Research On Ecological Flow Of Fish Spawning In Dam-building River

Water resources and hydropower projects play an important role in energy,flood control,agricultural irrigation and waterway transportation,and have a long-term,cumulative and potential impact on River Biological habitats.Spacially,the construction and operation of diversion hydropower stations have greatly changed the hydrological situation of the water-reducing reach formed between the sluice site and the powerhouse,and produced a series of concomitant effects on the river habitat.As one of the most important habitats,spawning grounds of fish are affected by the changes of hydrological conditions and the decrease of river connectivity,showing the phenomenon of migration,fragmentation and even disappearance.Therefore,how to scientifically formulate the scheme of ecological discharge to protect fish spawning is a hot topic of current ecological discharge research.However,the objective limitations of the research progress on the reproductive habits of fish species and the lack of systematic understanding of the impact of changes in external environmental factors caused by dam construction on spawning of fish are important reasons for restricting the scientific formulation of ecological discharge schemes.In order to protect the spawning behavior and spawning grounds of fish under the dam,this paper carried out the study of ecological flow process line,put forward the concept of ecological flow process line of fish spawning under the dam.constructed the technical framework of"process line".established the evaluation index system of fish spawning health,and formulated the ecological hydrological index set of fish spawning suitability.The formation technology of spawning ecological discharge process line of fish under dam was studied,and the research results were applied to the ecological restoration of fish spawning in Jinping Dahe Bay.The main contents are as follows:The paper constructed technological framework of the ecological discharge process line for spawning of fish under the dam.Combining with the previous research results,the concept of ecological discharge process line of fish spawning under dam is put forward,the theoretical and technical framework of "process line" is constructed,the research scale and principles are summarized,and the key theories,concepts and technologies are determined.Based on the study of the comprehensive effect of dam construction and reservoir construction on fish spawning grounds,an index system for evaluating the spawning health of fish under dam was established.Taking the spawning behavior and spawning grounds of fish as the research object.the comprehensive effect of dam construction on fish spawning was studied.The direct,indirect and cumulative effects of dam construction on fish spawning were sorted out from five aspects:hydrological situation,hydrodynamic conditions,water environment,river topography and aquatic organisms.Based on the above research results and according to the principle of index selection,an index system for evaluating the spawning health of fish under dam is constructed,which includes four aspects(water environment,river topography,aquatic organisms and fish stocks resources,and water environment includes three factors:hydrological situation,hydrodynamics and water environment).The evaluation criteria and qualitative or qualitative criteria for each parameter are determined.Quantitative evaluation method.The index system can be used to evaluate the main impact of dam construction on fish spawning grounds downstream,and help to clarify the focus and main direction of fish spawning protection.Aiming at the practical problems existing in the discharge of Jinping Dahe Bay,based on the principle of IFIM method,the target protected fishes in Jinping Dahe Bay,i.e.round mouth copper fish and schizophrenic fish,were screened.By simulating the representative hydrological process of fish breeding period,the spawning suitability curve of target fish was studied,and the suitable ecological flow rate(1200 m3/s for Round-mouth Copperfish and 432 m3/s for Split-bellied Fish)for spawning of Round-mouth Copperfish and Split-bellied Fish in Jinping Dahe Bay was obtained by River2D study,which provided support for the follow-up study of ecological flow process line.In view of the contradiction between the research demand of ecological discharge for fish spawning protection in mountain rivers and the difficulty of river topographic investigation,based on R2CROSS method,the related parameters were changed to water level rise rate,flow velocity and relative wet perimeter percentage,and the parameters standard was revised.The method was applied to the study of minimum ecological discharge peak value(298m3/s)of round mouth copper fish in Jinping Dahe LBay during spawning period.The traditional hydrological method Te was used.The results of ecological discharge were validated by nnant method and River2D numerical simulation.The formation technology of fish spawning ecological flow process line and the hydrological index set of fish spawning protection were constructed.Considering the ecological flow demand of different reproductive species of fish and the time and depth of the ecological flow process of gonad development,spawning and larval and juvenile development in spawning behavior of fish,based on the establishment of the hydrological index framework for spawning protection of fish,the ecological flow process line for spawning protection of fish was constructed,and the principles and flow of the formation technology of "process line" were put forward.Cheng improved the hydrological index set for spawning protection of fish.The steps of "process line"formation technology include:1)target fish screening,2)study on spawning suitability of target fish,3)determination of hydrological index set parameters,4)drawing of single target ecological flow process line,5)fitting of multi-objective ecological flow process line.Among them,the indicators of fish spawning eco-hydrological index set mainly include:discharge pulse peak flow,peak duration days,initial date of flood,the time of flood occurrence,the number of flow pulses,daily flood rate,duration days of flood duration,duration days of flow pulse process,end flow pulses and end flow pulses,totally 10 indicators.Combining with the reproductive ecology of fish,the ecological significance and determination method of each index are given.(4)The threshold of the characteristic index of fish spawning ecological flow in Jinping Dahe Bay was proposed,and the spawning flow process for fish w'as set up.On this basis,the main directions and measures of fish spawning habitat restoration were systematically studied.These include:1)adjusting water temperature reasonably to ensure the maturation of gonad and spawning time of fish;2)determining the discharge time of ecological flow reasonably to ensure the required velocity and drift distance of drifting eggs;3)strengthening the protection and artificial transformation of potential fish spawning grounds.