Numerical Simulation Of The Evolution Of The Delta

The evolution of the surface morphology is mainly derived from the denudation of denuded areas,the movement of materials and the deposition of sedimentary areas or catchment basins.As a natural geographic boundary,the watershed is closely related to the "source-sink" system of the earth’s surface,which is usually manifested by the denudation and flattening of the source area(watershed boundary)and deposition in the lowlands within the watershed.As the main sedimentary area in a watershed system,deltas are important in terms of ecology and resource distribution,especially shallow water deltas have become an important target for international oil and gas reservoir exploration in recent years.In order to shorten the simulation period and obtain more quantitative results,studies on delta evolution are gradually adopting numerical simulation methods.In the process of numerical simulation of delta evolution,the construction and solution of the model and its transformation to computer model are key issues,and the storage,analysis and visualization of the evolution results can effectively promote the scientific,standardization and process of the numerical simulation of delta evolution.Therefore,this paper adopts the front and back-end web separation technology,and builds a delta 3D evolution simulation cloud platform with data management and analysis,delta evolution simulation,Bayesian optimization of sedimentation simulation hyperparameters,visualization of evolution results,statistical analysis and cloud storage,taking the delta evolution numerical simulation algorithm as the core.Taking the delta of the middle branch of Ganjiang River in Poyang Lake as an example,the system is tested and evaluated,and the main conclusions are as follows:1.The main controlling factors for the evolution of the delta were analyzed.Topography,rainfall,stratigraphy,tectonic movement,sea(lake)plane and waves are the controlling factors,and the controlling factors interact with each other to drive the evolutionary growth of the delta.The abundant rainfall erodes the stratum along the direction of maximum slope drop and carries the water and sand to be deposited in the river,sea(lake)mouth and lowlands;the tectonic uplift and surface erosion promote each other;the sea(lake)plane is influenced by the tectonic movement and rainfall,and together with the wave action,affects the spatial distribution of deposition.2.Using erosion and sedimentation movement under the action of water force and diffusion movement under the action of gravity as the main material movement modes,the spatial discretization of the surface based on Voronoi polygons is carried out,and the discretization equations f(topography,rainfall,stratigraphy,tectonic movement,sea(lake)level,waves)are constructed.The discretization equations at different times are obtained by combining the time stepping strategy,and the simulation results of delta evolution are obtained by using the recursive solution of finite volume method.3.A 3D dynamic simulation system of delta evolution with Vue+Django+Hadoop as the technical system is constructed.It is mainly divided into six functional modules,such as data management and analysis,delta evolution simulation,superparametric Bayesian optimization of sedimentation simulation,visualization of evolution results,statistical analysis and cloud storage,which realize the whole process management and analysis of delta evolution numerical simulation.4、The delta of the middle branch of Ganjiang River in Poyang Lake is selected as the study area,based on numerical simulation algorithm for the evolution of the delta,the topographic data of 2000(SRTM data)is used as the initial topography,combined with the rainfall data and lake level data from 2000 to 2007,and the topographic data of2007(AW3D30 data)is used as the validation data,erodibility coefficient of erosion and deposition movement under hydraulic action,surface diffusion coefficient of diffusive movement under gravity and so on were selected optimally by using Bayesian optimization algorithm.The evolution of the delta of the middle branch of Ganjiang River in Poyang Lake(from 2000 to 2011)was simulated by combining the requested parameters,SRTM data,rainfall data and lake level data from 2000 to 2011,and finally the spatial distribution pattern was found to be in good agreement with the landsat remote sensing image data,which confirmed the feasibility of the algorithm.5、The deposition of the delta of the middle branch of Ganjiang River in Poyang Lake is a slow process,mainly in the shape of dolphin or bird’s foot,and the deposition area is mainly located near the river channel and near the entrance of the lake,and it is in the trend of pushing from the river channel to the entrance of the lake,and several obvious sand spouts have been formed at the entrance of the lake to extend to the center of the lake.The rise and fall of the lake level has a certain influence on the extent of the deposition area,the lake into the deposition area closer to the shore;lake retreat is extended to the center of the lake.Rainfall can affect the rate of material transport to a certain extent.