The familiar branching pattern formed by river networks is one of the most widespread features of Earth's surface. Yet explanations for this branching pattern based on erosion mechanics have proven elusive due to the difficulty of modeling large regions of Earth's surface and the lack of a unifying framework for relating the geometry of river networks to basic erosion laws. Consequently, many previous studies of river networks have focused on random or rule-based models. This project will develop a new framework for using erosion mechanics to explain the branching patterns of river networks. The new framework is based on the principle that the form of river networks reflects the degree to which erosion by incising rivers dominates erosion by rock and soil transport on hillslopes. The two main components of the research will be numerical experiments that simulate the development of large-scale river networks, which will provide a means of calibrating the new mechanics-based framework, and field studies of two landscapes that formed under simple geologic and tectonic conditions, which will provide independent tests of the theoretical predictions. In addition to generating an improved mechanistic explanation for the branching structure of river networks, the results of the study will provide a way to infer long-term landscape dynamics from present-day topography when measurements of erosion and sediment transport are impractical, and a way to quantify the influence of factors such as rainfall rate and rock type on the large-scale topography of Earth's surface.
River networks are the main conduit for sediment, surface water, and nutrients on the continents, and their structure is critical to ecosystem function, water resources, agriculture, and the carbon cycle. This research will improve our understanding of how major factors such as geology, climate, and biology control the branching structure of river networks. The results will not only help determine the dominant conditions under which a given river network has developed, but will also inform expectations of how river networks will respond to changes in rainfall, vegetation, and other factors. Through the development of new computational techniques, this project will also advance the ability of other researchers to model changes in Earth's surface environment.
