Nicholas Cohn

Engineer Research and Development Center - U.S. Army | ERDC US Army · Coastal and Hydraulics Laboratory

Traditionally, independent tools have been used to simulate wave- or wind-driven processes to simulate coastal morphology change. Coupled models that cross the land-sea division and integrate these collective processes can increase our knowledge on complex morphodynamic interactions and improve predictions of the foreshore, beach, and dune evolutio...

Sandbars are ubiquitous morphologic features found in the nearshore environment throughout the world, yet predictive capabilities of their evolution remain limited. In order to provide new insights on the relevant processes controlling sandbar morphodynamics, this study uses a 41‐year record of 637 monthly cross‐shore profiles from Duck, North Caro...

Natural and constructed dunes are increasingly being utilized to buffer flooding impacts from storms and rising sea levels along sandy coastlines. However, a lack of data at the appropriate spatial and temporal resolution often precludes isolating the total magnitude, specific timing, and alongshore variability of volumetric coastal dune changes re...

Wind flow over coastal foredunes adapts to vegetation, resulting in spatial gradients in bed shear stresses that contribute to the formation of localized bedforms. Understanding and having the capability to numerically predict, the distribution of sediment deposited within sparsely vegetated dune complexes is critical for quantifying the ecological...

Shoreline erosion over the last few decades along the Point Hope, Alaska, USA coastline has led to considerable loss of tundra behind the beach. Analysis of available remote sensing, morphology, and hydrodynamic datasets are used to inform the time scales and mechanisms of coastal land loss at Point Hope, in part through integration of these data i...

In sandy beach systems, the aeolian sediment transport can be governed by the vertical structure of the sediment layers at the bed surface. Here, data collected with a newly developed sand scraper is presented to determine high‐resolution vertical grain size variability and how it is affected by marine and aeolian processes. Sediment samples at up...

Plain Language Summary Wind can be an important contributor to landscape changes in sandy desert and coastal environments. There are complex mechanisms by which wind moves sand that are not yet entirely understood. To answer questions about how, when, and why sand is transported by wind, experiments commonly use point‐based sensors that are unable...

Sediment grain size has a first order control on aeolian transport rates due to threshold effects. However, there remain limited in‐situ approaches to measuring properties of sediment size within the saltation layer in field environments. Here a demonstration of in‐line holography for generating quasi‐3D images of saltating particles near the bed d...

Abstract Classifying images using supervised machine learning (ML) relies on labeled training data—classes or text descriptions, for example, associated with each image. Data‐driven models are only as good as the data used for training, and this points to the importance of high‐quality labeled data for developing a ML model that has predictive skil...

A large, low pressure Nor’easter storm and Hurricane Joaquin contributed to multiple weeks of sustained, elevated wave and water level conditions along the southeastern Atlantic coast of the United States in Fall 2015. Sea level anomalies in excess of 1 m and offshore wave heights of up to 4 m were recorded during these storms, as observed at the U...

Complex two-dimensional nearshore current patterns are generated by feedbacks between sub-aqueous morphology and momentum imparted on the water column by breaking waves, winds, and tides. These non-stationary features, such as rip currents and circulation cells, respond to changing environmental conditions and underlying morphology. However, using...

Coastlines are dynamic landforms which evolve in response to their geologic characteristics and gradients in sediment transport driven by tides, currents, waves, winds, and relative sea level changes. Coastal landforms include sandy beaches, rock and cliff-backed shores, deltas, estuaries, inlets, and carbonate systems. This article provides a broa...

Despite the importance of coastal dunes to many low-lying coastal communities and ecosystems, our understanding of how both climatic and anthropogenic pressures affect foredune evolution on time scales of years to decades is relatively poor. However, recently developed coupled numerical modeling tools have allowed for the exploration of the erosion...

Coastal dunes arise from feedbacks between vegetation and sediment supply. Species-specific differences in plant functional morphology affect sand capture and dune shape. In this study, we build on research showing a relationship between dune grass species and dune geomorphology on the US central Atlantic Coast. This study seeks to determine the wa...

Coastal foredunes are topographically high features that can reduce vulnerability to storm-related flooding hazards. While the dominant aeolian, hydrodynamic, and ecological processes leading to dune growth and erosion are fairly well-understood, predictive capabilities of spatial variations in dune evolution on management and engineering timescale...

The Pacific Northwest of the United States exhibits complex spatial patterns of storm-induced coastal foredune erosion. Using oceanographic and morphologic data from three field sites encompassing a range of subaqueous and subaerial coastal profile configurations, a relationship is found between morphologic characteristics and dune volume changes d...

Coastal landscape change represents aggregated sediment transport gradients from spatially and temporally variable marine and aeolian forces. Numerous tools exist that independently simulate subaqueous and subaerial coastal profile change in response to these physical forces on a range of time scales. In this capacity, coastal foredunes have been t...

Coastal dunes are often the first and primary form of defense against destructive surge and waves that accompany extreme storm events. Beach grasses are known to affect dune height, width, and stability, contributing to the dune’s ability to protect the hinterland from wave and flooding hazards (Hacker et al. 2012). However, the interaction and fee...

The US Army Corps of Engineers (USACE) Field Research Facility (FRF) located on the Outer Banks (Duck, NC, USA) is the site of one of the longest oceanographic and morphologic datasets in the world. While no active coastal management is currently carried out at the FRF, a ~1.2 M.c.y. beach nourishment project was completed in summer 2017 in municip...

Conlin, M.; Cohn, N., and Ruggiero, P., 2018. A quantitative comparison of low-cost Structure from Motion (SfM) data collection platforms on beaches and dunes. Observations of beach and dune geomorphology are critical for characterizing coastal processes and hazards. A relatively new approach for monitoring the coastline is Structure from Motion ph...

Coastal foredune growth is typically associated with aeolian sediment transport processes while foredune erosion is associated with destructive marine processes. New datasets collected at a high energy, dissipative beach suggest that total water levels in the collision regime can cause dunes to accrete ‐ requiring a paradigm shift away from conside...

Dissipative beaches in the U.S. Pacific Northwest are subject to a marked seasonality in wave climate and water levels, which leads to periodic oscillations in the morphology of the typically dry part of the beach profile. The back-and-forth, seasonal sediment exchange between the emerged and submerged parts of the beach system induces two main dry...

Seasonal variability in wave conditions drive corresponding cycles of erosion and accretion along sandy beaches. Despite the fact that these oscillations are well documented at numerous sites throughout the world, the physical processes driving beach recovery remain poorly understood. Using field data from a low sloping, dissipative beach in the U....

The El Niño-Southern Oscillation is the dominant mode of interannual climate variability across the Pacific Ocean basin, with influence on the global climate. The two end members of the cycle, El Niño and La Niña, force anomalous oceanographic conditions and coastal response along the Pacific margin, exposing many heavily populated regions to incre...

Summary of oceanographic forcing (data for Fig. 3) and coastal response (data for Fig. 4). Numbers in bold and highlighted in yellow are the maximum values of the time-series for each region. For wave direction the most negative (southerly shifts) are bolded/highlighted.

Data inventory for study site information.

Supplementary Figure

Managing multiple ecosystem services (ESs) across landscapes presents a central challenge for ecosystem-based management, because services often exhibit spatiotemporal variation and weak associations with co-occurring ESs. Further focus on the mechanistic relationships among ESs and their underlying biophysical processes provides greater insight in...

This paper shows the first results of measured spatial variability of beach erosion due to aeolian processes during the recently conducted SEDEX 2 field experiment at Long Beach, Washington, U.S.A.. Beach erosion and sedimentation were derived using series of detailed terrestrial LIDAR measurements of beach morphology during three low tide periods....

Findings from nearly two decades of research focused on the Columbia River littoral cell (CRLC), a set of rapidly prograding coastal barriers and strand-plains in the U.S. Pacific Northwest, are synthesized to investigate the morphodynamics associated with prograding beaches. Due to a large sediment supply from the Columbia River, the CRLC is the o...

Wave runup, an important contributor to storm-induced extreme water levels, is commonly predicted via empirical formulations that parameterize coastal morphology using simple metrics such as the foreshore beach slope. However, spatially and temporally complex nearshore morphology, such as subtidal sandbars, have the potential to alter surf zone wav...

Report available from the Quileute Tribe (https://quileutenation.org/natural-resources/climate-change/

Supply-limiting factors, like moisture content and sediment armoring, influence coastal aeolian sediment transport and subsequently dune evolution significantly. We organized a 6-week field experiment on the influence of spatiotemporal variations in supply on coastal aeolian sediment transport at the Sand Motor, The Netherlands. Due to the presence...

Field observations during summer 2014 in Newport, OR, USA indicate the importance of intertidal sandbar welding for shoreline recovery and growth. Over a two month period of low energy wave conditions subtidal and intertidal sandbars migrated onshore by approximately 1 m/day. There was 19 m3/m of sediment added to the system above mean low water an...

Many coastlines throughout the world are in a net erosional state due to factors such as climate change and anthropogenic activities. While most coastal erosion occurs episodically during major storms, beaches recover during extended periods of low wave energy. Despite the importance of beach recovery on limiting coastal vulnerability, the mechanis...

High energy events such as extratropical cyclones periodically impact coastal systems, bringing elevated water levels and mobilizing sediment in the backshore. Erosion of the beach face and dune systems is a major hazard to low-lying infrastructural resources, although storms similarly alter the subaqueous coastal landform. Driven by spatial gradie...

Coastal environments are characterized by complex feedbacks between flow, sediment transport, and morphology, often resulting in the formation of nearshore sandbars. In many locations, such as Hasaki (Japan), the Netherlands, and the Columbia River Littoral Cell (CRLC, USA), these sandbars exhibit a net offshore migration (NOM) cycle whereby these...

Shoaling within the jettied inlet at Newport, Oregon has increased by 30% since 2011. The U.S. Army Corps of Engineers (USACE) hypothesize that this shoaling is associated with increased rates of aeolian sediment transport to the navigation channel from the dynamic dune field at South Beach State Park (SBSP), located adjacent to the south jetty at...

The Columbia River Littoral Cell (CRLC) in the Pacific Northwest is a modally dissipative coastline characterized by fine-grained sediment and high wave energy. Storms of magnitude are frequent in this region, with significant wave heights exceeding 10 m approximately once per year. Sandbars in the CRLC have been observed to follow the interannual...

Although many storms impact the New England coast, events large enough to breach and reshape a barrier’s morphology are relatively rare. New England experiences 15-20 extratropical storms (northeasters) annually, but hurricanes occur much less frequently (1 every 4 yrs). Still, hurricanes are the storms of record in New England in terms of storm su...