Two approaches to modeling the initiation and development of rills in a man-made catchment

Surface erosion rills are dominant structures in young developing ecosystems, and as such they fundamentally affect water flows, for example by channeling surface runoff or by locally changing the infiltration capacity of the soil. To successfully model the systems hydrology it is indispensable to take the development of erosion rills into account. The goal of this study was to model the emergence of an erosion rill network with total length of 6 km formed during the last few years in the 6 ha large artificial catchment Chicken Creek near Cottbus (Germany). The length and connectivity of the evolving network were quantified from aerial images. This analysis showed that the major rill network established already during the first year of ecosystem development. We adapted two model approaches to simulate the emergence of erosion rills. First, we used a self-organized critical network approach with soil erosion and sediment deposition governed by a local critical shear stress. The second approach, based on Manning's equation, was developed to compare the results of the self-organized critical network approach with results from a simple but more physically based approach. Erosion was triggered in the case of high local shear stress and deposition was calculated from settling velocity of the suspended particles. Both models were able to reproduce the observed rill network. Geometric characteristics such as network length and rill depth were simulated in the right order of magnitude. The models also managed to describe the position and temporal evolution of the main erosion rills in the catchment.