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2.4.05 Water management in megacities – the role of the database

The water authority of the megalopolis Beijing knows all too well that correct decisions cannot be made without reliable information: since the region’s climate causes significant fluctuations in available water levels, accurate data is required to control and monitor the supply and consumption of water. A computer program addressing this need has now been developed as part of a Sino-German joint venture – in the face of highly challenging conditions. The results of the project may also prove extremely useful to other megacities in Asia.

The sustainable management of water resources in semiarid areas is an extremely complex task. As of a specific size (supply area, population) optimum management of multiple resources is required – both from a temporal and geographical perspective – whereby wastewater is also considered a resource in semi-arid areas. For megacities such as Beijing, with its 16 to 17 million inhabitants, this is a particularly challenging task.

Extreme situations

Due to its geographical situation at the northern edge of the North China Plain, Beijing has a semi-arid and intermittent semi-humid climate. Virtually the entire annual rainfall occurs over just two months (including flood events), while the area remains mostly dry for ten months of the year. The city’s water authority is therefore required to manage two very different, yet equally extreme situations.

The most water is required for agricultural purposes in the areas surrounding the metropolis, whereby demand is largely covered by the 40,000 to 50,000 local groundwater wells. Drinking water is currently obtained from surface water (predominantly water reservoirs) as well as from groundwater – both sources are overused. The water carried by the two major rivers in the region (Yongding and Chaobai) has been seasonally or geographically restricted for years. In addition, groundwater levels are dropping by one to metres every year.

To ensure continued water supply in the face of ever growing consumption, plans were made in 2007 to channel water into the Beijing region from the South-North water transfer. The link-up has been delayed, however, and is currently scheduled for 2012/2013. The transfer is to convey an annual water volume of 1.4 billion cubic metres into the metropolis, but suitable reservoirs to store the water are still required.

Example of a dry river bed in the area under examination

Example of a dry river bed in the area under examination
Example of a dry river bed in the area under examination
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These multifaceted tasks can only be addressed with the aid of a computer program tailored to these specific requirements. The creation of such an information system for the Beijing area was the remit of a Sino-German venture, which reached its conclusion in November 2009 with the delivery of the software system to the Beijing Water Authority (BWA). The project, which was supported by the Federal Ministry of Education and Research (BMBF), was overseen by the Fraunhofer Institute for Optronics, System Technology and Image Exploitation (IOSB).

Structure and functions of the information system developed for Beijing

Structure and functions of the information system developed for
Beijing
Structure and functions of the information system developed for Beijing
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Dried out littoral zone of Kunming Lake at the Summer Palace in Beijing

TDried out littoral zone of Kunming Lake at the Summer Palace in Beijing
Dried out littoral zone of Kunming Lake at the Summer Palace in Beijing
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Multilayered program

The resulting “Beijing Water Decision Support System” (DSS) collates data and information of varying quality, quantity and controllability (see figure). The information ranges from easily measurable data (e.g. water abstraction from a specific source) to uncertain estimates (e.g. consumer behaviour, groundwater recharge rate). The system maps all resources onto mathematical models on the basis of balance equations: this allows the BWA to simulate various scenarios to support its decision-making.

As was to be expected, significant problems were encountered with the creation of a comprehensive information base as well as with the derivation of representative model structures with spatial and temporal parameters. Data is generally held by different institutions and authorities, and is therefore fragmented, inaccurate, inconsistent and occasionally even contradictory – something which greatly hinders efforts to implement the required modelling detail. Another exacerbating factor was that many model parameters (or model input quantities) were to be determined as functions of location and time – i.e. in the form of charts – but the available measurement data was severely lacking.

Creation of water balance system

The project partners tackled this problem by creating a coherent, multilayered system for water balances: it can be used, for example, to balance the water levels of different sources, groundwater recharge and untreated water abstraction, water consumption as well as the treatment and disposal of wastewater. The results can be used to identify and correct implausible data and close any gaps. The system also enables automated multi-criteria optimisation, in which simulations of pre-defined parameter variations are used to identify the specific scenario representing the best possible water supply solution under given conditions. Due to the high complexity of this process, the system always checks the consistency, plausibility and completeness of user entries.

The work performed on the Beijing Water Decision Support System System gave rise to new methodical approaches for high-resolution modelling of water resources with meso-level analysis areas of over a thousand square kilometres (and larger), as well as for the determination of parameters on the basis of incomplete, inconsistent or contradictory raw data (as is usually the case with the water supplies of Asian or South American megacities). The success of these approaches was underlined by the high level of concordance between calculated and measured results as part of the verification of data from the period between 1995 and 2000.

Fraunhofer Institute for Optronics, System Technology and Image Exploitation (IOSB)
Prof. Dr. Michael Birkle
Fraunhoferstraße 1
76131 Karlsruhe, Germany
Tel.: +49(0)7 21/60 91-3 80
Fax. 07 21/60 91-5 56
E-mail: mb@iosb.fraunhofer.de
Internet: www.iosb.fraunhofer.de/servlet/is/12481/
Funding reference: 02WA0565, 02WA0849, 02WA1035
Ressource Wasser
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