Balancing Environmental Flows Needs and Water Supply Reliability

This paper describes an approach to the integration of environmental flows recommendations into water resources planning, and demonstrates its application to a case study in the Jiaojiang Basin, Taizhou, Zhejiang Province, the People's Republic of China. In this approach, environmental flows recommendations were provided to the process as a preferred regime, and also as one or more sub-optimal regimes. A risk assessment approach was used to derive the sub-optimal regimes from the preferred regime. The environmental flows rules were then incorporated into a wider water resources model which allowed testing of any number of development scenarios. The model-predicted daily time series' of river flows were passed through a sophisticated form of spells analysis to evaluate the degree of compliance with a specified environmental flows regime. This degree of compliance was balanced against the predicted security of supply to water users. This integrated approach allowed for a greater appreciation of environmental concerns by planners. It also provided an opportunity to the scientists who undertook the environmental flows assessment to contribute to the process of making rational trade-offs between risks to the environment and gains in security of supply.