Design And Implementation Of An Algorithm For The River Valley Cross-section Morphology Based On DEM

The research on rivers and geomorphic is one of the core themes that experts of geomorphic and hydrology concern about in domestic.However,in former researches,experts studied rivers mostly based on the data underwater including: areas of cross-section covered with water,the extract of the water system,the length of the water.But researches on themes besides river bed,the landforms of river valley are seldom seen.Especially research on the river valley cross-section.Such research needs large quantity of cross sections along the river,so there will be lots of data and it is more complex than research on the longitudinal profile.Researchers collect data mostly on measuring in field or draw maps by hand,which contains heavy labor,but has a narrow research field and it is always a little subjective.Confronting the need of classification of rivers,river detailed management,and river systematic management,an automatic calculating method is in urgent need,which can be used to study and manage the landforms of river valleys.So,the thesis raised a design of algorithm model for the river valley cross-section morphology based on DEM.This algorithm considers the morphologic characteristics of river valley cross-section and the different value of slopes between the bottom and the top of river valley.The writer designed the algorithm based on the theory of GIS spatial analysis method and the characteristics of DEM data,used LiDAR picture as the data resource,and also used river valley floor profile,river valley floor outline,and the width of river valley.Based on the rule of the theory about algorithm and the structural features of GIS data,the algorithm is divided into six steps.The writer also tested the algorithm by the data of V shaped river valley and U shaped river valley.And analyzed the applicability of the algorithm by combining with actual landforms of river valley.The main research contents and the results are as follows:(1)The thesis designed an algorithm model about river valley cross-section morphology based on DEM.On the basis of features of river valley morphology and the theory of geo-information system algorithm,the writer considered the characteristics of river valley cross-section in different time and the differences between value of slopes of top and bottom of river valley and raised an algorithm model based on DEM.There are nine algorithms including: fitting a straight line,curve segmentation,extract of the co-ordinate of the centre of river net,vertical line,slope value,explorative location calculation,river valley bottom outline,river valley width,and river valley bottom profile.By building the algorithm model,the thesis realizes the transition from theory study to practical application,thus provides a new technology method to study the morphology of river valley.(2)The proposed value of the angle threshold,the explore distance threshold and the the valley slope threshold is given by studying the actual samples of V shaped and U shaped river valley.After studying the actual samples,the algorithm model can draw the outline of river valley precisely.Through a correlation analysis with the river valley width from actual samples,the writer found that the calculation results are quite close to real ones.And the accuracy of U shaped valley is more than V shaped valley.By comparing the morphology profiles between the river valley cross-section from calculation and the reality,the writer found that they are in high consistency.Through comprehensive analysis about the questions occurred during the designing of the algorithm and the study of actual samples,the writer raised the optimization of algorithm and expectation in the future.(3)Design and realize the river valley cross-section morphology extract Plug-in based on ArcGIS Engine.In summary,the morphology algorithm of river valley cross-section based on DEM is an effective way to extract the outline of river valley bottom,to calculate the width of river valley,and draw the river valley cross-section.It has a better drawing effectiveness and higher accuracy,so it has a strong application value and potential in the study of river valley morphology field.