Geomorphic Transport Laws for Predicting Landscape Form and Dynamics

A geomorphic transport law is a mathematical statement derived from a physical principle or mechanism, which expresses the mass flux or erosion caused by one or more processes in a manner that: 1) can be parameterized from field measurements, 2) can be tested in physical models, and 3) can be applied over geomorphically significant spatial and temporal scales. Such laws are a compromise between physics-based theory that requires extensive information about materials and their interactions, which may be hard to quantify across real landscapes, and rules-based approaches, which cannot be tested directly but only can be used in models to see if the model outcomes match some expected or observed state. We propose that landscape evolution modeling can be broadly categorized into detailed, apparent, statistical and essential realism models and it is the latter, concerned with explaining mechanistically the essential morphodynamic features of a landscape, in which geomorphic transport laws are most effectively applied. A limited number of studies have provided verification and parameterization of geomorphic transport laws for: linear slope-dependent transport, non-linear transport due to dilational disturbance of soil, soil production from bedrock, and river incision into bedrock. Field parameterized geomorphic transport laws, however, are lacking for many processes including landslides, debris flows, surface wash, and glacial scour. We propose the use of highresolution topography, as initial conditions, in landscape evolution models and explore the applicability of locally parameterized geomorphic transport laws in explaining hillslope morphology in the Oregon Coast Range. This modeling reveals unexpected morphodynamics, suggesting that the use of real landscapes with geomorphic transport laws may provide new insights about the linkages between process and form.