Water Distribution System Leakage Control by DMA Management: A Case Study ABSTRACT

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1 Water Distribution System Leakage Control by DMA Management: A Case Study Yukun Hou Institute of Water Affairs Research, North China University of Water Resource and Electric Power, Zhengzhou , PR China ABSTRACT Water loss control in the distribution system, is not only to the benefit of the water utility performance improvement, but also to the benefit of the water resources saving. DMA(District Metered Areas) management, which is put forward by IWA, is as a tool for reducing the real loss. However, how to build a DMA in practical terms and how to pinpoint the suspected leakage area precisely and quickly, are the common issues which every water utility is faced with. According to the case study in Xiangtan city, China, this paper demonstrates the process of DMA management, from DMA design, zero pressure test, step test, the night minimum flow ( MNF) data analysis, to the valve checking,pinpoint the leakage, detection and repair works, summarizing the application of DMA overall. Keywords: Leakage control, DMA management, cast study 1 Background Not only has the water distribution system leakage wastes precious resources, but also impaired the service quality. Prompt awareness and effective control of leakage could enhance the supply security. A scientific and rational leakage management strategy has been proved efficient at timely assessment and warning of leakage and NRW reduction. The concept of DMA, originating in early 1980s when Malcolm Farley[1]et alproposed dividing an open system into smaller and more manageable metered areas or leak detection areas called district meter areas (DMAs), is an internationally accepted and well-established technique to control physical losses and determine where leaks occur. Later, John Morrison[2]et al suggested that the minimum night flow (MNF) should comprise the legitimate night flow (LNF)of household and nonhousehold and abnormal night flow on account of background losses and bursts, i.e. the physical losses. The Bursts and Background Estimates (BABE) concepts were also developed. Zhiping Hao[3]et al conducted on-site measurement and analysis of the night flow data to characterize the real losses, specifically by installing highly accurate flow meters, analyzing highly frequently measured night flow data from 2 to 4 am based on the confidence level of 95.5% and confidence interval of (μ-2δ, μ+2δ) and directly approximating the volume of night-time physical losses in DMAs. Nevertheless, actual cases concerning the DMA management process, physical losses estimation, the night flow and NRW relationship have been few documented. The paper attempts to summarize these issues from a practical perspective.

2 2 Methods With commercial losses ignored, MNF comprises LNF and leakage including bursts and background losses. Real losses are the total volume of individual leaks calculated from the leak flow rate and duration. BABE can be conducted on the basis of data like length, average DMA pressure, service connection number, length of private connections from property boundary to customer meter, etc. Bursts consist of reported bursts as well as unreported bursts and the volume is estimated in Table 1. Location of Burst Table 1 Flow Rate for Reported and Unreported Bursts[1] Flow Rate for Reported Bursts[L/h/m pressure] Flow Rate for Unreported Bursts [L/h/m pressure] Mains Service connection Source: IWA water loss task force. Background losses are individual events (i.e. small leaks and weeping joints) that flow at rates too low for detection by routine leak detection survey[1]. They can be estimated. Subtracting LNF from MNF gives summation of background losses and bursts. Then, deducting estimates for background losses and ordinary bursts gives excess bursts which should be given high priority in the leakage control strategy. In addition, commercial losses equal NRW volume minus physical losses. Scientific analyses of proportion of physical losses and commercial losses are conducive to establishing the DMA leakage control strategy with much of an aim. 2.1 Results and Discussion DMA Survey (1) A schematic of the pipe network

3 Fig. 1: Location map and pipe schematic of Nanpanling DMA (2) Primary distribution system data Nanpanling(Xiangtan city, China) DMA has one inflow equipped with a DN200 pipe electromagnetic flow meter logging the system input volume, one booster pump station serving four s distributing water respectively towards the east, south, west and north, system input volume of 158,369m3and total consumption of 72,741m3 from 20 January to 1 April Table 2: Primary distribution system data DMA Survey Data Note Name Nanpanling Location Seen in Figure 1 Statistics availability (Yes/no) Yes DWG Area Hectare Pipe length 8,936 Km, in total Main length 6,598 Km, DN100 Service connection number 850 Meter number 3,401 Average pressure 0.27 MPa Total consumption 230,000 M3, in 2015 Non-household consumption influencing night flow Recorded bursts or repairs --- Response time to bursts --- Hour Boundary valves DMA isolation Diameter and type of the bulk meter into the DMA 0 Closed Absolutely isolated DN200 Pipe electromagnetic meter Zero Pressure Test Inspect all valves either on the boundary or in the DMA, repair faulty ones, ensure all valves including the inlet one are closed and check whether the pressure in the DMA drops to zero. If the pressure does not drop to zero, then it is likely that another pipe is allowing water into thearea and therefore needs to be addressed. Nanpanling DMA passes the zero pressure test, seen in Figure 2.

4 3. Fig. 2: Zero pressure test result After investigation, the DMA boundary gets some alteration indicated as dotted lines in Figure Fig. 3: Altered DMA boundary Success in the zero pressure test renders Nanpanling DMA independent and isolated with a definite boundary and no external water source Step Test Step test is to gradually isolate pipe sections and respectively conduct flow tests within each pipe section. When a pipe section with possible leaks is isolated, pressure measured by the logging device declines notably in the graph. The pressure decline is proportionate to leakage. Step test can save time for leak location and help leak detection force focus on pipe sections where leakage is verified. Moreover, it is vital to know the current consumption type within the tested pipe section and the other network areas that are not isolated during step tests usually undertaken at night. The DMA is segmented into four supply zones of eastern, western, southern and northern. Eight critical valves are coded and closed in order during the testing period when flow into DMA is recorded by the bulk meter and observed.

5 Fig. 4: Close a valve during the step test Leakage step tests are undertaken three times in Nanpanling DMA. (1) The first test happens on the early morning of 26 February Eight critical valves are coded as Figure 5 indicates. Fig. 5: Location drawings of eight valves and valves around the inlet pump station Cod e Close eight valves in numerical order and flow varies as Table 3. Table 3: Valve shutoff sequence and flow variation during the first step test Event Tim e Flow rate before shutoff (m3/h) Flow rate after shutoff (m3/h) Flow rate variation (m3/h ) Close Valve 1 on the western Close Valve 2 (i.e. bulk valve on the southern ) Close Valve 3 near ZizhuCNY Close Valve 4 (i.e. bulk valve on the northern ) 1: : : :

6 Close Valve 5 at the gate of a driving school Close Valve 6 (i.e. bulk valve on the eastern ) Close Valve 7 on the DN200 Close Valve 8 (i.e. the bulk outlet valve ) 2: : : : Open Valve 8 3: The first test reveals the following. (a) After Valve 3 near ZizhuYuan residential district is closed, flow rate changes little. While after Valve 4 on the northern shuts off, flow rate drops by 9.6m3/h from 44.81m3/h to 35.21m3/h, implying leak occurrence in the pipe section between Valve 3 and Valve 4. (b) After Valve 1, Valve 2, Valve4, Valve 6 are shut off, the transient flow still measures 31.91m3/h. Hence, it could be inferred that some unknown pipe connects between the out from the pump station and Valve 2, as shown in red by Figure 6, and needs verifying in further tests. Fig. 6: Location of possible unknown pipe (2) The second step test takes place on the afternoon of 17 March Fig. 7: The second step test

7 Close the valves in numerical sequence as indicated in Figure 7. Flow rate varies as described in Table 4. Table 4: Valve shutoff sequence and flow variation during the second step test Code Event Tim e Flow rate before shutoff (m3/h) Flow rate after shutoff (m3/h) Flow rate variation (m3/h) 1 Close Valve 1 on the western 2 Close Valve 2 on the southern 3 Close Valve 3 on the eastern 4 Close Valve 4 on the northern 2: : : : During the second step test, with Valve 2 on the southern closed, flow rate descends by 40m3/h from 65 m3/h to 25m3/h, which proves the inference from the first test wrong. The reason might be incomplete shutoff of the valve on the southern. The second test also finds out that the southern supply zone merely occupying a relatively small portion of the DMA yet has a relatively large portion of the total flow into the DMA, which suggests that possible leak occurrence of large volume needs further investigation. (3) The third step test is undertaken on the afternoon of 25 March In the preliminary valve chamber survey, enormous amount of clear water is found pouring out in a certain drainage well in south DMA. Close Valve 2 and water effusion stops, verifying leak occurrence nearby. Flow rate variation before and after the valve shutoff is displayed in Figure 8. Fig.8: Flow graph during the third step test After Valve 2 is closed, transient flow rate decreases by 24.62m3/h from m3/h to 78.76m3/h. The leak is eventually located as Figure 9 exhibits.

8 Fig. 9: Leak location and nearby drainage well streaming with clear water It is shown that after leak repair, MNF of m3/h at 1 am on March 29 drops to m3/h at 3 am on March 30 by a margin of 23.7m3/h that is equivalent to the flow rate variation before and after shutting off Valve 2. Leakage is remarkably reduced. It can be concluded that no leaks on the southern pipe s. 2.2 Assessment and Economic Efficiency Analyses Calculating Water Losses in DMA (1) NRW For 72 days from 20 January to 1 April 2016, NRW volume totals 85,628 m3, accounting for 54.1% of the system input volume. The NRW rate is 54.1%. (2)Physical losses Transient flow from 24 February to 9 March 2016 is measured to analyze MNF components including burst losses, LNF and background losses, as Figure 10 exhibits. Fig.10: MNF component analysis from 24 February to 9 March 2016 The overall flow variation trend exhibits poor data reproducibility. The minimum volume of burst losses on February 26 is probably attributable to pressure decrease, while the maximum on March 8 might result from leaks. With two extreme valves excluded, the smallest burst loss

9 measures m3/d on March 2 that NFL is m3/d, bases on which physical losses over the 72-day period are calculated to be m3occupying 63.92% of the NRW volume. (3) Commercial losses Commercial loss volume sums up to 30,897.92m3, tacking up 36.08% of the NRW volume during the 72-day period. (4) MNF component variation before and after leak repair MNF component variation analysis is performed based on transient flow measured for seven days around March 29 when the leak gets repaired, as Figure 11 shows. Fig. 11: MNF component variation before and after leak repair Burst losses are reduced by m3/d (i.e m3/h) Analyses and Assessment (1) Estimating NRW volume In accordance with NRW of 85,628 m3at a rate of 54.1% with physical losses occupying 63.92% and commercial losses occupying 36.08%during the 72-day period, annual NRW volume reaches 434,086.39m3including physical looses of 27,7451.1m3 and commercial losses of 156,635.29m3. Distinct leakage occurrences make physical losses reduction a high priority. In south DMA, leak is located flowing water at a rate of 23m3/h measured during the step test. In the north, there still res room for physical losses reduction by means of further survey. (2) Achieved NRW reduction and economic efficiency assessment Over 28 days from April 1 to April after s repair and rehabilitation, the system input volume amounts to 47,306m3, water consumption totals 33,256m3, NRW slumps to 14,050m3at a rate of 29.7%. Thus, annual NRW volume can be reduced to 183,151.79m3. NRW volume declines by m3/d including m3/d, i.e m3/a for physical losses and m3/d, i.e. 51,776m3/a for commercial losses. Annually, physical losses reduction could save 159, CNY, with water production cost assumed at 0.8 CNY/m3. 3 Conclusions Physical losses reduction in the case of Nanpanling DMA(Xiangtan city,china) is implemented scrupulously in conformity with the DMA management process developed by the IWA. It can be concluded from the case study that zero pressure test is an essential prerequisite for DMA management and can define the boundary. Step tests conduce to improving the leak detection

10 efficiency. Location of one mere leak flowing at a rate of 23 m3/h with no detection survey undertaken reduces DMA volume by nearly 24% and thus could retrieve over 10 thousand yuan(cny) in terms of production cost. MNF component analyses enable accurate and authentic acquaintance with the leakage situation, and quantitative distinction between physical and commercial losses that offers specific technical guidance for further reduction activities. Each process of the leakage control strategy should be analyzed in terms of effectiveness and economic efficiency. Advises are made to carry out thorough investigation and leak detection in north of the DMA, locate all other leaks and perform timely repair. Eventually, it is anticipated to establish a leakage warning and monitoring mechanism in the DMA. In the case, commercial loss decrease with no control measures taken is initially regarded attributable to the boundary change, failed synchronization between meter reading and customer billing, meter inaccuracies, data handling errors, etc. Further analysis needs to be made on the issue. Finally, the paper also emphasizes that LNF(Legitimate Night Flow) estimation (or testing), separation the real loss and apparent loss from MNF are the keys for DMA application successfully. Water loss early warning mechanism is the ultimate goal water loss reduction. 4 References [1] Yukun Hou, Yingying Wang, Yuexia Xu and Chunhui Zhao, 2011.The Manager s Non-Revenue Water Handbook -- A guide to understanding Water Losses. Tongji University Press.. [2] John Morrison,Stephen Tooms and Dewi Rogers,2007.District Metered Areas Guidance Notes. [3] Zhiping Hao and Yukun Hou, Analysis Method and Case Study for the Minimum Night Flow in the District Metered Area of the Water Distribution System. South-to-North Water Transfers and Water Science & Technology. 11 (4). [4] Julian Thornton,2002.Water Loss Control Manual. The McGraw-Hill Companies Inc.