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 impacts and detection of attacks on various parts can be assessed. For example, looped parts (blocks) of the network are at a higher risk than branched subsystems (trees) since toxic matter can be distributed using alternate paths that depend on the particular water demand loading case whereas in a branched network only the system downstream the intrusion point is affected. The results of the risk analysis will be used for the creation of risk maps, efficient placement of sensors and the development of emergency plans. The specific differences of urban (mainly looped) and regional (mainly branched) supply networks will be demonstrated. The observation of water distribution systems with water quality sensors has been studied by researchers in detail over recent years. The application of the decomposition of the network graph to the sensor allocation problem will be demonstrated using the example network 2 of the Battle of the Water Sensor Networks (BWSN). The network is subdivided into tree, bridge and looped block components. It will turn out that tree structures should be excluded from application of sensor allocation algorithms using mathematical optimization since they are mostly responsible for non-detections. Decrease in calculation time can be further reached if separated blocks are identified in a preliminary analysis and the information is used for the solving the allocation problem. The crucial point of all sensor networks is that a full coverage of the system won’t be reachable and there will be a more or less 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.
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