Graph decomposition in risk analysis and sensor placement for water distribution network security

Abstract

Over the last decade considerable research in water distribution network modeling has focused on the security of water supply against terrorist attacks. In this paper, specific issues of urban and regional distribution systems as to their vulnerability against terrorist attacks with CBRN (chemical, biological, radiological, nuclear) substances, detection methods and emergency plans are investigated. As a first step, a risk analysis is carried out based on topological properties of different parts of the network, classification of building developments and customers. The decomposition of the network graph enables the differentiation of network components (into treed components, blocks and bridges). Following this subdivision, the different impacts and detection characteristics can be assessed. The results of the risk analysis can be used for the creation of risk maps. The specific differences of urban (mainly looped) and regional (mainly branched) supply networks are discussed. The decomposition of the network graph can be further used for reducing the problem size of the sensor allocation problem by pre-selection of events with little impact and aggregation of the network model. The main ideas are demonstrated by use of the example network 2 of the Battle of the Water Sensor Networks (BWSN). The crucial point of all sensor networks is that a full coverage of the system won't be reachable and there will be a considerably long time to detection. An alarm is not actually generated until the toxic substance has passed a sensor. In this study another approach is proposed. The case of intrusion of the toxic substance by pumping against the pressure of the network will be considered. This event is considered as a "positive" leak. Leak detection methods that are normally used for the observation of pipelines are applied to the investigation of the water hammer event caused by the intrusion. Finally, conditions for the practical applicability of the method will be put up for discussion.