Study On Ecological And Environmental Flow For The Fish Reserve In The Upper Reaches Of The Yangtze River

The study on the ecological and environmental flow plays a guiding role in the ecological operation for damming rivers, and is the important basis of rivers’ ecological protection and restoration practice for natural water regime. Recentely the National Nature Reserve of Rare and Endemic Fishes in the Upp er Yangtze River is under threat from the upstream cascade reservoirs. Carrying out the research on ecological and environmental flow for the reverve can not only improve the research theory and method about the ecological and environmental flow of Chinese large rivers, but also provide decision support for the developing water power resources of drainage basin. Based on the analysis results of fish in the reserve during the key reproduction period and in the hydrologic process of different reaches, the pap er analyzes the comprehensive ecological and environmental flow on the both aspects of fish resourcesprotection and rivers habitat preservation, and formulates the controllable range and process of release of water from the Xiluodu-Xiangjiaba cascade reservoirsupstream of the reserve from three aspects: the ecological base flow of different reaches, the water demand of the fishes with different laying eggs features during the key reproduction period, andthe controllable maximum flow of dissolved oxygen supersaturation which is an important water environmental factor. The research conclusions are as follows:Based on the related data of fish’s biological characteristics in the reserve, the paper summarizes that the key reproduction period of the fish in the r eserve is from March to August. According to the changing flow regime of different main stream and tributaries in the reserve and combining the key reproduction period of the fishes, the paper improves the hydrologic method based on the theory of river’s longitudinal and transverse connection, and calculates the annual runoff of the ecological basic flow of the upstream of main stream, tributary-Minjiang River and the downstream of main stream, which respectively are 843.7×108m3,523.1×108m3,1605.3×108m3, and respectively accounts for 58.6%, 61.8%, 60.2% of the long-term mean annual runoff. On this basis, the paper confirms the controllable minimum release process of water downstream of cascade reservoirs in the reserve within the year. The annual runoff of this process is 890.0×108m3,which accounts for 61.8% of the long-term mean annual runoff.From the perspective of two kinds of fishes which spawning pelagic eggs or adhesive egg, the paper identifies the main factors which affecting the fish reproduction respectively.The key controlled factors for the four major Chinese carps(Hypophthalmichthys nobili, Mylopharyngodon piceus, Ctenopharyngodon idellus and Hypophthalmichthys molitrix) which are the typical fishes that spawn pelagic eggs are selects. They are the condition of water temperature, the initial flow and average daily rate of flow increase. Through comparing the conditions between spawning site and non-spawning site, it can be found that the typical fishes laying adhesive egg(Acipenser dabryanus, Psephuyrus gladius and Myxocyprinus asiaticus) have evident preference on bothhydrologic and hydrodynamic condition. According to the response of the fishes’ reproduction to the hydrologic process, the ecological and environmental flow process of the spawning site with different fishes in the reserve and the proper release process of the upstream cascade reservoir s are determined.In order to avoid the death of fishes in the reserve caused by the dissolved oxygen supersaturationresulting fron the release of water downstreamof the cascade reservoirs, based on the measured data of the dissolved oxygen concentration after operating the Xiluodu-Xiangjiaba cascade reservoirs of the upstream of main stream in the reserve, the paper establishes the relationship of the dissolved oxygen saturation below dam of Xiangjiaba, water temperature and the ratio of the discharge of hydropower station of Xiangjiaba reservoir accounting for the total release of water, and confirms the process of controlling the maximum threshold of total release of water downstream of cascade reservoirs from June to November.