Modeling the Anthropogenic Effects on Landscape Evolution at a Watershed Scale Using Landlab: A Preliminary Example from the Chestatee River in Northern Georgia, USA

During the 21st century, anthropogenically modulated changes in climate and land cover will drive variations in sediment dynamics throughout rivers, reservoirs, and coastlines. These changes threaten the integrity of dams, levees, and riparian ecosystems, necessitating strategies to help mitigate their associated hazards and to detect and prevent adverse consequences of engineering solutions. To optimize these strategies, geomorphologists require calibrated, watershed-scale numerical simulations of sediment transport that can predict how fluvial networks will respond to different forcings. We aim to develop calibrated landscape evolution models of several U.S. rivers to explore how climate and land-use change over the coming decades to centuries will influence sediment dynamics. The Chattahoochee River in the southeastern U.S. is an ideal catchment to begin this work due to its recent urban development and sedimentation records near its outlet at Lake Seminole. Here, we present preliminary work applied to the Chestatee tributary of the Chattahoochee River and its outlet at Lake Lanier in northern Georgia. We begin by using the Landlab Python toolkit to develop a simple model structure employing three geomorphic transport laws: detachment-limited fluvial erosion, nonlinear gravitational transport, and spatially uniform tectonic uplift. We isolate a single parameter (the fluvial erodibility coefficient) and constrain different values representative of pre-industrial, modern, and future (RCP 4.5 and 8.5) environmental conditions. We run landscape evolution models using each of these values to predict topographic changes over the coming decades to centuries under their representative erodibility conditions. By comparing the results of each model, we can isolate and quantify the relative effects of anthropogenic land use and climate change throughout the watershed. After completing these experiments, we will integrate additional sediment transport processes into our model structure to explore relationships between anthropogenic activities and delta sedimentation in several reservoirs along the Chattahoochee River. In the future, we will repurpose these model structures to explore how sediment modulation by multiple dams further influences watershed evolution.