Simulation of topographic reconstruction of abandoned mine based on sub-watershed natural geomorphology

Abstract: Topographic reconstruction is a crucial part of land reclamation and ecological rehabilitation because the resulting geography landscapes are the foundations for all subsequent reclamation practices and the surfaces for future land uses. It is also ranked among the most important research technical problems. Nature can provide analogues for mined or mining landscapes during disturbed-land reclamation according to landscape stability and according to the reconstructed structure blending in with the surrounding undisturbed landscape. In terms of the watershed geomorphology and the principle of self-similarity theory, the sub-catchments and channels of abandoned mines were re-planned by using ArcGIS soft technology and a practical survey in this paper. At the same time, the topography characteristics of adjacent, undisturbed catchments were calculated by applying an ArcGIS Hydrologic analysis tool, which was taken as the following simulation reference standard. Then the topography in a sub-watershed unit in the Huangyuan abandoned quarry project of Fangshan county in Beijing city was reconstructed by using a Geofluv (Natural Regrade) module driven by geomorphic principles, in which this module simulated the function of the natural landscape that would evolve over time under the physical and climatic conditions present at the site to water and sediment from the land surface in a stable hydrologic equilibrium. Moreover, the theory and technical method of the reconstructed topography were studied. The initial study of the sub-watershed on the undisturbed landform in the project's vicinity were selected and calculated to develop a stable channel design and reconstruction guidelines by using GIS spatial analysis tools, and the selected geomorphologic characteristics index were first and second order sub-watershed, the average sub-watershed area, main channel, drainage density, watershed roundness, average elevation difference, and average slope, which provided targets for topographic reconstruction. In this case, the average second order drainage density that represented the stable sub-watershed size for the local condition was 13.84km/km2. Moreover, the average second order drainage density of the reconstructed topography which simulated the natural landform evolution to the stage in balance with the local environmental condition was 14.52km/km2 on the basis of a re-planning of reconstruction sub-watershed and main channel, which achieved the desired design goals. The results showed that the reconstructed Huangyuan topography in which the hydrologic and fluvial geomorphic analyses and stable channel parameters were determined, and based on site-specific data, were relatively economical, stable, and natural, which was similar to the undisturbed catchments' geomorphology. Finally, the relationship of geomorphologic characteristics between the reconstructed sub-watershed and the undisturbed ones was analyzed and the ratio of the index was almost similar. A topographic reconstruction simulated a relatively stable sub-watershed performed by geomorphic processes with the creation of a basin composed of slope and channels in orderly spatial arrangements and functioning for the transportation of water and sediment. The geomorphic information entropy analysis showed that the geomorphology changed very slowly after topographic reconstruction and the erosions on watershed were also gradually reduced. This study provided a novel viewpoint for the topographic reconstruction of an abandoned mine.