Quaternary Morphodynamics for two large rivers: the Fly River, PNG, and the Mekong River, Cambodia.

Friday, 19 December 2014: 5:45 PM
Rolf E Aalto, University of Exeter, Geography, Exeter, United Kingdom, John Wesley Lauer, Seattle University, Seattle, WA, United States, Stephen E Darby, University of Southampton, Southampton, United Kingdom, Miguel A Goni, Oregon State University, Corvallis, OR, United States and William E Dietrich, University of California Berkeley, Berkeley, CA, United States
During glacial marine transgressions, sediment & carbon are deposited due to the infilling of lowland fluvial systems, material that is then largely removed during ensuing regressions. Measuring & modelling these processes would help quantify the amount, timing, & preservation of these materials, providing insight into the morphodynamics of lowland fluvial systems in response to sea level change.
We investigated the infilling dynamics of the Fly and Strickland Rivers, Papua New Guinea. Field data include: 14C dated deep cores recording base level evolution over the Holocene, sonar imaging of floodbasin stratigraphy, and the observations of blocked valley lakes and weathered erosional remnants from LGM conditions. Similar research was conducted on the Mekong River, Cambodia, where we have imaged basin fill stratigraphy and recorded the extent of blocked valley lakes. Such field data provide tantalizing empirical glimpses into the landscapes & flux buffering exhibited by large tropical rivers during glacial-interglacial transitions.
We upscale our observations by modelling river system evolution, employing a GpU Lowland Landscape Evolution Model (GULLEM) to predict the evolution of the entire basin. A novel & powerful (>10 Tflops on an inexpensive computer) simulator, GULLEM models morphodynamics and estimates the accommodation space subsequently infilled during marine transgressions by representing a range of geomorphic processes, including: river & tributary incision, non-linear diffusion, sea level and isostatic change, hydraulic geometry, tectonic deformation, sediment production, transport & deposition, & tracking of the resulting stratigraphy. GULLEM's vectorized approach allows for massively parallel operation on GPUs (Graphics Processing Unit), making it practical to model coupled fluvial-landscape evolution for complex lowland river systems over large temporal and spatial scales.
Our combined approach affords estimates for the timing and budgets of sediment and carbon storage in Fly and Mekong River floodplains in response to sea level rise. This presentation will provide insights (& animations) illustrating river morphodynamics & resulting landscapes formed during the transgressions from glacial maximums to high-stand conditions. [Image: Fly River modelled during LGM]