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.
Sea-level Rise, Coastal Flooding, and Storm Events
Global sea-level rise since the Nineteenth Century is expected to eventually cause recession of many shores, however most swell-exposed sandy beaches have not yet shown such response. This study analysed a 70-year air photo and beach profile record for swell-dominated Ocean Beach (western Tasmania) to show an abrupt change of long-term shoreline position variability circa 1980, from episodic erosion and accretion since at least 1947 to persistent recession with no recovery up to the present. Dating of back-dune peats exposed in the dune scarp showed that recent shoreline recession exceeds any in the last 1800 years. Investigation of potential causes identified recent-onset sea-level rise (SLR) on a tectonically-stable coast and increasing winds driving increased wave-setup as drivers with sufficient explanatory power to account for the observed changes, although data limitations and residual uncertainties mean additional contributing factors such as interdecadal wave direction changes cannot be ruled out. We hypothesise that Ocean Beach has experienced earlier recession in response to SLR and other climate change effects than many other beaches owing to exposure to a very high-energy storm-dominated wave climate, littoral drift efficiently delivering eroded sand to a large-capacity active sand sink, and low variability in swell-wave directions and inter-annual sea-levels. We hypothesise that sea-level rise with higher onshore wind speeds generating increased wave setup at Ocean Beach since before the 1980s has increased upper beach erosion event frequency until the formerly stable or gaining sand budget reversed to deficit. A major storm or storm cluster abruptly tipped the beach into its current recessional mode when its sand budget was close to deficit. Factors causing an early shoreline response to sea-level rise at this site are applicable more widely as potential indicators of beaches likely to respond earlier than others to climate-induced changes including not only SLR but also wind climate changes.
Beach loss and shoreline retreat caused by sea level rise (SLR) is considered one of the most worldwide significant issues. The Mediterranean coastline of Egypt (approximately 1066 km) is likely to face beach erosion, particularly in the low-lying and sandy coastal areas in the future as a direct response to SLR. Consequently, the projection of future shoreline recession and corresponding beach loss due to SLR using the Bruun rule were investigated to assess the proper impacts of SLR on the shoreline recession and beach loss. In addition, the uncertainties ratios associated with SLR scenarios and sediment sizes were assessed. Furthermore, this study investigated the influence of local land subsidence in combination with SLR scenarios on the shoreline recession and associated beach loss along the Nile Delta coastline. The ensemble-mean regional SLR data included representative concentration pathway (RCP) scenarios and 21 models of the Coupled Model Intercomparison Project Phase 5 (CMIP5). The projected shoreline retreats and associated average beach loss in the future 2081–2100 were ranged from 12.6 m and 11.3 km2 to 41.9 m and 19.2 km2 for the ensemble-mean SLR RCP2.6 and RCP8.5, respectively. The uncertainty caused by the sediment size of 0.15 to 0.35 mm ranged from 17% to 30% for RCP2.6 and RCP8.5, respectively. The projected annual shoreline retreats ranged from 0.36 to 0.65 m/yr for the ensemble-mean SLR in combination with local land subsidence for RCP2.6 and 0.48 to 0.85 m/yr for RCP8.5, respectively. Highly vulnerable areas to shoreline recession for SLR and local land subsidence were detected from EL-Manzala lake to Port Said coastlines, Abo Qir bay, from Rosetta to Damietta promontories, and Alexandria coastline. Thus, shoreline retreat and associated beach loss due to SLR is an urgent issue that should be addressed through the integrated coastal zone management strategies of Egypt.
The response of a coastal region to sea-level rise depends on the local physical features, which should therefore be evaluated locally to provide an accurate vulnerability assessment. In this study, we conducted comprehensive analyses of the potential impacts of sea-level rise on the Pearl River Estuary (PRE), China with the aid of a fully calibrated three-dimensional hydrodynamic model. We found that in general, the salinity, stratification and tidal range will increase as the sea-level rises. Clear spatial variations were apparent in the response of these parameters, with different patterns occurring in different seasons. The strongest salinity increase was mostly at the front of the PRE, where freshwater and saltwater meets. In Lingding Bay (LDB), the rate of increase in stratification in response to the sea-level rise was found to be higher during high-flow conditions than that during low-flow conditions. The increases of tidal range and tidal current were amplified in the upstream direction, with the largest increase occurring in the upper tributaries. The change of vertical transport process in the PRE is not prominent and only in the upper LDB the vertical transport time increased for approximately two days. The upstream transport process was strengthened during the typical wet season and weakened during the typical dry season. The downstream transport slowed in both wet and dry seasons as the sea level rose. For a sea-level rise of 1 m, the dry season residence time increased by 8.5 days, while the wet season residence time showed only minor changes. It was also found that the fluvial input remained in the PRE for a longer time after the sea level rose, which would increase the retention time of dissolved substances and thus effect biogeochemical processes.
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.
This work analyzes the coastal impacts of the combined effect of extreme waves and sea level extremes, including surges and projected mean sea level rise in Bocagrande, Cartagena (Colombia). Extreme waves are assessed from a wave reanalysis that are propagated from deep waters to the beach considering the hydrodynamic processes and taking into account the interaction between waves and the coastal elevation within the study area. First, we consider present sea level, storm surges and waves affecting the area. Next, we analyze the effect of sea level rise according to a moderate (RCP4.5) climate change scenario for the 21st century (years 2025, 2050, 2075, and 2100). The most pessimistic scenario (year 2100) yields a percentage of flooded area of 97.2%, thus revealing the major threat that represents sea level rise for coastal areas in the Caribbean Sea.
Recent projections suggest worst-case scenarios of more than six ft (1.8 m) of global mean sea-level rise by end of century, progressively making coastal flood events more frequent and more severe. The impact on transportation systems along coastal regions is likely to be substantial. An analysis of impacts for Atlantic and Cape May counties in southern New Jersey is conducted. The impact on accessibility to employment is analyzed using a dataset of sea-level increases merged with road network (TIGER) data and Census data on population and employment. Using measures of accessibility, it is shown how access will be reduced at the block-group level. An additional analysis of low and high income quartiles suggest that lower-income block groups will have greater reductions in accessibility. The implication is that increasing sea levels will have large impacts on people and the economy, and large populations will have access to employment disrupted well before their own properties or places of employment may begin to flood (assuming no adaptation).
Sea level rise is one of the major challenges facing humanity in the 21st century, and could compound the risks posed by tsunamis to coastal cities. The authors conducted computer simulations of tsunami inundation and propagation into Tokyo Bay, and analysed the risks that such events pose to the cities of Yokohama and Kawasaki, for different sea level rise scenarios (and assuming a high tide situation). The results show that unless significant investment in improved coastal defences is made, the area that can potentially be flooded by such events will gradually increase in the course of the 21st century. However, the risk to the life of the inhabitants of these cities will broadly remained unchanged until sea levels become +1.0 m higher than at present. From then, the risk of casualties taking place will rapidly increase, as the depth and velocity of the tsunami wave will substantially rise. Such results provide some indication regarding the long-term planning strategy to manage coastal defences around Tokyo Bay, highlighting the need to eventually reinforce coastal defences and the important contribution of tsunami evacuation to minimize casualties during such events.
he sustainability of dynamic natural systems often depends on their capacity to adapt to uncertain climate-related changes, where different management options may be combined to facilitate this adaptation. Salt marshes exemplify such a system. Marsh sustainability under rapid sea level rise requires the preservation of transgression zones - undeveloped uplands onto which marshes migrate. Whether these uplands eventually become marsh depends on uncertain sea level rise and natural dynamics that determine migration onto different land types. Under conditions such as these, systematically diversified management actions generally outperform ad hoc or non-diversified alternatives. This paper develops the first adaptation portfolio model designed to optimize the benefits of a migrating coastal system. Results are illustrated using a case study of marsh conservation in Virginia, USA. Results suggest that models of this type can enhance adaptation benefits beyond those available through current approaches.
Hurricanes Irma and Maria, two powerful storms that hit the U.S. Virgin Islands less than 2 weeks apart in September 2017, caused extensive damage to the natural resources on St. John. Damage was particularly severe in a unique mangrove/coral ecosystem in three bays within Virgin Islands Coral Reef National Monument, a National Park Service marine protected area. Many Red Mangrove (Rhizophora mangle) trees were uprooted and tossed into the sea, and the prop roots of others were stripped of corals, sponges and other marine life. No other mangrove area in the Caribbean is known to have so many scleractinian corals (about 30 species before the storms). Although many corals were overturned or buried in rubble, colonies of most of the species, including four that are listed as threatened under the U.S. Endangered Species Act, survived. Recovery of this ecosystem will depend on Red Mangrove propagules becoming established and producing prop roots to support rich marine life along with a canopy to provide the shade that was critical to the biodiversity that was present before the storms. Unlike in many situations where major disturbances reduce coral cover, the substrate that must be restored for full recovery to occur is a living substrate—the prop roots of the mangroves. Larvae of corals and sponges will need to recruit on to the roots. Future storms could hinder this process.