| Based on biology,it is the main direction of ecological water demand research to simulate the habitat of rivers and lakes.As the top species in aquatic ecosystem,the adaptability of fish to water environment often reflects the health level of aquatic ecosystem.Fish reproduction includes migration,spawning and hatching,and the whole process needs to meet the basic hydrological conditions.On the other hand,as an important index of water self-purification capacity,dissolved oxygen is also a basic condition for fish survival and reproduction.However,the current construction of water conservancy projects has changed the original hydrodynamic conditions of rivers,resulting in the inability of fish to complete the reproductive process and a large reduction of fish resources.The deterioration of river water quality reduces the content of DO in water,which seriously threatens the normal survival of aquatic organisms.Therefore,it is necessary to study the hydrological conditions that fish reproductive process should meet,determine the physical influence mechanism of dissolved oxygen,and master the response relationship between dissolved oxygen and hydraulic factors.Taking typical fish as the research object,this paper,starting from meeting the appropriate hydrological conditions for fish survival and reproduction,conducted a series of experiments to discuss the appropriate hydrological conditions and thresholds for typical fish migration,and studied the minimum hydrodynamic conditions for typical drifting fish eggs hatching.In addition,DO concentration is taken as a representative indicator of fish survival to explore the correlation between DO concentration in water and flow velocity,water temperature,water depth and other indicators.Through the experimental research,the key parameters and threshold values of fish in the river ecological water demand calculation were obtained,the river ecological flow accounting method with physical mechanism was supported and developed,the ecological scheduling practice of water conservancy projects was supported,and the guidance for the healthy restoration of river ecology was provided.The main research results are as follows:(1)the suitable range of the migration velocity of adult grass carp is 0.4-1.0m/s,while the minimum velocity threshold to stimulate the migration of adult grass carp is 0.2m/s.When the flow velocity exceeds 1.1m/s,the success rate of migration is significantly reduced.(2)the limit threshold of the floating velocity of fish eggs is closely related to the water depth;The minimum threshold of 1m water depth is 0.25m/s,while the threshold of velocity under 0.75 and 0.5m water depth is 0.275m/s.It is preliminarily concluded that the decrease of water depth to some extent requires the increase of the minimum velocity threshold to prevent the death of fish eggs.(3)the minimum dissolved oxygen threshold for normal survival of grass carp,carp and bagrid is 2.26mg/L,2.35mg/ L and 1.87mg/ L respectively,and the asphyxia point is 0.46mg/ L,0.36mg/ L and 0.27mg/ L respectively.For class III water bodies,the flow rate reached 0.05m/s,the DO concentration increased by more than 50% compared with the static water body,and the saturation reached about 90%.The higher the water temperature is,the lower the DO concentration will be,but the water temperature does not affect the size of DO saturation;When the flow rate was below 0.05m/s,the influence of flow rate on dissolved oxygen concentration was dominant.When the flow rate exceeded 0.05m/s,the influence of water temperature dominated. |
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