INCORPORATING NONLINEAR RULES IN A WEB-BASED INTERACTIVE LANDFORM SIMULATION MODEL (WILSIM)

This paper presents a Web-based Interactive Landform Simulation Model (WILSIM) that integrates the simplicity of cellular automata (CA) algorithm and the complexity of nonlinear rules of sediment erosion and transportation. In CA, a rainfall event (termed precipiton) is randomly dropped onto a cell of a topographic grid and routed to the lowest of its 8 neighboring cells. The precipiton continues to flow downhill and, along the way, it erodes bedrock material and carries the sediment with it until it lands in a pit, reach the edges, or its carrying capacity is exceeded. This process is repeated (iterated) many times to simulate landform evolution. In the linear version of the model, the amount of erosion is linearly proportional to local slope and erodibility at any given cell and the precipitons (i.e., rainfall events) are independent of each other. The model is implemented as a Java applet, allowing for widest possible accessibility via a standard web browser and interactive user exploration, which is ideal for education purposes. However, the linear rules preclude the simulation of some nonlinear behaviors of the natural systems. Incorporating nonlinear rules into the CA-based Java applet brings the model closer to reality while maintaining its easy accessibility and interactiveness. In the nonlinear version, the amount of erosion at any given cell is a power function of slope and discharge, which is related to the contributing area (represented by the number of cells flowing into the cell under consideration, i.e., precipitons are no longer independent but interrelated). The linear version becomes a special case of the nonlinear version with power coefficients set to unity. Preliminary visual inspection of the simulation results indicates that the nonlinear model generates much more realistic-looking landforms than the linear counterpart. The effect of various factors on landform evolution will be evaluated by changing parameters such as lithology (high vs. low erodibility), climate (wet vs. dry) and tectonic uplift rate. Fractal dimensions and hypsometric curves of the evolving resultant landforms under different scenarios and between the linear and nonlinear versions will be compared and discussed. WILSIM can be accessed at http://www.niu.edu/landform . This project is funded by NSF.