The geomorphic significance of hurricanes on coral-fringed calcium carbonate coastlines: Hurricane Wilma 15-25 October 2005, northeastern Yucatan Peninsula, Mexico

<p>Hurricanes and tropical storms can cause large scale morphological changes to barrier beach systems in tropical environments. Many such systems are fronted by coral reefs; however, unlike siliciclastic barrier beaches, little is known about the significance of hurricanes to barrier beach evolution on coral-fringed calcium carbonate coastlines. This study provides a detailed assessment of the impacts of Hurricane Wilma, a major hurricane, on the reef-protected and exposed barrier beaches of northeastern Yucatan Peninsula, Mexico. The study considers both the short (0-8 months) and medium term (8-56 months) response, and postulates the significance of major storm events over the longer term. Hurricane Wilma made landfall in late October 2005 as a Category 4 hurricane, bringing sustained wind speeds of 67 ms-1, and storm waves with significant wave heights (HS) ≈ 13 m. The storm persisted for over 20 hours, while storm waves inundated the low lying barrier beaches and rainfall flooded inland wetlands and lagoons. To determine the impacts of Hurricane Wilma and quantify post-storm recovery of reef-protected and unprotected barrier beaches, geomorphic mapping and post-storm surveying (2006 and 2010) was completed at 49 locations between Punta Nizuc and Punta Maroma. In addition, 220 sediment samples were collected from across barrier beaches and the backreef lagoon for textural and petrographic analysis. Satellite imagery was also used to quantify immediate storm impacts and recovery of the shoreline. Barrier beaches were found to have responded to storm waves in two broadly different ways: reef-protected beaches accreted by between 2.1 and 24.6 m, as the beach and foredunes were reworked. In contrast, unprotected beaches underwent erosion of over 10 m. By 2006, reef-protected beaches had undergone rapid shoreface and beachface adjustment. Over the next four years, these beaches gradually transgressed landwards and aggraded subaerially as they readjusted to their pre-storm equilibrium beach profile. Exposed beaches responded much more rapidly than those protected by reefs, with shoreline adjustment occurring within eight months of the storm. Subaerial beach development was, however, much slower, requiring extended calm conditions to infill the eroded beach. The storm and post storm geomorphic responses were found to be highly variable alongshore, and influenced by several factors, including dune height, beach width, and wave exposure. The results indicate that under the contemporary climatic conditions hurricanes are key drivers of barrier beach evolution over the short (0-8 months) to medium terms (8-56 months), but are not so influential over longer time scales. However, an expected increase in the number of major storms (category 3-5) in the future may increase the significance of hurricanes to longer term barrier evolution, with the storm impacts likely to be greater and the recovery times longer. Understanding these responses is particularly critical as many areas continue to be developed, and as the coral reef protecting the coastline becomes threatened by the implications of climatic change.</p>

The geomorphic significance of hurricanes on coral-fringed calcium carbonate coastlines: Hurricane Wilma 15-25 October 2005, northeastern Yucatan Peninsula, Mexico

<p>Hurricanes and tropical storms can cause large scale morphological changes to barrier beach systems in tropical environments. Many such systems are fronted by coral reefs; however, unlike siliciclastic barrier beaches, little is known about the significance of hurricanes to barrier beach evolution on coral-fringed calcium carbonate coastlines. This study provides a detailed assessment of the impacts of Hurricane Wilma, a major hurricane, on the reef-protected and exposed barrier beaches of northeastern Yucatan Peninsula, Mexico. The study considers both the short (0-8 months) and medium term (8-56 months) response, and postulates the significance of major storm events over the longer term. Hurricane Wilma made landfall in late October 2005 as a Category 4 hurricane, bringing sustained wind speeds of 67 ms-1, and storm waves with significant wave heights (HS) ≈ 13 m. The storm persisted for over 20 hours, while storm waves inundated the low lying barrier beaches and rainfall flooded inland wetlands and lagoons. To determine the impacts of Hurricane Wilma and quantify post-storm recovery of reef-protected and unprotected barrier beaches, geomorphic mapping and post-storm surveying (2006 and 2010) was completed at 49 locations between Punta Nizuc and Punta Maroma. In addition, 220 sediment samples were collected from across barrier beaches and the backreef lagoon for textural and petrographic analysis. Satellite imagery was also used to quantify immediate storm impacts and recovery of the shoreline. Barrier beaches were found to have responded to storm waves in two broadly different ways: reef-protected beaches accreted by between 2.1 and 24.6 m, as the beach and foredunes were reworked. In contrast, unprotected beaches underwent erosion of over 10 m. By 2006, reef-protected beaches had undergone rapid shoreface and beachface adjustment. Over the next four years, these beaches gradually transgressed landwards and aggraded subaerially as they readjusted to their pre-storm equilibrium beach profile. Exposed beaches responded much more rapidly than those protected by reefs, with shoreline adjustment occurring within eight months of the storm. Subaerial beach development was, however, much slower, requiring extended calm conditions to infill the eroded beach. The storm and post storm geomorphic responses were found to be highly variable alongshore, and influenced by several factors, including dune height, beach width, and wave exposure. The results indicate that under the contemporary climatic conditions hurricanes are key drivers of barrier beach evolution over the short (0-8 months) to medium terms (8-56 months), but are not so influential over longer time scales. However, an expected increase in the number of major storms (category 3-5) in the future may increase the significance of hurricanes to longer term barrier evolution, with the storm impacts likely to be greater and the recovery times longer. Understanding these responses is particularly critical as many areas continue to be developed, and as the coral reef protecting the coastline becomes threatened by the implications of climatic change.</p>

Extreme Coastal Inundation Under Different Climate Scenarios: Fourchon Junction Case Study

Port Fourchon Junction is located within Chevron's Fourchon Terminal, just south of Port Fourchon and is operated by Shell Pipeline Company LP. This manifold metering station is a critical junction for the Mars Corridor oil, as oil production from Mars (MC-807), Ursa (MC-809), Titan (MC-941), Who Dat (MC-547), Medusa (MC-582), and Olympus (MC-807B) flows through this station via a 24" pipeline. Port Fourchon is at the edge of the Mississippi delta facing the sea, one of the world's most vulnerable low-elevation coastal zones. It is highly exposed to storm surge and wave-induced inundation under hurricanes which regularly visit the Gulf of Mexico. In addition, it experiences one of the largest rates of subsidence in the world, which combined with sea level rise, will increase the site vulnerability in the coming decades. This study assesses present and future scenarios of subsidence and sea level rise under extreme metocean conditions induced by hurricanes and their impact on Port Fourchon Junction. Local effects such as the differential settlement of the barrier beach have been also considered. Using results from the numerical model XBeach, a set of different present and future scenarios are modelled under extreme metocean conditions. These conditions and the subsequent design parameters calculated, are not obtained through traditional extreme value analysis methods, instead, they are estimated through the influence of boundary conditions forced with the corresponding return period values of the parameters. Boundary conditions for the simulations are extracted from Grand Isle and Port Fourchon sea level observations, and from FEMA and the Water Institute of the Gulf simulations. Port Fourchon site should be subject to flooding for 10-year return period conditions based on Grand Isle observations. For 5-6 years return period conditions some degree of milder partial flood should also be expected. This is well captured by the model. While the highest inundating level is mostly dependent on winds, waves and surge acting together, surge is the single most critical parameter that defines the asset's base inundation level. Design future conditions based on surge extreme from FEMA simulations are recommended over surge extremes derived from Grand Isle observations. The barrier beach and the breakwaters play a key factor in sheltering site from waves and surge. Even when submerged under extreme high return period conditions they dissipate the waves ensuring that the maximum water level (wave crest elevation) on site is lower than would otherwise be without them. It is then important to maintain them fit for purpose during the entire lifespan of the asset. Both Grand Isle and Port Fourchon subsidence scenarios yield similar results. Based on the importance of Port Fourchon Junction facilities, the design criteria obtained, and the higher subsidence level observed at Port Fourchon (compared to Grand Isle), it is recommended that a 1000-year return period and future scenario based on FEMA surge level and Port Fourchon Relative Sea Level Rise (RSLR) is adopted for design. The subsidence associated to this scenario is 9.8 mm/year. The sea level rise associated to this scenario is 2 mm/year.

Gravel Barrier Beach Morphodynamic Response to Extreme Conditions

Gravel beaches and barriers form a valuable natural protection for many shorelines. The paper presents a numerical modelling study of gravel barrier beach response to storm wave conditions. The XBeach non-hydrostatic model was set up in 1D mode to investigate barrier volume change and overwash under a wide range of unimodal and bimodal storm conditions and barrier cross sections. The numerical model was validated against conditions at Hurst Castle Spit, UK. The validated model is used to simulate the response of a range of gravel barrier cross sections under a wide selection of statistically significant storm wave and water level scenarios thus simulating an ensemble of barrier volume change and overwash. This ensemble of results was used to develop a simple parametric model for estimating barrier volume change during a given storm and water level condition under unimodal storm conditions. Numerical simulations of barrier response to bimodal storm conditions, which are a common occurrence in many parts of the UK were also investigated. It was found that barrier volume change and overwash from bimodal storms will be higher than that from unimodal storms if the swell percentage in the bimodal spectrum is greater than 40%. The model is demonstrated as providing a useful tool for estimating barrier volume change, a commonly used measure used in gravel barrier beach management.

An Intracoastal Waterway and Trading Port System in Prehispanic Northwest Yucatán, Mexico

Archaeological explorations and surveys, conducted over the course of the last 140 years, have documented a long history of human occupation of the northwest coast of Yucatán, from Middle Preclassic times (ca. 600 B.C.) to the present. Recent archaeological research, coupled with historic data and oral history, indicate that a 215 kilometer-long estuarine swamp, located behind the narrow coastal barrier beach, served as an intracoastal waterway between Celestún and Dzilám de Bravo. This waterway was a major navigation and trading route in prehispanic and historic times, until the mid-20th century.

Morphology and sedimentary filling of an ancient estuarine valley in an urban environment (Gijón, NW Spain)

&lt;p&gt;The city of Gij&amp;#243;n is located on the Cantabrian Coast (NW, Spain), and its subsurface is formed mainly by sand linked to an old estuarine mouth barrier (beach and dunes), sand bay and marshes. Under these sediments, there is a layer of clays related to the weathering of a Jurassic rock basement. This research addresses the setting of the estuary sediments in both the submerged area, located north of the city, and under the built-up area.&lt;/p&gt;&lt;p&gt;The seafloor morphology was investigated by means of a bathymetric survey with multi-beam echo sounder. A geophysical survey using high-resolution reflection seismic profiles allowed studying the thickness of the unconsolidated deposits that fill the bay of Gij&amp;#243;n. Likewise, the distribution of coastal sediments under the city was reviewed from boreholes collected within a GIS-based geotechnical database.&lt;/p&gt;&lt;p&gt;The bathymetric reconstruction led to the identification of a paleo-valley supposedly excavated by the main river of the city, with N-S orientation that evolves to NNE-SSW towards the north. It shows a sandy bottom with a very low slope, a length of about 4 km and a width that ranges between 400 and 800 m. In this channel, the unconsolidated deposits reach a maximum thickness of around 15 m while at S, in the urban subsurface, the thickness exceeds 20 m locally. With these data, it was also possible to investigate the geometry of the bedrock under the sedimentary filling.&lt;/p&gt;

Impact of Barrier Breaching on Wetland Ecosystems under the Influence of Storm Surge, Sea-Level Rise and Freshwater Discharge

Coastal wetland ecosystems and biodiversity are susceptible to changes in salinity brought about by the local effects of climate change, meteorological extremes, coastal evolution and human intervention. This study investigates changes in the salinity of surface water and the associated impacts on back-barrier wetlands as a result of breaching of a barrier beach and under the compound action of different surge heights, accelerated sea-level rise (SLR), river discharge and rainfall. We show that barrier breaching can have significant effects in terms of vegetation die-back even without the occurrence of large storm surges or in the absence of SLR, and that rainfall alone is unlikely to be sufficient to mitigate increased salinity due to direct tidal flushing. Results demonstrate that an increase in sea level corresponding to the RCP8.5 scenario for year 2100 causes a greater impact in terms of reedbed loss than storm surges up to 2 m with no SLR. In mitigation of the consequent changes in wetland ecology, regulation of relatively small and continuous river discharge can be regarded as a strategy for the management of coastal back-barrier wetland habitats and for the maintenance of brackish ecosystems. As such, this study provides a tool for scoping the potential impacts of storms, climate change and alternative management strategies on existing wetland habitats and species.

Analysis and prediction of storm water levels in Delaware inland bays

A simple approach based on an analytical model and available tide gauge data is proposed for the analysis of storm tide damping inside inland bays with complex bathymetry and for the prediction of peak water levels at gauge locations during storms. The approach was applied to eight tide gauges in the vicinity of inland bays in Delaware. Peak water levels at the gauge locations were analyzed for 34 storms during 2005-2017. A damping parameter in the analytical model was calibrated for each bay gauge. The calibrated model predicted the peak water levels within errors of about 0.2 m except for Hurricane Sandy in 2012. The analytical model including wave overtopping was used to estimate the peak wave overtopping rate over the barrier beach from the measured peak water level in the adjacent bay.