Incorporating Eco-environmental Water Requirements in Integrated Evaluation of Water Quality and Quantity—A Study for the Yellow River

River water has dual functions; it can be withdrawn for agricultural, industrial, and domestic uses and provides eco-environmental water (EEW) for riverine systems. A concept of intensity of ecological function of river water (IEFRW) has been put forward, and an integrated water quantity and quality evaluation method in combination with eco-environmental water requirements has been developed for a river. Based on the monthly data of water quality and quantity as well as the withdrawals during 1997 to 1999, an integrated evaluation of water resources has been conducted for the Yellow River. The results indicated that actual IEFRW can directly reflect the health state of riverine ecosystems. The actual increments of water resources availabilities caused by providing EEW for the riverine systems were lower than the eco-environmental water requirements of the riverine ecosystem, leading to the intermittent interruption of river flow and other eco-environmental problems of the Yellow River.