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1. Cyclical shoreline erosion: The impact of a jettied river mouth on the downdrift barrier island

   Fallon, Andrew R; Hein, Christopher J; Rosen, Peter S; Gannon, Halley L. (January 2015, Proceedings of the 11th International Symposium on Coastal Engineering and Science of Coastal Sediment Processes)

   Beaches and inlets throughout the U.S. have been stabilized for purposes of navigation, erosion mitigation, and economic resilience, commonly leading to changes in shoreline dynamics and downdrift erosion/accretion patterns. The developed beach of Plum Island, Massachusetts is highly dynamic, experiencing regular complex erosion / accretion patterns along much of the shoreline. We analyzed > 100 years of high-water line positions derived from satellite imagery, t-sheets, historical maps, and aerial photography. Unlike most beaches, the river-proximal sections of Plum Island are not uniformly retreating. Rather, the beach undergoes short-term erosion, followed by periods of accretion and return to a long-term mean stable shoreline position. These cycles occur over different time frames and in different segments of the beach, creating an ephemeral erosion ‘hotspot’ lasting as briefly as one year. The highly dynamic and spatially diverse nature of erosion along Plum Island provides insight into the complex nature of coupled inlet-beach dynamics over multiple timescales. 

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2. Patterns and processes of beach and foredune geomorphic change along a Great Lakes shoreline: Insights from a year-long drone mapping study along Lake Michigan

   https://doi.org/10.34237/1008926  

   Theuerkauf, Ethan; Mattheus, C. Robin; Braun, Katherine; Bueno, Jenny (May 2021, Shore & Beach)

   null (Ed.)

   Coastal storms are an important driver of geomorphic change along Great Lakes shorelines. While there is abundant anecdotal evidence for storm impacts in the region, only a handful of studies over the last few decades have quantified them and addressed system morphodynamics. Annual to seasonal lake-level fluctuations and declining winter-ice covers also influence coastal response to storms, yet relationships between hydrodynamics and geomorphology are poorly constrained. Given this, the Great Lakes region lags behind marine coasts in terms of predictive modeling of future coastal change, which is a necessary tool for proactive coastal management. To help close this gap, we conducted a year-long study at a sandy beach-dune system along the western shore of Lake Michigan, evaluating storm impacts under conditions of extremely high water level and absent shorefast ice. Drone-derived beach and dune topography data were used to link geomorphic changes to specific environmental conditions. High water levels throughout the year of study facilitated erosion during relatively minor wave events, enhancing the vulnerability of the system to a large storm in January 2020. This event occurred with no shorefast ice present and anomalously high winter water levels, resulting in widespread erosion and overwash. This resulted in 20% of the total accretion and 66% of the erosion documented at the site over the entire year. Our study highlights the importance of both antecedent and present conditions in determining Great Lakes shoreline vulnerability to storm impacts. 

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3. Factors controlling longshore variations of beach changes induced by Tropical Storm Eta (2020) along Pinellas County beaches, west-central Florida

   https://doi.org/10.34237/1008929  

   Cheng, Jun; Toledo Cossu, Francesca; Wang, Ping (January 2021, Shore & Beach)

   Tropical Storm Eta impacted the coast of west-central Florida from 11 November to 12 November 2020 and generated high waves over elevated water levels for over 20 hours. A total of 148 beach and nearshore profiles, spaced about 300 m (984 ft) apart, were surveyed one to two weeks before and one to eight days after the storm to examine the beach changes along four barrier islands, including Sand Key, Treasure Island, Long Key, and Mullet Key. The high storm waves superimposed on elevated water level reached the toe of dunes or seawalls and caused dune erosion and overwash at various places. Throughout most of the coast, the dune, dry beach, and nearshore area was eroded and most of the sediment was deposited on the seaward slope of the nearshore bar, resulting in a roughly conserved sand volume above closure depth. The longshore variation of beach-profile volume loss demonstrates an overall southward decreasing trend, mainly due to a southward decreasing nearshore wave height as controlled by offshore bathymetry and shoreline configurations. The Storm Erosion Index (SEI) developed by Miller and Livermont (2008) captured the longshore variation of beach-profile volume loss reasonably well. The longshore variation of breaking wave height is the dominant factor controlling the longshore changes of SEI and beach erosion. Temporal variation of water level also played a significant role, while beach berm elevation was a minor factor. Although wider beaches tended to experience more volume loss from TS Eta due to the availability of sediment, they were effective in protecting the back beach and dune area from erosion. On the other hand, smaller profile-volume loss from narrow beach did not necessarily relate to less dune/ structure damage. The opposite is often true. Accurate evaluation of a storm’s severity in terms of erosion potential would benefit beach management especially under the circumstance of increasing storm activities due to climate change. 

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4. Coastal topography and hydrogeology control critical groundwater gradients and potential beach surface instability during storm surges

   https://doi.org/10.5194/hess-26-5987-2022  

   Paldor, Anner; Stark, Nina; Florence, Matthew; Raubenheimer, Britt; Elgar, Steve; Housego, Rachel; Frederiks, Ryan S.; Michael, Holly A. (January 2022, Hydrology and Earth System Sciences)

   Abstract. Ocean surges pose a global threat for coastal stability.These hazardous events alter flow conditions and pore pressures in floodedbeach areas during both inundation and subsequent retreat stages, which canmobilize beach material, potentially enhancing erosion significantly. Inthis study, the evolution of surge-induced pore-pressure gradients is studied through numerical hydrologic simulations of storm surges. The spatiotemporal variability of critically high gradients is analyzed in three dimensions. The analysis is based on a threshold value obtained for quicksand formationof beach materials under groundwater seepage. Simulations of surge eventsshow that, during the run-up stage, head gradients can rise to the calculated critical level landward of the advancing inundation line. During thereceding stage, critical gradients were simulated seaward of the retreatinginundation line. These gradients reach maximum magnitudes just as sea levelreturns to pre-surge levels and are most accentuated beneath the still-water shoreline, where the model surface changes slope. The gradients vary alongthe shore owing to variable beach morphology, with the largest gradientsseaward of intermediate-scale (1–3 m elevation) topographic elements (dunes)in the flood zone. These findings suggest that the common practices inmonitoring and mitigating surge-induced failures and erosion, which typically focus on the flattest areas of beaches, might need to be revised to include other topographic features. 

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5. Quantifying Coastal Storm Impacts Using a New Cumulative Storm Impact Index (CSII) Model: Application Along the Virginia Coast, USA

   https://doi.org/10.1029/2022JF006641  

   Fenster, M. S.; Dominguez, R. (September 2022, Journal of Geophysical Research: Earth Surface)

   Abstract This paper presents a new empirical model, called the cumulative storm impact index (CSII), that quantifies the impact of coastal storms on sandy beaches. The new model utilizes user‐defined storm data to incorporate both individual storm magnitude and the cumulative effect of successive storms into an index, which is a proxy for beach erosion at a given time. Applying this model to long‐term water‐level data from a Virginia tide gauge showed that the greatest storm impact resulted not from the larger individual storms, such as the Ash Wednesday nor'easter of 1962, the “Perfect Storm” of 1991, or Hurricane Sandy of 2012, but rather from especially stormy winter seasons that occurred during the twenty‐first century. Additionally, the CSII model uncovered a trend—not detectable by single storm impact analyses—toward greater storm impacts, which began c. 1980 and continued to the present day. Finally, comparative analyses using wave power as a storm index shows CSII can capture decadal or seasonal scale storminess. We expect this model to have utility in many areas of the coastal sciences and engineering, including developing holistic response models, quantifying erosion potential at other locations, and managing coastal ecosystems. 

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