Research On Characteristics Extraction Of Sanchuan River Basin Based On DEM

Digital elevation model(DEM),one of the most important part in the spatial database,has been applied in many fields.In the background of digital basin,it has become a focus in hydrology study extracting basin characteristics from DEM.Basin characteristics are basic data of hydrological simulation and watershed management.It is directly related to the precision and efficiency of those studies that basin characteristics are obtained accurately and fast.Lately,with the continuous development of3S technology and continuous improvement of DEM accuracy and obtaining speed,there is a further development in automated extraction study,a lot of new theories and methods are proposed.In this paper, related knowledge of DEM is introduced systematically, research progress at home and abroad of extracting basin characteristics based on DEM is reviewed,basic conception about basin characteristics is introduced,algorithm base and method of automated extraction of basin characteristics based on DEM are discussed;taking Sanchuan river basin as an example,using advanced GIS technology,automated extraction of basin characteristics is realized and the accuracy of extracting result is analysed;in addition,the whole basin is segmented to many sub-basins,at the same time those sub-basins are divided into different kinds.Research results:(1) Extracting terrain factors are fit for the actual basin’s situation, which indicates the algorithm and means are mature and effective,the results show that average slope of basin terrain is13.34°,slope of river source is greater than river valley,when elevation reducing,the slope reduces continuously;there is a small variation in slope of river valley,on the contrary,a large variation in slope of ravine;slope variability can show clearly the position of ridge and valley line in river basin;slope in eight directions are evenly distributed;curvature characteristic show that valley area is flat and the rest of river basin is ravines crossbar.(2) Steps of extracting river network include pretreatment of DEM, determining flow direction of grid,calculating flow accumulation, determining optimal critical threshold,generation of raster river network, vectorization of raster river network,correction and smooth of river network.The new method by which optimal critical threshold can be determined,is proposed by the relationship between flow accumulation threshold and drainage density.Repeated tests show that when threshold is6500,extracting river network is fit for the actual situation, at the same time this shows he method is feasible.(3) The whole river basin is is divided into52sub-basins based on raster river network and raster flow direction data.Sub-basin coding and visual display are realized.Basin area, drainage density and basin shape are selected as classifing factor of sub-basin.Through the method of hierarchical classification,eight-types’ classifing standard system is built.52sub-basins are divided into eight types.Classification results show that most of sub-basins are narrow,ovoid and low in drainage density.In addition,steep-rise-fall flood is easily formed in river basin because of the high drainage density. What’s more,in river basin,soil erosion is serious because of topography broken and sparse vegetation.