A large amount of water is lost from the Al Ain water distribution system due to pipeline breakages that may have links to socio-economic and environmental impacts. The numbers of line failures in the region are too high. This study is an overview of the types and failure factors affecting water lines. Methods of repair and rehabilitation are described. Three case study locations were investigated. The incidence of water line breakages is relatively higher in the summer. Pipelines in the study region are comparatively new. The pipeline failures identified could be reduced by adopting modern detection techniques. Water line breakage control could improve water quality, reduce the maintenance budget and help the environment.

## INTRODUCTION

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.

## STUDY AREA AND METHODS

Water distribution and service pipes in the city of Al Ain, UAE, were considered in this study. Distribution and service pipe information, and records of pipe failures, and their repair and rehabilitation, were collected from the Abu Dhabi Distribution Company. The leakage and failure information were collected through site visits and consultation with different contracting companies involved in repair and rehabilitation works. The investigation was conducted from February to April 2015. Three suburban areas were selected to obtain water line failure rate data – see Figure 1. The areas receive 24-hour water supply to about 1,500 water service connections – 460 in area 1, −430 in area 2, and 510 in area 3.
Figure 1

Areal views of the study areas in Al Ain (area 1, top left, area 2, bottom, and area 3, top right) (source: Google Earth).

Figure 1

Areal views of the study areas in Al Ain (area 1, top left, area 2, bottom, and area 3, top right) (source: Google Earth).

## RESULTS

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.

### Service line failure

The water service line failure data collected covered a one-year period. The service line failure or breakage rates were about 43%, 30% and 16% respectively in areas 1, 2 and 3. The monthly failure distribution rates for the three areas are shown in Figure 2, where the seasonal influence on failures is very clear for areas 1 and 3. In these areas, the failure rate was higher in the harsh summer season (June to August), but that in area 2 is different, with a lower failure rate in summer. Overall, the higher failure rate in area 1 is thought to indicate that the service lines are relatively older there. Other possible causes of the relatively higher failure rate include differential geology, and/or different contractors installing the pipe work, and/or heavier traffic on the local roads where they run above the service lines, etc.
Figure 2

Numbers of service line failures, by month, in the three case study areas.

Figure 2

Numbers of service line failures, by month, in the three case study areas.

### Types of failure

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.

#### Circular breakage in small diameter pipes

Circular breakage occurs in pipes as a result of shear or over-bending, caused by external loads or forces – e.g., surcharge of heavy materials or rocks, heavy vehicle movement over the pipeline, etc. This type of failure is common in small diameter pipes and the cracks propagate around the pipe circumference, as shown in Figure 3(a). Pipes can also be fractured by soil shear, the fracture occurring perpendicular to the section.
Figure 3

(a–f) Water main failure types in the study area.

Figure 3

(a–f) Water main failure types in the study area.

#### Blow off

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.

#### Joint failure

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)).

#### Longitudinal cracks

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.

#### Pipe breakage by third parties

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.

#### Service line breakage

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.

### Causes of failure

#### Physical factors

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

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.

#### Pipe joints

Water pipes can break anywhere along their length, but, most of the time, they fail at the joints due to inadequate joint assembly and incorrect connection between joint components. This type of failure is common in Al Ain, often because the joints are dislodged. Such failure and the water loss arising can be large. Poor quality pipe installation also causes failures, as shown in Figure 4(a), where a joint has separated from the pipe bell because the pipe split from the fitting. The thrust in the pipe caused the rubber gasket and pipe end that it enclosed to come out of the joint seat.
Figure 4

(a–d) Causes of water pipe failure.

Figure 4

(a–d) Causes of water pipe failure.

#### Pipeline construction and alignment

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.

#### Trench backfilling

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.

#### Pipe coating

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.

### Environmental causes of pipe failure

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.

#### Corrosion

About 90% of water distribution pipelines in Al Ain are made of DI. The majority of such pipelines fail due to corrosion arising from exposure of the pipe surface to aggressive soils or other corrosive environments. The main factor leading to corrosion is the soil salinity in the Emirate. Figure 5(a) shows DI pipe corrosion in Al Ain. It is one of the most severe problems in water pipes. If they are not coated and protected from aggressive soil conditions, the pipe walls become thinner as the metal dissolves, leading to failure.
Figure 5

(a–c) Environmental causes of water pipeline failure.

Figure 5

(a–c) Environmental causes of water pipeline failure.

#### Oxidation

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.

#### Ground movement

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.

### Monitoring of pipe failure

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.

## CONCLUDING REMARKS

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.

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