Three-dimensional Riverbed Evolution Analysis Based On DEM

As the geographic information system (GIS), digital elevation model (DEM) andcomputer technology are developing steadily, they are used widely in the analysis ofRiver Bed Development. The methods of the fluvial processes based on ArcGIS andDEM are raised and studied.The analytical methods of riverbed evolution mainly analyze the variation ofriverbed’s siltation, the changes of riverbed thalweg line, the variation of riverbedcenter’s gravity lines, riverbed’s various bottom, displacement and area, riverbed scourand thalweg line analysis of the riverbed, based on DEM data, mainly analyze theevolution of the riverbed from two aspects of the riverbed horizontal and vertical.However, at this stage, extracting the valley ridge line of one model is widely used inthe terrain analysis.At the same time, the valley ridge analysis can be in line with thesurface in exploring the terrain of the spatial pattern of change and provide an importantway for riverbed topography changes study. So it becomes the current problems to studythe riverbed evolution analysis from the pattern structure of the riverbed space object.Using the GIS spatial analysis technology, the paper elaborates the methods ofextracting the thalweg line, extracting the valley ridge and calculating riverbed scourbased on DEM and the fundamental analysis methods of the fluvial processes.Meanwhile, we also proposed the weighted adjacency matrix method to adapt closedcontour lines method’s limitations.And then we can get the the changing pattern anddevelopment trend of the riverbed by analyzing the thalweg line and the valley ridgefrom DEM in recent years.Through the use of extraction bed thalweg line method and porosity analysis, thefollowing conclusions:(1). To extract thalweg from closed contour lines requires the establishment ofcontour tree according to the elevation of contours. However, due to intersecting andcoverage terrain contour elements and error while acquiring elevation values of contour and other reasons, the original closed contours become disconnected, merged, isolatedobjects, and elevation information is lost. The thalweg connected according to thetopology of the contour line through these objects can not correctly reflect the actualtopology of thalweg points. So for these situations when disconnected, merged, isolatedobjects exist, the method of using the weighted adjacency matrix to establish contourmulti-tree was presented.(2). The paper studies the effect of the porosity analysis methods in the riverbedterrain and contrasts to the fluvial from traditional methods with the fluvial from valleyridge line to verify the feasibility of using porosity analysis methods in the fluvialprocess, porosity analysis method can make riverbed change in the overall situation aswell as islet formation qualitatively reflected by the porosity curve., it demonstrates thatusing porosity analysis method to analyze the riverbed valley can provide anothereffective way for riverbed evolution.