Washover Fans Research Articles

Bayesian statistical analysis reveals spatial heterogeneity in Cyclone Thane deposits from Southeast India

Modern and geological records of storm sedimentary deposits preserved on siliciclastic coastlines are important archives to evaluate the past and current magnitude and impacts of.storms. Examination of modern storm deposits also offers the opportunity to evaluate the similarities and differences between storm and other coastal overwash processes and hazards.We examined the stratigraphy and sedimentary characteristics of the 31st December 2012 Cyclone Thane and underlying coastal units from 14 pits from six sites from the coastal zone of Tamil Nadu Province, southeast India. We analysed the grain size parameters, grain shape, and heavy mineral proportions of each deposit in high resolution and examined the sedimentary structures of each unit. For the first time, we use Bayesian factors to quantitatively evaluate the similarities and differences between the storm sedimentary deposits and other co-located coastal sedimentary deposits. At several sites, the storm deposits differ in several parameters from the underlying coastal deposits, but at some locations, distinguishing between different depositional units cannot be achieved. In comparing the storm deposits from the different sites, mean grain size results in the most coherent pattern with closely located sites having similar mean grain size, and more southerly sites being finer grained. The other measured parameters show a far less coherent pattern with adjacent sites often preserving larger differences than more distal sites attesting to very local hydrodynamic variations during sediment deposition. As with the sedimentary parameters, the sedimentary structures formed during sediment deposition preserved at each site are highly variable. To date, the presence of terminal foresets at the landward edge of washover fans remains the only diagnostic feature of storm deposition, but that this feature is not ubiquitous across all storm deposits. Our findings demonstrate the spatially heterogeneous nature of storm sediment deposition and the challenges of identifying storm deposits in coastal siliciclastic sequences. The use of Bayesian statistical approaches also offers a robust method for evaluating and discriminating between coastal sediment deposits that has many advantages over traditional frequentist approaches. This method can easily be applied to other sedimentary depositional environments.

Reconstructing the South American Miocene puzzle: An integrated analysis of the Paraná Formation (Argentina)

In recent decades, Miocene marine transgressions in South America have sparked ongoing debates concerning their boundaries, number of events, regional connectivity, and the existence of an epicontinental sea formed during the Andean orogeny. The bed-by-bed analysis of the Late Miocene Paraná Formation deposits in Entre Ríos Province (Argentina) allow defining six facies associations: (i) beach ridge, (ii) tidal inlet channel and washover fan, (iii) outer estuarine bioherms, (iv) central estuary, (v) tidal bar and sandflat, and (vi) tidal mudflat and creek deposits. Architectural and stacking pattern analyses reveal transgressive-regressive sequences typical of the coastal strip, encompassing shallow marine to estuarine sub-environments. The analysis identified diverse ecological guilds, including bivalve and gastropod assemblages in bioherms, and crustacean traces in tidal flats. Regressive units are characterized by wave-dominated shoreface deposits, while transgressive units comprise fine-grained estuarine deposits interbedded with bioclastic sandstones and storm deposits. The paleoenvironmental and paleoecological data indicate normal salinity marine environments with macroinvertebrates and estuarine components and suggesting tropical brackish conditions. Plant remains point to a range of vegetative communities, including mangroves, palm forests, grasslands, humid riparian forests, and dry upland forests, reflecting tropical to subtropical and humid to semiarid environments. This study concludes that the Paraná Formation correspond to a third-order transgressive system tract influenced by the Miocene Paranaense Sea. The basin-scale implications suggest that the distal Chaco-Paraná basin was affected by eustatic changes due to its low accommodation and topographic relief. The Chaco-Paraná foreland basin's evolution was driven by interactions between tectonic, climatic, and eustatic processes. The comprehensive analysis of sedimentary and fossil records provides a detailed paleogeographic reconstruction of the Miocene marine transgression in southern South America.

Regional assessment of overwash processes in a retrograding sand barrier (Paraíba do Sul River Deltaic Complex, Rio de Janeiro, Brazil)

Storm events are the primary mechanisms for generating overwash along the shoreline. This process occurs when wave runup exceeds the elevation of sandy features, often forming washover deposits. In retrograding barriers, overwash is the main driver of landward migration. Extreme wave energy events can lead to rapid changes in the morphology of these environments. On urbanized coastlines, storm impacts can be catastrophic and result in high reconstruction costs. Understanding the characteristics of storm events and the local morphological characteristics of these sandy features is crucial for risk assessments, hazard mitigation, and coastal area adaptations in the scenario of increasing storm events. The main objective of this study is to analyze the role of overwash processes in the retrogradation of the Quissamã barrier, located in the southern sector of the Paraíba do Sul River Delta Complex (PSRDC), on the coast of Rio de Janeiro. Using data from the global Wave Watch III model, sea warnings issued by the Brazilian Navy, atmospheric pressure charts, and astronomical tides, we identified storm events and mapped the washover fans formed after specific storm events. The washover fans were identified using PlanetScope images. The identified storm events were characterized by waves from the SE-S directions with high peak periods, and mostly occurred during spring tides or transitioning to neap tides. Additionally, the atmospheric pattern for most events was associated with the migration of cold fronts from high to low latitudes, leading to the development of extratropical cyclones. The geometry of the barrier also proved to be an essential morphological pattern. Considering the relative sea level along part of the Brazilian coast has been decreasing over the last 5500 years, storm events and associated processes are crucial for the retrogradation of barriers, maintaining the retrogradational characteristics of this coastal barrier.

Coleopteran burrows from foreshore settings in Florianópolis, Brazil

While insects are versatile animals capable of occupying harsh environmental conditions, not many are present in the marine environment, and has generally been discounted as trace makers in such settings. During the intra-congress field trip of ICHNIA 2024, however, we observed multiple surficial burrows on foreshore sediments that were constructed by beetle larvae. While there are several reports of insect burrows from backshores, eolian dunes, salt marshes, tidal creeks, washover fans, and distributary channels, we are not aware of ichnological studies of these burrows from the foreshore. Moreover, some of these studies failed to identify or mention the entity of the trace makers, and have not stressed enough the significance of burrowing marine insects on palichnology and paleoecology. Some entomologists on the other hand have recognized insects in marine environments, and some insect groups (such as Coleoptera and Diptera) have burrowing larvae in brackish to marine environments. Understanding the burrow morphologies of marine insects compared to freshwater insects or other marine invertebrates may help us understand the ecological significance and evolutionary history of insects in marine habitats.

High-Resolution Interannual Evolution of the Dune Toe at a Mesotidal Barrier (Camposoto Beach, SW Spain)

Over recent years, processes related to marine storms, sediment shortages and human intervention have caused the global retreat of many coastal systems and the degradation of their dunes. In this context, changes in the dune toe are commonly used as a proxy to study the interannual shoreline evolution, and it is usually analyzed using orthophotography, while high temporal- and spatial-scale resolution studies of dune toe evolution are not frequent. In this work, a quasi-monthly study of dune toe data was carried out between 2008 and 2018. These data, taken from the RTK-DGPS and UAS systems, were subjected to shoreline analysis, and they showed an average regression rate of −2.30 m/year, a higher value than the one registered until 2008 (1 m/year). This suggests an acceleration in the erosion suffered within the system, which was revealed to be more intense in the northern sector of the study area. Dune toe variability increased over the years, probably due to the presence of washover fans breaking the foredune that were reactivated and expanded during storm events. The ephemeral progradation of the dune toe was also noted, which could be explained with reference to wind events and/or beach nourishment that had been carried out over the studied period. From the analysis of the dune toe elevation, a decrease in this variable was obtained, especially in the areas affected due to washover fans. This finding is supported by the significant correlation of the dune toe elevation and erosion trend, suggesting that the areas where the dune toe was lower are prone to suffering a greater retreat. This correlation provides insight into the future evolution of the barrier, suggesting a state of degradation and a transition to a lower-resilience state.

Testing Digital Elevation Model of Difference (DoD) Estimation of Washover Fan Thickness, Matagorda Peninsula, Texas

Testing Digital Elevation Model of Difference (DoD) Estimation of Washover Fan Thickness, Matagorda Peninsula, Texas

Sediment transport and bed erosion during storm surge using a coupled hydrodynamic and morphodynamic model considering wave and current interaction

Storm surge, a major disaster in coastal areas, is generated by tropical cyclones. Strong currents and waves during storm surges often cause sediment transport and beach erosion, significantly damaging the coastal ecosystem. This paper presents a flow-wave-sediment-morphodynamic coupled model to predict morphodynamic changes caused by overwash during storm surges. In the model, the flow field is calculated using the generalized shallow water equations coupled with the Simulating Waves Nearshore (SWAN) model, while sediment transport and bed changes are computed using a non-equilibrium total-load sediment transport model. The model solves the governing equations by employing the explicit finite-volume approach based on a rectangular mesh. The Godunov-type central upwind scheme is adopted to calculate the interface fluxes, thereby solving the complex Riemann problem. A series of numerical experiments considering wave-induced longshore current and short-term bed erosion are conducted to validate the established model and demonstrate its ability to simulate waves, flow fields, and bed changes during storm surge. Specifically, we used the model to simulate the morphological evolution of the Santa Rosa barrier island caused by Hurricane Ivan's storm surge, and the results indicate that the model accurately predicts the real-case erosion process caused by storm surge and overwash during the hurricane. The simulated results clearly explain overwash development, including washover fans, foredune erosion, and back-barrier deposition. It demonstrates that the front dune significantly eroded with the Santa Rosa barrier island coastline retreating by a maximum of about 80 m during the storm surge. More than three breaches with a width of up to 135 m were formed on the sandy barrier due to wave overwash, while the topography at the breach changed significantly.

Wind–Wave Conditions and Change in Coastal Landforms at the Beach–Dune Barrier of Cesine Lagoon (South Italy)

Several coastal barriers experienced significant erosion and change in shape throughout the Mediterranean coasts over the past decades, and the issue has become of increasing concern for scientists and policymakers. With reference to a case study and by meteorological and geomorphological investigations, this note aims to define the wind–wave conditions, infer the net longshore transport, and detect the geomorphological processes that shape the landforms of the Cesine Lagoon barrier (South Italy). Despite the importance of the site in coastal defense and environmental conservation, there are still no specific studies. A challenge for this research was to obtain significant results from publicly available sources and simple and inexpensive methods. Geomorphological changes, such as the retreat of dune toes, accretion of washover fans, and formation of gravel beaches, are related to the analyzed wind–wave conditions. The net longshore transport is found in accordance with the direction of the more intense winds. The role of extreme events in the shaping of coastal landforms is yet to be established, even if they greatly increase the vulnerability to flooding of the study area. The results achieved so far are starting points for further data collection and analysis in the perspective of assessing the impact of climate changes and the threatening hazards on the lagoon barrier.

Sedimentology and stratigraphic architecture of Barremian synrift barrier island–estuarine depositional systems from blended field and drone‐derived data

ABSTRACTThe Lower Cretaceous (Barremian) Camarillas Formation in the Galve Sub‐basin of eastern Spain is an exceptionally muddy, synrift, aggradational then retrogradational paralic succession. Deposition within these arid, equatorial paralic systems was strongly controlled by crustal rifting of the Iberia plate linked to the geodynamic evolution of the Atlantic Ocean, the Bay of Biscay and the Tethys Ocean. Although synsedimentary extensional tectonics controlled thickness and facies distributions, the parasequence stacking patterns point to a superimposed high‐order allogenic control on the paralic succession. Field data and drone imagery are combined to document changes in sedimentology and three‐dimensional stratigraphic architecture of these deposits to interpret changes in depositional environments as this basin filled. Three evolutionary stages are identified: (i) tide‐dominated estuary; (ii) mixed‐energy estuary, with a well‐developed wave‐dominated barrier island system; and (iii) barrier island–tidal inlet suite. An exceptional record of back‐barrier‐island depositional interactions is preserved in this high‐subsidence, extensional‐basin setting, including deposition of washover fans, flood‐tidal deltas and ebb‐tidal deltas. Drone‐derived imagery facilitates three‐dimensional architectural characterization of these complex paralic deposits, including multi‐episodic tidal inlets, and correlation of basin scale stratigraphic markers. Spatio‐temporal interactions between climate change, sea‐level variations and rift‐related subsidence generated complex estuarine and barrier island geobodies. The general transgressive trend recorded in the Camarillas Formation correlates well with global eustatic sea‐level rise during the Barremian.

Sound‐Side Inundation and Seaward Erosion of a Barrier Island During Hurricane Landfall

AbstractBarrier islands are especially vulnerable to hurricanes and other large storms, owing to their mobile composition, low elevations, and detachment from the mainland. Conceptual models of barrier‐island evolution emphasize ocean‐side processes that drive landward migration through overwash, inlet migration, and aeolian transport. In contrast, we found that the impact of Hurricane Dorian (2019) on North Core Banks, a 36‐km barrier island on the Outer Banks of North Carolina, was primarily driven by inundation of the island from Pamlico Sound, as evidenced by storm‐surge model results and observations of high‐water marks and wrack lines. Analysis of photogrammetry products from aerial imagery collected before and after the storm indicate the loss of about 18% of the subaerial volume of the island through the formation of over 80 erosional washout channels extending from the marsh and washover platform, through gaps in the foredunes, to the shoreline. The washout channels were largely co‐located with washover fans deposited by earlier events. Net seaward export of sediment resulted in the formation of deltaic bars offshore of the channels, which became part of the post‐storm berm recovery by onshore bar migration and partial filling of the washouts with washover deposits within 2 months. This event represents a volumetric setback in the overwash/rollover behavior required for barrier transgression, but the new ponds and lowland habitats may provide beneficial habit for endangered species and will likely persist for years.

Circular Bedforms Due to Pit Foraging of Greater Flamingo Phoenicopterus roseus in a Back-Barrier Intertidal Habitat

The Greater Flamingo Phoenicopterus roseus is known as an ecosystem engineer, rearranging sediment in peculiar bedforms as a consequence of its filter-feeding behaviour. In recent decades, the populations of the Greater Flamingo have notably increased, and now the species is one of the most abundant waterbirds in Mediterranean wetlands. Owing to its range expansion, it inhabits and exploits new and suitable foraging sites detectable by foraging structures left on the sediment. There are few images of the foraging morphologies in the literature, possibly due to their ephemeral nature and difficulty in detecting them. In this manuscript, we present a very detailed UAV (Unmanned Aerial Vehicle) image of an aggregate of pit foraging structures of Greater Flamingo discovered on a back-barrier washover fan in the Marano and Grado Lagoon (Northern Adriatic, Italy).

Effect of Barrier Height on Magnitude and Character of Hurricane Harvey Washover Fans, Matagorda Peninsula, Texas, U.S.A.

Williams, H.F.L. and Rains, B.J., 2022. Effect of barrier height on magnitude and character of Hurricane Harvey washover fans, Matagorda Peninsula, Texas, U.S.A. Journal of Coastal Research, 38(1), 133–139. Coconut Creek (Florida), ISSN 0749-0208. This study uses topographic profiles, washover fan volumes, and shoreline retreat rates to explore relationships between barrier height, erosion, and storm washover sedimentation. Pre- and post-Hurricane Harvey topographic profiles were created along 15 transects using Bare Earth LIDAR (2016) and transit level surveys (2019). Washover fan thicknesses and areas were measured to estimate washover fan volumes. An inverse relationship was found between washover fan volume and pre- and poststorm barrier heights. One section of shoreline had a prestorm height of about 3 m, which almost completely blocked overwash, but may have contributed to a large increase in shoreline erosion. In contrast, a section of shoreline with a low prestorm barrier generated relatively large washover fans, but experienced lower shoreline retreat and was the only section to experience beach and dune recovery in the year after landfall. Shoreline retreat was further quantified between 2014 and 2018 using Google Earth imagery and LIDAR data from 2014, 2016, 2017, and 2018 to track migration of the shoreline. The entire shoreline in the study area is undergoing relatively rapid retreat, but the results suggest that Hurricane Harvey increased erosional retreat rates by up to 195%. The Colorado River Jetty borders the study area and may have acted as a barrier to wave erosion, contributing to enhanced marsh aggradation at marsh sites in close proximity to the jetty and promoting shoreline recovery in the poststorm period. The research results provide valuable information on the interaction of hurricane storm surge with natural and anthropogenic barriers, beach and dune erosion, and marsh aggradation along the coast of Texas.

Storm Driven Migration of the Napatree Barrier, Rhode Island, USA

Napatree Point, an isolated barrier in southern Rhode Island, provides a case study of barrier spit migration via storm driven overwash and washover fan migration. Documented shoreline changes using historical surveys and vertical aerial photographs show that the barrier had little in the way of net change in position between 1883 and 1939, including the impact of the 1938 hurricane. The barrier retreated rapidly between 1945 and 1975, driven by both tropical and extra-tropical storms. The shoreline position has been largely static since 1975. The removal of the foredune during the 1938 hurricane facilitated landward shoreline migration in subsequent lower intensity storms. Dune recovery following the 1962 Ash Wednesday storm has been allowed due to limited overwash and barrier migration over the last several decades. Shoreline change rates during the period from 1945–1975 were more than double the rate of shoreline change between 1939 and 2014 and triple the rate between 1883 and 2014, exceeding the positional uncertainty of these shoreline pairs. The long-term shoreline change rates used to calculate coastal setbacks in Rhode Island likely underestimate the potential for rapid shoreline retreat over shorter time periods, particularly in a cluster of storm activity. While sea-level rise has increased since 1975, the barrier has not migrated, highlighting the importance of storms in barrier migration.

Sedimentary facies and Holocene depositional evolution of the Maricá Lagoon, Rio de Janeiro, Brazil

This study aims to improve the knowledge on the geological evolution of the Maricá Lagoon (Rio de Janeiro) during the Holocene. One hundred and three samples from four boreholes and GPR data were acquired. Laboratory analyses included grain size and morphology, color, organic matter contents, fossils, mineral composition, and 14C dating. The results indicate that the 12.5 m thick sedimentary section studied here represents the last 8111 years of lagoonal deposition. Five sedimentary facies were identified: (1) subrounded sand facies (containing a gravel subfacies) which occur along the southern margin; (2) silty sand facies occurring at the transition from the margin to the lagoon center; (3) sandy silt facies and (4) silt/clayey silt facies which cover the calmer, central areas of the lagoon; and (5) angular sand facies which occur only at the surface of the northern margin. The organic matter content in the mud varied from 18% to 81%. Sedimentation rates up to 4277 cal years BP in the western margin were 0.27 cm/y and 0.15 cm/y in the deeper, central lagoon areas, and 0.20 cm/y since then. The sedimentary facies and organisms (molluscs and sponges) indicated that the Maricá Lagoon has changed little during the Holocene. At about 8111 cal years BP, the lagoon was an important freshwater basin with occasional saltwater influence. At about 5600–5000 years ago, during the maximum Holocene transgression, the lagoon attained its maximum dimensions and prevailing marine influences. Overwash processes and inlets enabled the formation of washover fans and flood-tidal delta deposits that have been recognized since the early formation stages of the Pleistocene barrier. From 4645 cal years BP to the present day, the connection between the lagoon and the sea has occurred sporadically at the southeast extreme of the lagoon (Barra Lagoon). Today's sedimentary dynamics are influenced by fluvial input (which is building up a lagoonal delta) and by winds, which transport sands from the barrier into the lagoon, in addition to generating waves capable of remobilizing the marginal and bottom lagoon sediments.

Barrier Breaching Versus Overwash Deposition: Predicting the Morphologic Impact of Storms on Coastal Barriers

AbstractWaves and water level setup during storms can create overwashing flows across barrier islands. Overwashing flows can cause erosion, barrier breaching, and inlet formation, but their sediments can also be deposited and form washover fans. These widely different outcomes remain difficult to predict. Here we suggest that a breach develops when the sediment volume transported by overwashing flows exceeds the barrier subaerial volume. We form a simple analytical theory that estimates overwashing flows from storm characteristics, barrier morphology, and dune vegetation, and which can be used to assess washover deposition and breaching likelihood. Our theory suggests that barrier width and storm surge height are two important controls on barrier breaching. We test our theory with the hydrodynamic and morphodynamic model Delft3D as well as with field observations of 21 washover fans and 6 breaches that formed during Hurricane Sandy. There is reasonable correspondence for natural but not for developed barrier coasts, where traditional sediment transport equations do not readily apply. Our analytical formulations for breach formation and overwash deposition can be used to improve long‐term barrier island models.

Characteristics of morphodynamic conditions in the shallows of Puck Bay (southern Baltic Sea)

Abstract Puck Bay is an unusual and thus interesting coastal water region, as it combines two different environments – a lagoon and the sea. They differ from each other in their seabed morphology, salinity, dynamics and water exchange. Their common elements are the extensive shallows and the vicinity of the Hel Peninsula. The shallows of Puck Bay have developed at various stages of its evolution, which began several thousand years ago and continues to this day. They have been shaped by varying morphogenetic factors resulting from changes in sea level and accompanying evolution phases of sand barriers, e.g. washover fans, as well as the intensity and directions of sediment transport. At present, the shallows cover more than 35% of the seabed area and are influenced by hydrodynamic factors and availability of sediments. The study area was divided into five fields, taking into account morphological and genetic criteria as well as recent hydrodynamic conditions. This study provides an updated map with classification and distribution of surface sediments and describes grain size parameters for sediment samples collected in the selected fields. Based on a comprehensive assessment of grain size parameters, lithodynamic equilibrium zones were determined and areas of sediment deposition and redeposition were identified.

Geomorphological and sedimentological records of recent storms on a volcaniclastic coast in Bicol, Philippines

Typhoon Durian in November 2006 was most notable for a series of devastating lahars that buried communities at the base of Mayon volcano in Bicol, Philippines. Typhoon Durian delivered extreme rainfall that remobilized volcanic debris that caused more than ~1200 deaths and extensive property damage. Although not as deadly as the lahar, Typhoon Durian also generated a storm surge that caused localized dune breaching on Malinao barrier sand spit in Lagonoy Gulf. In the absence of instrumental data of the storm surge, we used the geomorphical and sedimentary imprints including erosion scarps, washover fans and terraces to infer the inundation heights on the barrier spit. The surface elevations of washover fans, terraces and relic dunes indicate inundation heights above 1.5 m but not exceeding 3 m. Typhoon Durian's overwash deposit is characterized by typical washover fan stratigraphy, and exhibits horizontal to sub-horizontal lamination on the front to mid-fan and foreset stratification near the fan terminus. Subsurface stratigraphy using shore-normal ground penetrating radar (GPR) imaging reveals at least two buried erosional surfaces farther inland from the erosional surface of Typhoon Durian. Similar to Durian, the older erosional surfaces were probably sustained from previous typhoons. We infer that episodic erosional events most likely have repeatedly disrupted the prograding development of the Malinao barrier spit. Typhoon Durian highlights the exposure of volcanic landscapes to multiple hazards from cyclone landfall.

Modern coastal tempestite deposition by a non‐local storm: Swell‐generated transport of sand and boulders on Eleuthera, The Bahamas

AbstractThis paper presents an analysis of the transport conditions of a storm deposit (i.e. tempestite) produced by a non‐local cyclone. Observations and analysis of ‘sand to boulder’ transport and washover deposition in March 2018 at Gaulding Cay Quarry, Eleuthera, The Bahamas, confirm that swell waves can cause coastal change and affect the depositional record >1000 km from the storm centre. Drone video, news reporting, deposit stratigraphy, grain‐size measurements and wave data were all used to define three phases of washover fan construction: an aggradational phase associated with base‐level rise as the quarry filled with water; a progradational phase associated with quasi‐constant base‐level; and fan incision tied to base level fall as discharge through an outlet channel exceeded input discharge by overtopping waves. Washover fan location was controlled by antecedent topography and represented only a fraction of the swell‐impacted coastline. Sand and boulders were transported simultaneously, forming a complex poorly sorted deposit. Drone video, bedrock erosion and sediment‐transport estimates all indicated that overwash exceeded sediment availability. As a result, the measured washover fan was estimated to be an order of magnitude smaller than its potential volume if conditions had been transport‐limited. This study highlights the importance of pre‐event topography and independent measures of event duration on accurately reconstructing storm properties from the sedimentary record, as well as the challenges in reconstructing storm location, and therefore storm intensity and frequency, from sedimentary deposits alone.

A method for estimating sediment budgets of washover deposits using digital terrain models

AbstractWashover fans are located on small barriers in fetch‐limited micro‐tidal coastal environments in Denmark. These washover fans are formed during high‐energy storm events and we present a method to quantify their volumes and to estimate sediment exchanges between washover fans and their adjacent morphologies. We use high resolution digital terrain models (DTMs) based on light detection and ranging (LiDAR) data. We have delineated landforms using known methods of scale analysis and geomorphometric classification. We quantified volumes of the delineated landforms and estimated the related sediment budgets. These computed volumes were compared using different pre‐depositional surfaces. Finally, we assessed the sediment exchange and associated sources of sediments of the washover fans. We applied a scale analysis to determine suitable DTM resolution and focal statistics window size as input to a geomorphometric classification analysis. Landform areas and landforms were delineated using morphometric threshold values, and volumes and sediment budgets of the delineated landforms were computed using different assumptions to define the pre‐depositional surface. Resulting washover fan volumes were validated against digital elevation model (DEM) of difference (DoD) derived volumes. Sediment budgets were derived from representative volumes of the washover fans and adjacent berms. We show that quantification of washover features derived from DTMs, using geomorphometric analysis is feasible and that the presented approach provides estimates of washover deposit volumes with an accuracy between 1% and 28% compared to control volumes. © 2021 John Wiley & Sons, Ltd.

Revealing Sediment Transport Pathways and Geomorphic Change in Washover Fans by Combining Drone‐Derived Digital Elevation Models and Single Grain Luminescence Data

AbstractChronostratigraphic investigations on coastal sedimentary records such as washover fans or beach‐ridge sequences may be used to reconstruct storm chronologies on centennial to millennial time scales. However, modern analogs are pivotal in interpreting depositional processes and reducing uncertainty in evaluating the complex chronostratigraphic architecture of these landforms. Such a modern analog was provided by category 3 tropical cyclone (TC) Olwyn in 2015, which caused a significant storm surge in the Exmouth Gulf (Western Australia). Pre‐ and post‐TC Olwyn geomorphological surveys and high‐resolution drone‐derived topographical data of a large washover fan document a detailed history of erosion and deposition during the event. The modern analog deposits provided an excellent opportunity to evaluate the use of luminescence‐based proxies (luminescence inventories) for tracing event‐related sediment source environments and understanding transport processes. Sediments deposited during Olwyn show a systematic relationship between luminescence characteristics and washover fan position. Seaward and central washover sections are indicated by well‐bleached deposits due to the beach as the dominant source and/or long transport distances. Lateral washover deposits are characterized by rather local source areas and short transport distances, resulting in higher remnant ages of 70–140 a. Our data show that the combination of sediment source environments and sediment transport length across the fan represents the main control in resetting the luminescence signal and enabling reliable depositional ages to be calculated. It documents the benefit of investigating luminescence inventories when establishing chronologies from complex sedimentary records, thereby demanding a careful consideration of local processes and source areas when interpreting sedimentary TC records.