The Channel-Hillslope Integrated Landscape Development Model (CHILD)

Abstract

Numerical models of complex Earth systems serve two important purposes. First, they embody quantitative hypotheses about those systems and thus help researchers develop insight and generate testable predictions. Second, in a more pragmatic context, numerical models are often called upon as quantitative decision-support tools. In geomorphology, mathematical and numerical models provide a crucial link between small- scale, measurable processes and their long-term geomorphic implications. In recent years, several models have been developed that simulate the structure and evolution of three-dimensional fluvial terrain as a consequence of different process “laws” (e.g., Willgoose et al., 1991a; Beaumont et al., 1992; Chase, 1992; Anderson, 1994; Howard, 1994; Tucker and Slingerland, 1994; Moglen and Bras, 1995). By providing the much-needed connection between measurable processes and the dynamics of long-term landscape evolution that these processes drive, mathematical landscape models have posed challenging new hypotheses and have provided the guiding impetusbehind new quantitative field studies and DEM-based analyses of terrain (e.g., Snyder et al., 2000). The current generation of models, however, shares a number of important limitations. Most models rely on a highly simplified representation of drainage basin hydrology, treating climate through a simple “perpetual runoff” formulation. The role of sediment sorting and size- dependent transport dynamics has been ignored in most studies of drainage basin development, despite its importance for understanding the interaction between terrain erosion and sedimentary basin deposition (e.g., Gasparini et al., 1999; Robinson and Slingerland, 1998). Furthermore, with the exception of the pioneering work of Braun and Sambridge (1997), the present generation of models is inherently two-dimensional, describing the dynamics of surface evolution solely in terms of vertical movements without regard to lateral displacement by tectonic or erosional processes. Our aim in this paper is to present an overview of the Channel-Hillslope Integrated Landscape Development (CHILD) model, a new geomorphic modeling system that overcomes many of the limitations of the previous generation of models and provides a general and extensible computational framework for exploring research questions related to landscape evolution. We focus here on reviewing the underlying theory and illustrating the capabilities of the model through a series of examples. Discussion of the technical details of implementation is given by Tucker et al. (1999, 2000) and Lancaster (1998). We begin by briefly reviewing previous work in landscape evolution modeling. We then discuss the theory and capabilities of the modeling system, and present a series of examples that highlight those capabilities and yield some useful insights into landscape dynamics. 2. BACKGROUND