3D initial sediment distribution and quantification of mass balances of an artificially-created hydrological catchment based on DEMs from aerial photographs using GOCAD

摘要

The spatial distribution and properties of parent material components form the starting point for any soil and ecosystem. Initial phases of ecosystem development are predominantly characterized by the redistribution of sediment components. To improve the understanding of soil-landscape development, the initial sediments need to be quantified in space and time. This study aims at developing and testing methods for the quantification of initial sediment mass balances in the three dimensions of space and in time. The initial mass balance and composition of parent material in an artificially-created hydrological catchment were quantified from a 3D-model of the catchment's water storage layer. Multi-date digital elevation models (DEMs) were constructed from photogrammetrically derived elevation data after the assessment and improvement of elevation data quality. Three-dimensional models of volume change were constructed from the digital elevation models. Regions of significant volume change were identified. Mass changes were calculated from the volume changes in combination with bulk density information. Based on information about the catchment's construction, mass changes were separately analyzed in subregions of the models. Terrain attributes were computed to characterize surface structure and to examine correlations with mass change. From the 3D-model, an initial sediment volume of 122,608m3 was quantified. A variation of about ±12,300m3, due to uncertainty in DEMs from aerial photographs, was calculated. The 3D-model indicates differences in sediment properties between the western and eastern part of the catchment, which are most probably resulting from the dumping of two separate material deliveries during the construction. Models of volume and mass change are constructed for three time periods of catchment evolution. Spatial variations in volume and mass change are observed. The total mass balance reveals a considerable mismatch between the detected amounts of erosion and sedimentation, which gives reason to closely examine the quality of the DEMs. Terrain attributes of four elevation models reflect the diversification of surface structures. Correlations between volume change and surface structures show that erosion processes are dependent on initial surface structures and that these structures, in turn, are enhanced by the processes of sediment redistribution. Although there is a considerable uncertainty in the observed mass changes, the 3D-modelling approach allows a first approximation of the initial, mostly erosion-affected, surface structural dynamics of the artificial catchment. The comparison of multi-date elevation data allows a critical evaluation of the quality of models of change obtained from repeated topographical surveys.