Presenters-0657
From CSDMS
CSDMS 2024 Webinars
Migrating stripes and pulses that race to oblivion: Exploring gravel bed river morphodynamics with the Landlab NetworkSedimentTransporter
Abstract
Changes in river channel geometry and grain size can alter flood hazards and impact habitat, yet our ability to predict how perturbations will manifest as channel change remains incomplete. While flume studies are commonly employed to study the downstream effects of sediment pulses, these physical experiments cannot incorporate pulse material abrasion, a property that field observations suggest may be important in many natural landscapes. I use the Landlab Network Sediment Transporter (NST) to explore multi-grain size sediment transport dynamics at the channel scale. The NST is a morphodynamic model that allows for Lagrangian tracking of collections (‘parcels’) of sediment grains through a river channel, evolving the elevation and grain size distribution of the river bed. In this talk, I will present an exploration of gravel-bedded river morphodynamics using a simple model configuration with two goals: first, to explore migrating channel bedforms and grain patches that emerge from standard sediment transport calculations, and second, to explore the effects of bed material abrasion and sediment density on the downstream evolution of a gravel sediment pulse. With hundreds of ‘parcels’ of sediment per reach of river, uniform channel characteristics, and initial bed sediment recycled to the upstream boundary, I configure the model like a 50 km numerical recirculating flume. Allowing the channel to evolve under constant flow conditions, initially small differences in the grain size distribution of model links differentiate into coarse and fine zones that gradually migrate downstream. This emergent behavior, which mimics downstream migrating bedforms in natural channels and flumes, is controlled in the NST by the sediment transport hiding function. Next, I explore the downstream transport of sediment pulses, incorporating bed material abrasion and variability in sediment density, resembling that found in volcanic mass wasting deposits of the Pacific Northwest. I find that these properties speed the initial downstream propagation of the pulse, but limit its downstream endurance. The NST model provides us an opportunity to explore the complex interactions of heterogeneous sediment in the evolution of gravel river systems.
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