Shoreface Translation Model Research Articles

Geomorphological controls on the coastal response under projected sea level rise: A case study at an oceanic island (Trindade, Brazil)

Sea level rise (SLR) is one of the most threatening consequences of climate change. Despite considerable attention being paid to its impact on coastal zones, the studies concerning insular ecosystems remain scarce, particularly in the South Atlantic. In addition, large uncertainties still exist regarding the SLR rates and how islands respond to them. In this study we selected Trindade Island (Brazil), which exhibits a great variety of geomorphological beach systems, to investigate how geomorphological controls (e.g., profile geometry, composition, and sediment budget) influence the coastal behavior under SLR scenarios. To quantify the contribution of the aforementioned parameters to the coastal response, a set of experiments was conducted using the Random Shoreface Translation Model. Overall, the simulation results indicated that most of the analyzed beaches experienced shoreline retreat under the projected SLR scenarios for both 2040 and 2100 (retreat values ranged from 0 to −12.5 m for 2040 and from −0.5 to −47.1 m for 2100). The shoreface slope and composition exerted a strong influence on the coastal response of Trindade, wherein smoother profiles exhibited larger shoreline displacements. When the lower shoreface primarily comprised sand rather than rock, the retreat rates declined by more than 90% under most scenarios. Moreover, we highlight from the two associated experiments, the following: 1) the hard structures in the surf zone (e.g., calcareous reefs and volcanic rock outcrops) act as natural barriers to coastal displacement; and 2) the shoreline response was particularly sensitive to different sediment budget estimates. In conclusion, the results reveal the complexity involved in the investigation of geomorphological controls, emphasizing that a accurate delineation of such parameters is critical for providing reliable forecasts when modeling the coastal responses to SLR.

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.

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.

Effects of closure depth changes on coastal response to sea level rise: Insights from model experiments in southern Brazil

This study focuses on the impacts of variable shoreface closure depth limits on coastal responses to increases in sea levels along a sandy barrier in southern Brazil. Upper and lower shoreface limits for sediment exchanges are largely regulated by the wave climate and they tend to move offshore as the temporal scale increases. Therefore, because closure depth limits are a source of uncertainty in simulations of coastal response to sea level rise, to elucidate how important changes in these limits are under such conditions, four simulation experiments were performed with variable combinations of upper and lower shoreface closure depth values. Direct methods for closure depth delineation require long term data sets with field surveys, which are rarely available; therefore, indirect approaches are applied widely. To calculate closure depth values here, we apply Hallermeier's equations using two wave data sources: one measured (via wave buoys) and one modeled Wave Watch III and Simulating Waves Nearshore Model (WWIII/SWAN). Evaluation of coastal response under rising sea levels was possible via application of an aggregated coastal modeling approach using the random shoreface translation model (RanSTM). Shoreline retreat distances resulting from each combination of upper (hc) and lower (hi) shoreface closure depth values (cases) in model simulations were compared: Case 1 (hc = 7.4 m; hi = 42.1 m), Case 2 (hc = 7.4 m; hi = 35.7 m), Case 3 (hc = 6.2 m; hi = 35.7 m), and Case 4 (hc = 6.2 m; hi = 42.1 m). Statistical analysis via the Kruskal-Wallis test demonstrated that shoreline retreat was significantly affected (at P < 0.01) by the variations in lower shoreface limit. The recession distance was greater when the lower shoreface limit was deeper. Overall results indicate that the choice of lower shoreface limiting depth is indeed crucial in influencing coastal response to sea level rise, and hence in future shoreline position forecasts. Therefore, these results show the relevance of determining such limits with confidence when modeling coastal response to sea level rise, especially when this rise is being predicted over longer temporal scales.

Quantifying the geomorphologic and urbanization influence on coastal retreat under sea level rise

In response to increasing greenhouse gases emissions, the global climate is undoubtedly changing. As a consequence of rising temperatures, mean sea level also shows an increasing tendency globally, still, uncertainties in relation to its regional specific trends can be identified. Besides that, uncertainties also remain regarding regional and local coastal response to sea level rise. Coastal geomorphology (topography, bathymetry, and sediment texture) plays a relevant role, especially in defining how sediment exchanges occur in the active zone, thus inducing different morphodynamic readjustments. In this context, this study is focused on projecting the future coastline position for the years 2040 and 2100 along three sectors at Hermenegildo Beach, and on investigating the influence of site-specific geomorphological characteristics, urbanization and the presence of hard coastal protection structures on the coastal response under accelerated rates of sea level rise using a stochastic morpho-kinematic model, the Random Shoreface Translation Model. Model outputs as coastal recession distances were submitted to a Kruskal-Wallis test to verify if there were significant differences in coastal recession 1) amongst the three sectors (standard own topography and bathymetry); 2) due to changes in dune topography only; and 3) due to the presence or absence of hard coastal protection structures at the urbanized sector. Overall, the results indicate that the urbanized area presented the highest recession distance amongst the sectors. Differences in dune heights between the northern and southern dune field sectors at Hermenegildo Beach do not significantly influence the mean coastal retreat. On analyzing mean coastal recession results for the urbanized sector, with and without hard coastal protection structures, we conclude that the presence of urbanization and hard structures on the active dune and beach contributed to a maximum increase of 13.52% in mean coastal recession distance and that it significantly (P < 0.01) affects coastline recession in comparison to that in the case of a non-structured dune field for both the time horizons considered (2040, 2100). The results presented here provide a basis for future planning and management at the area, pointing out to the increased erosion risk caused by the existence of an artificially structured shoreline.

Modelling the effects of sea-level rise and sediment budget in coastal retreat at Hermenegildo Beach, Southern Brazil

Abstract Climate change effects such as accelerated sea-level rise, wave climate alteration and disturbances on sediment-budgets are anticipated to lead to a range of adverse impacts in coastal regions around the world. A rise in sea-level is expected to cause shoreline recession, and a sediment deficit can have a similar effect. Since large uncertainties exist in relation to sea-level rise rates and sediment budgets, it is relevant to determine how sensitive the coast is to each of these disturbances. In this context, this paper provides a quantitative evaluation of each of these parameters in terms of modeled coastal recession through risk-based assessments using an aggregated coastal model, the DRanSTM (Dilating Random Shoreface Translation Model). In each separate computer simulation, a sediment budget and a sea-level scenario were set for an erosional coastal stretch: Hermenegildo Beach, Rio Grande do Sul state in southern Brazil. Effects of changes in wave climate were not directly considered in this study. However, indirect measures of such changes should be reflected on coastal sediment budgets. Simulation results demonstrate that under present-day sea-level rise rates, sediment deficit exerts control over coastal recession. Conversely, under the higher forecasted sea-level rise for the year 2100, mean shoreline recession will be dictated by sea-level rise, considering historical sediment deficit will be sustained.

Modelling climate change effects in southern Brazil

ABSTRACT Figueiredo, S.A., 2013. Modeling climate change effects in southern Brazil. Along the coast of Rio Grande do Sul state, southern Brazil, differences on coastal configuration are generally accompanied by changes in substrate slope, where steeper gradients characterize coastal projections and gentle gradients the coastal embayments. This study focus on coastal response to climate change effects at two sectors along RS coast: Cassino embayment and Conceicao lighthouse projection. The former has been under very high rates of progradation, on the order of at least 3 m/yr at geological and historical time scales. Whereas Conceicao region has been undergoing rates of recession reaching −3.6 m/yr. In order to forecast coastal response to the effects of climate change at these sites over several time horizons (2030–2070–2100), model simulations using the DRanSTM (Dilating Random Shoreface Translation Model) were performed. Simulation results have demonstrated that Cassino sector is particularly vulnerable...

Shoreface translation model: Computer simulation of coastal-sand-body response to sea level rise

The response of coastal sand bodies to sea level rise can be modelled using computer simulation of large scale coastal behaviour based only on principles of sand-mass conservation and geometric rules for shoreface and barrier morphology. The model simulates horizontal and vertical translation of coastal sand bodies over the pre-existing coastal substrate which undergoes reworking as a consequence. This produces changes in position of the coastline as well as reconfiguration of the backshore and inner-continental shelf morphology and stratigraphy. Application of the model is illustrated with examples from mineral exploration of the continental shelf and assessment of coastal erosion risks in the face of sea-level rise due to the enhanced greenhouse effect.