Comprehensive risk assessment of river basins using Fault Tree Analysis

Due to the increasing need of human societies and diverse biological species for adequate and reliable water resources, river basins play an important role in reliable water supply. A comprehensive index for assessing the performance of river basins can prevent unintentional events by accurately identifying vulnerabilities and threats. In the present study, comprehensive risk assessment of a river basin is carried out using Fault Tree Analysis (FTA) to determine the undesirable events. The FTA method, based on a logical diagram, reveals the relationships of basic events and the top event by logical gates and is capable of providing quantitative and qualitative analysis of the river basin. It can show the failure paths and calculates the degree of basins' reliability. In this study, undesirable ecological status, low quality and scarcity of water resources, and economic and social anomalies were studied as unfavorable events of the Urmia Lake Basin. To do this, an FTA model is presented in which Water Resources Failure Risk of Urmia Lake Basin is the top event. The probability of occurrence of basic events and top event was calculated based on the information available for the area and using experts' opinions. The results of the study show that quality failure have the most impact on top event occurrence. The effective basic events in the occurrence of the top event are Inappropriate governance, low awareness level, Entrance of industrial and domestic wastewater to groundwater, Entrance of agricultural wastewater to groundwater, and Meteorological drought, respectively. The index derived from the FTA can provide water resources managers and decision makers with comprehensive measure to improve and compare the status of internal and external effective factors in river basins.