Simulation Of Hydrodynamics Of The Jingjiang-Dongting River-Lake System And Drifting And Transport Of Yangtze's Carp Eggs

The Jingjiang-Dongting River-Lake(JDRL)system in the middle Yangtze is of unique and complex hydrodynamics and important river-lake coupling relationship.After the initial regulation of the Three Gorges Reservoir(TGR),the hydraulic condition and hydrodynamic characteristics of the downstream JDRL system have been impacted and changed a lot.Also,in the Jingjiang River(JR),the early resources of Yangtze's Four Major Carps(YFMC)have showed certain and attracted declines in the field abundance of drift-sampled carp eggs.As TGR regulates the downstream river-lake relation and introduces ecological spawning regulation compensation for YFMC,a clear understanding is imperative on the complex river-lake relationship as well as the intimate link between the river hydrodynamics and the important characteristics of the transport,distribution and suspension hatchability of the drifting carp eggs.Seeing these needs and for support of JDRL management and YFMC protection as well as ecological measures evaluation,this thesis has conducted a combined modeling study on JDRL's hydrodynamic characteristics and carp eggs drifting and transport in JR.Aiming at JDRL,a one-dimensional(1D)–two-dimensional(2D)coupled numerical model for shallow water flows in large complex river network-lake systems is developed.For model coupling,an improved water stage prediction-correction(IWSPC)method of good numerical performance is proposed,with better stability and about 8%iterative efficiency improvement.To enlarge the implicit coupling time-step sharing 1D and 2D solutions,a large time-step solver for the 2D submodel is established,with the overall time-step increased by 1?5 times and the coupling computational efficiency greatly improved.Theoretical analyses and validation of simulation of the JDRL hydrodynamics demonstrate the validity,practicality and computational superiority of the proposed method and model for simulating the coupled complex flow of the JDRL system.The proposed model is then applied to investigate JDRL's important hydrodynamic characteristics by simulating a long-term hydrodynamic process of the JDRL system after TGR's initial regulation.By analyzing the results,the intermittent flow characteristics of JR's Three Diversion Outlets(TDO)and their connected downstream river networks as well as the water surface shrinkage of Dongting Lake(DL)in the dry season are summarized,with consideration of TGR's influence and role.Also explored are the monthly variations of flow and stage distributions in JR and DL as well as their connecting main flow passages.Besides,the water exchange between JR and DL and the hydraulic relations at their confluence are quantitatively discussed.Finally,practical and quantitative discharge relations of JR and TDO,stage-discharge relations of TDO and stage-volume relations of DL are established,and the good correlationship of each relation demonstrates their function in providing boundary conditions and quantitative knowledge for JDRL's simulation and research.Based on the summarized flow characteristics of JR,a quasi-three-dimensional fluvial fish eggs drift model coupling hydrodynamics and particle tracking is further developed,particularly including the influence of river topography and hydrodynamic characteristics.The model is validated by simulating two published lab flume experiments and a field egg release and capture experiment in a real-life river,with good agreements between the simulated results and experimental data.The model is then applied to analyze the hydrodynamic mechanism of the eggs'drifting behavior,characterize their transport and dispersion dynamics in JR,and quantify the influence of different flow discharges released by TGR.Results show that more than 10000 m~3/s discharge from TGR could help above 80%carp eggs to maintain suspension in a relative water depth of 0.9.Based on the egg transverse distributions,the inaccuracy of the widely-used traditional method for resources estimation of drifting eggs is addressed,and an effective way of correction using the developed model is reasonably proposed.The improvement and effectiveness of the proposed correction is finally validated with the post-correction errors of the method reduced significantly,compared with the field egg capture data.The good verification and application performance of the developed models demonstrate that this study provides a useful and powerful research tool and reference for investigation of complex river-lake relations in the middle Yangtze and research and protection of fish eggs resources as well as evaluation of ecological measures.