakage and past investment. Figure 4.1 Methods of leakage control and cost analysis Source: (Farley and Trow, 2003) 4.3 District Metered Areas The strategy currently established in all the UK water companies is to divide the network into a hierarchy of Water Resource Zones (WRZs), Demand Zones (DZs) and further subdivisions of the network known as District Metered Areas (DMAs). The flow of water into each DMA is then monitored (particularly during the minimum flow period in the middle of the night) to look for unexpectedly high levels or sudden increases. The measured night flow is compared to expected value, which is based on an assessment of the number and type of properties contained within the DMA. DMAs were conceived in the 1970s as an aid to leakage management. They are the basis of the bottom up approach to calculating leakage (see Section 4.4) and comparing leakage in different DMAs can aid a water company in effectively allocating resources, setting targets and measuring the progress and efficiency of leakage reduction schemes. WRc plc

26 DMAs are created by shutting valves and installing meters at the boundaries of the network area such that the flow of water into the area can be recorded using one (preferably) or more meters. DMAs are generally sized so that they include between 500 and 3000 properties. The most important factor in determining the area covered by a DMA is how easily it can isolated from the rest of the network (Morrison, 2004) to allow flow rate into the area to be accurately monitored. Most DMAs have a single feed meter, although multi-feed DMAs are also common. Figure 4.2 outlines a typical DMA arrangement. Figure 4.2 Diagram of a typical Water Resource Zone with DMA subsections Source: (UK Water Authorities Association, 1980) DMAs are also an important feature of pressure management (Section 6) as the distribution pipes entering a DMA are an ideal location to install Pressure Reducing Valves (PRVs) and Pressure Modulating Valves (PMVs). Carefully choosing the boundaries of a DMA allows for consistent pressure throughout the DMA, thereby simplifying the task of pressure control in the network. 4.4 Calculating total loss of water due to leaks Using leakage information gathered from yearly water balances and night flow analysis, targets can be set for the water company. Sophisticated models are used to estimate the WRc plc

27 economic level of leakage, and the data is used to agree targets with the regulators (see Section 3). There are two basic methods for calculating leakage across a network: The top down approach, known as the annual water balance; and Bottom up approach, known as night flow analysis Yearly water balances The first method of calculating leakage is via the top down water balance, a mass balance, which attempts to calculate the water lost from the system. This balance uses data from metered input from reservoirs and water consumed by businesses and households. Table 4.1 Annual water balance This method is used to determine a value for the company s total volume of water loss. Each company prepares an annual water balance, which is used to determine the reported leakage value reported for Ofwat. Several companies are able to complete a monthly water balance which helps them determine whether they are on track to meet their annual leakage target. This information is used to compare water companies performance and is also used in the long term planning process. However, it has limited use in helping a company to manage leakage by directing ALC resources to different parts of the network during the course of the year as it has no information on the components of detectable bursts and background losses. It can however be used to check for major errors in bottom up analysis (Fanner, 2004). Inaccuracies in the Yearly Water Balance The inflow into the network, known as Distribution Input (DI), is determined from meters at the source and treatment works, adjusting for imports and exports from and to neighbouring companies. Instrument errors estimated at between 1 and 5% occur on these flow monitors. Incorrectly installed flow monitors can increase this level of uncertainty higher still. The water balance calculation can suffer from inaccuracies due to the high number of uncertainty factors: WRc plc

28 Use by unmetered customers is determined from consumption monitoring of individual households, which determines a per capita or per household estimate that can be used across the region. Households are classified (e.g. by ACORN type 1 ) and an estimate of consumption is applied according to the makeup of different property types in an area. Metered water use is subjected to small inaccuracies due to meter faults and criminal activity. Illegal and unknown connections are accounted for by estimations only and are difficult to corroborate. Estimates of Trunk Mains (TM) and Service Reservoir (SR) leakage vary significantly from one company to another and there is currently no standard industry wide approach. Some of the estimating methods in use have been employed for over 30 years despite significant advances in other areas of leakage estimation and management. As TM and SR leakage accounts for between 10 and 20% of the total this issue is significant and it is currently being addressed. Lastly, not all water lost is due to leakage; unknown overflows are also grouped together with leakages for the purpose of the calculation. The accuracy and extent of the metering has much improved since 1995 with improvements in meter quality and greater knowledge of the causes of meter failure, such as grit becoming lodged in the mechanism of mechanical meters, air ingress, misting of registers causing misreading, wear, the drift and interference of electromagnetic and ultrasonic meters and general fact that meters will under-record at low flows. Improved installation procedures and better meters have reduced the likelihood of these events. More recently, there has been a drive by regulators and water companies to increase the number households are metered, but the degree of household metering varies considerably across the UK from less than 1% of properties in Scotland to over 75% in the Anglian Water region. Almost all non-household (commercial and industrial) premises are metered. Approximately 60% of houses in the UK were unmetered in 2011 but schemes are in place to reduce this number to 20% by 2020 to provide more accurate assessment of water loss. Even with a high penetration of metering, the meter reading cycle which varies from one month to one year typically (depending on usage) means that a large degree of forecasting and statistical estimation is still required to determine metered use for the water balance. Various forms of automated meter reading (AMR) systems are being employed in some areas to track patterns of water use to aid the estimation of leakage. 1 ACORN is a segmentation tool which categorises the UK s population into demographic types. Other segmentation tools are also available. WRc plc

29 Despite the limitations the yearly water balance must be greater than 95% accurate to meeting reporting requirements. This accuracy is achieved due to good approximations used by the water industry Night flow analysis The second method of calculating leaks is to focus on the analysis of night flows. At night the use of water should be at its lowest and therefore the leakage can be more reliably distinguished from normal legitimate water consumption. This method is a bottom-up approach which is used for internal comparisons, and as a counterpart to the top-down method of annual leakage estimation (Hamilton, 2008). Night flow analysis works by hydraulically isolating a DMA or smaller areas and calculating the expected flow of water into the district to meet night-time demands using standard night use allowances and meter readings from larger non-household customers. The actual volumetric flow rate into the district is measured using data loggers (see Section 5). The results are analysed using a computer program (of which there are several suppliers) that compares the actual flow rate with the expected flow rate. Areas with unexpectedly high night flow are then targeted for further investigation. Night flow analysis is used to assign resources and set reduction targets for individual DMAs based on the current leakage. Areas with low leakage will have resources diverted from them to areas where high leakage is indicated. DMA night flows can be used to monitor the success of a newly introduced strategy or technology on a small scale before wider use. Table 4.2 Night flow analysis balance Inaccuracies arising from night flow analysis Similar to the annual water balance, the night flow analysis makes use of a number of assumptions that can lead to inaccuracies if not correctly applied. There is uncertainty about the water usage by customers. The work is carried out at times of minimal water usage use to simplify the calculations. However this can introduce large errors as there can be significant legitimate night use. The exact time that minimum flow occurs WRc plc

30 varies from DMA to district DMA making it hard to compare leakage rates between areas (Fanner, 2004). Minimum night flow can be influenced by annual variation in water consumption and factors such as the start of university terms and Ramadan resulting in sudden increases in night time usage in specific areas. Operational problems such as a burst in a neighbouring DMA might result in a boundary valve (closed to ensure the DMAs are isolated from one another) being opened to maintain supply or pressure to the neighbouring DMA. This would result in an increased demand in the DMA being considered. The boundary valve should be closed after the repair is made, but this action is sometimes overlooked. Finally, inaccuracies from oversized or undersized meters may also introduce errors in the calculation of the flow rates into, and out of, the areas in question. 4.5 Leak location Leak location in an area will be initiated once a certain threshold in water lost is detected in a DMA. The process is usually carried out in two stages localisation and pinpointing. In effect the night flow analysis is a localisation technique used to identify which DMAs show evidence of leakage. Localisation methods are used to judge which sub section of a DMA has a leak and then narrow down the location of a leak to a single pipe. Pinpointing a leak covers the different methods by which the exact locations of any leaks are traced so that a repair can be made. Localisation is vital in ensuring that resources for more accurate leak location are allocated to where they are needed. It would be impractical to inspect the full length of the pipe in a DMA using pin pointing technologies due to time and financial constraints. Localisation techniques are used as they are cheaper and quicker per length of network than leak pin-pointing techniques. Localisation techniques lack the accuracy to determine where on the length of a pipe a leak has occurred. Generally, it is impossible to determine anything about the nature of the leak(s) other than the estimated volume of water being lost on that pipe section Pin-pointing Once a leak has been narrowed down to a single pipe, the leak can be pinpointed by a host of different methods and technologies. The operation and characteristics of these technologies are described in Section 5.2. Accurate pin-pointing is highly important in avoiding dry holes, where no leak is detected in the excavation and extended holes where a leak is only detected by extending the excavation WRc plc

31 beyond its original scope. Both situations are time consuming, expensive and potentially inconvenience the public. 4.6 Conclusion Several options are available to water companies to audit the level of leakage across the network. Top-down annual water balancing is useful for comparing company performance while bottom-up night flow analysis is used to identify problematic sections of the network and successful schemes. Combinations of both are used to ensure accuracy and completeness. Central to leakage control in the UK are DMAs, isolated sub-sections of the network typically servicing properties. DMAs provide for improved and more efficient leak detection and pressure management. The water industry uses a number of methods to control the level of leakage across the network. In addition to ensuring rapid response times, all water companies are engaged in active leakage control to reduce backlog. Constant monitoring of the DMAs allows operators to detect changes in water consumption that may indicate a leak. Detecting leaks involves using localising techniques to narrow down the search to a single sub-district, street or pipeline. Localizing leaks in this manner reduces time and resource demands. Other techniques used in leakage control include pressure management and renovation schemes to replace aging pipe work. All techniques are coordinated and prioritised to ensure optimum leakage management. WRc plc

32 5. Active Leakage Control Technologies 5.1 Leak Localisation As described in Section 4.5, leak localisation is enabled by the use of DMAs. There are parts of the network where this cannot be achieved due to the high cost of installing (multiple) meters or due to the uncertainty over the estimates of customer use e.g. urban city centres. Within DMAs and in areas not covered by DMAs, a variety of methods are used to localise leaks. These methods are described below. Step testing The general principle of step testing is to isolate (turn off) sections of a DMA in turn and see what effect that has on the total (night) flow into the DMA. The expected change can be calculated based on the estimated demands of the isolated sector. This is compared to the actual change in demand from the network. Should this change be greater than expected, there is a high probability that there is a leak in the area or street that has been isolated. Most water companies have increased the area measured in each step test to decrease the potential issues with water quality that this method can create (Dray, Loveday, Tod, & Tooms, 2010). With new data transmission technology fitted to the district meter, the flow change can be seen instantly on a hand held portable device, so that isolating individual streets for short periods is seen as an efficient and less disruptive form of step testing. Step testing is particularly effective in areas with predominately plastic piping as step testing is less susceptible to the issues that affect other localisation technologies based on acoustic detection of leaks. However, it is best avoided on pipework in poor condition due to the potential for pressure shocks to be introduced. Finally, step testing is best carried out at night when customer demand is expected to be lowest. Pressure testing Pressure testing involves the pressure being raised in a controlled manner along an isolated section of network. Once a designated pressure is reached the section is completely isolated and the pressure is monitored. The rate of pressure decline is a function of the rate of leakage from the pipe. Too rapid a drop in pressure indicates serious leakage from the pipe section. While effective, the greatest disadvantage of pressure testing is the risk of creating a burst. It is therefore not recommended for use on older pipes in the water industry, and is generally limited to new mains and trunk mains. Like step testing, it is potentially disruptive to the service so is best carried out at night. WRc plc

33 Acoustic loggers A large number of water leak detection and pinpointing techniques use detection of the noise produced by the leak to identify the presence of a leak or to pin-point its location. Acoustic loggers are units that are deployed in groups of between 6 to15 and are mounted on the pipes or fire hydrants m apart from each other. The devices record the noise detected on the pipework. This information can then by analysed for unusual noise patterns, which can indicate potential leaks. The most sophisticated noise loggers are self-learning, which allow the filtering out of disruptive background noise. The recorded noise can be monitored over a period of several days and weeks by either accessing them directly or in passing with a receiver to pick up their signals (Dray, Loveday, Tod, & Tooms, 2010). Flow meters Flow meters have also been used to localise leaks down to a sub-dma level. This involves dividing the DMA into smaller hydraulically distinct areas and installing (temporary) flow meters on the mains feeding each sub-dma. Some companies have a hierarchy of smaller LCAs (leakage control areas) inside DMAs which are not isolated permanently. Alternative routes into the sub-dma can be isolated via valves on a temporary basis. The flow rate into the sub-dma can be monitored over the course of 24 hours for unusual activity that indicates a leak, for example high flow rates or little variation in the flow rate over the course of the day (Hunaidi, Detecting Leaks in Water-Distribution Pipes, 2000). This method has the advantage over step testing in that it will not interrupt service. In addition, due to the fact that the flow meters use telemetry to communicate information back to the office, it is less labour-intensive than step testing and pressure testing but does require access points or fittings to allow for the additional metering. Tri-parameter systems Tri-parameter systems measure flow, pressure (including transients) and noise. By maintaining a record of the normal pattern for a position within the network, they create a footprint from which any deviation can indicate the presence of a leak or other significant network event. These systems include Hydroguard and Trunkminder. The systems are usually permanently installed or installed for extended periods. Typically the cost of the installations (including data connections) mean these techniques are used only on critical, large diameter trunk mains. WRc plc

34 Photograph 5.1 Tri-parameter system in operation Source: (Martinek Water Manafement, 2014) Hydroguard are battery operated monitors that measure, record and transmit the flowrate, pressure and noise data from trunk mains. Trunk mains are generally large diameter mains that transfer water from one area to another. Hydroguard is designed to learn the flow and pressure profiles of the pipe it is installed on over a pre-determined length of time. Information can be sent to back to computers in the central office or to mobile phones. Should there be anomalies in the recorded data, the system can raise the alarm and increase in the frequency that it logs data. Trunkminder is another permanently installed sensor that provides real-time data to the operator. It feeds the data it gathers (pressure, flow and vibro-acoustic) through a series of algorithms that allows it to alert operators to identify emerging problems on the pipeline and help screen out false positives allowing it to give accurate early warnings of potential leaks. Modelling hotspots Computer network modelling can be used to localise new leaks. Data relating to flow and pressure is gathered from an investigated DMA and is fed into the model, which in turn will predict the most likely leakage hotspots. These computer models are based on hydraulic models with algorithms to model pipe conditions and other factors. The greatest advantage of leakage hotspot modelling is that it can localise potential leakage locations across a large area extremely quickly. It is also not labour intensive compared to traditional methods of leak localisation which are timely and costly. However, the accuracy of these models depends on the quality of the model used and the quality of the input data. WRc plc

35 Frequently several runs are conducted for each DMA and an average taken to reduce the risk of making decisions based on one set of anomalous input data. Leak detection models have been used by United Utilities on DMAs with historically high leakage with some success on small catchment areas (Wu, 2008). Thames Water has recently invested in TaKaDu infrastructure monitoring systems across London in a move to help locate hotspots where leakage is most prolific. TaKaDu uses a smart grid covering the network and data gathered from the company on pressure and flow rate as well as weather and local holidays to flag potential problems. Not all leakage modelling is used for locating leaks. The Met office has developed a model, in conjunction with Thames Water that predicts, among other things, the likelihood of increased bursts across the network due to weather conditions (heat, cold etc.) for use in management planning. 5.2 Leak location and pinpointing on small pipes The following techniques can be used to indicate the general location of the leak, or to pinpoint it prior to excavation for repair. These techniques are either limited to, or are most effective, on pipes less than 150 mm in diameter. Pin-pointing currently involves work teams inspecting the length of the pipe and recording where any suspected leak locations are for repair. Newer technologies such as correlating data loggers can cut down the number of teams needed to pin-point a leak thanks to the ability to monitor the pipes for a prolonged period of time and communicate automatically. Acoustic and electronic listening sticks One of the most basic and widespread techniques used in the water industry to locate and pinpoint leaks is listening for the noise produced by the leak. The most basic tool is the listening stick which consists of an ear piece mounted onto a metal or wooden rod. One end of the rod is placed on the ground or on part of the water pipework and the operator listens to the other end. The rod transmits the sound to the operator s ear. More expensive battery powered electronic devices are also available. These use a microphone, amplifier and headphones to magnify the amplitude of the signal to increase sensitivity (Hunaidi, Chu, Wang, & Guan, 2000). These tools require a degree of experience from the operator to determine whether a noise is due to a leak or to some other cause. Some newer systems do not require the human ear, but will automatically sense the presence of a leak at the push of a button. WRc plc

36 Photograph 5.2 Acoustic listening sticks Source: (Charalambous, B, 2010) Listing sticks are inexpensive and widely available but they require experience to use and are vulnerable to interference. One of their greatest advantages is that they can be used through the ground without requiring direct access to the water pipework. For larger leaks under high pressure they are highly cost effective but quieter leaks are harder to detect over background noise (Hunaidi, Chu, Wang, & Guan, 2000). The ability to detect sound through the ground is limited by the depth of the pipework at which the pipes are buried. Often soundings are taken off fittings on the network as any leak noise WRc plc

37 will be carried along the pipe better than through the ground. The noise level at adjacent fittings can be compared to give an indication of the leak location relative to the fittings. Electronic listening sticks have the theoretical advantage of being able to give a clearer signal. However, they are less robust and more expensive than traditional listening sticks and may face opposition amongst more conservative members of a leak detection team. Ground microphones are a more substantial form of electronic listening stick specifically designed to detect leak noise through the ground; they can include a display of the amplitude and frequency of the leakage noise. The operator traces the pipe and records the amplitude of noise as they progress. The position where the noise is loudest is likely to correspond to the actual leak position. Like all noise based detection systems, ground microphones are less effective on soft ground (Dray, Loveday, Tod, & Tooms, 2010). Photograph 5.3 Ground microphone in operation Source: (Sewerin, 2014) Leak Noise Correlator The most popular device for leak location in recent years is the leak noise correlator, which is used to detect the position of a leak between two sensors placed on a length of pipe. A schematic of this type of device in use is shown in Figure 5.1. A sensor is placed at each end of the pipe section, usually at existing fittings such as hydrants or valves. The sensors are connected to a signal processing unit that takes the signal from each sensor, amplifies it and then compares the signal shape detected at each end. The principle is to look for the time delay of the noise from the leak reaching each sensor the closer the leak is to the sensor the earlier the noise arrives in comparison to the other sensor. Knowing the length and material of the pipe and the speed of sound in that size and material of pipe, the approximate WRc plc

38 location of the leak relative to the two ends can be determined. Typically, a listening stick is then used to confirm the exact location of the leak from above ground. The poor transmission of sound along plastic pipes makes the use of correlators on plastic less successful. Recent developments in correlator technology have improved the lengths of plastic pipe over which leaks can be located. Figure 5.1 Schematic of leak noise correlator Source: (Pipefix, 2014) Photograph 5.4 Leak noise correlator Source: (HMW, 2011) Two different types of sensor can be used with the leak noise correlator accelerometers or hydrophones. Accelerometer type sensors are designed to detect the vibration induced into the pipe walls by a leak. They have the advantage that they can be attached to the outside of the pipe (or to a fitting) and so are simple to use. Accelerometers are recommended for WRc plc

39 metallic pipes between 50 and 300 mm. Larger pipes see a drop off in effectiveness due to rapid attenuation of the vibrations along the pipe wall for larger pipes. Hydrophone type sensors are placed directly in contact with the water allowing the device to measure vibrations in the water as opposed to measuring vibrations along the pipe wall, and hence are less affected by pipe material. Typically they are used at hydrants where gaining direct access to the water is relatively easy. Pre-location noise loggers Noise loggers are a combination of an acoustic sensor and data logger. They are attached, via magnetic fittings, to the outside of an accessible pipe fitting such as a valve stem or hydrant, where they will detect and record the acoustic noise in the surrounding network. The data collected is processed and analysed to look for changes that might indicate the presence of a leak. Loggers can either be long term monitors permanently attached to the pipe or used in temporary deployments to detect a leak. Permanent deployment tends to take place in cities or other areas where routine survey work would be difficult. Battery life is typically 5 years. Some of the more advanced models are self-learning, capable of detecting anomalies from normal flow and flagging them up for passing technicians. Most modern designs are designed to transmit their data directly to the water company s local office. The distance between noise loggers depends heavily on the type of pipe they are attached to. Noise loggers are more effective on metallic pipes less than 150 mm diameter. In such a situation the loggers can be deployed up to 250 m apart. Noise loggers are less effective on larger pipes and pipes made of plastic (due to poor noise transmission along the pipes) and therefore require closer positioning, often less than 50 m. It is the density of noise loggers required and the associated cost that has prevented them being used more often as permanent installations. However, the cost of noise loggers is steadily reducing creating more opportunities for them to be permanently installed. Noise loggers are non-intrusive, and do not require extensive training as the associated software does the analytical work. They are less affected by ambient noise compared to traditional noise detection having been buried beneath the ground and in close proximity the pipe. Noise loggers can be more cost effective than acoustic sounding at reducing leakage levels within a short period of time. However, like more traditional sounding techniques, noise loggers have difficulty with detecting small leaks (typically below 80l/hr). Noise loggers are considered as leak localisation devices rather than pin pointing devices. Precise planning is needed to gain the best results (Dray, Loveday, Tod, & Tooms, 2010). WRc plc

40 Correlating noise loggers The correlating noise logger is a more sophisticated version of the noise logger. It pinpoints a leak by having two or more detectors placed on a pipe and measuring the noise. The correlating noise loggers feed the data through a cross-correlation algorithm and calculate the distance along the pipe to the leak from the detectors. The two readings can be crossreferenced to determine the location of the leak. Unlike conventional noise loggers, they are used almost exclusively for temporary deployments to aid in leak pin-pointing. They should not be confused as a replacement for noise loggers as their function is different. They are used on smaller, metallic pipes and suffer the same limitations to sensitivity as leak noise correlators when deployed on larger pipes and plastic pipes (Hunaidi, Detecting Leaks in Water-Distribution Pipes, 2000). They are attached to pipe fittings using a magnet in a similar manner to a traditional noise logger and can be accessed by direct inspection, use of a passing patrol vehicle with a receiver or via telemetry depending on the type. Correlating noise loggers can be resilient to background noise and are effective over long distances in the right conditions. They do not require signals to be sent between units, reducing the sound interface and detection error. However, they cannot be used for live in situ correlations, instead requiring the data gathered to be downloaded for analysis. They also require a greater degree of training compared to traditional noise loggers (Dray, Loveday, Tod, & Tooms, 2010). Magic carpet The magic carpet is a form of acoustic sensor used in pin pointing water leaks. The device consists of a plastic mat, 1.5 m long, with evenly spaced acoustic sensors. The magic carpet is placed on the ground where a leak is expected. The acoustic sensors inside the mat are used to triangulate the location of the leak. Magic carpets are accurate to 0.3 m in ideal conditions and are more resistant to background noise interference compared to other acoustic devices. Several water companies have started to adopt the technology as part of their leak detection toolkit. WRc plc

41 Photograph 5.5 Magic carpet device Source: (Stest, 2014) Gas Tracing Gas tracing may be used for leak detection on small pipes (less than 4 ) but it is not in common use in the UK. At larger diameters, the cost of the gas is prohibitive, and is likely only to be used as a last resort. A gas (either hydrogen mixed with nitrogen or sulphur hexafluoride) is fed into an isolated and drained pipe, or bubbled into a pipe under pressure. The gas will escape through any leaks and infiltrate its way through the soil to the surface. This gas is then picked up by sensors moved along the line of the pipe by the operative. The gases are chosen to be non-toxic, non-polluting and non-flammable (at the concentrations used). WRc plc

42 Photograph 5.6 Gas tracing equipment Source: (Edenbros, 2014) The biggest advantage of this method for pin-pointing a leak is that it will work on plastic pipe networks. It is also highly sensitive, as it can diffuse out of leaks only a few thousandths of a millimetre across (Pregeli, Drab, & Mozetic, 1997). The ability of this method to pin point a leak depends heavily upon the ground surface. The gases will percolate through loose soil, block and flag pavement and gravel but will have difficulty penetrating dense clay, concrete and tarmac. Inaccuracies can occur as the gas takes the easiest path to the surface and the technique is poor for large pipes due to the time it takes for the pipe to fill with the gas (Dray, Loveday, Tod, & Tooms, 2010). Ferret Ferret is a relatively new technology that uses pressure monitoring to locate the source of a leak. It is highly accurate in smooth bore pipes (including PE and PVC pipes). The Ferret system consists of a head which is inserted into the pipe via a stop cock, meter or fire hydrant connection (and sized for a specific diameter of pipe) and a flow sensor that can be used to determine the scale of a leak. The Ferret head is inflated and is pushed along the pipe. The pressure between the entry point and the ferret is then raised and monitored. A pressure drop indicates there is a leak in the section being checked. The Ferret is then gradually withdrawn until the pressure can be maintained. At this point the Ferret will have been withdrawn past the leak location. WRc plc

43 Figure 5.2 Operation of a ferret Source: (Ferret, 2012) The Ferret can detect small leakage rates (0.03 litres per hour) and is most suitable for pipes between 10 mm and 40 mm in diameter. Whilst it is only available for service connections and small bore mains at present, larger diameter versions are being considered. Photograph 5.7 Ferret equipment Source: (Ferret, 2012) 5.3 Leak location and pin pointing on large pipes Larger pipe diameters present their own challenges for leak detection. Sound waves are transferred down larger pipes in a different manner to smaller pipes and is attenuated significantly as it passes along the pipe. This makes acoustic techniques where transmission WRc plc

44 of the sound along the pipe is required ineffective over all but short distances. Inaccuracies in metering techniques means that only large leaks can be detected using flow metering. In-pipe acoustic detection In-pipe acoustic detection systems are intrusive leak detection devices that comprise of a sound sensor and recorder. The device is inserted into the water main and is carried down the length of the pipe by the water flow. As it does so, it listens for the sound of water escaping through a leak. There are two basic models: tethered, where in the hydrophone sensor is attached to an umbilical cable allowing its position to be controlled in the pipe; and free swimming, where the sensor is carried down the pipe and is retrieved (using a net or similar capture device) at a designated point. Some designs also feature a camera. Tethered devices are the most developed technology with several systems on the market including WRc s Sahara system. Tethered systems are more limited in their range (typically 1-2 km, but geometry and layout of the pipe can reduce this) but are capable of giving real time feedback and precise leak location information. They have been proven to work reliably and are the method of choice for trunk main leak detection in some UK water companies. Figure 5.3 Sahara leak detection system Source: (WRc, 2014) Free swimming devices include Smartball and Urchin. They are capable of traveling through several kilometres of main (more than 12 miles in a single deployment (Kurtz, 2006)). They can also traverse pipe bends and other restrictions far more easily than a tethered device. However, the system requires receivers to be attached to the pipe walls to calculate the position of the leaks. Free swimming devices should only be used where the pipe is known to have no branch connections. WRc plc

45 There are plans to evaluate SmartBall for use in gas transmission mains. Pure Technologies are seeking government funding for trials in Canada. Figure 5.4 Free swimming detection device Source: (Pure Technologies, 2014) Aerial Surveys Aerial surveying allows for large areas of land to be quickly surveyed making it extremely useful in investigating leaks in rural areas. It is often accurate enough to pinpoint a leak. Light aircraft are most commonly used at present, but helicopters and unmanned aerial vehicle (UAVs) could also be potentially used. The aircraft used in the surveying work can be equipped with a variety of electromagnetic sensors including ultra-violet, visible, near and long wave radiation. Modern thermal imaging is particularly useful as the temperature of water saturated soil, potentially caused by a leak, can differ by as much as 2 C from ambient conditions. Dry earth will change temperature quicker than moist earth, which can further indicate a leak through repeated fly-overs. Temperature differences are most noticeable on warm dry days with results being harder to gain during cold days when standing water is present on the ground. As such it is often deployed during periods of drought. The data gathered is analysed with the aid of computer programs for anomalies indicating a water leak. Aerial imaging is capable of detecting the presence of water invisible to the naked eye. It is highly accurate, up to 1 m from the source of the leak. The resolution an aerial image produces is superior to that created by hand-held thermal imaging. However, aerial imaging requires considerable technical expertise to operate the equipment and to process the data such that potential leakage sites can be separated from natural water sources. WRc plc

46 5.4 Experimental technology for leak detection and location The following technologies are currently being investigated for their use in the water industry. They are either in development or are not yet currently being deployed on a large scale. Thermography Thermography involves the use of infra-red sensors to detect changes in temperature along the length of pipe. Anomalies in the temperature may hint at a potential leak as the water will be cooler/hotter than the surrounding area. In addition, the water may change the thermal characteristics of the ground. Initial surveys with the technology have been promising and similar devices have been used in indoor plumbing. Thermal imaging is used by several companies such as Leak Detection Specialist in detecting leaks on mains. It has also been used successfully to detect leaks on pipes in the concrete decks of road bridges in America (Hunaidi, Detecting Leaks in Water-Distribution Pipes, 2000). However, the technology has yet to be widely adopted in the water industry because it can be heavily influenced by season, local effects on ambient temperature such as thermal noise, particularly in urban areas, cloud cover and relative humidity. The technology is seen primarily as a potential localisation technology in the water industry (Hunaidi, Detecting Leaks in Water-Distribution Pipes, 2000). Time domain reflectrometry The process involves attaching a set of wires to the length of the pipe while the pipe is being installed. The wires are attached to a measurement instrument allowing operatives to check the pipe length for leaks. An electric current is passed down the wire and the reflected waveform is analysed allowing for the resistance of the wires to be determined and from that any changes in resistance caused to the wire coming into contact with a leak. The technique is similar to the Electric Resistance Monitoring (ERM) system used in Europe. WRc plc

47 Figure 5.5 Diagram of TDR leak detection Source: (Farley and Trow, 2003) TDR is very accurate, especially if an overlapping inspection regime is adopted where accuracies of 0.3 m/1 km are obtained, is relatively cheap to install and operate and can be installed on pipes of any material. TDR can transmit its data in real time. WRc plc

48 6. Pressure Management Pressure management is extremely effective at reducing the background leakage rate and the flow rate from both the reported and unreported leaks running in the network at any time. In areas where pressure management has been applied there has been a significant drop in the frequency of bursts occurring. In Auckland, New Zealand, a reduction in average pressure from 7 bar to 5.2 bar in Ecowater s distribution system resulted in the lowest frequency of new leaks occurring on the network in 8 years (Lambert, 2001). Similarly, in the UK, recent investment of 1.5 million in new pressure control systems has already saved South East Water half million litres a day in water through reduced leakage. When the pressure control system is fully operational it is expected to reduce leakage by 5-6 million litres a day. It is only in the past 10 years that the water industry has fully appreciated the significance of pressure on burst rate and developed new techniques to analyse the relationship. Pressure management is one of the most cost-effective methods of reducing water leakage; its initial capital cost (primarily the cost of pipework, fittings, chambers and covers rather than the cost of the PRV itself) being far outweighed by the savings made. However the degree to which it is effective depends on the size of the area, the topography, and the current performance of the network. 6.1 Theories behind Pressure Control There has been a steadily evolving understanding of the effects of pressure on the rate of leakage over the past 20 years. Laboratory tests on sections of metal pipe with holes in them show a square root relationship between pressure and flow rate. The equation explaining the relationship is given below (Equation 6.1). Equation 6.1 Theoretical leakage/pressure relationship Where: V= velocity of water lost (m/s) C d =discharge coefficient g= gravitational acceleration (m/s 2 ) P= pressure in Pascals The volumetric flow rate (Q in m3/s) is the velocity times the area (A in m2) of the leak (Q = V x A). So, in the case of a fixed orifice, leakage flow rate Q varies with pressure to the power 0.5 (a square root relationship). WRc plc

49 However, tests in water distribution systems show the relationship is more pronounced than expected; Work in Japan, Brazil and the UK, and many other places around the world over the past 40 years shows that on average the leakage rate varies with pressure to the power of For practical application, leakage is proportional to the power N1 (see Equation 6.2). Equation 6.2 Empirical relationship between leakage rate on pressure: ( ) The exact N 1 value can vary enormously depending on the piping material and the level of leakage. Plastic and steel pipes tend to have higher N 1 values than cast iron. The reason is that the area of the leak also varies with pressure in many cases as the leak path increases and decreases. This theory is known as fixed and expanding paths, and N 1 can typically lie between 0.5 for metal systems and 1.5 for plastic systems. Figure 6.1 Fixed area discharge Circular hold drilled in pipe N1 typically 0.5 Variable area discharge Split in flexible pipe N1 typically 1.5 Source: (Tomsensori, 2011 (left), Wimpsy Plumbing, 2014 (right)) In practice, the rule of thumb, where no specific information is known, is to assume a linear relationship between the level of leakage and the average pressure in the water mains (i.e. N 1 =1.0). So, a 10% reduction in average pressure will result in a 10% reduction in average leakage. The latest thinking on the relationship between pressure and burst rate is that the pressure dependent burst rate varies with the maximum pressure to the power of N 2, a general correlation factor (which is valued around 3 i.e. a cubic relationship) above an underlying nonpressure dependent rate. Formulae have been developed to estimate the non-pressure dependent rates for systems for mains and service connections separately. WRc plc

50 The physical mechanism which governs the cubic relationship is not yet clear, and research is ongoing. However, it has been borne out by the results of pressure management projects around the world, and there is now sufficient confidence to use the methodology to predict the impact of pressure management on burst rate. A theory known as the Straw that Breaks the Camels Back suggests that small reductions in pressure result in a large change in burst rate in areas which have a relatively high initial burst rate. Equation 6.3 Graph of ressure to leakage failure for different pipe conditions Source: (A Lambert, 2001) 6.2 Transient pressure Surges or pressure transients (more commonly called water hammer) are the result of rapid changes in liquid velocity down the pipe length. Due to the relatively incompressible nature of water, these can damage fittings, pipes, valves and instrumentation. Bursts caused by transient pressure changes are more likely to occur on sections of pipe weakened by other factors (e.g. corrosion). Reduction of surges is therefore also an aim of water companies. Recent investigations have shown the extent and significance of transients on burst frequency in the water network. Transient pressure can be caused by a number of factors including inadequate pump control (fixed speed motors are gradually being replaced by variable speed drives to remedy this), opening and closing of ball valves in tanks or rapidly opening and closing valves in the distribution system. These factors can be reduced by altering the types of valves and adjusting the pressure control system to produce smoother pressure changes. Companies have also embarked on awareness and training programmes for their operational staff to highlight the benefits of careful valve operation to reduce pressure transients. WRc plc

51 6.3 Pressure control in practice Major progress has been made since the early 2000s in pressure management. It is estimated that average UK pressure was 50 m (5 bar) in 1994, and by 2009 this had been reduced to 44 m (4.4 bar). Despite the obvious topological difference across the UK, the average pressure at a company level weighted by where people live is remarkably consistent at between 40 m (4 bar) and 45 m (4.5 bar). One company is planning to reduce average system pressure to 36 m (3.6 bar) in the next 5 years Implementing a Pressure Management System Pressure management progresses in stages; the first step is to establish an accurate picture of the different pressures in the network and to establish the potential savings versus financial cost from reducing the pressure. Other factors such as the impact (both positive and negative) on the consumer need to be taken into account. The basis for pressure management is to establish Pressure Managed Areas (PMAs), with inlet pressures controlled by Pressure Reducing Valves (PRVs) or (more rarely) variable speed drive pumps. PMAs are usually based on District Metered Areas (DMAs) but they can be a sub-area of a DMA, or they may include several DMAs. For a network with no existing pressure management its introduction is targeted on areas with high levels of pressure complaints and/or a high burst rate. Other areas for investigation may also include DMAs serviced by multi inlets or where there are uncontrolled branches off trunk mains feeding large areas. Anglian Water has recently announced a 0.5 m scheme to control pressures on the mains supplying Peterborough (Gaines, 2014). Areas with a high variation between day and night time pressures are also worthy of examination to see whether it is possible for modulation of pressure to be introduced (see Section 7.2). It used to be recommended that such pressure management should be introduced where night time pressures can be reduced by at least 10 m (1 bar). However, recent evidence shows that even small reductions of less than 5 m (0.5 bar) over a large area can produce economic benefits. This is largely due to the better knowledge of the impact of pressure on burst frequency. Once the measures are installed, long term management of the PMA with pressure control must ensure that the pressure management system remains in good working order and adapts to changing conditions. Such factors for operators to be aware of include changing customer consumption and the addition of new properties to an area Reduction of pressure Pressure control can be achieved through a combination of measures such as installing pressure reducing valves (PRVs), break pressure tanks, pump speed control, reservoir inlet and outlet controls, and trunk main controls. Properties at high elevations and high-rise buildings can limit the potential for pressure reduction across the area generally, but the use of local booster pumps can be cost effective in these situations. WRc plc

52 Pressure Reducing Valves Pressure reducing valves (PRVs) are control valves that regulate the pressure on the downstream pipe independently of the upstream pressure or the flow rate into the area. They are available in a variety of types ranging from simple fixed outlet pressure types to modulated control (where outlet pressure varies with time of day and/or flow rate) and actively controlled devices that can have the pressure output varied depending on parameters monitored elsewhere in the network (see Sections 7.1 and 7.2). Pressure control valves are usually installed with the meter on the inlet to a DMA (see Section 4.3 for a description of DMAs). Further valves may be installed inside the DMA allow for finer control if the DMA is in a region with steep terrain. Break Tanks Break tanks (effectively a small reservoir with the surface at atmospheric pressure) can be installed along strategic mains to break the hydraulic gradient at a convenient point. This technology is often used where there is considerable undulation in the terrain where high static pressures can be present at the base of a gradient. Re-zoning Re-zoning to ensure that areas all can operate a similar pressure is also an important part of pressure management. Re-zoning is done by altering the supply routes into an area by laying new mains and/or opening and closing line valves so that pipes which require high pressure are separated from pipes that require low pressure. Siting Reservoirs Another method to reduce average pressure is siting reservoirs so that the gravity head is not excessive. This reduces pressure downstream but is difficult to apply to existing water networks. Pumping Unnecessary pumps can be removed from the network to avoid both excessive pressures and create a smoother pressure gradient across the system (avoiding pressure transients). Stopping and starting pumps, or increasing and decreasing the speed of variable drive pumps can be used to adapt the pressure to meet changing demands. Booster pumps may be used to locally increase pressure but they increase operating costs. They are occasionally used in circumstances where there are advantages in pressure reduction in zone but where doing so would leave parts of the network with pressures below the required levels. WRc plc

53 6.4 Pressure Requirements and Regulation There is a regulatory requirement to maintain the water pressure at a customer s property at a standard reference level of 10 metres (1 bar) of pressure at a flow rate of 9 litres / minute into the property. In practice the companies use a surrogate reference of 15 m (1.5 bar) of pressure in the water mains. Customers can claim compensation under The Guaranteed Standards Scheme (Ofwat, 2008) if they receive water below this standard pressure. As low pressures can be disruptive to customers, fuelling complaints, the water companies are also assessed against a Service Incentive Mechanism (SIM) which has financial incentives for reducing unwanted calls from customers. Any pressure management system must take account of these regulatory factors. In practice this means that the water pressure is monitored at the high points (lowest static water pressure) and at the extremities of the controlled network where pressure drop under high flow conditions may be greatest. Data loggers and hydraulic models are used to assess the pressure at these critical points in the network. The perceived need for high water pressure for fire fighting has traditionally prevented the pressure from being reduced as far as it could be. This is in spite of the volume of water being more important than pressure in fire fighting. However, newer fire tenders carry a supply of water, reducing reliance on immediate access to network hydrants. 6.5 Pressure management control systems There are several levels of control that can be used by a water company to control PRVs falling into the following broad categories; fixed outlet pressure reduction, time control, flow control, and forms of remote control based on historic data, or real time control with a feedback loop. The exact selection depends on the needs of the network. Most companies have shifted to using some form of flow modulation and several have adopted automatic pressure optimisation systems (self-learning control systems) across much of their network Fixed Pressure reduction Fixed outlet pressure control valves are designed to reduce the pressure to a set amount (in metres head) regardless of the demand for water in the network or the upstream pressure. Fixed outlet control is suitable for areas with little or no demand-related head loss, and they are in common use Timed control Timed remote control allows the operator to determine the pressure profile over a period of 24 hours usually at 15 minutes intervals to better meet demand (for instance ensuring higher pressure to meet peak demand in the morning and evening and low pressure for night flow). The simplest time based controller is designed to make two adjustments a day between day settings and night settings. These controllers are inexpensive and ensure that pressures are WRc plc

54 lower during non-peak flows during the night through they cannot account for other variations during the day Flow Modulation Flow modulation sets the outlet pressure of the PRV against the flow rate into an area allowing it to be adjusted to overcome demand-related head loss. The flow rate pressure relationship is calculated by company engineers based on previous historic data. Flow modulation allows the pressure to adapt to changing flow rates reducing unnecessarily high pressures during night flow. Flow modulation control is best used on PMAs with a single inlet. PMAs with multiple inlets have the risk of interactions between inconsistent flow modulation creating fluctuations around the desired pressure value (known as hunting ). However, newer, more intelligent systems can overcome this effect Remote control and remotely adjusted local control Basic remote control allows operators to define outlet pressure on a PRV based on information they have received from data logged by network sensors and their knowledge of demand and service challenges. Remote control uses one of the following methods: Manual operation via SCADA telemetry or from one of the newer web based portals using battery systems. Remotely adjusted profiles. In this method, the profile in a local controller is altered by manual intervention. Feedback control. In this method, data from the critical point sensors are used automatically to adjust the setting of the valve. The sophistication of these systems varies, with most intelligent using self learning algorithms capable of maintaining pressures at the critical points in the network within 1 m (0.1 bar) at all times of the year. They also learn about changes to the flow and head loss characteristics of the network under control without manual intervention. WRc plc

55 7. Technologies for Pressure Management 7.1 Pressure Reducing Valves (PRVs) The selection of pressure reducing valves depends on their function in the network, the size, and the configuration of the piping Sluice, butterfly and plug valves Sluice, butterfly and plug valves are traditional on/off type valves but can be utilised for controlling pressure. There have been examples of multiple valve pressure management systems making partial use of sluice and butterfly valves. Sluice valves are poor at controlling the pressure due to their extremely limited movement and the potential to cause cavitation, wire drawing and noise when partially open. Photograph 7.1 Butterfly PRV Spring loaded diaphragm valves Source: (Indiamart, 2014) Spring loaded diaphragm valves are designed to produce a constant outlet pressure using the pressure in the pipe to self-actuate. This is achieved by having a spring control the gap between a nozzle and the plug seat. The downstream pressure acts against the spring tension (which can be adjusted to change the setting) in such a way that the outlet pressure is fixed regardless of inlet pressure or flow rate. WRc plc

56 Photograph 7.2 Spring loaded diaphragm valve Source: (The irrigation shop, 2014) This type of valve is most commonly used on pipes less than 100 mm and is used inside buildings as well as in the distribution system. Manufactures include Honeywell and JRG, but there are many others. The cost of constructing the valve becomes prohibitive and less reliable at extremes of flow rates on pipes with diameters greater than 100 mm (WRc, 1994) Globe type diaphragm operating valve Globe type hydraulically operated diaphragm valves are the most common type of valve for controlling pressures in water distribution systems. They range from 40 mm to 600 mm diameter. Diaphragm valves have a pilot similar in design to a small spring loaded valve which is used to set the fixed outlet pressure. The pressure on the outlet of the valve will be controlled to within 1 m head (0.1 bar) regardless of upstream pressure or flow rate. The pilot controls the flow of water into and out of a chamber above the diaphragm which acts on a plunger to create a head loss which is the correct amount to give a fixed pressure on the outlet of the valve, whatever the flow rate or upstream pressure. WRc plc

57 Figure 7.1 Globe type valve fitted with a hydraulic pilot rail and an i20 system Source: (i2o Water Ltd, 2014) The valve is connected to the inlet pressure sensor in the upstream chamber of the main valve it is attached to by the sensing line (also known as the control loop); a series of filters, fixed orifices, needle control valves, and/or pipes. The control loop is arranged in parallel with the main valve and therefore has a pressure gradient from the inlet to outlet, the gradient pressure allows for a control pressure to be introduced into the control chamber. This in turn allows the valve to control to a desired pressure. The outlet is matched to the desired control pressure via a compressed spring which is adjusted with a small spanner to give the required fixed outlet setting of the main line valve. 7.2 Pressure Modulation There are several methods in use in the water industry to modulate the pressure at the outlet of a PRV in order to overcome the head loss in the district and maintain a constant pressure at the critical points. They fall into three general categories: Hydraulic Valve manufacturers and suppliers offer hydraulic systems which increase the outlet pressure in some way proportional to flow. The valves have additional pilots and can provide continuous control or two-stage (high and low setting). WRc plc

58 Figure 7.2 A diaphragm valve fitted with additional hydraulic modulation Source: (Cla-Val, 2014) Further details can be found on the valve manufacturers web sites some of which are listed below: Electric actuation Where there is mains power available at the valve site, such as trunk mains and service reservoirs, valves can be actuated by one of two methods: By fitting an electrically powered actuator to a gate, butterfly, or plug valve. By using low voltage (24V) solenoids to control the flow of water into and out of the top chamber of a globe type valve. WRc plc

59 Either of these methods allows remote manual operation by SCADA or by a local PLC (programmable logic controller) into which a flow or time and pressure profile has been scheduled. Local Battery Powered Various manufacturers supply battery powered equipment to retrofit to a PRV in order to alter the outlet setting of the valve. This is the most common form of modulation at a DMA level due to the absence of mains power. There are a small number of systems using the street lighting electricity. There are also micro turbines which fit into the PRV pilot loop to provide a backup power supply and a trickle charge. The major manufacturers are those who supply data loggers i.e. Technolog, Halma and i2o. Technolog and Halma have electronic units which control the pressure in a bias chamber which retrofits to the manufacturers pilot on the PRV. This acts on the spring tension in the pilot to change the setting. Solenoids in the control unit feed water or compressed air into the chamber above a diaphragm which pushes down the spring in the pilot. Photograph 7.3 Retrofitted bias chambers to allow local control Source: (Technolog, 2014) Some manufacturers have trialled true closed loop systems to provide true real time control, but these have some disadvantages; They are prone to communication faults, including vehicles being parked over the critical point sensor which usually sits in a fire hydrant chamber. Water is compressible to some extent and so there is a delay in the cause and effect loop between a change of PRV setting and the impact being shown at the critical point. WRc plc

60 They tend to operate on a trial and error basis i.e. they do not know the degree of change required to achieve the required critical point pressure. i2o have developed their own advanced pilot valve (APV) which replaces the manufacturer s pilot. It has a stepper motor which provides a rotary motion which changes the position of an orifice and hence the setting of the valve. The key features of the i2o system are shown in Figure 7.3: A logger at the critical point (P3) transmits pressure data to a central server. A controller at the PRV sends flow and pressure data to the server. The server analyses the data to learn the relationship between flow, head loss, time of day, day of week, and season. An intelligent algorithm produces the required pressure setting for the valve for the next time period (12 or 24 hours). The profile is downloaded to the controller that then does not reply on continuous communications. If there is any abnormal event in the system, alarms are sent. The settings can be overridden from a web-based portal, and the user can take manual remote control. A similar arrangement is now used to control the outlet pressure of variable speed pumps. Figure 7.3 i20 system components Source: (i2o Water Ltd, 2014) WRc plc

61 8. Flow and Pressure Monitoring 8.1 Introduction All UK water companies monitor the flows and pressures of water in their distribution systems by two basic means: Strategic points will be monitored in real time by the SCADA control system at sites where mains power is available. The data is used to actively control pumps and electric valves in order to maintain supplies to customers using the sources of water available. Service reservoir stocks are also monitored. Battery powered data loggers are used to record pressures at points within each DMA. Some companies have only one logger at the AZP (average zone pressure) point. Others have loggers at the DMA inlet, the AZP and the critical point(s) in the network. Where there is a PRV, many companies also monitor both the inlet and outlet pressure. DMA meters are all fitted with data loggers to allow flow profiles to be measured at a maximum of 15 minute intervals. Many large customer meters are also logged. Some data loggers have to be downloaded manually on site, but the majority now have communication capability to transmit the data at regular intervals. There are several manufacturers of flow and pressure loggers in use in the UK water industry but the major suppliers include Technolog, Halma (HWM) and i2o. Flow and pressure data is analysed in routinely to determine leakage rates, to monitor the effectiveness of existing pressure management, and to assess the scope for further reductions. Knowledge of flow rate through the system is vital in predicting water losses due to leakage. A flow meter will be installed on the inlet to a DMA. Traditionally mechanical meters have been used but many of these have been replaced by more reliable electromagnetic meters. Other flow meters may be located on sub sectors of the DMA for use in step testing (see section 3.1). Action is taken to locate the leaks when there is a sudden, large increase in water consumption or the flow rate into the DMA becomes too high suggesting intolerably high leakage. There are procedures in place to determine the economic intervention policy for proactive leak detection. Online monitoring allows for data to be accessible anywhere there is an internet connection; basic data processing can be done via a website. The technology is still recent and costs are WRc plc

62 continuing to fall. As with telemetry broadcasting, reception can suffer from interference if the equipment is installed inside a pit. Some companies such as Thames Water have developed special street furniture to accommodate the electronics and the aerial to make communications more reliable. However, with refinements in the technology it is likely we will see far more use in the future due to the advantages in allowing operators, engineers and leak detection teams to access up to date network parameters and characteristics away from the office. Meter Accuracy Meter accuracy depends on its type, age, condition of the meter and water quality. Poorly sized meters induce inaccuracy and can increase head loss. The most common types of flow meters are as follows: Mechanical meters including vortex flow meters, paddle flow meters and turbine meters. These are moderately accurate (±1-2%) when there is sufficient flow. During low flows their accuracy drops to ±5%. Some types of mechanical flow meter include two meters in combination, one for large flows one for small flows, which increases the range of flows they can measure accurately. Electro-magnetic meters: These either mains or battery powered and are highly accurate, often achieving ±0.1%, however their accuracy can decrease at low flows. Ultrasonic meters: These meters can be operated in-line (intrusive) or simply attached to the pipe exterior (clamp-on). However they normally require a mains power supply. Venturi and Dall meters: these are hydraulic meters which relate flow rate to a head loss. They require long straight sections of piping to work. Even then they are unlikely to have better accuracy than ±5%. Insertion probe electromagnetic or turbine meters are used to check the accuracy of large diameter meters, and to survey flows as a temporary measure or prior to the installation of a permanent meter facility and for calibration of an existing meter. Clamp on ultrasonic meters are used in a similar manner and are steadily replacing more traditional insertion probes used for in situ testing due to being faster. Both methods have limits to their accuracy however. Household meters tend to be read manually at intervals of 6 months or 1 year, although trials of various forms of AMR (automated meter reading) systems are being carried out. Non-households are all metered, with reading intervals varying from continuous via data logging, to monthly, quarterly and annual manual readings. WRc plc

63 Leakage Management Software All companies use one of a number of systems to analyse flow and pressure data routinely to derive estimates of leakage, and to direct active leakage control and pressure management operations. The estimates of leakage are based on trends in daily average flows and night flows, when leakage is a higher proportion of the total flow into a DMA. The software contains the fixed attributes of the DMA such as length of mains, number of properties, night use allowances for households and non-households, sub meters into other DMAs and large users. It also contains the live data (usually downloaded from the logger each day) at 15 minute intervals, and the historic data. Some systems have been developed by logger manufacturers, some by consultants (LMARS from RPS, Netbase from Crowder Consulting as examples) and some has been developed in house. Anglian Water has recently completed the commissioning of an Integrated Leakage and Pressure Management system (ILPM). There are also new methods of analysing the data automatically to detect the outbreak of leaks as soon as they occur. Consultants such as Takadu and Bentley have methods to fingerprint a DMA and to determine abnormal changes in flow and pressure which could indicate the presence of a new leak. WRc plc

64 9. Transferability of water industry practice 9.1 Methodology In light of the knowledge gained from discussions with the GDN s and the review of water industry leakage and pressure management practices, technologies along with best practice were identified that could be transferred to the gas industry as part of this task. The next stage of the project was to review and assess the transferable practice which could be actually utilised in the gas industry. 9.2 Matrix tables In order to provide an overview of all the technologies assessed, a matrix was drawn up which summarised each individual technology in turn. The full matrix is outlined in Table 9.1. The technologies that are most relevant to the gas industry are then identified and summarised in Table 9.2 WRc plc

65 Table 9.1 Full list of transferable pressure and leakage practices from water to gas high medium low na Task 1 Category Leak management Leak technologies Sub Category Leak localisation Measure Active leakage control Passive leakage control District metered areas Annual balance Night flow analysis Software Step testing Pressure testing Acoustic loggers Flow meters Transferable pressure and leakage practices from water to gas Possible to Transfer from Water Sector Explanation All water companies in the UK implement active leakage control. The challenge is to find the optimum mix of activities and the optimum extent of each. Gas do a little by surveying 'critical mains' though this is somewhat similar to the pre 1980 water industry approach of regular sounding on mains fittings (every 1 or 2 years). Current primary form of detection, relying on PREs for repair. Well selected DMA boundaries are beneficial to pressure management and simplify the task of pressure control in the water sector. Difficulty in measuring changes in gas flow accurately negates the benefit of DMAs. Difficulty in measuring flow to required accuracy negates the benefit of a mass balance approach. Requires good knowledge of customer demand to reduce uncertainty. The use of the SLM as the gas industry leakage model negates the transferability of the water industry's top down and bottom up mass balance approach. Difficulty in measuring flow into discrete areas to the required accuracy to detect leaks. This inaccuracy is compounded by uncertainty about gas usage by customers. Large errors can be introduced by legitimate night usage. Leakage in gas distribution 0.5%; Leakage in water distribution 15%. Level of leakage too low to be observable through this method. Analysis software is based on metering flows. Metering of governors would be required. Low level of leakage decreases opportunity for transfer. Potential for identifying large leaks (big enough to be detected by this method) is limited as sniffers would be more effective. Potential to burst older mains creates too high a safety risk. New PE network could be tested but aside from the fact that leakage on these is considered negligible, there is still the possibility of disrupting service. Potential to use governors or services as listening points provided that the sound propagates sufficiently. Noise from the governor may obscure leaks. Difficulty in measuring flow to required accuracy. Limited access points available for additional meter/fittings. Potential Added Value Explanation Opportunities to reduce absolute level of leakage. Potential to reduce PREs/ reduce network operating pressures/service failures (points of entry for water ingress). An active leakage control programme would facilitate closer link with mains rehabilitation programme. Current method used by GDNs. Limited value of any transferable practices. Security of supply is reduced if networks are hydraulically isolated with a single feed. Potential as additional tool in detecting/locating leaks in certain applications. Potential for use to inform proactive maintenance program. Accurate flow readings if possible would allow demand to be monitored, and help in determining the true level of leakage to direct capital maintenance. Ease of Implementation WRc plc

66 Pressure management Leak location and pinpointing on small pipes Leak location and pinpointing on large pipes Experimental technology for leak detection and location Control Strategy Tri-parameter systems Modelling hotspots Acoustic and electronic listening sticks Leak noise correlator Pre-location noise loggers Correlating noise loggers Magic carpet Gas tracing Ferret In-pipe acoustic detection Aerial surveys Thermography Time domain reflectrometry Pressure management areas Critical point monitoring Potential application for critical mains, but these are likely to be covered as part of a mains rehabilitation program as the risk driver is far higher in the gas industry. Modelling pressure data against flow data (could be customer demand modelling) would allow for exception reporting where modelled behaviour differs from the observed behaviour. Dependent on ability of sound from a leak to be transmitted and to what extent. Dependent on ability of sound from a leak to be transmitted and to what extent. Most popular device for leak location in recent years in the water industry. Dependent on ability of sound from a leak to be transmitted and to what spatial extent. Dependent on ability of sound from a leak to be transmitted and to what spatial extent. Dependent on ability of sound from a leak to be transmitted and to what spatial extent. Current primary method of leak location in gas industry. Low pressures and compressibility of gas makes the ferret an unlikely candidate. Dependent on ability of sound from a leak to be transmitted and to what spatial extent. Technology exists and has been used to good effect in water industry. Parameters may be different for gas but it is likely to be appropriate in certain applications, if not pinpointing, then perhaps localising over long length of main in non-urbanised areas. A small number of different technologies available. Not in sufficient use in the water industry for a judgement to be made on transferability. Not in sufficient use in the water industry for a judgement to be made on transferability. In establishing PM, the first step is to establish an accurate picture of system pressures. This is followed by establishing PMAs. The location of the lowest (critical) pressure points can change. There is a regulatory requirement to ensure a minimum level of pressure. In the water industry, critical points (elevation, extremities etc.) are monitored using data loggers and simulated using hydraulic models. Better failure prediction will allow for more efficient repex and increased network performance. Potential ability to act on PRE vs. pressure relationships. Links with the water industry and understanding of water bursts may help reduce the impact on gas industry assets (e.g. water ingress, pipe failures etc.) Potential as additional tool in detecting/locating leaks in certain applications. Potential for use in informing proactive maintenance program. Potential as additional tool in detecting/locating leaks in certain applications. Potential for use in informing proactive maintenance program. Potential as additional tool in detecting/locating leaks in certain applications. Potential for use in informing proactive maintenance program. Potential as additional tool in detecting/locating leaks in certain applications. Potential for use in informing proactive maintenance program. Potential as additional tool in detecting/locating leaks in certain applications. Potential for use in informing proactive maintenance program. GDNs already very familiar with this as primary method of leak location. Potential as additional tool in detecting/locating leaks in certain applications. Potential for use in informing proactive maintenance program. Potential for large scale and remote transmission leaks as well as some bespoke operational situations. Following a strategic approach to how the network is controlled using water industry experience may give added value. Understanding operational network pressures and defining/understanding PMAs is important first step of any pressure management initiative. A potential restructure of the network may result in efficiency gains. Increased network understanding through expansion of pressure sensing will allow for more informed PM programmes. Water industry experience in logging and monitoring should transfer to improved pressure monitoring and sensor location. Local Control Fixed pressure reduction Currently in use in gas industry. In water industry Fixed pressure reduction is part of the 'early WRc plc

67 Remote control Timed control Flow modulation Manual operation remote control Remotely adjusted profiles Feedback control Software fixed outlet pressure valves reduce the pressure to a set amount regardless of demand and are suitable for areas with little or non demand-related headloss. Currently in use in gas industry. Water industry has greater experience with these systems and has the potential to transfer best practice and technologies to GDNs. Best used on PMAs with a single feed. Single feeds are not as common in gas networks as in water networks. Flow modulation unlikely to be as successful as in the water in reducing over-pressured networks without accurate flow monitoring, and the inherent damped response of the gas network to changes in demand (compressibility). (As per the above controls but dial in operation). Currently in operation by both industries. Potential for communications, technology and management best practices to be shared. Currently in operation by both industries. Potential for communications, technology and management best practices to be shared. Utilising (improved) network sensing/communications and information to lower operating pressure to minimum possible. Currently in operation by both industries. Potential for communications, technology and management best practices to be shared. (Integrated smart software solutions) 'Self learning' already in use and closed loop systems not desirable. Similarity in technology and network design should allow for high transferability. gains' already achieved by most GDNs. Further opportunity to formalise selection process for PM technology selection. Timed control pressure reduction is part of the 'early gains' already achieved by most GDNs. Further opportunity to formalise selection process for PM technology selection. Achieve significant proportion of the benefits possible from PM without extensive communications requirements. Allow for further pressure reductions in areas not requiring full monitoring/control. The water industry has more established PM programmes. As the control/technology increased in sophistication it is likely that the water industry could provide increasing information and transferable practices. The water industry has more established PM programmes. As the control/technology increased in sophistication it is likely that the water industry could provide increasing information and transferable practices. The water industry has more established PM programmes. As the control/technology increased in sophistication it is likely that the water industry could provide increasing information and transferable practices. Reduction in PREs and Opex. A complete and comprehensive package solution in continuous development by the vendor(s). Allows for a continually refined product to be utilised 'off the shelf' without the need for substantial in-house development, development risk is borne by the vendor(s). Opportunity to introduce and encourage competition in the market. WRc plc

68 Table 9.2 Shortlist of transferable pressure and leakage practices from water to gas Shortlist Modelling hotspots Pressure management areas Critical point monitoring Feedback control Software Acoustic loggers Leak noise correlator Pre-location noise loggers Correlating noise loggers Magic carpet In-pipe acoustic detection Possible to Transfer from Water Sector Explanation Modelling pressure data against flow data (could be customer demand modelling) would allow for exception reporting where modelled behaviour differs from the observed behaviour. In establishing PM, the first step is to establish an accurate picture of system pressures. This is followed by establishing PMAs. The location of the lowest (critical) pressure points can change. There is a regulatory requirement to ensure a minimum level of pressure. In the water industry, critical points (elevation, extremities etc.) are monitored using data loggers and simulated using hydraulic models. Utilising (improved) network sensing/communications and information to lower operating pressure to minimum possible. Currently in operation by both industries. Potential for communications, technology and management best practices to be shared. (Integrated smart software solutions) 'Self learning' already in use and closed loop systems not desirable. Similarity in technology and network design should allow for high transferability. Potential to use governors or services as listening points provided that the sound propagates sufficiently. Noise from the governor may obscure leaks. Dependent on ability of sound from a leak to be transmitted and to what extent. Most popular device for leak location in recent years in the water industry. Dependent on ability of sound from a leak to be transmitted and to what spatial extent. Dependent on ability of sound from a leak to be transmitted and to what spatial extent. Dependent on ability of sound from a leak to be transmitted and to what spatial extent. Dependent on ability of sound from a leak to be transmitted and to what spatial extent. Potential Added Value Explanation Better failure prediction will allow for more efficient repex and increased network performance. Potential ability to act on PRE vs. pressure relationships. Links with the water industry and understanding of water bursts may help reduce the impact on gas industry assets (e.g. water ingress, pipe failures etc.) Following a strategic approach to how the network is controlled using water industry experience may give added value. Understanding operational network pressures and defining/understanding PMAs is important first step of any pressure management initiative. A potential restructure of the network may result in efficiency gains. Increased network understanding through expansion of pressure sensing will allow for more informed PM programmes. Water industry experience in logging and monitoring should transfer to improved pressure monitoring and sensor location. The water industry has more established PM programmes. As the control/technology increased in sophistication it is likely that the water industry could provide increasing information and transferable practices. Reduction in PREs and Opex. A complete and comprehensive package solution in continuous development by the vendor(s). Allows for a continually refined product to be utilised 'off the shelf' without the need for substantial in-house development, development risk is borne by the vendor(s). Opportunity to introduce and encourage competition in the market. Potential as additional tool in detecting/locating leaks in certain applications. Potential for use to inform proactive maintenance program. Potential as additional tool in detecting/locating leaks in certain applications. Potential for use in informing proactive maintenance program. Potential as additional tool in detecting/locating leaks in certain applications. Potential for use in informing proactive maintenance program. Potential as additional tool in detecting/locating leaks in certain applications. Potential for use in informing proactive maintenance program. Potential as additional tool in detecting/locating leaks in certain applications. Potential for use in informing proactive maintenance program. Potential as additional tool in detecting/locating leaks in certain applications. Potential for use in informing proactive maintenance program. Ease of Implementation WRc plc

69 9.3 Conclusions Based upon consultation with the steering group on Table 9.1 and Table 9.2, we concluded that there were four main areas where there is either technology or best practice knowledge that could be taken forward for testing/evaluation as part of Task 4, these included: Modelling of relationships between PRE/pressure and pressure/failures Pressure management practices and implementation Acoustic sensing for leak location Sensing for water ingress The project steering group agreed to take forward three out of four of the areas identified for further investigation based on the project resources available. Water ingress was excluded as it was deemed to be too large a subject to be covered in this project in sufficient detail. Proposals for bespoke research into acute and chronic water ingress are under development by WRc. The results from the assessment of these technologies can be found in individual reports which area summarised below. The results of the PRE modelling can be found in WRc Report G Pressure Management is covered in WRc Report G A summary of the acoustic testing can be found in WRc report G A comparison document summarising the key findings and conclusions from this project is provided as WRc report G WRc plc

70 References BBC (2006) Leaking London Gallery, [Online], Available: [24 September 2014]. Beal, S., Trow, S., & Haywood Smith, B. (2012). Calculation of the sustainable economic level of leakage and its integration with water resource planning. Contract on behalf of: Environment Agency, Ofwat, Defra. Beckett D., Bond, A., Trow, S. and Spain K. (2015) Management Techniques and Technologies for Leak Detection Control in the Water Industry. WRc Report G Butler, D., & Memon, F. A. (2006). Water Demand Management. London: IWA Publishing. Bold, M. and Bond, A. (2015) Pressure Management System i2o. WRc Report G Bond, A. and Goldblatt, S. (2015) Using acoustic sensors to locate gas leakage. WRc Report G Bond A., Homewood, S. and Kowalski,M. (2015) Summary report for GP1303 Technologies and strategies to reduce gas leakage - a review and demonstration of water network sector practice. Consumer Council for Water. (2013, November). Water Issues - Leakage. Retrieved August 04, 2014, from Davey, A., Kowalski, M. and Goudie, A. (2015) Making the business case for pressure managemnent to resuce PREs. WRc Report G Dray, S., Loveday, M., Tod, R., & Tooms, S. (2010). A survey of practices for the detection and location of leaks. Report: UKWIR Ref No. 11/WM/05/45. Fanner, P. (2004, April). Assessing real water losses: a practical approach. Water21(6.2), Farley, M., & Trow, S. (2003). Losses in Water Distribution Networks: A Practioner's Guide to Assessment, Monitoring and Control. London: IWA Publishing. Ferret. (2012). How ferret works. Retrieved August 05, 2014, from WRc plc

71 Hamilton, S. (2008). When is a DMA not a DMA? Journal of Indian Water Works Association, 40(3/4), Hunaidi, O. (2000, October). Detecting Leaks in Water-Distribution Pipes. NRC CNRC Construction Technology Update, 40. Hunaidi, O., Chu, W., Wang, A., & Guan, W. (2000). Detecting Leaks in Plastic Pipes. Journal of American Water Works Association, 92(2), Kurtz, D. W. (2006, July 24). Technical Paper - Developments in Free-Swimming Acoustiv Leak Detection Systems For Water Transmission Pipelines. Retrieved August 05, 2014, from 7.pdf Lambert, A. (2001). What do we know about Pressure:Leakage Relationships? IWA Conference Proceedings 'System Approach to Leakage Control and Water Distribution Systems Management'. Brno (Czech Republic): IWA. Morrison, J. (2004, February). Managing leakage by District Metered Area: a practical approach. Water21(6.1), Ofwat. (2003, October 30). Security of supply, leakage and the efficient use of water: report. Retrieved August 05, 2014, from Ofwat. (2008, April). The guaranteed standards scheme (GSS), Applicable to England and Wales from 1 April Retrieved August 05, 2014, from Ofwat. (2009, December 14). PR09/39: Relative efficiency supporting information Retrieved August 05, 2014, from Pearson, D., & Trow, S. W. (2005). Calculating Economic Levels of Leakage. Leakage Conference Proceedings. Nova Scotia. Pregeli, A., Drab, M., & Mozetic, M. (1997). Leak Detection Methods and Defining the Sizes of Leaks. The 4th Internalional Conference of Slovenian Society for Nondestructive Testing "Application of Contemporary Nondestructive Testing in Engineering". Ljubljana (Slovenia). UK Water Authorities Association. (1980). Report 26 Leakage Control & Practice. WRc. (1994). Managing leakage. Report G: Managing Water Pressure. On behalf of the U.K. Water Industry: Swindon (UK), ISBN WRc plc

72 WRc. (2014). Investment Prioritisation in Distribution Systems. Research Report: G Wu, Z. Y. (2008). Innovative Optimization Model for Water Distribution Leakage Detection. Bentley Systems Inc.: Watertown (USA). WRc plc