Shoreline Recession Research Articles

A multi-hazards coastal vulnerability index of the east coast of Peninsular Malaysia

In Southeast Asia, an increase of 20 million people in the coastal zone have accentuated the infrastructure risk. In Malaysia, littoral erosion due to seasonal monsoons can critically affect the coastal population and the country lacks practical plans to attenuate coastal erosion. In this study, a systematic coastal vulnerability assessment that covers 10 physical and 5 socio-economic variables has been conducted at 16 districts from 4 states. The aim is to highlight the most vulnerable districts with respect to a potential catastrophic event. Multivariate statistical analyses facilitated realistic and meaningful interpretations for optimal coastal zone planning. We show that socio-economic variables are extremely relevant in all states except in southern Terengganu because it faces a direct impact of monsoon waves. Gender composition was found to be the most dominant coastal vulnerability factor for two states: Kelantan and Terengganu (north) due to the abundance of women involved in coastal trade and commerce. Besides, agriculture indicates a primary concern in the district of Johor. The results were categorized from very low to very high of vulnerability. The northern states of the east coast of Peninsular Malaysia show very high to high vulnerability relative to the southern states, which reveal moderate to very low vulnerability. In statistical analysis, it is shown that there is a similarity of 81.25% between Coastal Vulnerability Index (CVI) and Hierarchical Agglomerative Cluster Analysis (HACA). The authorities could utilize the findings of this study to forecast potential shoreline recession and establish adaptation measures to their coastal erosion adaptation plan.

Beyond physical control: Macrofauna community diversity across sandy beaches and its relationship with secondary production

Our understanding of the response of macrofauna diversity patterns to the variability of sandy beaches across spatial scales is limited. Defining relationships between diversity and ecosystem productivity is key to understanding the ecological consequences of the current global rates of biodiversity loss. Here, we conducted a study across a large spatial gradient of 39 sandy beaches involving a wide range of environmental conditions and macrobenthic diversity to (1) explore macrofauna diversity patterns (2) estimate secondary production and (3) quantify how much of the variability in beach secondary production can be explained by macrofauna diversity. Beach macrofauna showed a clear increase in α-diversity across a beach geographic gradient linked to oceanographic conditions. Partitioning of β-diversity implied the replacement of some species by others between beaches (i.e. spatial turnover) instead of a process of species loss (or gain) from beach to beach (i.e. nestedness). Variance partitioning analyses revealed that environmental and oceanographic variables (i.e., sea surface temperature, beach size, slope, and exposure rate), but also macrofauna diversity (i.e., species richness and Shannon index), largely determine beach secondary production. We showed that an increase in macrofauna diversity enhances beach secondary production, promoting energy transfer across trophic levels. The positive exponential relationship between macrofauna diversity and secondary production supports the idea that macrofauna plays an essential role in maintaining beaches as productive coastal ecosystems. Consequently, macrofauna diversity loss due to the ongoing shoreline recession and coastal occupation, exacerbated by climate change might cause exponential reductions in beach secondary production, which would affect the functioning of these sea-land interface areas.

Disposable or readily relocatable infrastructure to aid managed coastal retreat

Infrastructure can become a major determinant as to whether a defense or a retreat strategy is adopted at a coastal location. A significant investment in expensive networks of roads, water supply, and sewerage systems, along with power and telecommunications distribution infrastructure, can tip the defense/retreat debate and the associated cost-benefit analysis in favour of a defense approach. Often the increasingly expensive and sophisticated infrastructure servicing a coastal community has evolved over time, from simple beginnings. However, with upgrades and expansions coastal communities have become totally dependent on complex centralized systems that are vulnerable to disruption by erosion, shoreline recession, and/or oceanic overwash. For a strategy of managed retreat to be practical and achievable at any location, a policy which encourages self-sufficient or low-cost infrastructure that can be readily abandoned or relocated is desirable. There is also a need to re-think the forms of coastal subdivision layout and infrastructure provision that are most amenable to progressive retreat.

Monitoring 23-year of shoreline changes of the Zengwun Estuary in Southern Taiwan using time-series Landsat data and edge detection techniques

More than 80% of sandy beaches in Taiwan have been experiencing a severe recession, although the sediment discharge of rivers in Taiwan is significantly higher than the world average producing almost 2% of global fluvial sediment discharge. This contradiction is primarily due to the widespread constructions of reservoirs and intensive anthropogenic activities in coastal regions. In addition, coasts are particularly vulnerable to hazards due to climate change, such as sea-level rise, as they are located at the transition zone of terrestrial and marine environments. Along with the fact that Taiwan is an island and is one of the most climate-vulnerable regions globally, coastal management and sustainability are nationally critical topics, especially considering the ongoing reformation and legislation of Taiwan's coastal conservation laws.As stated in the Sustainable Development Goals (SDGs) goal 14, accurate and continuous shoreline positions information is essential for coastal conservation. However, by reviewing previous global studies and projects commissioned by the Taiwanese government aiming at monitoring shoreline changes, they usually exhibit several limitations, such as limited band selections or conservative band ratio-derived water indices, relying on either manual digitization or simple thresholding methods, focusing on either artificial or smoothly shaped coasts, and using images acquired at considerably different tidal height levels.Therefore, in the present study, a subpixel shoreline extraction approach based on a sustainable cross-generation dataset and a robust edge detection algorithm is proposed. This approach is exemplified by the Zengwun River Estuary located in southwestern Taiwan—Taiwan's most critical coastal preservation region. By quantitatively analyzing the resultant time-series shoreline positions from 1999 to 2021, several hotspots of shoreline recession have been identified: an extreme erosional rate up to −69.4 m year−1 is revealed in the northern sand bank; while the offshore sand bar demonstrates an overall landward retreat rate of −35.4 ± 1.24 m year−1.

Historical reconstruction of shoreline evolution at the Nam Dinh Coast, Vietnam

ABSTRACT Hai Hau, located in northern Vietnam, has suffered from severe coastal erosion with a retreat rate reaching 20 m/yr in recent years. Based on a systematic review of the literature, the shoreline recession trend along the Hai Hau is associated with the decline of water and sediment discharged from the So River, assumed to be active after a great flood in 1787, resulting in channel bifurcation and abandonment of the former channel. A historical analysis of the shoreline evolution of approximately a thousand years (the year 1000 – present) was conducted along this scenario using a modified one-line model. The simulated shorelines agreed well with the results of carbon-14 dating analysis, the historical reference points and shoreline positions extracted from the old maps, and the recently measured shoreline change derived from Landsat imagery. The present study demonstrates that the erosion at the Hai Hau has been ongoing from the end of the 18th century rather than the beginning of the 20th century, as proposed by some previous works. We regard the combined effects of the decrease in river sediment load, and other processes (subsidence and sea level rise (SLR)) are the major causes of long-term erosion on Hai Hau Coast.

The geomorphic role of large wood in the coastal zone: Mobilization threshold and beach morphology impacts in the North American Great Lakes

While large wood has been extensively studied in fluvial settings, where it functions as a key component of both physical and biological systems, the role of large wood in the shoreline-nearshore zone has received little attention to date. To address this gap, we examined large wood as a geomorphic agent along an eroding beach shoreline of southwestern Lake Michigan using high-resolution orthoimagery and DEM datasets. Erosion of the site and the liberation of woody materials from the strand were enhanced by rising lake levels. We digitized positions and evaluated the physical characteristics of 2627 pieces of large wood from 5 aerial images (2009–2017) and 11 seasonal drone surveys (2018–2020). This high temporal data resolution allowed us to track 374 unique pieces of large wood over time, revealing common transport pathways and sedimentary impacts of large wood along a wave-dominated beach shoreline. Results indicate that, while large wood has local, transient impacts on beach geomorphology, its presence has little bearing on longer-term beach evolutionary trajectories. Large wood offers little natural shoreline protection along high energy, dynamic shorelines, but may promote backshore accretion and foredune growth under other hydrodynamic and sediment-supply conditions. Our analysis of decadal shoreline evolution reinforces the importance of antecedent topography and coastal habitat elevation as primary controls on rates of shoreline recession.

Effect of alongshore sediment supply gradients on projected shoreline position under sea-level rise (northwestern Portuguese coast)

Shoreline changes are associated with natural and anthropic factors, such as sea-level rise, sediment budget, and beach fills. Shoreline retreat is mainly related to sediment deficit and sea-level rise. Some studies show that by the end of the 21st century some beaches may be lost, with the erosion of sandy beaches becoming predominant across the globe. The main purpose of this work is to model the shoreline evolution for 2050 and 2100 along a sandy coastal stretch in the NW Portugal, considering different scenarios of sea-level rise, to evaluate the influence this parameter and sediment budget have on shoreline displacement, as well as estimate the nourishment volume necessary to hold the shoreline in case of shoreline retreat. For this, we applied the stochastic version of the Random Shoreface Translation Model (RanSTM), in four cross-shore topo-bathymetric profiles, which are representative of alongshore coastal compartments. The overall results indicate that the key drivers in shoreline migration along the coastal stretch are not the same for the different profiles; in areas with a sediment supply deficit, shoreline recession increases, and hence the volume of sand required to hold the shoreline position in those zones is much greater. In contrast, positive sediment budgets can mitigate or reverse the erosion caused by sea-level rise.

Emerging Downdrift Erosion by Twin Long-Range Jetties on an Open Mesotidal Muddy Coast, China

Downdrift shoreline recession associated with the construction of a shore-crossing hard structure represents one of coastal erosional hotspots that must be addressed for an integrated, sustainable coastal zone management. To prevent siltation within the navigation channel, two rubber-mounted jetties were installed at the Sheyang River mouth on the open mesotidal muddy coast in Jiangsu province, China, in October 2013. The north jetty is 7.9 km long, while the south jetty is 7.8 km long. The net longshore sediment transport is from the north to the south due to flood-tide dominance. As disclosed by high-resolution satellite images, a 36-km-long downdrift shoreline stretch had experienced remarkable retreats at alongshore varying rates by March 2019. The eroding shoreline planform does not resemble a classic “S” shape, a crescentic shape, or a parabolic shape but an irregularly indented curved shape. Transect topographic survey also reveals an almost immediate response of the downdrift coast from the original accretionary scenery to an erosional regime, with the erosion front translocating downcoast at a much faster speed than a normal speed of 1–1.5 km/yr. Using FVCOM and SWAN, 2DH process-based numerical simulations are performed to simulate the flow, the sediment transport, and the yearly-magnitude accretion/erosion distribution in the jetty-affected area by a representative tidal force and an annual-magnitude wave force. The results demonstrate that the reciprocal tidal flow is predominantly responsible for the muddy sediment accretions at downdrift intertidal and surf zones shallower than a 4.0-m isobath, whereas big wind waves play a decisive role in triggering and developing the downdrift erosional process. The predicted spatial extent of the downdrift erosional segment matches closely the actual eroding front. The loss of the net annual longshore sediment transport volume, i.e., 3.08 million m3 due to the blockage by the twin jetties is recovered from a much larger spatial extent than the 36-km-long retreating shoreline stretch. With regard to the Bruun model, the one-line model, the headland-bay model, and the 2DH numerical model, the potential maximum recession length and the planform shape of the downdrift erosional shoreline arc are further elaborated to gain new insights into the spatial and temporal impact of a hard structure on the adjacent shoreline and flat (beach).

Semi-Analytical Model for the Evaluation of Shoreline Recession Due to Waves and Sea Level Rise

The climate change process is leading to an increase in the sea level and the storm intensity. The associated shoreline recession can damage coastal facilities and also beaches protected by submerged/emerged breakwaters whose defense action can become ineffective. The application of cross-shore numerical models does not allow the performance of long-term analyses. In this paper, a semi-analytical model for the evaluation of shoreline recession due to waves and sea-level rise for free and protected beaches is proposed. The model is an extension of the Dean’s approach in which some limitations on the beach profile are overcome and the effects of breakwaters on the wave height (wave transmission) and on the water level (piling-up) are considered. The model takes into account a wide range of parameters for wave, sea level, beach profile, and breakwater characteristics. Among the breakwater parameters, the freeboard and the berm width are found to mainly affect the shoreline recession. For submerged breakwaters, an optimal value of the freeboard can be computed depending on the sea level and the offshore wave characteristics. The results of the model are then used to find prediction relations of the shoreline recession, with r2 > 0.99, for both free and protected beaches, depending on the main hydrodynamic/geometrical characteristics.

The value of beach nourishment on a complex shoreline

Lee County has the most complex shoreline among Florida’s 25 counties where beach nourishment has been placed. It has eight shoreline breaks such as passes (inlets) that have produced a very complex pattern of both significant shoreline recession and accretion since 1858. Beach nourishment would seem problematic on those shorelines that have experienced significant long-term recession. However, nourishment has been very successful, widening beaches an average of 132 ft from their first nourishments to 2018 along shorelines that had historically receded hundreds of feet. Tourism is the backbone of Lee County’s economy, supporting one of every five jobs. Beaches are the key to the county’s tourism, with more day visits annually than to the 12 most visited National Parks in America. Over 80% of Lee County tourists are beach tourists, and they had a 2019 economic impact in Lee County of $4.3 billion. Beach tourists generated $843 million in total taxes to federal, state, and local governments with these governments receiving $580, $160, and $40, respectively, in taxes for each $1 that they spent on beach nourishment. Moreover, Lee County received an economic impact of $690 for every $1 spent on beach nourishment. International beach tourists spent $462 million in Lee County in 2019, providing a gain in the U.S. international balance of payments. An investment in beach nourishment produces such compelling returns in taxes generated by beach tourists that the state and federal governments should reassess their priorities for this investment versus investments in inland flood control and navigation.

Seven decades of shoreline changes along a muddy mangrove coastline of the Upper Gulf of Thailand

AbstractThis study evaluates the historical coastal change and development along the eastern coastline of the Upper Gulf of Thailand between 1953 and 2019 based on a series of aerial photographs and satellite images. Long‐term (~70 years) and short‐term (~10 years) shoreline movement rates were analysed using the Digital Shoreline Analysis System (DSAS). Results of this analysis indicate that the shoreline along the western coast (WBK) of the Bang Pakong River mouth has undergone severe coastal degradation, with a land loss of about 980 ha over the last seven decades. Meanwhile, the eastern coastline (EBK) has developed continuously over this time span, resulting in a land growth of about 552 ha. Based on historical shorelines recorded since 1954, the shoreline recession along the WBK coast accelerated over five decades. The average shoreline change rate reached approximately −9 m/year in 2002 and is shown to be related to land subsidence, which was due to groundwater withdrawals. The WBK coastline stabilized in 2009 and became an accretionary coast after 2016 due to the introduction of engineered coastal protection measures. In addition, the construction of major dams on the Chao Phraya and Bang Pakong rivers did not result in severe shoreline recession along the WBK coast. A significant reduction in sediment supply to the coastal zone due to damming was not observed. In contrast, the EBK coastline has advanced continuously since 1953, with average growth rates between 0.5 and 7.6 m/year over 50 years as a result of increased riverine sediment supply. Our results also indicate that mangrove deforestation was not a major factor causing shoreline retreat, and mangrove reforestation was not a successful coastal protection approach in this coast.

Rapid lake Michigan shoreline changes revealed by UAV LiDAR surveys

The recent record-breaking Laurentian Great Lakes water levels have led to severe erosion along many shorelines, but quantification of this erosion has not yet been widely reported. In this paper, novel shoreline measurements of Lake Michigan erosion, using a LiDAR-equipped unmanned aerial vehicle (UAV). The vehicle surveyed two beaches, Dune Acres and Beverly Shores, along the Indiana shoreline of southern Lake Michigan over the period 2018–2019, which are compared to existing aircraft-based LiDAR surveys. The UAV surveys reveal extensive shoreline erosion and recession at both beaches since the low water conditions of 2012–2013, with both beaches losing 70.7 and 64.8 m3/m of dry beach volume. Shoreline recession over this period was nearly 35 m for both beaches. In the period 2018–2019, the UAV measurements reveal continued beach erosion and the transition of beach topography to a steep, actively eroding foredune. Storm erosion resolved by short-interval surveys highlight the episodic nature of shoreline erosion, with 8 m3/m of material lost over a stormy two-week period at Dune Acres. While large, the erosion and recession observed at both beaches is in keeping with limited historical observations of shoreline change during high water episodes. However, the observed overall shoreline recession slopes of 1:29 (water level rise : recession) are much less than historical slopes, suggesting that the beaches are not yet in equilibrium with the high water levels and that erosion will continue in the foreseeable future while lake levels remain high.

The failure of NSW coastal management reform

In New South Wales (NSW), Australia, awareness of coastal erosion and shoreline recession had its genesis in the late 1920s when storms damaged houses at Collaroy one of Sydney’s northern beaches (Figure 1). At about the same time the Coogee “Fun” Pier, located on a southern Sydney beach and built between 1924 and 1928, was so damaged by wave attack that the remains had to be removed in 1934. Again in 1945 a new seawall at Cronulla, another southern Sydney beach, was damaged beyond repair and at the same time more houses were lost at Collaroy. This was followed in 1967, 1974, and 1978 by major erosion events that threatened both houses and high-rise buildings at Collaroy, resulted in the loss of houses at Bilgola, a northern Sydney beach and in 1978 the loss of houses at Wamberal, 46 km north of Sydney Harbour (Table 1). Unlike the United States of America (USA) where coastal management comes under both federal and state jurisdictions, in Australia it is the province of the governments of each of the states. The federal government does provide some aspirational guidance, but not significant legislative or financial support. There is also no equivalent to the U.S. Army Corps of Engineers to provide project delivery services. In Australia, the states devolve delivery down to local councils through Acts of Parliament and formal policies that can also have legislative force. However, the failure of the State of NSW to provide all the legislative tools necessary to effectively manage coastal matters at a local council level results in coastal management being abdicated rather than delegated by the state, particularly in relation to private development.

The economic value of beach nourishment in South Carolina

Tourism has become increasingly important in South Carolina’s economy, particularly beach tourism that accounts for two-thirds of tourist spending. Maintaining beaches is a requirement for a successful beach tourism industry. In the past 30 years, about 1.7 million yd3 of sand has been placed annually on South Carolina beaches. The annual cost has been $20.2 million in 2019 dollars or $13.9 million (2019 dollars) if federal mitigation and emergency sand placements are not included because their purpose was not in support of tourism. Beach nourishment has been very successful in combating shoreline recession. From 1984-1987 through 2006, South Carolina shorelines that were not nourished receded 101 ft on average, and shorelines that were nourished advanced 110 ft on average — and tourism boomed. South Carolina beach tourists generate $16.6 billion annually in South Carolina economic development and about $1.8 billion in taxes. For each $1 spent on beach nourishment, South Carolina receives over $1,200 in economic development generated by beach tourists and federal, state, and local governments receive almost $130 in taxes. Beach tourists have options, and with the state government spending only $3.1 million annually on beach nourishment versus the Florida state government spending $50 million on Florida beaches, South Carolina must be careful to maintain its beaches to continue attracting tourists at record levels.

A rules-based shoreface translation and sediment budgeting tool for estimating coastal change: ShoreTrans

Predicting change to shorelines globally presents an increasing challenge as sea level rise (SLR) accelerates. Many shoreline prediction models use the simplistic ‘Bruun rule’ for dealing with SLR profile translation, in-part due to alternative approaches being too complex and time-consuming to implement. To address this, we introduce ShoreTrans: a simple, rules-based, user-input driven, shoreface translation and sediment budgeting model, that applies the surveyed 2D-profile (not a parameterization), for estimating change to realistic coastlines, resulting from SLR and variations in sediment supply, while accounting for armouring, hard-rock cliffs and outcropping rocks. The tool can be applied to sand, gravel, rock and engineered coasts at a temporal scale of 10–100 years, accounting for shoreline trends as well as variability. The method accounts for: (1) dune encroachment/accretion; (2) barrier rollback; (3) non-erodible layers; (4) seawalls; (5) lower shoreface transport; (6) alongshore rotation; and (7) other sources and sinks. Uncertainty is accounted for using a probabilistic distribution for inputs and Monte Carlo simulations. We provide a first-pass assessment of two macrotidal UK embayments: Perranporth (sandy, dissipative, cross-shore dominant transport) and Start Bay (gravel, reflective, bi-directional alongshore dominant), then use idealised profiles to investigate the relative importance of forcing controls on shoreline recession and beach width. For the dissipative sandy site, the primary modes of coastal change are predicted to be short-term storm erosion and SLR translation while long-term trends may be important but are highly uncertain. For the reflective gravel site, the primary mode is multi-decadal longshore sediment flux, while short-term alongshore rotation and SLR translation are secondary. Relative to the ShoreTrans approach, the Bruun rule under-predicts shoreline recession in front of cliffs, seawalls and for low barriers that rollback, and over-predicts where large erodible dunes are present. ShoreTrans directly addresses change in beach width, with beaches in front of seawalls and cliffs predicted to shrink, such that narrow beaches (<50 m width) may disappear under 1-m SLR. As a standalone tool, ShoreTrans is transferable to many coast types and will provide coastal practitioners with a simple first-pass estimate of how the 2D appearance of a complex profile may change under SLR. A future benefit will be to combine this approach with existing hybrid modelling techniques to augment SLR translation predictions.

Human Impact on the Spatiotemporal Evolution of Beach Resilience on the Northwestern Yucatan Coast

The northern Yucatan peninsula is prone to coastal flooding and erosion owing to its low-land elevation and high exposure to storms. Therefore, it is important to assess the capability of the beach-dune system to resist, recover, and adapt from storms in the context of coastal development and climate change. This work aims to investigate the role of human impacts on the spatiotemporal evolution of the Coastal Resilience Index (CRI) in the area. The study is conducted on a prograding micro-tidal beach located on the vicinity of coastal structures. Beach and dune morphometrics, characteristic beach parameters, and maximum shoreline recession were determined from the analysis of beach profiles undertaken along a 2-km straight of coastline during the 2015–2020 period. Moreover, the maximum extreme water levels were estimated using in situ data and numerical models. This information is employed to assess the alongshore and temporal variability of the beach resilience. The results suggest that the beach and dune morphology present alongshore and temporal variability due to the human impacts associated to the dune degradation and the presence of coastal structures. The analysis shows that coastal resilience has been increasing over the past years but presents significant alongshore variations. High CRI values were found at beach transects presenting low anthropogenic impact, whereas low resilience was observed at transects with a degraded dune or located in the vicinity of coastal structures regardless of presenting high progradation rates. The observed beach response during the passage of recent tropical storms is consistent with the CRI values.

Hydro-morphological simulation for Blue beach, Gaza Strip, Palestine

Man-made improvements to the coastal areas can have a drastic short- and long-term impact on the sediment balance. This paper investigates the morphological changes at the Blue beach, Gaza Strip, Palestine. The Blue Beach resort is extremely deteriorated due to shoreline recession, where the width of the beach at some locations is less than 0.5 m. On the other side, the new recreational groin is unstable because it is not adequately designed to serve as a breakwater from a technical point of view. Firstly, this paper uses the integrated Digital Shoreline Analysis System (DSAS) with the Geographic Information System to detect changes in the coastline along the Blue Beach coast in Gaza during the 2011–2019 period. Shoreline change rates in the form of erosion and accretion patterns are automatically quantified by the End Point Rate. In addition, a proposed plan consists of two main stages to mitigate the current problems raised by severe erosion through numerical investigation; restoration of the existing beach by sand nourishment in addition to reducing the exposure of the coast to erosion and boost the protection of the recreational groin by implementing submerged offshore breakwaters. Hydro-morphological modeling is applied to study the processes of the coastal zone, hence, evaluating the diverse alternatives mentioned above. Delft3D software package is used to numerically simulate the different scenarios at different times: 1, 5, and 8 years, respectively. In addition, the existing structures are rehabilitated in accordance with current conditions. DSAS results show that during the period (2011–2019) there was a major recession to the shoreline with a peak erosion rate of -4.16 m/year. From the numerical modeling, it is concluded that the two submerged breakwaters managed to restore the beach by minimizing the amplitude of the wave and thus trapping the sediments behind it. In fact, the sediments grew offshore beyond the submerged breakwaters for the long term.

Seawalls as maladaptations along island coasts

Owing to their high shoreline-to-land-area ratios, islands are especially sensitive to coastal change and their inhabitants especially vulnerable to associated impacts. In places along island coasts where shoreline recession is particularly noticeable and/or its impacts most severe, perhaps because adjacent population densities are unusually high, a common response has been to build a seawall. While this solution may appear instinctively correct, studies suggest otherwise, even to the point where seawall construction, particularly outside urban areas, might be considered maladaptive – neither solving the intended problem in the short-term nor helping coastal peoples cope effectively with longer-term shoreline change. Seawall construction can be viewed as part of a broader group of maladaptive solutions that are uncritically embraced by island peoples who may judge the efficacy of these solutions by their success in (wealthier) continental or urban contexts. More effective and sustainable approaches involve nature-based solutions in the short term and planning for transformative responses involving relocation in the longer term.

ENHANCED SHORELINE MODELLING USING DATA ASSIMILATION TO INCLUDE NON-STATIONARITY IN WAVE CLIMATES

Coastal zone planning requires tools to predict shoreline response to changes in waves, water levels and sediment supply at time scales ranging from daily to decades. Despite the complexity of the underlying processes driving coastal change, the emergence of a range of semi-empirical models is proving to be increasingly successful at predicting shoreline response at seasonal to interannual timescales (e.g. Davidson et al., 2013). Recent improvements include the addition of processes such as longshore sediment transport and shoreline recession by SLR (e.g. Vitousek et al., 2017). But notably, in all these model formulations to-date, free-parameters are assumed to be time-invariant, relying on calibration over relatively short periods to measured shorelines and wave climate. Adopting a time-invariant set of model free-parameters ignores the bias introduced by the training dataset and any likely future changes in beach state and forcing conditions. The alternative approach presented here allows for time-varying model parameters, with the potential to improve model predictability due to non-stationarity in the underlying forcing. This work makes significant advances on previous shoreline modelling efforts by considering model parameters as potential time-varying quantities, as is common in the field of hydrology (e.g. Pathiraja et al., 2016). This is achieved by adopting a suitable data assimilation technique (Dual State-Parameter Ensemble Kalman Filter, EnKF) within the established shoreline evolution model, ShoreFor (Splinter et al., 2014). The method is first tested and evaluated using synthetic scenarios, specifically designed to emulate a broad range of natural sandy shoreline behavior.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/doAvC89vs4s

Quantifying the influence of shoreface shape on coastal responses to sea level rise

The coastal zone is a very dynamic region, constantly seeking to reach a state of equilibrium due to variations in the external forces. The shallow zone along the inner continental shelf known as the shoreface, can be divided into the upper and lower shoreface. While the former responds to processes operating across time spans ranging from that of a single event, such as storm, through to seasonal variations in environmental conditions, the latter evolution's occurs in geological scale, more in response to mean trends in environmental conditions (decades to millennia). These zones are connected via sedimentary exchanges, by a transition zone that adapts to changes imposed from behaviors and displacements of the upper and lower shoreface, such as upward profile displacement with sea level rise, aeolian transport, alongshore transport gradient, cross-shore transport. To analyze the influence of shoreface morphology variations on coastal response to mean sea level rise (MSLR), computer simulations were performed using synthetic shoreface profiles with variable shoreface shape parameter (‘m’) values. The random shoreface translation model (RanSTM) was used to simulate coastal response through variations in the shape of shoreface profiles. The ‘m’ value was changed in the upper and lower shoreface separately, to check the sensitivity of coastal response (in this case, shoreline recession distance) as a function of morphological change in each of the two zones. In addition, the variations of ‘m’ were analyzed with a variable and a fixed transition zone length (in order to isolate effects of a variable ‘m’). The simulations indicated that changes in ‘m’ on the upper shoreface have minimal influence on shoreline recession distance, especially when the transition zone remained constant. Conversely, profiles with higher ‘m’ values in the lower shoreface exhibited greater shoreline recession. It was also observed that, a longer transition zone produced a higher shoreline recession. Profiles adjusted with ‘m’ values of 0.66 and 0.4 in both shoreface zones had the highest and lowest shoreline recession distances (141.4 and 203.7 m), respectively. Sensitivity tests have shown that an increase of only 0.02 units in ‘m’ in the lower shoreface had a strong positive correlation (r = 0.97, p < 0.01) with increased shoreline recession. The results obtained in this study demonstrate the control that lower shoreface shape variations have on coastal response during MSLR. Critically, even small variations in shoreface shape parameter, such as those that occur along adjacent coastal sectors, and due to climate change effects may have implications for management and adaptation on a regional scale.