مدل‌سازی هیدرولیکی و ارزیابی آب بدون درآمد در شبکه آب طبس گلشن

Background and objectives: Non-revenue water (NRW), comprising real losses (physical leakages from pipes and fittings) and apparent losses (unrecorded consumption due to meter errors, unauthorized connections, or data recording inaccuracies), represents a major challenge for urban water distribution networks in arid and semi-arid regions like Iran. This phenomenon reduces the economic and operational efficiency of water supply systems and increases operational costs. In Tabas, a city in South Khorasan Province characterized by a hot, dry climate and limited water resources, effective water management is critical. Zone 1 of the Tabas Golshan water distribution network was selected for study due to its size and significance. This research aims to develop a hydraulic model of the Zone 1 network, perform precise calibration using field data, accurately estimate NRW, and differentiate between real and apparent losses. The study's innovation lies in integrating water balance methods, minimum night flow analysis, and the FAVAD approach to precisely estimate leakages and propose practical solutions for loss reduction in arid regions. This research aligns with the objectives of the Journal of Water and Soil Conservation Research by contributing to sustainable water resource management, reducing water wastage, and enhancing the efficiency of water distribution networks in water-scarce environments. Additionally, it provides a scientific approach to water management in regions with aging infrastructure or limited monitoring, serving as a model for similar areas in Iran and globally.
Materials and methods: The study was conducted in Zone 1 of the Tabas Golshan water distribution network, located in South Khorasan Province, Iran, a region facing significant challenges in potable water supply due to its hot, arid climate. A hydraulic model was developed using WaterGEMS software, based on updated AutoCAD and GIS maps containing detailed information on pipes, valves, reservoirs, and network nodes. Consumption data from 2,640 subscribers during the fourth and fifth periods of 2021 (October and November) were collected, including hourly consumption rates, usage types (residential, commercial, green spaces, etc.), and geographic coordinates. These data were used to determine consumption patterns and allocate demand to model nodes. Field data included tank outflow rates from a telemetry system, hourly pressure measurements from two automatic loggers in the Amiralmomenin and Maskan-e-Mehr areas, flowmeter data from a transmission line, and manual pressure and flow measurements at various network points. Model calibration was performed at two levels: macro (matching tank outflow) and micro (matching node pressures). Macro-calibration involved comparing tank outflow with telemetry data, while micro-calibration aligned simulated pressures with logger measurements. Minimum night flow analysis (1–5 a.m.) was employed to estimate leakage rates and distinguish real from apparent losses. Emitter coefficients and pressure exponents (assumed as 1.5 for longitudinal cracks) were calculated using the FAVAD method, as outlined in Publication 556 of the Iran Water and Wastewater Company. Pipe roughness coefficients were determined based on material (PE, GRP, asbestos) and pipe age, and adjusted during calibration. A field experiment on December 6–7, 2021, increased the pressure-regulating valve setting from 1.1 to 1.9 bar and then reduced it to 1.0 bar to assess the pressure-flow relationship, aiding in the analysis of pressure impacts on leakage and consumption.
Results: The modeling results indicated that NRW in Zone 1 of Tabas accounts for approximately 37.5% of the input water, with over 90% attributed to physical leakages (real losses) and the remainder to apparent losses (meter errors and unregistered consumption). The calibrated hydraulic model showed good agreement with field data from October and November 2021. The pressure difference between the model and logger data from 1 p.m. to 7 p.m. was approximately 1 meter, likely due to assumptions of uniform consumption patterns, homogeneous leakage distribution, or calibration errors in pipe roughness coefficients. Minimum night flow analysis revealed that leakage flow during low-consumption hours ranged from 0.016 to 0.022 m³/s (16–22 L/s). Emitter coefficients for the Amiralmomenin and Maskan-e-Mehr areas were calculated as 0.002 and 0.000653, respectively, indicating variations in leakage intensity across these regions. The field experiment increasing pressure from 1.1 to 1.9 bar showed that flow rates increased by up to 0.0012 m³/s (1.2 L/s) during peak consumption hours, while the increase was approximately 0.0002 m³/s (0.2 L/s) during low-consumption hours. The pressure exponent ranged from 1.32 to 1.5, consistent with the predominant types of pipe failures (longitudinal cracks and joint separations). Telemetry data indicated tank outflow rates of 0.062 m³/s (62 L/s) in July and 0.042 m³/s (42 L/s) in November, influenced by climatic conditions (summer heat and water cooler usage) and pressure-regulating valve settings. Subscriber consumption analysis showed average consumption rates of 0.0168 m³/s (16.8 L/s) in the fourth period and 0.01307 m³/s (13.07 L/s) in the fifth period, with the reduction likely due to seasonal variations. Residential usage accounted for over 90% of total consumption. Additionally, an annual consumption increase of 0.00115 m³/s (1.15 L/s) and an additional per-subscriber consumption of 24.9 liters per year highlighted growing water demand in the region.
Conclusion: This study, utilizing hydraulic modeling in WaterGEMS and precise calibration with field data, provided an effective tool for analyzing NRW in the Zone 1 Tabas water distribution network. The 37.5% NRW rate, predominantly from physical leakages (over 90%), underscores the urgent need for active pressure management and leakage detection strategies. The study’s innovation lies in employing the FAVAD method, minimum night flow analysis, and region-specific emitter coefficients, which are applicable to similar arid regions. Precise adjustment of pressure-regulating valves can significantly reduce leakage, particularly during peak consumption hours when pressure increases have a greater impact. Limitations, such as outdated data, limited measurement equipment (only two pressure loggers and one flowmeter), and simplifying assumptions (e.g., uniform consumption patterns), affected result accuracy. Recommendations include collecting pressure and flow data across seasons using more precise tools (e.g., smart sensors), which can lead to a 15-25% reduction in real losses through continuous monitoring and early leak detection. Continuously monitoring pressure-regulating valves, which, based on similar studies, can reduce leakage by 20-30%. Applying machine learning algorithms for more accurate consumption and leakage estimation, with potential for 20% NRW reduction. Developing District Metered Areas (DMAs) and installing continuous monitoring equipment could further reduce losses by 15-20%. These findings are valuable for improving the efficiency of water distribution networks in arid regions and align with the Journal of Water and Soil Conservation Research goals of promoting water conservation and sustainable management. The results can guide long-term planning and implementation of loss reduction measures in other arid cities in Iran and similar regions worldwide.