The PI will merge all the existing results from the MARGINS Gulf of Papua focus site in a high resolution numerical model to represent the entire Fly River system. This holistic approach will allow determining how transport through the entire system alters the magnitude and delivery of sediments to marine depositional sinks. The PI will spend each semester of the two years postdoctoral fellowship at a different institution (Boston University, University of Washington, UC Berkeley and Colorado University), collaborating with scientists actively engaged in research projects in the Fly River system. The developed model will interface thorough the exchanges of water and sediment fluxes four components (middle Fly and Strickland rivers, tidal river, tidal delta, and continental shelf) and will be able to follow the path of water and sediments from the uplands to the shelf slope. The synthesis model will be used to determine the sediment dispersal pathways and fluxes in the entire system and assess gaps in the Source to Sink program. The model will also simulate how tides modulate sediment and water fluxes in the lower reaches of the river, the role of tidal floodplains in storing sediments and how sea-level rise and backwater effects create blocked valleys and tie channels in the middle Fly and Strickland rivers, among others. Broader impacts include the support of new, young post-doc who will teach undergraduate classes and provide a proof of concept for CSDMS. It will also lead to a comprehensive model for large rivers solving both terrestrial and marine processes can be used as a predictive tool to assess the impact of climate change, sea-level oscillations, and human activities on coastal areas. The societal relevance of the project is global, since many large rivers are densely populated.
Deltas are vulnerable to both anthropogenic and natural changes, such as sea level rise, variations in sediment supply, increase in storm activity and hurricane frequency, urbanization, and changes in land-use practices. Human activities continuously threaten these valuable environments, and new efforts are required to improve their management and restoration strategies. Our results show that the delta of the Fly River, Papua New Guinea, is very sensitive to variations in sediment supply, caused for example by mining in the upper reaches of the river or dam construction. If the sediment discharge delivered by the river is increased, sediment deposition would reduce the flow depth. The river is not able to flush out the sediments, and the delta would experience massive aggradation. On the contrary, a reduction in sediment discharge would lead to widespread scour, possibly associated with bank erosion and widening of the estuary. The Fly River is a one of the few pristine rivers in the world, so our results are an excellent example of how a natural system functions. The results derived from this project can also be applied to other tidal deltas around the world, and will help protect, manage, and restore these delicate environments, their ecosystems, and the communities that live on them. In this project we have developed a computer model to calculate fluxes of sediments and variations in water depth in a tidal delta. The model, made available to the public through the website of the Community Surface Dynamics Modeling System, can be used by engineers to assess navigation risk in deltas also in presence of fluid mud. Finally, our long-term results of tidal delta evolution both at the large and small scale can be of help in determining the presence of natural resources (oil and gas) in these environments.
