Moreover, the development of infrastructure networks was not always pursued in a continuous way, and the useful life of individual pipelines varies considerably. In correspondence with the different “laying periods”, every infrastructure network features its own characteristics, which inevitably leads to overlaps in rehabilitation needs. Therefore, the quality of supply, too, differs regionally. As a comparison of water loss rates shows, the need for renewal is particularly obvious in CEE countries. By signing the EU Water Framework Directive/WFD, the member countries of the European Union agreed to take account of the principle of recovery of the costs of water services (Article 9, WFD). Appropriate measures have to be implemented until 2010. In accordance with the polluter pays principle, these measures have to include environmental and resource costs. The efficient use of existing drinking water resources is explicitly mentioned as a prerequisite for achieving these objectives.
The list of the WFD requirements also includes all measures for the rehabilitation of ailing sewer networks, which discharge sewage into groundwater, or, due to hydraulic overload, into running waters. In this context, the German Environment Ministry has published estimates on investments in 2000, which will be necessary in the water sector to meet the requirements of the EU environmental legislation in some of the new EU countries.
Efficient maintenance management required
Under these basic conditions, the supply and disposal utilities are required to develop an efficient and sustainable maintenance management for their pipe networks. This shall contribute to the improvement of the decision basis and to a more transparent decision-making. For the future, this means: Stop following the "fire brigade" strategy and start using an anticipatory renewal planning!
Sufficient information on the state of the infrastructure, or rather its assessment, is a prerequisite for anticipatory planning. Last but not least through the efforts of the International Water Association/IWA, performance indicators have become a frequently used instrument to assess the condition of facilities and their efficiency in national and international comparison. The determination of performance indicators again requires efficient data compilation. A comparison of performance indicators discloses the deficits to the company, which have to be analysed and the reasons for which have to be found.
The frequency of failures in pipelines rises in proportion to their age. This process, however, is not the same in all pipelines. The aging process and thus the useful life of a pipe are determined by different internal and external factors. Determining factors include: material, corrosion protection, manufacturing and laying method, external load and soil aggressiveness. It must be noted that the failure rate is often not the only cause for an exchange of pipes.
Calculation of the renewal need
The utilisation period of a pipeline type actually features an expected value, which applies to the individual pipe with a certain statistically measurable spread. The evaluation of failure and renewal statistics allows to group pipe types with homogenous aging features and to mathematically determine their "survival function".
The future renewal need is calculated on the basis of information on the condition of the network and the analysis of the useful time. This forecast calculation serves as a basis for the development of alternative scenarios for the selection of a suitable rehabilitation strategy. Investment costs, current costs, cost savings, the development of the rehabilitation rate, future failure rates, and the development of the net asset value are in this context the most important indicators for the evaluation of the efficiency of a strategy.
Strategies are developed and budgets determined on the level of the pipe network. The distribution of funds among the most cost-efficient rehabilitation projects is supported during the planning phase by a systematic state evaluation and an efficiency analysis. The selection of the pipes to be rehabilitated per year is a multi-criteral procedure, since, in addition to the failure frequency, the location in the network, the coordination with other construction work, and a multitude of other factors have to be considered, too.
Today, the question increasingly arises, whether a selected renewal strategy will be able to be financed in the future at all, or whether it meets the requirements, which service companies will probably have to face. The answer is a clear “Yes”. Thus, failure analyses and aging models allow an anticipatory rehabilitation management, which leads to a cost-avoidance on a long-term basis and thus to secured investment funds.
A rehabilitation strategy is close to the optimum, if external factors, too, which influence corporate policy, are taken into account. Examples in this context are scenarios on demography, consumer behaviour, and the availability of natural and financial resources. Infrastructure development plans establish the frame within which a service enterprise will be able to act.
The DUT Chair of Urban Engineering
The Chair of Urban Engineering at the Dresden University of Technology has been involved in the above complex of topics for more than ten years. In 2003, the research work resulted in the creation of the engineering office INFRA-REHAB. Meanwhile, more than 50 expertises and applications have been compiled throughout Europe and Northern America.
Among them were for example studies on the drinking water and gas supply networks in Vienna and Innsbruck, or in the North Bohemian supply area Teplice, but also for the German Verband kommunaler Unternehmen (VkU) as well as the German Verband des Gas- und Wasserfachs/DVGW.
(Source: aqua press Int. 4/2004, DI Ingo Kropp, Dr. Ing. Rolf Baur)
Contact & Information:
Technical University Dresden
Dr. Inf. Rolf Baur
INFRA-REHAB Ingenieur Consult
DI Ingo Kropp
