Risk-based water quality decision-making under small data using Bayesian network

ZHANG Qing-qing(张庆庆), XU Yue-ping(许月萍), TIAN Ye(田烨) , ZHANG Xu-jie(张徐杰)

(Institute of Hydrology and Water Resources, Civil Engineering, Zhejiang University, Hangzhou 310058, China)

Abstract:A knowledge-based network for Section Yidong Bridge, Dongyang River, one tributary of Qiantang River, Zhejiang Province, China, is established in order to model water quality in areas under small data. Then, based on normal transformation of variables with routine monitoring data and normal assumption of variables without routine monitoring data, a conditional linear Gaussian Bayesian network is constructed. A “two-constraint selection” procedure is proposed to estimate potential parameter values under small data. Among all potential parameter values, the ones that are most probable are selected as the “representatives”. Finally, the risks of pollutant concentration exceeding national water quality standards are calculated and pollution reduction decisions for decision-making reference are proposed. The final results show that conditional linear Gaussian Bayesian network and “two-constraint selection” procedure are very useful in evaluating risks when there is limited data and can help managers to make sound decisions under small data.

Key words:water quality risk; pollution reduction decisions; Bayesian network; conditional linear Gaussian Model; small data