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1. DATA-MODEL COMPARISONS OF STORM PROCESSES DURING HURRICANE HARVEY

   https://doi.org/10.9753/icce.v36v.waves.40  

   Anarde, Katherine; Figlus, Jens; Cheng, Wei; Horrillo, Juan; Tissier, Marion; Lynett, Patrick; Shi, Fengyan (December 2020, Coastal Engineering Proceedings)

   null (Ed.)

   During tropical cyclones, processes including dune erosion, overwash, inundation, and storm-surge ebb can rapidly reshape barrier islands, thereby increasing coastal hazards and flood exposure inland. Relatively few measurements are available to evaluate the physical processes shaping coastal systems close to shore during these extreme events as it is inherently challenging to obtain reliable field data due to energetic waves and rapid bed level changes which can damage or shift instrumentation. However, such observations are critical toward improving and validating model forecasts of coastal storm hazards. To address these data and knowledge gaps, this study links hydrodynamic and meteorological observations with numerical modeling to 1) perform data-model inter-comparisons of relevant storm processes, namely infragravity (IG) waves, storm surge, and meteotsunamis; and 2) better understand the relative importance of each of these processes during hurricane impact.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/kUizy8nK3TU 

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2. 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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3. Understanding the Natural Variability of Still Water Levels in the San Francisco Bay Over the Past 500 yr: Implications for Future Coastal Flood Risk

   https://doi.org/10.1029/2022JC019012  

   Mukhopadhyay, Sudarshana; Leung, Meredith; Cagigal, Laura; Kucharski, John; Ruggiero, Peter; Steinschneider, Scott (February 2023, Journal of Geophysical Research: Oceans)

   Increasing exposure to coastal flood hazards will potentially induce an enormous socio‐economic toll on vulnerable communities. To accurately characterize the hazard, we must consider both natural water level variability and climate change‐induced sea‐level rise. In this study, we develop a paleo‐proxy‐based reconstruction of coastal flood events over the last 500 yr to capture natural water level variability and superimpose that reconstruction onto expected sea‐level rise to explore interannual and multidecadal variability in plausible future coastal flood risk. We first develop reconstructions of leading principal components (PCs) of sea surface temperature anomalies from 1500 CE onwards, using tree‐ring, coral, and sclerosponge chronology‐based El Niño Southern Oscillation reconstructions as predictors in a wavelet autoregression model. These reconstructions of PCs are then used in a stochastic water level emulator to develop ensemble simulations of hourly still water levels (SWLs) in the San Francisco Bay. The emulator accounts for multiple relevant processes, including monthly mean sea level (MMSL) anomalies, storm surge, and tide, all varying at different timescales. Accounting for natural variability in water levels over 1500–2000 CE increases coastal flood risk beyond that suggested by instrumental records alone. When superimposed on 0.22 m of sea‐level rise (approximately the amount experienced over the previous century), the simulations show that while high tides and large storm surges cause the smaller extreme SWLs, the larger extreme SWLs occur during concurrent high MMSL, high tides, and significant storm surges. Our findings thus highlight the need to consider natural water level variability for coastal adaptation and planning. 

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4. Extreme sea levels along coastal China: uncertainties and implications

   https://doi.org/10.1007/s00477-020-01964-0  

   Fang, Jiayi; Wahl, Thomas; Zhang, Qiang; Muis, Sanne; Hu, Pan; Fang, Jian; Du, Shiqiang; Dou, Tingfeng; Shi, Peijun (February 2021, Stochastic Environmental Research and Risk Assessment)

   null (Ed.)

   Abstract Extreme sea levels (ESLs) due to typhoon-induced storm surge threaten the societal security of densely populated coastal China. Uncertainty in extreme value analysis (EVA) for ESL estimation has large implications for coastal communities’ adaptation to natural hazards. Here we evaluate uncertainties in ESL estimation and relevant driving factors based on hourly observations from 13 tide gauge stations and a complementary dataset derived from a hydrodynamic model. Results indicate significant uncertainties in ESL estimations stemming from using different EVA methods, which then propagate to the inundation assessment. Amplification factors due to sea-level rise (SLR) are highly sensitive to local relative SLR and the shape of the exceedance probability curve, which in turn depends on the selected EVA method. The hydrodynamic model hindcast indicates that high ESLs mainly occurred in eastern coastal China due to typhoon-induced storm surge. Larger uncertainties in the modelled ESLs are found for the coasts of the Yangtze River Delta, and particularly in the river mouth region. Future research and adaptation planning should prioritize these regions given expected future rising sea level, compound flood events, and human-induced factors (e.g. subsidence). This study provides theoretical and practical references for adaptation to ESL-related hazards along coastal China, with implications for coastal regions worldwide. 

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5. Evaluating the response of a pilot dune restoration project on an urban beach to an extreme wave surge event

   https://doi.org/10.34237/1009243  

   Emery, Kyle; Baxter, Timothy; Callahan, Maxmilian; Cavanaugh, Kyle; Dugan, Jenifer; Engeman, Laura; Hubbard, David; Johnston, Karina; Walker, Ian; Wisniewski, Jenna (November 2024, Shore & Beach)

   Coastal dunes are globally recognized as natural features that can enhance coastal resilience and protection from wave events, storm surges, coastal flooding, and longer- term sea level rise. As a result, dune restoration is being increasingly used along urban and natural coasts as an adaptation option for climate change. However, information on the performance of restored dunes in response to extreme events is limited. On urban beaches where management includes grooming, dunes are often degraded or absent, leaving coastal communities more vulnerable to flooding and erosion during storms and wave events. Following an extreme wave surge event in December 2023, we compared the performance of a small (1.2 hectare) pilot dune restoration on an intensively groomed urban beach in southern California to an adjacent mechanically groomed control site. We used total water level (wave setup, tide, wave runup) as a proxy for flooding potential. The average wave runup incursion distance was extended 13.6 m farther inland on the groomed control site compared to the dune restoration site. This result demonstrates the potential for restored dunes to enhance flood protection and the potential for increasing coastal resilience using nature-based solutions on urban beaches. 

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