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.
A structure model describes the boundary geometries and the three-dimensional solid phase distributions of the catchment. In contrast to an established ecosystem, feedback relations can be assumed for an initial geosystem between the development of spatial structures and the water and element fluxes. The objective was to develop a hydrological catchment model as a three-dimensional spatial database of the solid phase that allows an integrative analysis, a periodical mass balance, and the generation of distributed model parameters for the developing system. Data were from the constructed catchment “Chicken
Creek.” The initial texture and bulk density distributions were generated by imitating sediment dumping, segregation, and compaction. Boundary geometries and changes in surface topography due to erosion and sedimentation processes were quantified on the basis of digital elevation models (DEMs) derived from aerial photographs. The catchment was visualized with the three-dimensional software GoCad; the “emergence” of the water table and other structures (e.g., soil horizons, root zone) could be spatially assigned and quantified to identify regions with specific processes. A combination of three-dimensional catchment with time-dependent two-dimensional surface models allowed generating the development of spatially distributed erosion–deposition patterns that formed new initial surfaces. The three-dimensional distributed solid phase structure of the catchment allowed for a more direct comparison with observations using minimal invasive methods. The mass balance of the solids could be related with pedologic development and transfer to other geopedologic systems achieved by adapting sediment transport and deposition in the descriptions of the model. This model may help improve the integrative analysis of hydrological catchments.
The formation of erosion rills and gullies is a critical step in land surface development, but possibilities to study initial unaffected surface development under natural conditions and with well-defined initial and boundary conditions are rare. The objective of this study was to characterize rill network development from ’point zero’ in the artificially-created catchment ‘Hühnerwasser’. To ensure unaffected development, the study was largely restricted to the analysis of remotely-sensed data. We analyzed a series of photogrammetry-based digital elevation models (DEMs) for 10 points in time, over a period of five years and beginning with the initial state. The evolving erosion rill network was quantitatively described based on mapping from aerial photographs. DEMs and rill network maps were combined to specifically analyze the development of morphometry for different parts of the network and to characterize energy dissipation and connectivity. The restriction to remote-sensing data did not allow for analyzing specific processes governing rill network development, nevertheless, two major development phases could be characterized. We observed a phase of growth of the rill network along with variations in drainage patterns during the first two years of development and a subsequent phase of reduction of its area along with comparably stable patterns. Region-specific analysis of morphometry indicates that, besides effects of changing sediment characteristics and vegetation cover development, locally evolving hydro-geomorphic feedback cycles influenced this development. Results show an increasing similarity of overall statistical characteristics (e.g. drainage density) for two parts of the catchment, but a persistent influence of initial conditions on specific rill geometry. The observed development towards higher orderliness and increased connectivity is consistent with experiments and concepts on drainage network evolution across scales; however, we did not observe major influences of rill piracy and cross grading or a reduction of energy dissipation with network development.