RISK AND VULNERABILITY ASSESSMENT ("ROS-ANALYSIS") OF THE BERGEN WATER SUPPLY SYSTEM - A SOURCE TO TAP APPROACH

The paper provides an overview of the application and results of a risk and vulnerability analysis (in Norwegian: ROS-analyse) of Bergen's water supply system covering all elements from source to tap (i.e. catchment, source, treatment plant, and distribution). The analysis gives an overview of the risk-picture for the water supply system. The main conclusion is that the flexible and redundant water system of Bergen, where five independent waterworks feed water into the same system, reduces the consequences from many of the undesired events which might happen. This puts Bergen in a unique situation compared to many other water companies in Norway. However, resulting from the analysis, we have identified new possible risk reducing measures for all elements in the water supply system which will improve the safety of the system to an even higher level. Within the project a new procedure for assessing the strength of the hygienic barriers represented by the water treatment step and the disinfection step has been developed. By using large datasets from the SCADA-system, long time-series of water quality data has been aggregated into easy understandable risk measures represented by duration curves. The risk analysis is organised and carried out within a database system, making it easy to update and improve the analysis at later stages.