Study Of Saltwater Intrusion In Estuary By Simulation Modeling

With the increased graveness of the saltwater intrusion, more efforts have been put on the research activities on saltwater intrusion in estuary. By establishing a numerical model of current and salinity, and simulating the movement of salinity in estuary, the characters of salinity distribution and influence of those hydrodynamic factors in estuary impacted on movement of salinity can be discussed and analyzed, and all these will benefit the prevention and cure of saltwater intrusion in estuary.Traced the recent directions in the worldwide research on saltwater intrusion, used the numerical modeling method to do a series of study on the saltwater intrusion in estuary, the content includes the 1-D (one-dimensional), 2-D (two-dimensional), 1-D and 2-D coupled and 3-D (three-dimensional) numerical simulation of current and salinity, discuss of some basic points in establishing and running of the models, analysis of influence of runoff, tide difference, wave and wind impacted on the saltwater intrusion in estuary, and the salinity simulation of the Pearl River Estuary Lingdingyang. In the paper, a series survey data were used to verify the models and the phenomenon of saltwater intrusion in estuary were reflected in reason. To sum up, the contents of the paper are as follows:1. Concluded and introduced the harm, complexity and main influencing factors of saltwater intrusion in estuary in system, together with the study method of it and the study status of the saltwater intrusion in the world wide.2. According to the different characters of the water networks in the upstream of the estuary and the estuary that the first one is dense with lots of branches, while another is wide and broad, the 1-D, 2-D, 1-D and 2-D coupled numerical models of current and salinity were established. Combined with practical engineering examples, the models were verified and influences of different projects impact on the saltwater intrusion were estimated, respectively. What's more, the relations between the extent of saltwater intrusion with the runoff flux and tide difference were discussed.3. A three-dimensional nonlinear baroclinic salinity numerical model in horizontal orthogonal curvilinear coordinate and verticalσcoordinate was established, and the processes of discretisation, solution, the disposal of parameters and boundary conditions were given, and the wave and wind were included in the salinity simulation system for the first time. Used the survey data of the winding river course Zhoutouzui, the 3-D current model and disposal of moving boundaries were verified. More, by the modification of grid coefficient near shore, a mend of the traditional dry or wet discriminance method was presented, which can decrease the error in definition of simulation area, and reflect the continuous move of boundaries.4. The 3-D current and salinity numerical model under effect of runoff, tide, temperature, wave and wind in ideal estuary was established. By the contrast of the saltwater intrusion simulations with and without wave, with and without wind, but under same boundary, initial conditions, the influence of wave and wind impact on the saltwater intrusion in estuary were discussed.5. Established the 3-D salinity model in Lingdingyang, used plenty of survey data to verify the model, and the three dimensional distribution characters in Lingdingyang and the influence of wave and wind impact on salinity movement were studied. Moreover, the problems of initial salinity field in salinity circulatory simulation was discussed.The innovations of the paper were embodied in the above contents 2-5, by the studies of the paper, the following valuable conclusions can be get:1. Judge from the simulation results of examples in the paper, it can be conclude that the established models in the paper could reflect the influence of different engineering projects impact on saltwater intrusion and the 3-D distribution characters of salinity in estuary correctly, use the 1-D, 1-D and 2-D coupled and 3-D numerical model to study the saltwater intrusion problems in delta and estuary is feasible. Moreover, the modifying of moving boundary disposal and discussion of problems of initial salinity field in salinity circulatory simulation will be good to advance the accuracy and efficiency of salinity numerical simulation.2. Runoff and tide are two main factors impact on saltwater intrusion. The extent of saltwater intrusion and salinity of each cross section decrease with the increasing of runoff flux in upstream, and is a linear variety. When the tide difference enlarged, that is the tide flux increase, the saltwater intrusion distance and each cross section salinity increase, and the distance of saltwater intrusion and the tide difference are in linear relation, while the relation between salinity of each cross section with tide difference is curvilinear.3. Simulation in ideal estuary and Lingdingyang give plenteous proof to prove that wave has influence on saltwater intrusion in estuary. Under the action of wave provided in the paper, the salinity fronts in estuaries move towards the upstream, and the salinity isolines increase. In the whole, the influence of wave increases with the strengthening of wave. Otherwise, affect by the vertical distribution of wave radiation stress, the salinity variation in surface layer is larger than that in bottom layer.4. Wind has some influence on saltwater intrusion in estuary. Under action of wind in same direction with flood and for the reason of surface stress, the whole salinity both in surface layer and bottom layer are increase a little, while, the practical cases in estuary are complicated, and the existence of wind may effect on the distributaries between groove and shoal, so exceptions will be natural. And in the outer broad sea area, the salinity in surface layer increase but that of bottom layer decrease for the reason of vertical circulation induced by wind.In a word, from the 1-D model in delta, 1-D and 2-D coupled model to 3-D current and salinity model in estuary, from the trim of data in initial period, model solving, parameters confirmation to computation of examples, verifying of models, from influence analysis of runoff, tide difference to wave and wind and etc, the work of the paper includes many aspects of study on saltwater intrusion in estuary. Some important problems were analyzed in the paper, and the models and experience in the paper provided profitable reference to farther study on saltwater intrusion in estuary.