A Numerical Modeling Study Of Transient And Steady State Landforms Focused On The Influence Of Rainfall Patterns
The interactions and feedbacks among climate, tectonics and surface erosion are complex but fundamental in geomorphological studies, and the mechanisms that control these processes are still not well understood. This thesis uses numerical models to address the specific question of how spatial rainfall patterns impact bedrock incision and the morphology of fluvial landscapes. This thesis includes three major chapters. In the first major chapter, I perform a series of model experiments to explore the impact of orographic rainfall on channel profile incision under different tectonic conditions. I find that the pattern of rainfall gradients may be more clearly reflected in transient channel profiles than in steady-state profiles. I apply the model to explore how rainfall patterns may lead to the convex upstream and concave downstream channel profiles on the wet side of Kohala, Hawaii. I find that if rainfall gradients lead to a gradient in bedrock erodibility, in addition to discharge variability, climate could explain the complex morphology of these channels. In the second major chapter, I integrate a linear orographic precipitation module into the CHILD landscape evolution model, providing a 2-D quantitative tool to explore the interactions between orographic rainfall and landscape evolution. Using the coupled model, I find that spatial rainfall patterns can affect the channel profile and planform morphologies, and when considered as a whole, the profiles of smaller channels with relatively uniform rainfall may more clearly illustrate rainfall patterns than those of larger channels that flow across rainfall gradients. I also observe a quantifiable change in network characteristics between landscapes with uniform and non-uniform rainfall. In the third major chapter, I employ the CHILD landscape evolution model to explore the mechanisms that control the characteristic length of hillslopes and valley spacing of fluvial channels. I find that the characteristic length is a primary control on the valley spacing of different order streams, and the valley spacing ratio is also well constrained by the counterbalance between the characteristic length and the stream order of dominant channels. However, factors such as initial topography and orographic precipitation likely impact network organization and the valley spacing ratio.