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- Forschungszentrum Landschaftsentwicklung und Bergbaulandschaften (FZLB) (46) (remove)
BTU
For systems such as soils or watersheds, the initial distribution of sediment mass and composition at the starting point of the development are mostly not well-known. The development of such systems, however, has frequently been assumed to depend on boundary and initial conditions including the solid phase. Here, an experimental watershed of about 6 ha surface area was artificially-created in order to imitate an initial stage just at the beginning of the geo-ecosystem development. However, sediment homogeneity could not be achieved for this large-scale field experiment, and the 3D spatial distribution of structures and components remained uncertain. The objective of this study was to quantify and reconstruct the initial sediment distribution and the first development stages using aerial photographs, point information, and a 3D model. The watershed was made of coarse-textured sediments of quaternary origin with a low permeable clay liner as the bottom boundary. A 2D horizontal digital elevation model (DEM) of the surface and a DEM of the subsurface clay layer are used to construct a 3D triangulated numerical grid of the catchment’s initial spatial structure using the 3D-GIS software GOCAD. Physical and chemical soil properties obtained from borehole samples are assigned to this model and interpolated onto the 3D grid. The volumetric changes in space and time are quantified and related to material properties to obtain the mass changes. Correlations between terrain attributes, sediment properties, and mass changes are explored specifically in regions of differing source materials. A temporal sequence of surface DEMs is obtained from photogrammetric, high-precision ground based laser scanning and airborne laser scanning data. 3D models of elevation change are constructed from these DEMs. The processes following the initial state are mainly characterized by runoff-induced erosive mass relocations related to the distribution of surface and subsurface structures and sediment properties. The results suggest that both sediment structures and mass translocations differ between the western and eastern parts of the watershed and that correlations between initial surface structures and subsequent mass changes exist.
The effect of surface variability factors on wind-erosion susceptibility: A field study in SW Niger
(2009)
Many processes in a developing catchment can only be fully understood if the spatial
heterogeneity is adequately described. Process-based modeling allows reproducing
specific key structural elements of catchments. Constructed catchments are ideal test
objects because of the well-known spatial conditions. In our study, we (i) modeled the
entire process chain of catchment construction, (ii) established a consistent sediment mass/
volume balance between the excavated outcrop and the generated catchment model, and
(iii) provided consistent three-dimensional distributions of texture and bulk density for
deriving soil hydraulic properties. Data are from the 6 ha Hühnerwasser catchment (Chicken
Creek, Lower Lusatia, Germany), which was constructed from overburden sediments in an
open-cast lignite mine. Uncertainty about the parent material origin was captured in a
multiscenario approach based on a geological model of the outcrop site and the simulation
of excavation procedures. Generated distributions are incorporated in a gridded threedimensional
volume model (GOCAD), and results were evaluated by semivariogram
analysis and by quantifying point-to-point deviations. Filling and compaction are modeled
based on three-dimensional volume analysis and mass balances of dumped sediments.
Heterogeneities reflect both the batch-wise sediment variation and the succession of
excavated geological units. The scale of the generated spatial models can be adjusted for
three-dimensional hydrological catchment modeling while three-dimensional sediment
mass balances can be used for analyzing soil and ecosystem development processes.