Dynamics of Steady-State Drainage Basins
In recent years geomorphology has experienced a rejuvenation of interest in landscape scale erosion. Landscape evolution modeling has become almost routine, and new models continue to be developed that incorporate greater complexity and feedback between climate, tectonics, and erosion. Our (Les Hasbargen and Chris Paola) approach has been to take a step back, and compare results from the least complicated models with results from a similarly simplified physical experiment. We have built an erosion facility that allows a miniature landscape to erode through several relief distances at constant base level fall and rainfall rates. This kind of experiment permits observation of drainage basin dynamics at steady forcing, offering a view into the internally generated behavior due solely to feedback between stream erosion and transport, and hillslope sediment supply. The landscapes in our basin develop dendritic 3-5 order drainage basins. Dominant erosional processes include stream incision and hillslope failures. We note that knickpoint generation and migration is very common. While it is quite simple to force knickpoint generation with abrupt drops in base level, knickpoints form in our experiments under constant base level fall conditions. The relative activity of erosive processes is sensitive to rainfall and base level fall rates. For instance, rapid uplift (i.e., base level fall) forces larger hillslope failures, and result in larger oscillations in sediment flux leaving the basin. We have conducted 6 runs in the facility thus far. Below you will find a smattering of visual data from the experiments. We collected time lapse video, digital still photographs from stereo locations, and sediment and water flux measurements at the outlet to the basin. All of the runs begin with an initial flat surface with very low surface roughness. The drainage basin forms by headward erosion from the outlet. A rough balance between erosion and uplift (i.e. 'base level fall) is reached shortly after complete dissection of the surface.
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