Modeling in Landlab: Long-Profile Evolution of Transport-Limited Gravel- and Sand-Bed Rivers

Alluvial river adjustment occurs in response to altered sediment and water inputs, driven by both natural and anthropogenic climate change, changes in land use and/or land cover, and/or imposed by tectonic boundary conditions. This river response is ultimately reflected in the geometry of the bankfull channel, the planform characteristics of the river, and the longitudinal profiles of the mainstem river and its tributaries. This study utilizes analyses of river longitudinal profiles and provides a powerful tool to detect the change and extend it to long-term landscape evolution. Wickert and Schildgen (2019) developed the model, GRLP, to compute transient and steady-state solutions for the long-profile evolution of transport-limited gravel-bed rivers with self-forming channel-width adjustments. Following an analogous approach to that taken by Wickert and Schildgen (2019) and linking sediment transport and river morphodynamics, we developed a model describing the long-profile evolution of a transport-limited sand-bed river. This sand-bed model allows for planform adjustments as a function of excess shear stress (following Parker, 1978, and Dunne et al., 2018) thereby linearizing the sediment-transport response to changing river discharge. Ultimately, the resultant equations suggest a diffusive form for sand-bed river long-profile form and evolution. Both models were further built to work with the Landlab component library. Here, with these Landlab compatible models, we further present examples of sand- and gravel-bed river long-profiles under a variety of water- and sediment-supply boundary conditions, and present the transition into models of linked tributaries reproducing river-network evolution over both human and geological time scales.