UNH Ocean Seminar

Coastal Dune Morphodynamics Across Time and Space Scales: Upscaling from Grain Scale Measurements to Decadal Scale Predictions

Nick Cohn, Ph.D.
Research Oceanographer

U.S. Army Corps of Engineers
Engineer Research and Development Center’s
Coastal and Hydraulics Laboratory 

Friday, Jan. 26, 2024, 3:10pm
Chase 105

Wind-blown (aeolian) sediment transport is an important modifier of landscape change in coastal environments. Gradients in the transport field contributes to the building of coastal foredunes, which are topographically high features that are increasingly relied on to protect low-lying infrastructure from storm-induced flooding hazards along sandy coastlines. While skill in predicting wave-induced dune erosion during storms is generally improving, there are currently limited reliable quantitative tools for predicting the recovery and subsequent growth of dunes by aeolian processes in coastal systems. This deficiency limits the ability for USACE and other coastal managers to develop nature-based engineering solutions that leverage natural processes in their design to reduce flooding risk from storms and for quantifying the longevity of those features in a changing climate. As part of improving fundamental understanding of the mechanisms and time/space scales of coastal foredune growth and applied capabilities for simulating long term dune evolution, this talk discusses a series of field and modeling projects at USACE-ERDC-CHL. Specifically, this work details the use of two disparate efforts that cover end-member timescales. First, the use of novel in-line holography and sequence lidar scanning sensors for measuring properties of particle scale, wind-driven sediment transport at sub-second timescales is presented. These field studies provide new approaches for inform details on what wind and bed conditions allow for sediment mobilization. Secondly, in part using field-derived understanding of wind-driven sediment transport dynamics, new efficient numerical modeling approaches for simulating both marine-driven dune erosion and wind-driven dune growth are coupled with a climate emulator to enable long-term (up to century) scale predictions of dune stability. These parallel field and model-based efforts give a glimpse into federal agency led research on coastal sediment transport dynamics that play a role in quantifying present and future coastal change hazards along the nation’s coastline. 


Nick Cohn completed a B.S. in Earth Sciences from Boston University in 2010 and a PhD in Geology from Oregon State University in 2018. Nick is currently a Research Oceanographer at the US Army Corps of Engineers (USACE) Engineer Research and Development Center’s (ERDC’s) Coastal and Hydraulics Laboratory (CHL) where he runs a research program involving field data collection, data analysis, and numerical modeling focused on nearshore-beach-dune morphodynamics. Current work is largely focused on developing or advancing process-based numerical models for simulating marine, aeolian, and ecological processes on coastal landform evolution in both sandy and Arctic coastal systems.