Dynamics of and Transport by Buoyant Coastal Ocean Currents Driven by Spatially Distributed and Highly-Time Dependent Coastal Mountain Rivers

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Small mountainous river (SMR) systems have been shown to contribute a significant fraction of the global sediment and particulate organic carbon fluxes to the ocean. They are also important intermittent sources of nutrients and trace metals to the coastal ocean. Large-scale storm events are the dominant source of freshwater for these systems. Subsequent discharge to the coastal ocean occurs coherently across the river system as a large episodic pulse during which winds and waves are typically strong over the ocean. The dynamics of river plumes and buoyant coastal flows from these intermittent, but large pulses of discharge have received little scientific attention. This numerical modeling study will quantify the dynamics of the combined buoyancy and wind driven flows of an SMR system. Models of an idealized SMR system and the SMR system of the Oregon coastal range will be used to characterize the transport pathways of freshwater and river derived materials under different discharge and wind regimes. Intellectual Merit: The dynamics of buoyant coastal flows from the coherent but highly intermittent discharge of rivers of an SMR system, such as that of Oregon coastal range, have received very little scientific study. Yet the instantaneous combined discharge from these rivers can be greater than 20,000 m3/s during the winter, exceeding the discharge of the larger Columbia River to the north. Buoyancy forcing on the inner shelf must be important during these periods. This study will quantify the significance of SMR buoyancy forcing, characterize the interactions between the buoyancy driven and wind driven circulation of the Oregon inner shelf and quantify the fate of materials derived from SMR estuaries and the connectivity between SMR estuaries along the Oregon coast. Broader Impact: The principal investigator will collaborate with Lincoln County School District teachers to develop high school curriculum material focused on watershed transport processes, the impact of rivers on the coastal ocean, and scientific methods used to study river, estuary, and coastal flow including modeling and measurement methods. The curriculum will be shared broadly through online dissemination. In addition, model predictions of current variability and a description of the dominant forcing regimes of the Oregon inner shelf will be provided to the Northwest National Marine Renewable Energy Center in order to facilitate their wave energy research, development, device testing and impact studies off the Oregon coast. A PhD graduate student will be trained under this grant. The focus of her/his research will be on understanding the role of SMR systems on buoyant coastal circulation off of Oregon.