Leakage control in water supply systems and rehabilitation of wastewater infrastructure

A. Pretner¹

1 DFS Engineering, n. 5 Dongzhimen South Avenue, Dongcheng District, Beijing, P. R. of China - augusto.pretner@sgi-spa.it

Keywords: Leakage; Simulation; Models; Monitoring; Wastewater

Abstract Nowadays water and wastewater utilities strive to optimise their operational performance whilst ensuring quality of services to clients and due respect to the environment. Aged infrastructure, deferred maintenance and investment constraints make asset management an arduous task, aggravated by the fact that most assets are hidden underground. DFS has developed in-depth expertise in the use of advanced monitoring, modelling and information technologies to support operators and decision makers in their strategic planning and day to day operation of water and sanitation infrastructure. The present paper gives an overview of the methodology and technologies that DFS has employed in numerous projects around the world to reduce leakage in water distribution systems and rehabilitate wastewater infrastructure.

Leakage management and control in water supply systems

Most water networks in our cities were built in the first half of last century to serve a smaller population. With the growth of cities, infrastructure developed in a piecemeal fashion and asset maintenance was neglected. The present result is high levels of water losses with negative operational, economic and environmental consequences. Large volumes of water need to be abstracted, treated and transported and much of the precious resource is lost before reaching customers.

The values of Non Revenue Water (NRW) can vary significantly around the world. In well managed systems NRW can range between 5 to 20% of the water produced, but in poorly maintained systems it can be above 50% of the water put into supply. The Volume of NRW is split into real (or physical) losses which are the leaks along the network and apparent (or administrative) losses which correspond to the volume of water that is actually supplied to customers but is not billed. This last category includes under-readings of inaccurate meters, public uses of water that are not billed and illegal connections.

Since the 1980’s the European water industry has increasingly focused on solving the problem of leakage. Prior to that date, water leaks were managed in a passive way, just repairing the breaks as they appeared on the surface. However it has been demonstrated that less than 10% of the water losses occur through reported leaks. The remaining 90% remains below the ground. For this reason new technologies and methodologies have been developed to tackle leakage with a proactive approach aimed at locating hidden leaks.

DFS has pioneered the application of advanced leakage control techniques in Italy and since the early 90s has been actively involved in the adaptation of these practices around the world. Other than in Italy, DFS has carried out projects in Albania, Croatia, Cyprus, Egypt, Greece, Jordan, Norway, Republic of Mauritius, Cina Algeria Iraq Senegal and Romania

Our methodology for leakage control is based on sequential steps aimed at gaining insight into the network’s operation and putting in place the most cost-effective actions to reduce and sustain the economic level of leakage, which is the value at which the cost of leakage control measures exceeds the marginal value of water recovered.

As initial step, DFS collects, organises and analyses the existing data in order to diagnose the current status of the network in operational and leakage terms. Topographical surveys, geographic information systems (GIS) and water balances are activities conducted under this initial diagnostic phase. Also a mathematical model that simulates the network’s operation can be built and calibrated in order to facilitate the subdivision of the network into District Metered Areas (DMAs).

The set up of DMAs is the next step. It entails the subdivision of the network into smaller areas by closing the valves in the mains that link neighbouring areas. Each DMA generally has one or two feeding mains where flow monitors are mounted. The flow and pressure within the DMAs are measured at strategic locations in order to detect sudden variations that can be associated to an increase of the leakage levels. The analysis of the measured flows entering each DMA serves to calculate the level of leakage in each DMA. District metering has demonstrated to be crucial in identifying the areas where leakage is most critical, and where interventions are most urgent and cost-effective. The district metering methodology is the basis of Active Leakage Control, the proactive approach to manage leakage.

Once critical DMAs have been established, the next action consists in the detection and pinpointing of leakages using correlators and noise loggers. This equipment is based on the analysis of the noise wave generated by a leak on a pressurised pipe. Based on the time delay and the pipe material, this instrument pinpoints the accurate location of the leak.

The positioning of leaks is reported to the utility’s maintenance team that will repair the hidden leaks. The measurement of recovered water will be made next in order to demonstrate the benefits achieved with the leakage control campaign. However the sustainability of the attained leakage levels in the long term will require that the utility requires the necessary resources to the leakage control activity. Experience has shown the effectiveness of setting up a long term strategy for leakage control involving a dedicated team of engineers and field technicians (the Leakage Control Unit) responsible for maintaining the Active Leakage Control in place. The development or extension of the SCADA (Supervisory Control and Data Acquisition) is also an effective way to increase the control of leakage in the network.

DFS has been the Coordinator of a project co-funded by the European Commission called TILDE which is focused on the development of software tools to facilitate the adoption of best available technologies (BAT) for leakage control. TILDE products allow operators to benchmark the performance of their networks, and guide them in the process to reduce and manage losses. Additionally the project has produced a data management system (TILDE DMS) that elaborates all leakage related data (e.g. monitored flows, pressures, calculated leakage, etc.) and prioritises leakage control actions.

Rehabilitation of wastewater infrastructure

Sewer systems and wastewater treatment plants play an important role in our lives as they ensure the safe collection, transport and treatment of our domestic and industrial wastewaters and storm waters. Their performance is important to prevent unhygienic conditions, urban flooding and pollution of our receiving waters. Nevertheless their structural and operational condition is on the whole poor or unknown. The same as water supply networks they were built for smaller populations and lacked appropriate maintenance. Today they must cope with increased hydraulic and pollution loads whilst complying with more stringent environmental legislation.

DFS has operated in the wastewater sector for over eighty years, and a good part of it has been dedicated to master plans for the upgrading and rehabilitation of existing wastewater systems. DFS employs cutting-edge technologies for data analysis, hydraulic and water quality monitoring, mathematical modelling of networks and receiving waters, performance analysis, operational categorisation of assets, selection of most appropriate trench-less techniques for pipe rehabilitation and optimisation of asset management to achieve operational savings (e.g. energy) and comply with water quality standards.

Our master plans follow a step-by-step approach that consents to gradually identify the networks’ bottlenecks, define optional solutions to solve current problems and, based on a cost-benefit analysis, prioritise interventions.

A substantial part of our work is spent in developing, calibrating and using mathematical models that help us understand the current functioning of the system and develop solutions to optimise operation. Mathematical models are capable of simulating how the network operates under critical conditions, and for example indicate the parts of the network that are overburdened under critical rainfall conditions, the volumes and quality of spills through combined sewer overflows and whether the treated effluent has an adverse impact on the receiving body. Mathematical models are calibrated using measured data to make sure that the model simulation adjusts to reality. For this purpose rainfall, flow and water quality are monitored at significant points in the system and the measured values are compared with the modelled ones. The model is adjusted to ensure that both simulated and measured data fit within a set tolerance range.

Other information source about the internal condition of sewers is the closed conduit television (CCTV) inspections made by a camera that runs through the sewers to identify deficiencies in the network. The analysis of CCTV inspections consents the identification of targeted rehabilitation techniques that optimise costs and minimise disruption of traffic.

The combination of these technologies along with other tools such as GIS, SCADA and Real Time Control systems, consent the development of advanced decision support systems that can help operators both in their long term planning and the daily operation of networks.

Conclusions

Asset management is a challenge for today’s water operators. The costs for rehabilitation are huge, demand for water and wastewater services increases, and the need for environmental sustainability is imposing strict limitations to preserve water quality and prevent overexploitation.

In such context the application of the advanced technologies described in this paper can be extremely helpful and cost effective. These technologies help to collect, organise and analyse data in order to establish the performance of water and wastewater assets, identify critical areas, and help to define strategies and interventions to improve efficiency cost-effectively.

The reduction of water losses in municipal distribution networks is gaining more and more relevance, particularly in places suffering from water shortage. Active Leakage Control and TILDE technologies offer a great opportunity to operators aiming at increasing their knowledge about water loss management and setting a strategy to deal with water losses following the internationally recognised best practice.

Mathematical models, monitoring technologies and systems such as GIS and SCADA are extremely important tools to enhance the operation of wastewater facilities and prevent pollution of receiving waters. The application of these tools consent water operators to review and update data on the systems, increase the knowledge about the asset operation and advance their technological know-how. These technologies can help in making informed decisions about their capital and operational planning and daily management of their systems.

Asset management and planning must be backed by extensive data analysis, and the support that technologies offer today for monitoring and analysing what is happening in our hidden, underground assets is of crucial importance to facilitate and optimise the work of water and sanitation operators. With their application, DFS is capable to evaluate the maintenance and rehabilitation needs of infrastructure and propose schemes to optimise capital investment and operating costs.