Bruno Castelle

Mitchell D Harley

Ch.22 Extreme events: impact and recovery

Keywords: Coastal storms, beaches, coastal dunes, erosion, recovery, shoreline, subaerial beach

Sandy coast changes on timescales from days to years and sometimes decades, primarily result from the erosion-recovery (im)balance that is controlled by the respective contributions of storms and recovery conditions. Over the last decade, our understanding and predictive ability of storm-driven erosion and subsequent multi-day to multi-annual recovery has greatly improved, notably thanks to long-term and rapidresponse coastal monitoring programs. This chapter gives a broad overview of the definitions and processes that control storm-driven beach and dune erosion and subsequent (partial, complete or excess) recovery. Key conceptual concepts are illustrated using two well-documented case studies: response and (partial) multi-annual recovery from (1) over a severe winter period along the Atlantic coast of Europe characterised by unusually strong storm clustering episode; and (2) from a single severe storm with an anomalous wave direction along the southeast coastline of Australia. Finally, future perspectives and knowledge gaps in relation to impacts and recovery from extreme events are discussed.

Introduction

Coastal change on sandy coasts is driven by a wealth of processes interacting with each other across a wide range of temporal and spatial scales [START_REF] Stive | How important is global warming for coastal erosion? An editorial comment[END_REF][START_REF] Cooper | Identifying storm impacts on an embayed, high-energy coastline: examples from western Ireland[END_REF]. The primary cause of major episodic morphological variability at the coast are coastal storms, during which beach and dune erosion [START_REF] Castelle | Impact of the winter 2013-2014 series of severe Western Europe storms on a double-barred sandy coast: Beach and dune erosion and megacusp embayments[END_REF], cliff failure [START_REF] Earlie | Coastal cliff ground motions and response to extreme storm waves[END_REF] and transport up to even boulder deposits [START_REF] Cox | Extraordinary boulder transport by storm waves (west of Ireland, winter 2013-2014), and criteria for analysing coastal boulder deposits[END_REF] can be observed as a direct result of storm-driven wave action. Except along coastal embayments, where longshore transport can dominate a shoreline change signal as a result of beach rotation (Ruiz de Alegria-Arzaburu and [START_REF] Ruiz De Alegria-Arzaburu | Storm response and beach rotation on a gravel beach, Slapton Sands[END_REF], on most open coasts, storm-driven beach and dune erosion largely involves cross-shore sediment transport [START_REF] Yates | Equilibrium shoreline response: Observations and modeling[END_REF]Splinter et al., 2014a). During storms, sediment from the beach and nearby dune is transported rapidly seaward by bed return flow (undertow) (e.g., [START_REF] Hoefel | Wave-induced sediment transport and sandbar migration[END_REF]. During post-storm conditions, wave nonlinearities slowly move sediment from the upper shoreface back to the subaerial beach [START_REF] Hoefel | Wave-induced sediment transport and sandbar migration[END_REF][START_REF] Ruessink | Modeling cross-shore sandbar behavior on the timescales of weeks[END_REF][START_REF] Dubarbier | Process-based modelling of beach profile behaviour[END_REF], which can subsequently feed the eroded coastal dune through aeolian transport [START_REF] Bauer | Aeolian sediment transport on a beach: Surface moisture, wind fetch, and mean transport[END_REF]. Longerterm (i.e., decades and centuries) coastal change is largely affected by longshore processes (e.g., [START_REF] Hansen | Sub-weekly to interannual variability of a high-energy shoreline[END_REF], sea level rise (Le [START_REF] Cozannet | Uncertainties of sandy shoreline change projections as sea level rises[END_REF] and large-scale sediment budget [START_REF] Cooper | Predicting coastal evolution using a sediment budget approach: a case study from southern England[END_REF].

On shorter timescales, i.e. from weeks to years and sometimes decades, coastal change primarily results from the erosion-recovery (im)balance that is controlled by the respective contributions of storms and recovery conditions. Quantifying beach recovery is therefore as important as beach erosion, and is required to increase our ability to understand and further predict coastal evolution on a wide range of timescales.

While a single, isolated, severe coastal storm can have a dramatic and long-lasting impact on the coast [START_REF] Thom | Behaviour of beach profiles during accretion and erosion dominated periods[END_REF][START_REF] Harley | Extreme coastal erosion enhanced by anomalous extratropical storm wave direction[END_REF], the combined impacts of a series of less severe storms can also lead to severe coastal erosion [START_REF] Ferreira | The role of storm groups in the erosion of sandy coasts[END_REF]. Indeed, coastal storm events sometimes occur in rapid succession separated by a short time interval (~2-3 days), which is commonly referred to as a storm cluster, storm group or sequence of storms. Storm clustering, for instance, is a frequent synoptic feature in the Euro-Atlantic area with serial storm clustering occurring in both the flanks and downstream regions of the North Atlantic storm track [START_REF] Pinto | Serial clustering of extratropical cyclones over the North Atlantic and Europe under recent and future climate conditions[END_REF]. In addition, average storm event based on the probability distribution of wave height can have a significant impact on the coast if coinciding with other hazards, such as spring high tide and/or storm surge. It is therefore critical to address the synchronicity of environmental parameters to better assess extreme events [START_REF] Cooper | Identifying storm impacts on an embayed, high-energy coastline: examples from western Ireland[END_REF][START_REF] Guisado-Pintado | Multi-scale variability of storm Ophelia 2017: The importance of synchronised environmental variables in coastal impact[END_REF]. As such, in the presence of storm clusters, a positive storm surge may last for several days and the probability that it coincides with a high tide or even brackets several tidal cycles, including a spring high tide, is greatly enhanced.

There has been considerable research interest in the impact of storms and storm groups on shoreline and beach dynamics (e.g., [START_REF] Birkemeier | The effects of the 19 December 1977 coastal storm on beaches in North Carolina and New Jersey[END_REF][START_REF] Zhang | Do storms cause long-term beach erosion along the U.S. east barrier coast?[END_REF][START_REF] Ferreira | Storm groups versus extreme single storms: Predicted erosion and management consequences[END_REF][START_REF] Ferreira | The role of storm groups in the erosion of sandy coasts[END_REF][START_REF] Loureiro | Extreme erosion on high-energy embayed beaches: Influence of megarips and storm grouping[END_REF]Splinter et al., 2014b;[START_REF] Coco | Beach response to a sequence of storms[END_REF]Karunarathna et al., 2014;Masselink et al., 2016a). Beach and dune recovery after these events however, have received less attention by the coastal research community. This is despite the fact that the timing and magnitude of recovery can provide useful proxy measures of coastal resilience, which is critical in the context of a rapidly changing climate. However, recently there has been increasing interest in the topic, with research providing new insights into patterns and timescales of recovery and modelling predictability (Houser et al., 2015;[START_REF] Scott | The extreme 2013/2014 winter storms: beach recovery along the southwest coast of England[END_REF]Castelle et al., 2017a;Philipps et al., 2017;[START_REF] Burvingt | Climate forcing of regionally-coherent extreme storm impact and recovery on embayed beaches[END_REF][START_REF] Dodet | Beach recovery from extreme storm activity during the 2013/14 winter along the Atlantic coast of Europe[END_REF][START_REF] Phillips | Modes of berm and beachface recovery following storm reset: observations using a continuously scanning Lidar[END_REF].

In this chapter, the definitions of extreme events, storm impact and beach/dune recovery are initially reviewed, highlighting a variety of concepts and thresholds and calling for clearer and more consistent definitions and communication to support understanding and management of extreme events. Secondly, we examine the means by which we can characterise storm impacts and recovery (considering both alongshore uniform and alongshore-variable responses). The third section describes recent examples of storm impacts and recovery on sandy coasts involving: response and (partial) recovery from: (1) a severe winter along the Atlantic coast of Europe characterised by exceptional serials of storm clusters and widespread coastal erosion; and (2) a single severe storm with an anomalous wave direction along the southeast coastline of Australia. In the last section, a summary and discussion is provided on future perspectives and knowledge gaps in our understanding of actual impacts and recovery from extreme storm wave events.

Definitions

Extreme events

In coastal sciences, like in other fields, there are many ways of deciding what defines an event 'extreme'. In coastal research and engineering, there is no semantic difference between storm and extreme storm. Storm events along the coast can be characterised by variables such as storm magnitude (in terms of significant wave height and wind speed), storm direction, storm duration, tidal stage and water level surge relative to the storm event [START_REF] Guisado-Pintado | Multi-scale variability of storm Ophelia 2017: The importance of synchronised environmental variables in coastal impact[END_REF]. Other definitions can also include impacts (e.g., coastal dune erosion, storm demand, marine flooding), which blurs the distinction between extreme 'event' and extreme 'impact ' (McPhilipps et al., 2018). Hereafter, the definitions of extreme events are essentially based on meteorological and oceanographic forcing variables.

On wave-dominated coasts, a storm is usually defined as an event in which the wave height exceeds a certain threshold HT, known as the peak-over-threshold (POT) approach (Fig. 22.1a; see the review of [START_REF] Harley | Coastal Storm Definition[END_REF]. Such a threshold has often been proposed subjectively (e.g. 2.5 m offshore of Sydney in [START_REF] Short | Wave climate of the Sydney region, an energetic and highly variable ocean wave regime[END_REF]; 6 m along the Portuguese coast in Ferreira (2005)) as a limit above which significant erosion is typically observed along the coast of interest. A more objective and transferable peak-over-threshold approach is the use of the probability distribution of the wave height, for example the 0.5% exceedance level (Luceno et al., 2006) or the 5% exceedance level [START_REF] Castelle | Impact of the winter 2013-2014 series of severe Western Europe storms on a double-barred sandy coast: Beach and dune erosion and megacusp embayments[END_REF]. Storm duration can therefore be defined as the duration over which wave height exceeds this threshold, but initiation and end of the event can also be defined as the time when wave height exceeds another quantile (e.g. the 25% exceedance level in [START_REF] Masselink | Role of wave forcing, storms and NAO in outer bar dynamics on a high-energy macro-tidal beach[END_REF]. The meteorological independence criterion [START_REF] Harley | Coastal Storm Definition[END_REF] restricts the period of time between individual storm events, with anything shorter considered to be part of the same storm (Fig. 22.1a). This arbitrary criterion can vary from 30 hours [START_REF] Almeida | Thresholds for storm impacts on an exposed sandy coastal area in southern Portugal[END_REF] to two weeks [START_REF] Corbella | Multivariate return periods of sea storms for coastal erosion risk assessment[END_REF]. Also arbitrarily defined is the maximum time for which two storms are considered part of the same cluster, for example this is defined as 9 days in Karunaranthna et al. (2014), 14 and21 days in Ferreira (2005) and up to 39 days by [START_REF] Lee | Storm-driven variability of the beach-nearshore profile at Duck, North Carolina, USA, 1981-1991[END_REF]. The wide range of definitions and thresholds can produce dramatic differences in the number and duration of defined storm events (Fig. 22.1b). Storm wave conditions (defined by the above thresholds) coinciding with spring high tides and (positive) storm surge, or increases in incident wave exposure due to differing offshore wave directions, can also increase the coastal erosion hazard. The compound effects of waves and water levels can be assessed using complex process-based models, or by summing the tide level, the empirical vertical wave runup and storm surge estimation [START_REF] Ruggiero | Wave runup, extreme water levels and the erosion of properties backing beaches[END_REF][START_REF] Young | Observations of coastal cliff base waves, sand levels, and cliff top shaking[END_REF].

Beach and dune erosion

In basic terms, beach erosion is defined as a net loss of beach sediments over a particular vertical (2D) section of the beach profile and time scale of interest. This net sediment loss is manifested in a number of morphological signatures on the coast, including: a reduction in subaerial beach area; a landward migration of the shoreline; an overall lowering of the subaerial beach profile; presence of erosion scarps; and ultimately an undermining of dunes, cliffs and any back-beach infrastructure that may be present. Beach erosion is one of the most common impacts of extreme storm events, as elevated wave energy, in combination with winds, currents and elevated water levels drive sediment offshore from shallow to deeper waters. For particularly extreme events, this net loss of sediment might extend across the entire active beach profile i.e., from the dune or cliff maxima down to a depth of negligible beach profile change known as the depth of closure. Such an immense loss of sediment may take decades for the beach system to recover from, if at all. In most cases however, storm events cause a simple redistribution of beach sediment, such that the subaerial beach experiences erosion while the subaqueous surf zone gains sediment lost from the subaerial beach. An example of a typical beach profile response from an extreme storm is presented in Fig. 22.2. In this example, sediment is redistributed by the storm waves from the subaerial beach to a single storm bar a few hundred metres offshore. Here the dune toe is defined by the 3 m elevation contour.

Beach erosion due to storms is usually defined by the loss in beach sediment volume specifically above mean sea level (given in units m 3 /m, refer Fig. 22.2b). For exposed, open-coast locations with large sandy dune systems, subaerial beach volume losses of up to 350 m 3 per alongshore metre of beach/dune system have been observed locally in the alignment of megacusp embayments (Castelle et al., 2017a). This subaerial volume change is often a good proxy for shoreline change [START_REF] Robinet | Statistical modeling of interannual shoreline change driven by North Atlantic climate variability spanning 2000-2014 in the Bay of Biscay[END_REF], since the majority of sediment lost from the subaerial beach occurs in the vicinity of the shoreline itself [START_REF] Farris | Shoreline change as a proxy for subaerial beach volume change[END_REF][START_REF] Harley | Assessment and integration of conventional, RTK-GPS and image-derived beach survey methods for daily to decadal coastal monitoring[END_REF]. The magnitude of subaerial beach volume change caused by a storm or storm cluster is an important variable in coastal engineering as it helps guide the determination of appropriate setback lines due to coastal storms [START_REF] Callaghan | Quantifying the storm erosion hazard for coastal planning[END_REF]. In planning coastal setback lines, it is typically assumed that a storm event or storm cluster with a given return period (e.g. a 1-in-100 year event) will result in an equivalent loss in subaerial beach volume known as the storm demand. Once this value is known, an appropriate buffer distance separating valuable infrastructure and residential properties from the shoreline can then be estimated [START_REF] Kinsela | Second-pass assessment of potential exposure to shoreline change in New South Wales, Australia, using a sediment compartments framework[END_REF].

Similar to subaerial beach erosion, dune erosion is a measure of the volume of dune sediment lost per alongshore metre of beach (also in m 3 /m, refer Fig. 22.2b). This value is typically defined by the volume of dune sediment above the dune toe, whose elevation is site-specific and related to the tidal range, local wind and wave conditions as well as sediment characteristics. The practical difficulties in accurately identifying the dune toe means that this threshold is often defined by a representative elevation contour (e.g. the 3 m contour as per Fig. 22.2b). While the dune volume change usually represents only a small fraction of the overall subaerial beach volume change, it is of critical importance to evaluating coastal storm impacts, as volume lost from the dunes due to storms can undermine nearby infrastructure (e.g. roads and residential properties) and lead to major inundation of the coastal hinterland. Dune volume losses also take many times longer to recover naturally compared to the rest of the subaerial beach profile (refer Section 22. 3.2 below).

Dune erosion also supplies sand to the surf zone and consequently reduces the demand and erosion of the subaerial beach.

Recovery

In general terms, the word 'recovery' is defined as "a return to a normal state of health, mind or strength" or "the action or process of regaining possession or control of something stolen or lost" (Oxford Dictionary of English, 2010). This broad definition masks a considerable variability when it comes specifically to beach recovery. A wealth of morphological indicators of beach recovery can be considered depending on morphological settings and the cross-shore region of interest. Philipps ( 2018) reviewed all existing morphological indicators. Amongst 16 different morphological indicators, the most commonly used are: subaerial beach volume in the subaerial region (e.g. [START_REF] Birkemeier | The effects of the 19 December 1977 coastal storm on beaches in North Carolina and New Jersey[END_REF][START_REF] Morton | Stages and durations of post-strom beach recovery; Southeastern Texas Coats, USA[END_REF]; shoreline position, of which definition can vary, in the foreshore region (e.g. Philipps et al., 2017); dune volume (e.g. [START_REF] Suanez | Dune recovery after storm erosion on a high-energy beach: Vougot Beach, Brittany (France)[END_REF] or dune crest height (Houser et al., 2015) in the backshore. Due to the difficulties in monitoring the nearshore region, only a small number of studies have used a subaqueous morphological indicator (e.g. offshore sandbar position) for beach recovery. Consideration of subaqueous indicators can however, provide a broader description of beach recovery in addition to the more commonly observed subaerial indicators (see Section 22.5).

Storm erosion and the post-storm recovery signal is affected by other natural modes of variability, such as longer-term trends due to additional sediment sources or sinks (e.g., river mouth, inner shelf) or gradients in longshore sediment transport. Building on observations along a 30-km stretch of coast in Texas, USA, [START_REF] Morton | Stages and durations of post-strom beach recovery; Southeastern Texas Coats, USA[END_REF] proposed four different post-storm recovery scenarios (Fig. 22.3): complete recovery (Fig.

22.3a)

; no recovery with continued erosion (Fig. 22.3b); partial recovery (Fig. 22.3c) and excess recovery (Fig.

22.3d

) relative to pre-storm conditions. It is important to note that, within cycles of erosion/recovery, which can be sub-to multi-annual, intermediate storm activity during recovery can result in smaller sub-cycles of erosion and recovery in the subaerial beach. Erosion/recovery cycles can also be multi-decadal or even longer, for instance on beaches adjacent to estuaries and tidal inlets (Castelle et al., 2018a). These systems disrupt the longshore drift and sediment supply and exhibit cyclic and/or migrating behaviour [START_REF] Ridderinkhof | Cyclic behaviour of sandy shoals on the ebb-tidal deltas of the Wadden Sea[END_REF]. Coastal lagoon openings are additional processes implying more complex and longer erosion/recovery cycles (e.g., [START_REF] Costas | Persistence of storm-induced morphology on a modal low-energy beach: A case study from NW-Iberian Peninsula[END_REF][START_REF] Baldock | Morphodynamic evolution of a coastal lagoon entrance during swash overwash[END_REF]. [START_REF] Morton | Stages and durations of post-strom beach recovery; Southeastern Texas Coats, USA[END_REF].

Characterisation of storm impact and recovery

Storm impacts

Storm impact regimes

The impacts of coastal storms are multi-faceted and span a range of socio-economic indicators [START_REF] Ciavola | The RISC-KIT storm impact database: a new tool in support of DRR[END_REF]. Focusing specifically on the hydro/morphological impacts of coastal storms, [START_REF] Sallenger | Storm impact scale for barrier islands[END_REF] recognised a gradation of impacts depending on the vertical (2D) extent of storm influence on the localised beach profile. Specifically, [START_REF] Sallenger | Storm impact scale for barrier islands[END_REF] proposed four storm impact regimes according to the maximum (Rhigh) and minimum (Rlow) wave runup levels of the storm relative to the elevations of the localised dune crest (Dhigh) and dune toe (Dlow). Maximum and minimum wave runup levels are defined in this impact scale by the 2% and 98% exceedance threshold levels, which can be calculated using the empirical wave runup equations of [START_REF] Stockdon | Empirical parameterization of setup, swash and runup[END_REF] or others (e.g. [START_REF] Holman | Extreme value statistics for wave run-up on a natural beach[END_REF]. Because of its ability to capture a range of hydro/morphodynamic processes related to storm impacts, the Sallenger storm impact scale has since been adopted as a standard measure of storm impacts on a range of coastlines (e.g. [START_REF] Armaroli | Critical storm thresholds for significant morphological changes and damage along the Emilia-Romagna coastline, Italy[END_REF][START_REF] Plant | Examples of Storm Impacts on Barrier Islands[END_REF]. The four regimes -namely, swash, collision, overwash and inundation, are described in more detail below and presented schematically in Fig. 22.4.

1) Swash regime (Rhigh < Dlow): this regime, representing the lowest of the four impacts regimes, occurs when storm wave runup is confined to the berm and beachface and does not interact with the dune profile. Since waves do not reach the dunes, the potential for erosion and inundation in this regime is theoretically limited to the lower subaerial beach (i.e., below the dune toe) and the storm impacts are considered relatively minor.

2) Collision regime (Rhigh > Dlow, Rlow < Dlow): the collision regime occurs when storm wave energy and/or ocean water levels are sufficiently elevated that some waves collide with the seaward face of the dune. Depending on the duration and force of these collisions, as well as dune structure (e.g. geometry, composition and vegetation), this can lead to significant dune recession (i.e., a landwards displacement of the dune toe) and dune erosion [START_REF] Larson | An analytical model to predict dune erosion due to wave impact[END_REF][START_REF] Palmsten | Laboratory investigation of dune erosion using stereo video[END_REF].

3) Overwash regime (Rhigh > Dhigh, Rlow < Dhigh): in storm conditions with particularly elevated water levels (e.g. large storm surge combined with spring high tides) and/or on low-lying coastlines, storm wave runup might exceed the dune crest and flow down the lee slope of the dune. This overwash process typically results in a major lowering of the dune crest, significant dune erosion and minor-moderate inundation of the coastal hinterland [START_REF] Matias | Overwash Processes: Lessons from Fieldwork and Laboratory Experiments[END_REF]. Overwash can also deposit sand many 10s to 100s of metres landwards of the dune crest as overwash fans and is responsible for the landward migration, or rollover, of barrier islands (topographic sedimentary barriers protecting the mainland coast from storm impacts) over time [START_REF] Plant | Examples of Storm Impacts on Barrier Islands[END_REF]. 4) Inundation regime (Rlow > Dhigh): the inundation regime represents the most extreme of the four impact regimes. In this regime, even the lower vertical bound of storm wave runup exceeds the localised dune crest, such that the entire beach profile is submerged during the storm. In such instances, the entire subaerial beach and dune system is exposed to energetic surf-zone processes, which can completely remove the dune system and result in catastrophic flooding of the coastal hinterland.

Localised three-dimensional impacts

The storm impact scale described above represents a 2D framework based on the assumption that storm impacts are uniform alongshore. However, storm impacts can be localised and/or show large alongshore variability (Fig. 22.5), which can greatly complicate field assessment of storm impacts. For instance, localised storm impacts are often observed along barrier islands that show a large range of geomorphic form [START_REF] Otvos | Coastal barriers -nomenclature, processes, and classification issues[END_REF] and exposure to storms. As a result, barrier islands can undergo a wide variety of responses to storms (see the review by [START_REF] Plant | Examples of Storm Impacts on Barrier Islands[END_REF], which differ from that observed along other coastal settings. Stormdriven overwash processes [START_REF] Matias | Overwash Processes: Lessons from Fieldwork and Laboratory Experiments[END_REF], inlet opening and barrier breaching [START_REF] Sherwood | Inundation of a barrier island (Chandeleur Islands, Louisiana, USA) during a hurricane: Observed water-level gradients and modeled seaward sand transport[END_REF] can have dramatic localised impact on the overall barrier morphology (Fig. 22.4a), and are key to the long-term change in position and shape of the entire barrier island system [START_REF] Plant | Examples of Storm Impacts on Barrier Islands[END_REF]. Storm impact can also be locally increased (Fig. 5b) as a result of the presence of hard structure through scouring (end) effects and/or because of downdrift sediment deficit causing the coast to become set-back (e.g. [START_REF] Brown | Coastal retreat and/or advance adjacent to defences in England and Wales[END_REF]. Localised erosion is also almost systematically observed along eroding cliffs (Fig. 22.5c) although in this case erosion is often not caused by storms but rather by the progressive cumulative effects of marine and continental (physical and chemical weathering of cliff material) processes. Sometimes, beach and dune erosion can show striking patterns of alongshore periodicity (refer Chapter 13 Rhythmic patterns in the surf zone), with large megacusp embayments resulting in rhythmic cuspate-type erosion scarps (Fig. 22.4d).

Megacusp embayments can be considered as the erosive signature at the shoreline of the presence of rip channel currents (see Chapter 11 Rip Currents), which are reasonably regularly spaced self-organised patterns in the sand (Falquès et al., 2000). These megacusp embayments can form in lee of major stationary rips during severe storms when, during high tides, dune erosion can occur in the embayments where the beach is the narrowest, as it is more vulnerable to undercutting by swash [START_REF] Thornton | Rip currents, mega-cusps, and eroding dunes[END_REF]Castelle et al., 2015).

Beach and dune recovery

Once destructive storm conditions subside, a period of constructive beach and dune recovery ensues. In this recovery period, the various hydro/morphological impacts related to the storm event (summarised above) are reversed to varying degrees, depending on the amount and spatial extent of sediment redistribution due to the storm as well as the prevailing recovery conditions. The temporal progression of beach and dune recovery follows a number of semi-discrete modes, each characterised by common morphodynamic processes. These recovery modes have been described piecewise by various authors (e.g. [START_REF] Wright | Morphodynamic variability of surf zones and beaches: a synthesis[END_REF][START_REF] Morton | Stages and durations of post-strom beach recovery; Southeastern Texas Coats, USA[END_REF][START_REF] Hesp | Foredunes and blowouts: initiation, geomorphology and dynamics[END_REF][START_REF] Phillips | Modes of berm and beachface recovery following storm reset: observations using a continuously scanning Lidar[END_REF], although to-date no holistic morphological model of the complete beach and dune recovery cycle exists [START_REF] Phillips | Wave-driven recovery of sandy beaches following storm erosion[END_REF].

Starting with the recovery of storm deposits from the subaqueous and alongshore-uniform storm bar (e.g. Fig. 22.2), [START_REF] Wright | Morphodynamic variability of surf zones and beaches: a synthesis[END_REF] describe six morphodynamic beach states (Chapters 16 and 18) that the beach system transitions through as sediment is returned to the beachface. These six beach states, in order of 'least' to 'most recovered', are: the dissipative beach state; four intermediate beach states (the longshorebar-trough, the rhythmic-bar and beach, the transverse-bar and rip and the low tide terrace); and, the reflective beach state. This recovery cycle has been found (Wright and Short, 1985;[START_REF] Short | Wave-dominated beaches[END_REF][START_REF] Davidson | A simple equilibrium model for predicting shoreline change[END_REF] to be strongly controlled by the progressive lowering of incident wave energy following the storm, described in particular by the dimensionless fall velocity Ω (also known as the Dean parameter or Gourlay number). Subsequent temporary increases in wave energy (e.g. during a successive, more moderate, storm event) can interrupt this cycle, potentially resulting in a backwards transition towards a less-recovered beach state and an overall prolonging of the entire beach recovery process. The end member of the [START_REF] Wright | Morphodynamic variability of surf zones and beaches: a synthesis[END_REF] recovery cycle, i.e. the reflective beach state, is characterised by a steep beachface, a wellestablished berm and minimal surf zone morphology. This end member however is rarely obtained on many beaches, particularly those of finer grain sizes and/or in higher-energy wave climates. In these cases, sediment may be returned to the beachface and berm from the complex coupling of multiple sandbars and the shoreline.

Continuing the beach and dune recovery cycle, [START_REF] Morton | Stages and durations of post-strom beach recovery; Southeastern Texas Coats, USA[END_REF] focused specifically on recovery of the subaerial beach and dunes and developed a conceptual model based on only four recovery modes. The first of these modes, described by Morton et al. as berm reconstruction and forebeach accretion, essentially captures in an overarching manner the same wave-driven return of subaqueous storm deposits to the beachface described in the morphodynamic beach state model of [START_REF] Wright | Morphodynamic variability of surf zones and beaches: a synthesis[END_REF]. The second mode in this Morton et al. recovery model represents a more advanced stage of recovery, whereby the backbeach aggrades (i.e., grows vertically) as a result of wave overtopping of the recently re-established berm crest and occasional aeolian deposition. The final two modes describe the ultimate stages of beach recovery, namely the complete re-establishment of the dune system [START_REF] Lynch | Aeolian fetch distance and secondary airflow effects: the influence of micro-scale variables on meso-scale foredune development[END_REF] previously eroded by storm forces (i.e., during the collision, overwash or inundation storm impact regimes described in Section 3.1.1 above).

These final modes are separated into an initial dune formation phase and a later dune expansion and vegetation recolonization phase. A more comprehensive morphological description of foredune initiation following storm removal is presented by [START_REF] Hesp | Foredunes and blowouts: initiation, geomorphology and dynamics[END_REF].

Rates of beach and dune recovery reported in the literature vary significantly and depend on the stage of recovery over the complete cycle as well as the morphological indicator used to track recovery progression (refer Phillips, 2018 for a comprehensive review). Houser et al. (2015) analysed recovery of barrier island morphology following several large hurricanes and mathematically characterised recovery rates over the complete recovery cycle by a sigmoid curve. This sigmoid curve describes a slow rate of recovery in the initial stages, before rapidly increasing in the middle stages and slowing down again in the most advanced stages of recovery. Morphologically, this curve reflects the initially slow transport of deepwater storm deposits from the shoreface back to the surf zone, followed by a more rapid transfer of sediment from the inner surf zone to the beachface and berm and, finally, the slow growth and revegetation of the foredune(s). Recent highresolution observations of beach recovery rates largely agree with the sigmoid curve model of Houser et al. (2015). [START_REF] Scott | The extreme 2013/2014 winter storms: beach recovery along the southwest coast of England[END_REF], for example, found that the initial recovery of deep-water storm deposits was multi-annual and relied on moderate storm waves from successive winters to return sediment onshore towards the beachface. Using 10 years of daily shoreline observations from a coastal imaging system, Phillips et al. ( 2016) also showed that recovery of the shoreline was initially slow on average (approximately 0.1 m/day for the study site) when storm deposits were detached from the beachface, but rapidly increased (~0.4 m/day) as sediment welded to the beachface and promoting berm progradation. Shoreline recovery was then observed to slow considerably again to approximately 0.05 m/day as the more advanced stages of recovery (berm aggradation and dune re-establishment) took hold [START_REF] Morton | Stages and durations of post-strom beach recovery; Southeastern Texas Coats, USA[END_REF].

Example observations from Europe and Australia

Impact and recovery from the 2013-14 winter along the Atlantic coast of Europe

During the 2013/2014 winter, the combination of a very intense polar vortex and unusually strong North Atlantic jet stream caused a succession of deep, low pressure systems to cross the North Atlantic [START_REF] Davies | Weather chains during the 2013/2014 winter and their significance for seasonal prediction[END_REF] and reach western European coasts. The combination of high cyclone frequency and above-average cyclone intensity resulted in considerable impacts across the entire European Atlantic seaboard, down to Morocco (e.g., [START_REF] Thorne | Geographies of UK flooding in 2013/4[END_REF][START_REF] Castelle | Impact of the winter 2013-2014 series of severe Western Europe storms on a double-barred sandy coast: Beach and dune erosion and megacusp embayments[END_REF][START_REF] Blaise | Review of winter storms 2013-2014 on shoreline retreat dynamic on Brittany coast[END_REF][START_REF] Autret | A comprehensive hydro-geomorphic study of cliff-top storm deposits on Banneg Island during winter 2013-2014[END_REF]Masselink al., 2016aMasselink al., , 2016b;;[START_REF] Burvingt | Climate forcing of regionally-coherent extreme storm impact and recovery on embayed beaches[END_REF][START_REF] Cox | Extraordinary boulder transport by storm waves (west of Ireland, winter 2013-2014), and criteria for analysing coastal boulder deposits[END_REF]. Although a positive phase of the North Atlantic Oscillation (NAO), which reflects an intensification of the latitudinal pressure gradient between the Azores High and the Icelandic Low [START_REF] Hurrell | Decadal trends in the North Atlantic Oscillation: Regional temperatures and precipitation[END_REF], is supposed to enhance storminess in the North Atlantic, that particular winter was associated with an average positive NAO. Instead, the latitudinal atmospheric dipole of pressure anomaly strengthened but more importantly shifted 15° southward, which is represented by the West Europe Pressure Anomaly index (WEPA, Castelle et al., 2017b). That winter was characterised by the highest winter average wave height since at least 1948 (Masselink et al., 2016a), and likewise the highest WEPA. Large waves were generated along the entire coast of Europe (Fig. 22.6a), down to northwest Africa, with the anomaly peaking at +1.62 m at approximately 50°N, which corresponds to an approximately 40% winter mean wave height increase along the entire Bay of Biscay (Fig. 22.6b). There was no particularly exceptional storm occurrence during that winter, instead the clustering was itself outstanding, and particularly from mid-February 2015 to early March 2014 (see the zoom onto the period January 20 -March 6, 2014 in Fig. 22.1b). The number of storms and the total storm duration during the 2013/2014 winter was, depending on definition, generally at least 100% larger than the second most energetic winter since at least Contrasting responses occurred at the more sheltered sites such as Porsmilin and Vougot. At Slapton Sands, the middle profile (SP10) experienced a subaerial beach volume loss of 100 m 3 /m, whereas accretion of a similar amount occurred at the north profile (SP18) owing to unprecedented beach rotation (Masselink et al., 2016b). Portrush did not experience any erosion, as it was reasonably sheltered from the storm waves during that winter. Fig. 22.7 shows that the recovery signature is site-specific and multi-annual. Only one of the studied beaches fully recovered after two years in terms of beach-dune volume (Truc Vert beach,Fig. 22.7g). However, it is important to highlight that shoreline recovery was not complete, as most of the sand that came back primarily fed the beach rather than the incipient foredune after 2 years (Castelle et al., 2017a), therefore embodying the first berm reconstruction and forebeach accretion mode of beach recovery according to the model of [START_REF] Morton | Stages and durations of post-strom beach recovery; Southeastern Texas Coats, USA[END_REF]. During the subsequent 2 years incipient foredune formation was observed, suggesting that Truc Vert is about to enter the dune expansion and vegetation recolonization phase. Three sites only partially recovered with large difference in magnitude after two years (60% and 90% at Perranporth and Porsmilin, respectively). Patterns are also different, with the eastern profile at Slapton (SP18) showing no subaerial volume recovery, like at Vougot although partial shoreline recovery is observed at this latter site. A more detail assessment of the recovery process [START_REF] Dodet | Beach recovery from extreme storm activity during the 2013/14 winter along the Atlantic coast of Europe[END_REF] shows that beaches recover during the spring-summer-autumn period at modest and relatively steady rates (not much inter-annual variability). However, it is the energetic winter conditions that primarily control the time it takes for beaches to recover from extreme erosion as energetic winter conditions stall the recovery process whereas moderate winter conditions accelerate it, which further emphasise the strong link between the dominant wave climate indices (WEPA and NAO) and coastal response (severe erosion and multi-annual recovery). [START_REF] Dodet | Beach recovery from extreme storm activity during the 2013/14 winter along the Atlantic coast of Europe[END_REF].

Impact and recovery from the 2016 east coast low in SE Australia

In June 2016, a severe extratropical storm known as an east coast low or cyclone, impacted the coastline of SE Australia. While storms of this type are not unusual for this coastline and occur on average 55.5 days per year [START_REF] Pepler | A new, objective database of East Coast Lows[END_REF], the June 2016 event was notable for its unique synoptic characteristics whereby the low pressure system combined with a blocking high in the South Tasman Sea to result in a large (>2000 km) and relatively stable north-easterly wind fetch directed at the coastline for several days. Waves generated from this system peaked at a deepwater significant wave height between 4.5-8.5 m along the coastline [START_REF] Mortlock | The June 2016 Australian East Coast Low: importance of wave direction for coastal erosion assessment[END_REF], which is equivalent only to a modest average recurrence interval on this coastline of between 1-in-2 to 1-in-5 years [START_REF] Shand | NSW coastal inundation hazard study: coastal storms and extreme waves[END_REF]. Crucially though, the unusual fetch created by this synoptic pattern meant that these waves were from an anomalous easterly wave direction relative to the modal southerly swell and storm waves that dominate this coastline. This anomalous wave direction had the effect of significantly enhancing the exposure sections of beaches to anomalously high incident storm wave energy, since southerly waves are usually attenuated to a significant degree by large rocky headlands that dominate the southern extremities of beaches on this embayed coastline [START_REF] Short | Beaches of the New South Wales Coast: a guide to their nature, characteristics, surf and safety[END_REF]. The impacts of this event were also exacerbated by the fact that the storm coincided with winter solstice spring tides.

A rapid-response coastal monitoring program captured high-resolution Airborne Lidar measurements both immediately prior to and following the June 2016 storm along 178 km of embayed sandy coastline (Harley et al., 2017a). These measurements recorded an impressive 11.5 M m 3 of subaerial beach erosion due to the threeday event over this survey region, equivalent to an average subaerial volume loss of 65 m 3 /m (maximum recorded localised volume loss = 228 m 3 /m). Beach erosion was enhanced approximately fourfold on sections of sandy beach embayments directly exposed to the incident easterly waves, relative to more sheltered southerly and northerly-oriented beach sections (Harley et al., 2017a). At the Narrabeen-Collaroy long-term coastal monitoring station, where beach measurements have continued uninterrupted at monthly frequency since 1976 [START_REF] Turner | A multi-decade dataset of monthly beach profiles and inshore wave forcing at Narrabeen, Australia[END_REF], beach erosion due to this event was found to be the largest in four decades (Harley et al., 2017a). This monitoring period included storm events of much larger deep-water significant wave heights, but from more usual southerly wave directions, highlighting the critical importance of storm wave direction on embayed coastlines such as those of SE Australia.

Monitoring using Airborne Lidar over the same 178 km coastal stretch in the 12 months following the storm found that recovery was initially rapid, with 49% and 66% of the total subaerial volume lost during the storm returning in the first three and six months alone. More detailed inspection of this recovery observations reveal that this return of sediment was confined to the berm and beachface, embodying the first berm reconstruction and forebeach accretion mode of beach recovery according to the model of [START_REF] Morton | Stages and durations of post-strom beach recovery; Southeastern Texas Coats, USA[END_REF]. Similar to the erosion response of the storm itself, incident wave exposure was also to found to significantly control rates of recovery on this embayed coastline. In the first six months of beach recovery, the most rapid recovery rates were observed at sites directly exposed to the milder southerly waves that characterised wave conditions over the initial recovery period. At the same time however, these more exposed locations also made them more vulnerable to a subsequent southerly storm event typical of this coastline, causing a reversal in beach recovery in these regions [START_REF] Harley | Observations of beach recovery in SE Australia following the June[END_REF]. The culmination of these effects was that despite the rapid initial recovery, most beaches exhibited only partial recovery over the 12-month period following the storm. More-sheltered embayed beach stretches generally indicated more gradual, but steady, beach recovery, whereas more-exposed locations exhibited very rapid initial recovery, but also significant interruptions and reversals in recovery due to a subsequent storm event.

An example of the beach erosion and recovery cycle due to the June 2016 storm in SE Australia is presented in Fig. 22.8. This figure charts the evolution of beach erosion and recovery in the vicinity of the Narrabeen-Collaroy coastal imaging station [START_REF] Harley | Assessment and integration of conventional, RTK-GPS and image-derived beach survey methods for daily to decadal coastal monitoring[END_REF][START_REF] Turner | A multi-decade dataset of monthly beach profiles and inshore wave forcing at Narrabeen, Australia[END_REF]. In this example, the subaerial beach is observed to recover in just 11 months (Fig. 22.8i,j) and subsequently indicates excess recovery that reaches a maximum at the 13.5 month mark.

Future perspectives and knowledge gaps

Deficits in large-scale sediment budgets (see Chapter 23 Coastal sediment compartments, wave climate and sediment budget) combined with increases in extreme coastal water levels (e.g. [START_REF] Marcos | Increased extreme coastal water levels due to the combined action of storm surges and wind waves[END_REF] and/or extreme wave heights (e.g. Castelle et al., 2018b;[START_REF] Young | Multiplatform evaluation of global trends in wind speed and wave height[END_REF] result in increased coastal erosion hazards. In addition, the risk of coastal erosion has been observed to increase in some regions primarily because of increased exposure of assets to coastal storms [START_REF] Lazarus | Building back bigger in hurricane strike zones[END_REF]. Better understanding and further mitigation of coastal risk is therefore one of the greatest challenges for future coastal scientists, engineers and managers. Such advances in understanding require the development of a better, holistic, definition of storm events, storm-driven erosion and subsequent recovery. As we have seen in this chapter, existing definitions cover a variety of concepts, thresholds and coastal compartments, which often limit the broad scale application of findings regarding storms and storm impacts. Generic qualitative definitions of storm events such as that proposed in [START_REF] Masselink | Role of wave forcing, storms and NAO in outer bar dynamics on a high-energy macro-tidal beach[END_REF] must be encouraged. Such an objective definition based on the wave climate (the probability distribution of the significant wave height using the 5% and 25% exceedance levels) is recommended for generic use. Similar definitions based on, for instance, the magnitude of storm impact to the subaerial beach volume, must also be developed to build a suite of generic quantitative definitions which will allow for robust inter-site comparisons.

The large natural variability in coastal response and recovery presented in this chapter and through the two examples in Europe and Australia demonstrates the value of coastal monitoring programs implemented across a wide range of representative sites with different geological settings, tidal regimes and degrees of wave exposure (Guisado-Pintado and Jackson, 2018). These observational records are crucial to understanding and further developing the necessary techniques to manage and predict coastal behaviour across the full range of coastal systems which vary considerably across the globe, regionally and even locally.

However, the cost of implementing such programs has meant that long-term, continuous records of coastal change are rare and have tended to focus more on the subaerial domain [START_REF] Turner | A multi-decade dataset of monthly beach profiles and inshore wave forcing at Narrabeen, Australia[END_REF]. There is a need therefore to monitor the complete erosion/recovery cycle from the shoreface to the beachface -and up to the dune where present. This will enable accurate quantification of the coastal sediment budget and further examine inter-and multi-annual variability including extreme storm erosion and post-storm recovery (e.g. [START_REF] Scott | The extreme 2013/2014 winter storms: beach recovery along the southwest coast of England[END_REF][START_REF] Ruiz De Alegria-Arzaburu | Beach recovery capabilities after El Nino 2015-2016 at Ensanada Beach, Northern Baja California[END_REF]. Remote sensing techniques, such as depth inversion from video images [START_REF] Palmsten | Laboratory investigation of dune erosion using stereo video[END_REF], satellite-derived bathymetry [START_REF] Pacheco | Retrieval of nearshore bathymetry from Landsat 8 images: A tool for coastal monitoring in shallow waters[END_REF] and large-scale data inferred from satellites [START_REF] Luijendijk | The State of the World's Beaches[END_REF][START_REF] Vos | Sub-annual to multi-decadal shoreline variability from publicly available satellite imagery[END_REF] are starting to provide more insight into long-term coastal changes (see Chapter 26). Such large-scale data must be combined with shortterm shoreface and surfzone measurements [START_REF] Aagaard | Sediment supply to beaches: Cross-shore sand transport on the lower shoreface[END_REF]; see Chapter 27) and seabed characteristics and sediments to better understand the sediment exchanges and pathways between the different compartments (dune, subaerial beach and lower shoreface) and, in turn, the processes controlling storm erosion and subsequent recovery [START_REF] Kinsela | Second-pass assessment of potential exposure to shoreline change in New South Wales, Australia, using a sediment compartments framework[END_REF].

Numerical modelling is a promising avenue to hindcast, understand and ultimately predict the response of beaches to storm and their subsequent recovery. These models can be classified into three categories, namely process-based, hybrid and data-driven models. Process-based models, which rely on a detailed description of the dominant hydrodynamics and sediment transport processes, are powerful tools to describe storm-driven erosion on small scales (<km) pending calibration (e.g. [START_REF] Roelvink | Modelling storm impacts on beaches, dunes and barrier islands[END_REF]. However, these models show limited skill to simulate beach changes on larger temporal and spatial scales, typically associated with recovery periods. In contrast, simpler hybrid models which are based on general principles (e.g. behavioural law) can be successfully applied over larger temporal and spatial scales and, in turn, be used to investigate shoreline erosion and recovery processes in more detail. Within this hydrid model category, [START_REF] Dodet | Beach recovery from extreme storm activity during the 2013/14 winter along the Atlantic coast of Europe[END_REF] showed that equilibrium models (e.g., [START_REF] Yates | Equilibrium shoreline response: Observations and modeling[END_REF][START_REF] Davidson | A simple equilibrium model for predicting shoreline change[END_REF]Splinter et al., 2014a) have significant skill in reproducing the shoreline erosion during the 2013/2014 winter described above and the subsequent (partial or complete) recovery on the most exposed, cross-shore transport dominated sites. At other sites, such as in coastal embayments where the rotation signal may dominate (refer Chapter 24 Beach rotation), more complex hybrid shoreline models must be developed and applied. Such models have been recently developed [START_REF] Vitousek | A model integrating longshore and crossshore processes for predicting long-term shoreline response to climate change[END_REF][START_REF] Robinet | A reduced-complexity shoreline change model combining longshore and cross-shore processes: the LX-Shore model[END_REF][START_REF] Montano | Shorecasts: a blind-test of shoreline models[END_REF] which open up new perspectives to improve our understanding and predictive ability of shoreline response to storm and recovery in complex hydrodynamic and geological settings. A third model category, referred to as datadriven models range from simple autoregressive models to machine learning techniques (e.g. [START_REF] Beuzen | Bayesian Networks in coastal engineering: Distinguishing descriptive and predictive applications[END_REF] refer to Chapter 28 Machine learning and coastal processes). In a recent effort of the coastal research community (Montaño et al., 2019), a "blind" comparison between approximately 20 state-of-the-art hybrid and machine learning shoreline models has been performed. Most of these models indicated good skill in capturing seasonal changes (seasonal recovery cycles) but often failed to predict large changes or changes occurring at shorter timescales (storm-driven erosion). Multi-model ensemble (i.e., aggregating predictions across different models) is also shown to improve the reliability of the predictions, providing additional information on model-related uncertainty. Hybrid and data-driven models therefore need to be further improved and tested against other datasets with different hydrodynamics and geological settings, which once again motivate the development of ambitious coastal monitoring programs.

Over the last decade, our understanding and predictive ability of storm-driven erosion and subsequent multiday to multi-annual recovery has greatly improved. Although there is still considerable room for further improvement, there is also a need for a better coordination between output from the research community and what is translated to end-users/practitioners (refer Chapter 29 Applying beach morphodynamics to management). This is reflected by the recent development of early-warning systems for coastal flooding and erosion hazards, typically providing warning a few days ahead (e.g. [START_REF] Vousdoukas | Towards reliable storm-hazard forecasts: XBeach calibration and its potential application in an operational early-warning system[END_REF][START_REF] Turner | A multi-decade dataset of monthly beach profiles and inshore wave forcing at Narrabeen, Australia[END_REF]. In addition, it is now well-established that extreme coastal wave climate is strongly affected by large-scale climate patterns of atmospheric variability (refer Chapter 3 Wave climates: deep water to shoaling zone). Given the strong correlation of certain climate indices on winter wave climate and coastal response in different regions of the world [START_REF] Barnard | Coastal vulnerability across the Pacific dominated by El Niño-/Southern Oscillation[END_REF][START_REF] Dodet | Beach recovery from extreme storm activity during the 2013/14 winter along the Atlantic coast of Europe[END_REF], the ability of climate models to predict these dominant climate indices a few months ahead will also be crucial to anticipate potential impacts months or years in advance (e.g. [START_REF] Davidson | Annual prediction of shoreline erosion and subsequent recovery[END_REF]. It will also provide supplementary information for predicting the potential for recovery and thus ultimately help coastal management approaches.

Figure 22

 22 Figure 22.1. (a) The Peaks-Over-Threshold (POT) method for defining storm events from a significant wave height time-series after Harley (2017) and (b) application to a real time series of significant wave height measured during the winter of 2013/2014 in about 50-m depth offshore of Truc Vert beach, southwest France after Castelle et al. (2015), using different arbitrary values of wave height threshold and independence criterion (I).

Figure 22

 22 Figure 22.2. Example of beach and dune erosion resulting from an extreme storm: (a) pre and post-storm surveys of the entire beach profile, indicating the redistribution of sediment from the subaerial beach to an offshore storm bar; (b) close up of the subaerial beach response, highlighting the overall subaerial beach volume loss due to the storm (ΔV = 106 m 3 /m in this example) as well as the dune volume loss (ΔVd =12 m 3 /m).

Figure 22

 22 Figure 22.3. Scenarios of post-storm recovery from a given morphological indicator: (a) complete recovery; (b) no recovery; (c) partial recovery; (d) excess recovery. Modified after[START_REF] Morton | Stages and durations of post-strom beach recovery; Southeastern Texas Coats, USA[END_REF].

Figure 22

 22 Figure 22.4. Examples of the four storm impact regimes according to[START_REF] Sallenger | Storm impact scale for barrier islands[END_REF]. Rlow and Rhigh denote the minimum (98% exceedance) and maximum (2% exceedance) runup levels reached during each regime in

Figure 22

 22 Figure 22.5. Examples of localised storm-driven erosion patterns. (a) Barrier breaching at Chandeleur Island, Louisiana, USA (Ph. Jim Flocks, USGS, src. www.earthsky.org); (b) accelerated beach and dune erosion next to a hard coastal structure at the end of the 2013/2014 winter at Lacanau, southwest France (Ph. J. Lestage); (c) Localised cliff erosion near Veulettes sur Mer in north France (Ph. S. L'Hôte); (d) rhythmic cuspate-type erosion scarp along the Gironde coast, southwest France, at the end of the 2013/2014 winter (Ph. J. Lestage).

Figure 22

 22 Figure 22.6. Winter (DJFM) 2013/2014 distribution of (a) winter-averaged significant wave height and (b) percentage relative to the long-term (68 years) winter average. (c) Location of the Atlantic coast beaches studied in Masselink et al. (2016a) and Dodet et al. (2019) with PT = Portrush (Northern Ireland); PP = Perranporth (southwest England); SP = Slapton Sands (southwest England); VG = Vougot (northwest France); PM= Porsmilin (northwest France) and TV = Truc Vert (southwest France).

Fig. 22 .

 22 Fig. 22.8 shows the time series of beach volume and dune toe position at the Atlantic coast study sites shown in Fig. 22.7c, with outstanding storm erosion impacts during the 2013/2014 winter leaving the majority of the sites in their most depleted state since measurements began. The most exposed sites Perranporth and Truc Vert lost in excess of 80 and 200 m 3 /m of subaerial beach volume, respectively, and such storm response was observed to be typical of most exposed beaches along the coast of southwest England and France.

Figure 22

 22 Figure 22.7. Time series of beach volume at the six European beach study sites (with two profiles shown for

Figure 22

 22 Figure 22.8. Temporal evolution of beach erosion and recovery at Narrabeen-Collaroy Beach (SE Australia) due to the June 2016 east coast low storm. a) immediately pre-storm; b) mid storm (day 1); c) mid storm (day 2); d) immediately post-storm (day 3); e) +3 month recovery; f) +6 month recovery; g) +11 month recovery; h) +13.5 month recovery; i) surveyed beach profiles at PF6 during different stages of the erosion/recovery cycle; j) time-series of monthly subaerial volume evolution at profile PF6 following the storm. All images are taken