Towards Quantitative Modelling of Landform Evolution through Frequency and Magnitude of Processes: A Model Conception

In recent years, various process-based models for the evolution of regional landform systems have been developed (Coulthard, 2001). Quantitative models have considerable use in applied geomorphology, but also represent a good means we have for testing and developing theoretical models. Nevertheless, there remains a considerable gap between the detailed quantitative representation of individual process behaviour and its integration across spatial and temporal scales that are relevant to landform evolution (Hergarten and Neugebauer, 1999a). A major research issue that must be confronted is the differing frequencies and magnitudes of the various processes that contribute to regional landform evolution. A unifying concept that offers promise is that of the sediment cascade, i.e. viewing geomorphic processes as contributing to the general system of sediment flux through the landscape. In this paper, we present a formulation for modelling sediment flux at the Holocene timescale and at regional spatial scales (3rd/4th order drainage basin, Preston and Schmidt, 2003). The temporally integrated production of sediment from individual geomorphic units is derived through reference to frequency/ magnitude distributions of process behaviour. The model operates at coarse spatial scales, providing a framework for linking individual geomorphic systems as components within a regional scale sediment flux model. The proposed modelling approach combines classical conceptualisation of landscapes into units with process-based flux modelling concepts and therefore represents an upscaling approach for models of landscape evolution. A series of issues with respect to contemporary geomorphologic research are discussed on the basis of the presented model approach.