Jaap Nienhuis

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Research Summary

I study the plan-view evolution of river deltas, landforms that develop as rivers deposit sediment in a lake or sea. Many active deltas face rising sea level, reduced river sediment supply and a subsiding delta plain, which makes them increasingly vulnerable to marine forces such as hurricanes. My thesis work will advance understanding of the effects of waves on deltas by investigating delta sedimentology and active sediment transport near the river mouth.

I am currently working with a detailed hydro-and-morphodynamic numerical model under the supervision of Andrew Ashton and Liviu Giosan of the Geology and Geophysics department. Using this model, I study the interaction between river mouth jets and wave-driven alongshore transport of sediment. River mouth jets are the fast flowing, sediment-laden plumes that form as a river enters a lake or the ocean.  Different properties of the river jet, such as sediment concentration, flow velocities and bottom friction, affect the morphology of the river mouth. Waves alter jet properties, but also set up a current that carries sediment alongshore. Feedbacks between waves and the jet can influence the shape of the entire delta.  The model I work with simulates the interplay between these forces in order to quantify their effects on delta morphology.

Understanding how river mouth sedimentation works in the presence of waves on timescales of 10 to 100 years will enable more focused management interventions and enable studies of river mouth evolution in changing environments. Additionally, studies of the spatial structure of sediments in these depositional environments can be used in hydrocarbon exploration.