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This paper is not subject to U.S. copyright. The definitive version was published in Sherwood, C. R., van Dongeren, A., Doyle, J., Hegermiller, C. A., Hsu, T.-J., Kalra, T. S., Olabarrieta, M., Penko, A. M., Rafati, Y., Roelvink, D., van der Lugt, M., Veeramony, J., & Warner, J. C. Modeling the morphodynamics of coastal responses to extreme events: what shape are we in? Annual Review of Marine Science, 14, (2022): 457–492, https://doi.org/10.1146/annurev-marine-032221-090215., This review focuses on recent advances in process-based numerical models of the impact of extreme storms on sandy coasts. Driven by larger-scale models of meteorology and hydrodynamics, these models simulate morphodynamics across the Sallenger storm-impact scale, including swash,collision, overwash, and inundation. Models are becoming both wider (as more processes are added) and deeper (as detailed physics replaces earlier parameterizations). Algorithms for wave-induced flows and sediment transport under shoaling waves are among the recent developments. Community and open-source models have become the norm. Observations of initial conditions (topography, land cover, and sediment characteristics) have become more detailed, and improvements in tropical cyclone and wave models provide forcing (winds, waves, surge, and upland flow) that is better resolved and more accurate, yielding commensurate improvements in model skill. We foresee that future storm-impact models will increasingly resolve individual waves, apply data assimilation, and be used in ensemble modeling modes to predict uncertainties., All authors except D.R. were partially supported by the IFMSIP project, funded by US Office of Naval Research grant PE 0601153N under contracts N00014-17-1-2459 (Deltares), N00014-18-1-2785 (University of Delaware), N0001419WX00733 (US Naval Research Laboratory, Monterey), N0001418WX01447 (US Naval Research Laboratory, Stennis Space Center), and N0001418IP00016 (US Geological Survey). C.R.S., C.A.H., T.S.K., and J.C.W. were supported by the US Geological Survey Coastal/Marine Hazards and Resources Program. A.v.D. and M.v.d.L. were supported by the Deltares Strategic Research project Quantifying Flood Hazards and Impacts. M.O. acknowledges support from National Science Foundation project OCE-1554892.

In this study, we estimate the shoreline retreat, the vulnerability and the erosion rates of an open beach-dune system under projected sea level rise (SLR) and the action of wind-waves (separately and in combination). The methodology is based on the combination of two state-of-the-art numerical models (XBeach and Q2D-morfo) applied in a probabilistic framework and it is implemented in an open sandy beach in Menorca Island (Western Mediterranean). We compute the shoreline response to SLR during the 21st century and we assess the changing impacts of storm waves on the aerial beach-dune system. Results demonstrate the relevant role that the beach backshore features, such as the berm, play as coastal defense, reducing the shoreline retreat and dune vulnerability rates in the near-term (a few decades ahead) and highlighting the importance of simulating the beach morphodynamic processes in coastal impacts assessments. Our findings point at SLR as the major driver of the projected impacts over the beach-dune system, leading to an increase of ~25% of the volume eroded due to storm waves by the end of the century with respect to present-day conditions., Postprint (published version)

In the light of challenges raised by a changing climate and increasing population pressure in coastal regions, it has become clear that theoretical models and scattered experiments do not provide the data we urgently need to understand coastal conditions and processes. We propose a Dutch coastline observatory named ICON.NL, based at the Delfland Coast with core observations focused on the internationally well-known Sand Engine experiment, as part of an International Coastline Observatories Network (ICON). ICON.NL will cover the physics and ecology from deep water to the dunes. Data will be collected continuously by novel remote sensing and in-situ sensors, coupled to numerical models to yield unsurpassed long-term coastline measurements. The combination of the unique site and ambitious monitoring design enables new avenues in coastal science and a leap in interdisciplinary research.

In this study, we estimate the shoreline retreat, the vulnerability and the erosion rates of an open beach-dune system under projected sea level rise (SLR) and the action of wind-waves (separately and in combination). The methodology is based on the combination of two state-of-the-art numerical models (XBeach and Q2D-morfo) applied in a probabilistic framework and it is implemented in an open sandy beach in Menorca Island (Western Mediterranean). We compute the shoreline response to SLR during the 21st century and we assess the changing impacts of storm waves on the aerial beach-dune system. Results demonstrate the relevant role that the beach backshore features, such as the berm, play as coastal defense, reducing the shoreline retreat and dune vulnerability rates in the near-term (a few decades ahead) and highlighting the importance of simulating the beach morphodynamic processes in coastal impacts assessments. Our findings point at SLR as the major driver of the projected impacts over the beach-dune system, leading to an increase of ~25% of the volume eroded due to storm waves by the end of the century with respect to present-day conditions.

Infragravity (hereafter IG) waves are surface ocean waves with frequencies below those of wind-generated "short waves" (typically be- low 0.04 Hz). Here we focus on the most common type of IG waves, those induced by the presence of groups in incident short waves. Three related mechanisms explain their generation: (1) the development, shoaling and release of waves bound to the short-wave group envelopes (2) the modulation by these envelopes of the location where short waves break, and (3) the merging of bores (breaking wave front, resembling to a hydraulic jump) inside the surfzone. When reaching shallow water (O(1-10 m)), IG waves can transfer part of their energy back to higher frequencies, a process which is highly dependent on beach slope. On gently sloping beaches, IG waves can dissipate a substantial amount of energy through depth-limited breaking. When the bottom is very rough, such as in coral reef environments, a substantial amount of energy can be dissipated through bottom friction. IG wave energy that is not dissipated is reflected seaward, predominantly for the lowest IG frequencies and on steep bottom slopes. This reflection of the lowest IG frequencies can result in the development of standing (also known as stationary) waves. Reflected IG waves can be refractively trapped so that quasi-periodic along-shore patterns, also referred to as edge waves, can develop. IG waves have a large range of implications in the hydro-sedimentary dynamics of coastal zones. For example, they can modulate cur- rent velocities in rip channels and strongly influence cross-shore and longshore mixing. On sandy beaches, IG waves can strongly impact the water table and associated groundwater flows. On gently sloping beaches and especially under storm conditions, IG waves can dominate cross-shore sediment transport, generally promoting offshore transport inside the surfzone. Under storm conditions, IG waves can also induce overwash and eventually promote dune erosion and barrier

Infragravity (hereafter IG) waves are surface ocean waves with frequencies below those of wind-generated "short waves" (typically be- low 0.04 Hz). Here we focus on the most common type of IG waves, those induced by the presence of groups in incident short waves. Three related mechanisms explain their generation: (1) the development, shoaling and release of waves bound to the short-wave group envelopes (2) the modulation by these envelopes of the location where short waves break, and (3) the merging of bores (breaking wave front, resembling to a hydraulic jump) inside the surfzone. When reaching shallow water (O(1-10 m)), IG waves can transfer part of their energy back to higher frequencies, a process which is highly dependent on beach slope. On gently sloping beaches, IG waves can dissipate a substantial amount of energy through depth-limited breaking. When the bottom is very rough, such as in coral reef environments, a substantial amount of energy can be dissipated through bottom friction. IG wave energy that is not dissipated is reflected seaward, predominantly for the lowest IG frequencies and on steep bottom slopes. This reflection of the lowest IG frequencies can result in the development of standing (also known as stationary) waves. Reflected IG waves can be refractively trapped so that quasi-periodic along-shore patterns, also referred to as edge waves, can develop. IG waves have a large range of implications in the hydro-sedimentary dynamics of coastal zones. For example, they can modulate cur- rent velocities in rip channels and strongly influence cross-shore and longshore mixing. On sandy beaches, IG waves can strongly impact the water table and associated groundwater flows. On gently sloping beaches and especially under storm conditions, IG waves can dominate cross-shore sediment transport, generally promoting offshore transport inside the surfzone. Under storm conditions, IG waves can also induce overwash and eventually promote dune erosion and barrier

Infragravity (hereafter IG) waves are surface ocean waves with frequencies below those of wind-generated "short waves" (typically be- low 0.04 Hz). Here we focus on the most common type of IG waves, those induced by the presence of groups in incident short waves. Three related mechanisms explain their generation: (1) the development, shoaling and release of waves bound to the short-wave group envelopes (2) the modulation by these envelopes of the location where short waves break, and (3) the merging of bores (breaking wave front, resembling to a hydraulic jump) inside the surfzone. When reaching shallow water (O(1-10 m)), IG waves can transfer part of their energy back to higher frequencies, a process which is highly dependent on beach slope. On gently sloping beaches, IG waves can dissipate a substantial amount of energy through depth-limited breaking. When the bottom is very rough, such as in coral reef environments, a substantial amount of energy can be dissipated through bottom friction. IG wave energy that is not dissipated is reflected seaward, predominantly for the lowest IG frequencies and on steep bottom slopes. This reflection of the lowest IG frequencies can result in the development of standing (also known as stationary) waves. Reflected IG waves can be refractively trapped so that quasi-periodic along-shore patterns, also referred to as edge waves, can develop. IG waves have a large range of implications in the hydro-sedimentary dynamics of coastal zones. For example, they can modulate cur- rent velocities in rip channels and strongly influence cross-shore and longshore mixing. On sandy beaches, IG waves can strongly impact the water table and associated groundwater flows. On gently sloping beaches and especially under storm conditions, IG waves can dominate cross-shore sediment transport, generally promoting offshore transport inside the surfzone. Under storm conditions, IG waves can also induce overwash and eventually promote dune erosion and barrier

Coastal zones in the vicinity of tidal inlets are commonly utilised for navigation, fishing, sand mining, waterfront development and recreation and are under very high population pressure. Any negative impacts of climate change (CC) on inlet environment are therefore very likely to result in significant socio-economic impacts. CC driven variations in mean water level (i.e. SLR), wave conditions and riverflow are likely to affect the stability of, particularly, the thousands of Small Tidal Inlets (STIs, or bar-built/barrier estuary systems) around the world. The combination of their predominant occurrence in developing countries, socio-economic relevance and low community resilience, general lack of data, and high sensitivity to seasonal forcing makes STIs potentially very vulnerable to CC impacts. This article summarises potential CC impacts on the stability of STIs and discusses means by which these CC impacts maybe quantified using existing modelling tools. As presently available process based models cannot be confidently applied with concurrent time varying water level, wave and riverflow forcing over typical CC impact assessment time scales (~100 years), a ‘snap-shot’ simulation (~1 year duration) approach using process based coastal area morphodyamic models is proposed for qualitative assessments of CC impacts on STIs. As the modelling approach will by necessity depend on the level of data availability, two different‘snap-shot’ modelling frameworks for ‘data rich’ and ‘data poor’ environments are presented. Process based multi-scale coastal area morphodynamic models and scale aggregated (or reduced complexity) morphodynamic models are identified as modelling approaches that may be pursued in the future to obtain more reliable assessments of CC impacts on STI stability.

This interim report describes activities in the second quarter of the second year of the project `Modeling of Hurricane Impacts'. In agreement with the funding agency, the work was carried out over the period August-December 2007. Three main lines of work are described in this report, viz. dissemination of model and results, model improvements and testing.

This fifth interim report describes ongoing development and validation of the XBeach model as part of the MORPHOS project and other activities over the period September-December 2007 (period extended due to delay in funding)., Prepared in cooperation with WL Delft Hydraulics, Delft, Netherlands; Delft University of Technology, Delft, Netherlands; and University of Miami, Florida. Task no. 1002. Sponsored in part by US Army Corps of Engineers, Engineer Research and Development Center (ERDC), European Research Office. The original document contains color images.

This fourth interim report describes ongoing development and validation of the XBeach model as part of the MORPHOS project and other activities over the period March-August 2007 (period extended due to late approval to continue), The original document contains color images. Prepared in collaboration with WL|Delft Hydraulics, Delft Univ. of Technology, Delft, The Netherlands, and Univ. of Miami, Florida.

This first annual report describes ongoing development and validation of the XBeach model as part of the MORPHOS project and other activities over the period 1 March 2006-1 March 2007 and provides documentation and user manual for the present version of the model., The original document contains color images. Task no. 0004. Prepared in cooperation with WL/Delft Hydraulics and Delft University of Technology, Delft, Netherlands. Sponsored in part by the U.S. Army Corps of Engineers, Engineer Research and Development Center.

The long-term goals are to provide accurate and detailed predictions of nearshore hydrodynamics and bathymetric evolution using an advanced process-based model (Delft3D). Observations of dense remotely-sensed and sparse in situ data will be assimilated to continuously improve model performance, and where the data is uncertain or absent, the model will be used to fill in the gaps and construct a more complete estimate of current or near-future conditions. The objectives of the proposed study are to: (1) Develop methods for estimating relevant Delft3D model inputs and outputs from airborne and shore-based video and radar observations. (2) Develop and implement techniques to assimilate these data in Delft3D. (3) Validate the assimilation model by hindcasting with the remote observations and sparse in situ data sampled from field experiments. (4) Improve numerical model formulations to narrow error bands on model predictions (5) Generate nowcasts and forecasts of the nearshore environment., Sponsored in part by contract nos. N00014-05-1-0227 and N00014-05-1-0199

The long-term goals are to provide accurate and detailed predictions of nearshore hydrodynamics and bathymetric evolution using an advanced process-based model (Delft3D). Observations of dense remotely-sensed and sparse in situ data will be assimilated to continuously improve model performance, and where the data is uncertain or absent, the model will be used to fill in the gaps and construct a more complete estimate of current or near-future conditions., Prepared in cooperation with Delft Hydraulics, Delft, The Netherlands, the School of Physical, Environmental and Mathematical Sciences, Australian Defence Force Academy, University of New South Wales, Canberra, Australia, CSIRO Marine and Atmospheric Research, Wembley, Western Australia, the Ohio State University, Columbus, and Delft University of Technology, Delft, The Netherlands. Also sponsored by ONR N00014-05-1-0226, N00014-05-1-0226, N00014-05-1-0227, N00014-05-1-0199. The original document contains color images.