Wave-induced extreme water levels in the Puerto Morelos fringing reef lagoon

Wave-induced extreme water levels in the Puerto Morelos fringing reef lagoon are investigated by means of a phase-resolving non-hydrostatic wave model (SWASH). This model solves the nonlinear shallow water equations including non-hydrostatic pressure. The one-dimensional version of the model is implemented in order to investigate wave transformation in fringing reefs. Firstly, the numerical model is validated with (i) laboratory experiments conducted on a physical model (Demirbilek et al., 2007)and (ii) field observations (Coronado et al., 2007). Numerical results show good agreement with both experimental and field data. The comparison against the physical model results, for energetic wave conditions, indicates that high- and low-frequency wave transformation is well reproduced. Moreover, extreme water-level conditions measured during the passage of Hurricane Ivan in Puerto Morelos are also estimated by the numerical tool. Subsequently, the model is implemented at different along-reef locations in Puerto Morelos. Extreme water levels, wave-induced setup, and infragravity wave energy are estimated inside the reef lagoon for different storm wave conditions (<i>H</i><sub>s</sub> >2 m). The numerical results revealed a strong correlation between the offshore sea-swell wave energy and the setup. In contrast, infragravity waves are shown to be the result of a more complex pattern which heavily relies on the reef geometry. Indeed, the southern end of the reef lagoon provides evidence of resonance excitation, suggesting that the reef barrier may act as either a natural flood protection morphological feature, or as an inundation hazard enhancer depending on the incident wave conditions

Characterising beach intertidal bar systems using multi-annual LiDAR data

This is the peer reviewed version of the following article: Miles, A., Ilic, S., Whyatt, D., & James, M. R. (2019). Characterising beach intertidal bar systems using multi‐annual LiDAR data. Earth Surface Processes and Landforms, which has been published in final form at https://doi.org/10.1002/esp.4594. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-ArchivingIntertidal bars are common in meso-macrotidal low-to-moderate energy coastal environments and an understanding of their morphodynamics is important from the perspective of both coastal scientists and managers. However, previous studies have typically been limited by considering bar systems two-dimensionally, or with very limited alongshore resolution. This paper presents the first multi-annual study of intertidal alongshore bars and troughs in a macro-tidal environment using airborne LiDAR data to extract three-dimensional bar morphology at high resolution. Bar and trough positions are mapped along a 17.5 km stretch of coastline in the northwest of England on the eastern Irish Sea, using eight complete, and one partial, LiDAR surveys spanning 17 years. Typically, 3 – 4 bars are present, with significant obliquity identified in their orientation. This orientation mirrors the alignment of waves from the dominant south-westerly direction of wave approach, undergoing refraction as they approach the shoreline. Bars also become narrower and steeper as they migrate onshore, in a pattern reminiscent of wave shoaling. This suggests that the configuration of the bars is being influenced by overlying wave activity. Net onshore migration is present for the entire coastline, though rates vary alongshore, and periods of offshore migration may occur locally, with greatest variability between northern and southern regions of the coastline. This work highlights the need to consider intertidal bar systems as three-dimensional, particularly on coastlines with complex configurations and bathymetry, as localised studies of bar migration can overlook three-dimensional behaviour. Furthermore, the wider potential of LiDAR data in enabling high-resolution morphodynamic studies is clear, both within the coastal domain and beyond

Tidal stream and ocean current energy - the benefits of harvesting lesser energetic flows

An optimum utilisation of the energy available in the ocean could meet our global energy demands. The implementation of tidal stream technologies is striving faster compared to other offshore technologies, aside from the offshore wind sector. Highly energetic tidal energy streams with peak flow velocities in the order of 2.5 – 5.0 m/s are limited around the globe and therefore, the sector may be constrained to a few worldwide locations. To overcome this limitation, attention has been drawn to the exploration of complementary flow streams with lesser energetic flows. This work thus intends to compare the feasibility of harvesting hydrokinetic energy using horizontal axis turbines from two different sites: a typical tidal stream site in the North of Scotland and an ocean current site in the Mexican Caribbean, characterised by developing slower but more stable flows. The viability of using ocean currents against tidal stream sites is analysed in terms of annual energy output, capacity factors and an initial estimation of the levelized cost of energy which considers the size of the turbine and rotor characteristics. As expected the annual energy produced by tidal devices is overall greater than that provided by marine currents but the capacity factor achieved with a typical tidal turbine can be in the order of 44% whereas the capacity factor calculated for a turbine operating in the Yucatan current can achieve factors in the order of 77%, giving confidence that the development of marine projects in lesser energetic flows may be the next step forward to advance this sector. This research also proposes the optimal turbine diameter to reduce the levelised cost of energy for a marine converter installed in a tidal or an ocean current site

Phytoplankton blooms associated with upwelling at Cabo Catoche

In this work, the spatial and temporal implications of the Non-Eastern Boundary Upwelling (Non-EBUS) on the bio-productivity from coastal shallow waters have been studied. At the coast of Cabo Catoche, on the Yucatán shelf, two 12-day field campaigns (April and July) were conducted. Cross-shore CTD-fluorescence profiles, water samples, and plankton were collected each day. Nutrients, ocean temperature and currents times series from two moorings (8 and 12 m depth) were analyzed, as were temperature and chlorophyll (Chl-a) from satellite data. The water masses from the Yucatan channel reached the coast of Cabo Catoche in both study periods. The Yucatan Upwelling Water (YUW, ~ 19.6–22.5 °C) supplied the surface and subsurface water, up to 6 km offshore, with nutrients during the upwelling pulses from 2 to 5 days. Nutrients were higher in April (nitrate, ammonium < 5, 18 μmol L ), but the phytoplankton bloom was more consistent in July (Chl-a mean, 1.45 mg m ) showing greater distribution across the coast. The steady upwelling plume (cold water, high nutrients) recorded in Cabo Catoche and observed on the north shelf, could have been the result of dynamic uplift in the Yucatan Channel prior to the field campaign. Through the way to the shelf, the plankton increased, explaining the high temporal association between low temperatures and the phytoplankton bloom at the coast. The Non-EBUS has strong implications for the pelagic ecosystem from Cabo Catoche, enhancing productivity and triggering energy flow by the physical process. −1 −

Beaching and Natural Removal Dynamics of Pelagic Sargassum in a Fringing‐Reef Lagoon

International audienceMassive quantities of the pelagic brown macroalgae Sargassum spp. (sargassum) have been invading the Caribbean and West African shores since 2011, causing devastating effects on the coastal ecosystem and local economy. Little is known about sargassum beaching dynamics and the capacity of the coastal system to naturally remove beached sargassum. Here, we characterize the temporal variation in arriving and beached sargassum in a reef lagoon using a 5.2-year data set of hourly optical imagery, and identify the governing hydrometeorological conditions. Image classification reveals interannual variability in the start, duration, and intensity of the sargassum arrival season. Arrivals are associated with relatively low energy onshore directed winds and waves, and offshore abundance of sargassum. Furthermore, nearshore sargassum mat size is found to decrease with decreasing wave/wind energy. Once sargassum beaches, a berm of wrack is formed. Natural wrack removal was observed under elevated water levels and increased wave action. Three types of wrack removal were distinguished, depending on the water level urn:x-wiley:21699275:media:jgrc24766:jgrc24766-math-0001 with respect to the berm crest height urn:x-wiley:21699275:media:jgrc24766:jgrc24766-math-0002 and berm crest toe urn:x-wiley:21699275:media:jgrc24766:jgrc24766-math-0003: gradual berm destruction with gaps developing in the seaward berm edge that grow larger with time (Type I; urn:x-wiley:21699275:media:jgrc24766:jgrc24766-math-0004) and abrupt berm destruction with part of the wrack depositing on the upper beach (Type II; urn:x-wiley:21699275:media:jgrc24766:jgrc24766-math-0005) or in the dunes (Type III; urn:x-wiley:21699275:media:jgrc24766:jgrc24766-math-0006). Higher energy waves activate the reef circulation, which is suspected to flush part of the wrack out of the reef lagoon. We propose a conceptual model of nearshore sargassum dynamics in a reef lagoon system

Data presented in the paper “Maintaining Tropical Beaches with Seagrass and Algae: A Promising Alternative to Engineering Solutions”

The ability of seagrasses and calcifying macroalgae to protect beaches against erosion was investigated with in situ experimental measurements of a lagoon in St Martin, Caribbean and long term monitoring of beach profiles along the Yucatan Peninsula of Mexico. Threshold shear velocity values of different vegetation patches were collected with a portable uni-directional field flume, and the time that stained sediment stayed in place in different patches within the lagoon are used as a measure of sediment stabilisation by the vegetated communities. Sediment grain size of the study areas are also reported. Regular beach profiles of Cancun and Puerto Morelos in Mexico, measured with dGPS, are reported from June 2008 - March 2012

Beaching and Natural Removal Dynamics of Pelagic Sargassum in a Fringing-Reef Lagoon

Massive quantities of the pelagic brown macroalgae Sargassum spp. (sargassum) have been invading the Caribbean and West African shores since 2011, causing devastating effects on the coastal ecosystem and local economy. Little is known about sargassum beaching dynamics and the capacity of the coastal system to naturally remove beached sargassum. Here, we characterize the temporal variation in arriving and beached sargassum in a reef lagoon using a 5.2-year data set of hourly optical imagery, and identify the governing hydrometeorological conditions. Image classification reveals interannual variability in the start, duration, and intensity of the sargassum arrival season. Arrivals are associated with relatively low energy onshore directed winds and waves, and offshore abundance of sargassum. Furthermore, nearshore sargassum mat size is found to decrease with decreasing wave/wind energy. Once sargassum beaches, a berm of wrack is formed. Natural wrack removal was observed under elevated water levels and increased wave action. Three types of wrack removal were distinguished, depending on the water level (Formula presented.) with respect to the berm crest height (Formula presented.) and berm crest toe (Formula presented.) : gradual berm destruction with gaps developing in the seaward berm edge that grow larger with time (Type I; (Formula presented.)) and abrupt berm destruction with part of the wrack depositing on the upper beach (Type II; (Formula presented.)) or in the dunes (Type III; (Formula presented.)). Higher energy waves activate the reef circulation, which is suspected to flush part of the wrack out of the reef lagoon. We propose a conceptual model of nearshore sargassum dynamics in a reef lagoon system.Environmental Fluid Mechanic

Maintaining tropical beaches with seagrass and algae: a promising alternative to engineering solutions

Tropical beaches provide coastal flood protection, income from tourism, and habitat for flagship species. They urgently need protection from erosion, which is being exacerbated by changing climate and coastal development. Traditional coastal engineering solutions are expensive, provide unstable temporary solutions, and often disrupt natural sediment transport. Instead, natural foreshore stabilization and nourishment may provide a sustainable and resilient long-term solution. Field flume and ecosystem process measurements, along with data from the literature, show that sediment stabilization by seagrass in combination with sediment-producing calcifying algae in the foreshore form an effective mechanism for maintaining tropical beaches worldwide. The long-term efficacy of this type of nature-based beach management is shown at a large scale by comparing vegetated and unvegetated coastal profiles. We argue that preserving and restoring vegetated beach foreshore ecosystems offers a viable, self-sustaining alternative to traditional engineering solutions, increasing the resilience of coastal areas to climate change

Maintaining Tropical Beaches with Seagrass and Algae: A Promising Alternative to Engineering Solutions

Tropical beaches provide coastal flood protection, income from tourism, and habitat for flagship species. They urgently need protection from erosion, which is being exacerbated by changing climate and coastal development. Traditional coastal engineering solutions are expensive, provide unstable temporary solutions, and often disrupt natural sediment transport. Instead, natural foreshore stabilization and nourishment may provide a sustainable and resilient long-term solution. Field flume and ecosystem process measurements, along with data from the literature, show that sediment stabilization by seagrass in combination with sediment-producing calcifying algae in the foreshore form an effective mechanism for maintaining tropical beaches worldwide. The long-term efficacy of this type of nature-based beach management is shown at a large scale by comparing vegetated and unvegetated coastal profiles. We argue that preserving and restoring vegetated beach foreshore ecosystems offers a viable, self-sustaining alternative to traditional engineering solutions, increasing the resilience of coastal areas to climate change