Leakage and failures of water distribution mains in the city of Al Ain, UAE

Water distribution pipe failures and breakage, and associated water and economic losses, are common. The World Bank (2006) estimates that about 32 billion m³ of potable water is lost annually globally due to water distribution pipe failures and leaks, and about half of these losses happen in developing countries. In the United States, there are about 237,600 water pipe breaks every year (Clark & Thurnau 2011). Water main failures have economic impacts from both the water losses and the effort, time and material requirements of repair or rehabilitation works. There is also high water contamination potential from failures (Renzetti & Dupont 2013). Infrastructure collapse – roads, building foundations – are also associated with such failures. Water mains failure is considered one of the major factors increasing the maintenance and management budgets of water supply systems.

Significant potable water losses from leakage and distribution mains breakages are reported throughout the Middle East. For example, water loss in Syria is about 45% of supply and it is about 50% in Jordan. In Bahrain, about 20 to 23% of water is wasted through leakage, while in Qatar it is about 30% and in Saudi Arabia about 35%. Water losses in the United Arab Emirates (UAE) are not well reported, but amount to about 18 or 20% (personal communication, EAD 2015). The costs of repair and rehabilitation associated with water main failure are huge. The estimated average annual repair and rehabilitation cost in the Sultanate of Oman is about US$ 39 million, whereas in the United States it is approximately US $2.8 billion (Clark & Thurnau 2011).

The hyper arid climate, lack of surface and groundwater resources, and huge water demand triggered the Emirate of Abu Dhabi, UAE to use expensive desalinated water for domestic supplies. The water infrastructure has been constructed mostly since 1990, so the distribution network is relatively new. Historic water leakage data are not available, but measures are taken by the Abu Dhabi Water and Electricity Authority (ADWEA) to limit water losses. Understanding of leaks and failures, and their causes, along with economic studies, helps in determining maintenance and rehabilitation works requirements. In this study some leakage and water supply network failures in Abu Dhabi were investigated, with their causes, the repair, rehabilitation and monitoring processes, and the water losses.

Both service line and fitting failures were identified in the water supply systems. Distribution line failures usually result in the largest proportional water loss. In the study area, about 90% of transmission and distribution pipes are either carbon steel or ductile iron (DI), the remainder being high density polyethylene (HDPE). Service lines to customers are medium or low density polyethylene (MDPE or LDPE) with gunmetal or brass fittings.

The water pipeline failure information was obtained from site visits and by consulting the repair and rehabilitation contractor companies. The failures occurred in different ways for many reasons, including material type, pipe size and type of load applied to the pipe.

Blow off usually occurs in highly corroded pipelines, as shown in Figure 3(b). It usually occurs due to reduction in pipe wall thickness at points where the internal pressure blows the weakened pipe wall. The problem is common in all sizes of water pipeline.

In this type of failure, cracks start at pipe joints and grow towards the pipe's end. This is usually caused by application of excessive torque stresses and high temperature differentials. Thermal expansion and contraction lead to the development of high stress levels, and the formation and propagation of joint cracks (Figure 3(c)).

The causes of longitudinal cracks include heavy loads on the pipe from vehicle movements and inter-thrust forces due to fluctuations in the flowing water mass. These usually develop undesirable negative pressures, or surges, which can create and are associated with water hammer. Longitudinal cracks can arise from pipe wall weaknesses and reductions in pipe wall thickness, because of either corrosion pitting or manufacturing defects. Figure 3(d) shows a longitudinal crack observed in the study area.

Third party damage is common in the region. There are no general reasons for it, but a common cause is construction machinery operated by inexperienced operators. Other factors are also related to construction work, when the correct permission and control systems are not used. The scale of damage by third parties varies and water authorities usually have a standard penalty system for reinstatement, which is reclaimed through the legal municipal procedure. Figure 3(e) shows pipe failure caused by a third party.

The service lines usually comprise MDPE or LDPE pipes, manufactured for use at low operating pressures compared to the distribution lines. Pressure fluctuation in distribution lines due to shutdown or the start of pumping can cause this type of leak, which was very common in the study areas. The numbers of leaks in service connections are usually higher than in water distribution lines, although the quantity of water lost through service lines is normally less than that from mains and distribution lines. The number of leaks in service connection lines usually increases in cold weather. Figure 3(f) shows a service line breakage.

Physical factors often contribute to and accelerate pipeline failures. They can include issues like pipe material, pipe wall thickness, pipe lining and coating, pipe age and the jointing method. Another problem source is poor quality distribution or service line installation, especially when combined with high numbers of joints, fittings, interconnections and relatively short pipe lengths, which all increase the opportunities for line breakage.

Material selection plays a key role in achieving the best water pipeline performance. Usually pipes are selected on the basis of their life length, but some important factors like corrosion and material decay mechanism in harsh environment are usually ignored during their selection process. A balanced approach should be adopted between practicality – e.g., pipe strength – and operating and maintenance costs, when selecting water system pipe materials. For example, corrosion can be minimized by selecting materials that resist corrosion with respect to the particular soil surrounding the pipe and local environmental conditions.

The incorrect installation of pipes and joints can cause line failure at times of high operating pressure, as shown in Figure 4(b). Equally, poor pipe handling during construction and installation can damage them structurally. In general, physical damage to the pipe, pipe wall or coating, will affect pipe strength, potentially leading to failure. In particular, damage to the coating on steel pipes can lead to corrosion and, thus, degradation of pipe wall thickness.

The improper backfilling of pipeline trenches or erosion of the backfill material can cause water line breakage. Figure 4(c) is a picture of poor quality backfilling in the study area. Ignorance of the correct procedure for pipe laying in trenches can affect pipe performance, and unwanted stress on the pipe wall may cause leakage from the pipe and/or joints. Exposure to direct sunlight for long periods can also affect pipe strength, leading to line failure.

Pipeline protection is very important in retaining strength. Poor quality protection can lead to corrosion, affecting the steel pipe wall severely externally and giving rise to failure. The soil in the study area has high sodium content, so, proper internal and external pipe protection is needed for pipes, to help the material resist the corrosive environment and pipe surface inhibit corrosion. Several coating applications and methods are available in Abu Dhabi Emirate for protecting steel pipe. Bituminous paint, and zinc or galvanizing coatings, are applied to pipe surfaces and these methods have been used for many years. Polyethylene sleeves and external bituminous wrapping are also available to protect in aggressive soils. Figure 4(d) shows a pipe with improper protection and backfilled with corrosive materials.

Water distribution lines are normally exposed to the environment, whether buried or running above ground. Many environmental factors in the study area tend to increase pipeline failure. They include temperature, soil salinity, the water table and ground movement, etc.

Metal oxidation causes pipe failure. The oxidation of steel pipe converts the pipe wall into an oxidized – rusty – surface. This type of corrosion often reduces pipe capacity, as shown in Figure 5(b), and is usually a function of water chemistry and corrosive environments.

Water pipes are generally laid underground. The pipes are subject to internal loads from the operating pressure and external loads from the backfill. The external loads are not uniform – e.g., because of vehicle loading and soil weight. Ground movement and settlement are natural phenomena. If ground movement is excessive, and vehicle loads are high above or near the pipeline, the pipes experience high stress levels, leading to pipe or joint breakage. Figure 5(c) shows a pipe failure caused by ground movement arising from heavy traffic.

Breakage/failure monitoring is an essential part of line maintenance, because line breakage has adverse economic, health and environmental effects. As a result, permanent line failure monitoring systems are becoming increasingly common around the world. The Abu Dhabi has the most advanced water line breakage monitoring system in the Gulf Cooperation Council countries and ADWEA started a modern and comprehensive monitoring systems in 2011. The Al Ain Distribution Company (AADC) has also initiated its monitoring program, which consists of noise loggers and an online hydraulic model of the system that detect bursts when they occur. More than 10,000 loggers were installed in Al Ain in 2011 and 2012 (personal communication, AADC 2015). The Al Ain system is based on acoustic equipment that ‘listens’ for the noise originating from line breaks, collates it through a leak-noise logger and transmits it immediately to a desktop or hosted website. This is an advanced monitoring system covering the whole city and it can provide alarms for failures anywhere in the water distribution network through constant monitoring.

The Al Ain region water distribution system comprises more than 90% DI. The remainder consists of HDPE or PVC pipes. Supply service lines comprise only MDPE or LDPE. The water line failure rate is high in old pipes and where the soil is very aggressive. Generally, however, line failure frequency is not high, due to the relatively new and modern regional water infrastructure. Water authority maintenance staff and contractors usually repair water line failures. The numbers of breakages in water service lines are too high compared to those in water mains. The service lines are usually small, between 20 and 65 mm diameter.

There are many reasons for service line breakage, including high residual pressure in the mains, use of MDPE and LDPE pipes, and high ambient temperatures. The commonest repair method for service lines is to replace the broken or damaged parts, and a new length of pipe. There are many possible causes of water line failure. They include aging, poor installation, inadequate corrosion protection, and poor maintenance. Several factors influence pipe failure, too, such as incorrect material selection, joining methods and poor workmanship. Physical, environmental and operational factors can also cause failure – e.g., varying temperature affects pipe materials, as do water velocity fluctuations and water hammer. Beyond this, traffic load, equipment vibration, and soil movement around a pipe can all lead to high stress development and failure.

An advanced water distribution asset management system is necessary to monitor and repair the leakage and breakage of pipes. The AADC has already established an acoustic-equipment based, advanced monitoring system. It is expected that appropriate management of the system will minimize the losses of expensive desalinated water in the region.