Edgar Mendoza

Morphodynamic Evolution and Sediment Transport Processes of Cancun Beach

ABSTRACT González-Leija, M.; Mariño-Tapia, I.; Silva, R.; Enriquez, C.; Mendoza, E.; Escalante-Mancera, E.; Ruíz-Rentería, F., and Uc-Sánchez, E., 2013. Morphodynamic evolution and sediment transport processes of Cancun Beach. Large-scale construction of tourist infrastructure on beaches around the world is consistently linked to unwanted morphological changes that lead to coastal erosion. Dune destruction, alteration of sediment sources, and the rigidisation of the coastal system are known to be the main causes of erosive behaviour on many tourist beaches. To plan sound shoreline management strategies, detailed understanding of the sediment transport processes is necessary. The present contribution focuses on the main sediment transport processes that take place at Cancun, Mexico, a large (12 km) and highly developed tourist beach. High-resolution quarterly beach profile monitoring from September 2007 to June 2009 is used to calculate volumetric changes that are reasonably well explained by the spatial patterns of modelled sediment transport potential. This parameter was calculated using the wave propagation model WAPO of Universidad Nacional Autonoma de Mexico, which explicitly solves diffraction and reflection processes that are particularly important in systems with pronounced rocky headlands, such as the northern and southern ends of Cancun beach. Results show a dominance of northward longshore transport in most of the system, and an important transport divergence with consistent southward transport at the southern end. Cross-shore transport seems to dominate the middle-north section of the beach. This behaviour is consistent with recent advances in the understanding of wave circulation in embayed beaches. The method used here is considered a good approximation of sediment transport patterns when local (surf zone) morpho- and hydrodynamic data are absent or difficult to acquire.

Simple settling velocity formula for calcareous sand

From the analysis of 1557 calcareous sand grains, a new equation for the computation of particle settling velocity is derived. The proposed expression involves only the dimensionless particle diameter and the Reynolds number, meaning that the estimation of the settling velocity is quick and easy. This formula is compared with expressions available elsewhere and its improved accuracy is demonstrated. When the formula was applied to Hallermeiers database [(1981). Terminal settling velocity of commonly occurring sand grains. Sedimentology 28(6), 859–865], which has been used in previous studies to develop settling velocity equations, it was also found to have the smallest root mean square error. The equation reported in the paper is one of very few expressions specifically developed for calcareous sand.

Beach Erosion Driven by Natural and Human Activity at Isla del Carmen Barrier Island, Mexico

ABSTRACT Escudero, M.; Silva, R., and Mendoza, E., 2014. Beach erosion driven by natural and human activity at Isla del Carmen Barrier Island, Mexico. The study site is located on the Gulf of Mexico and is part of the most valuable lagoon-estuarine system in Mexico, not only in ecological terms but also as an important economic and social site for the country. Although the current state of the environment is still reasonably healthy over much of its area, the natural equilibrium has been greatly affected by human activities, as in many of other coastal lagoons worldwide (e.g., infrastructure and building construction, installation of inappropriately designed defense structures, degradation of vegetation and an artificial lagoon opening). The consequence is a sediment deficit that, combined with the impact of tropical cyclones and the absence of an external sand supply, has led to persistent beach erosion. The analysis of the physical settings, historical shoreline changes and hydrodynamic patterns of the study site has helped to identify the critical elements affecting the current state of the beach. This paper proposes a shoreline protection scheme, based on the understanding of the current functioning of the site, in order to reduce local flooding and erosion risks, which affect the population and tourism, and to preserve the natural environmental services of the area.

An artificial reef improves coastal protection and provides a base for coral recovery

ABSTRACT Silva, R.; Mendoza, E., Mariño-Tapia, I.; Martínez, M.L., and Escalante, E. 2016. An artificial reef improves coastal protection and provides a base for coral recovery. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 467-471. Coconut Creek (Florida), ISSN 0749-0208. In 2007, Hurricane Dean caused extensive damage along the coast of Riviera Maya, exceptionally large mass of wind-transported sand was deposited on the beach front and gardens of the former NH Hotel in Puerto Morelos. Due to the chaotic sea state and the debris carried by the storm, the sand was contaminated with various pollutants, including terrigenous materials and biogenic matter. As an emergency measure, this sand was used to create an artificial dune in the grounds of the hotel. Given the high probability of future storms of such magnitude, it was decided that some form of sediment transport control was needed to protect the beach so an artificial reef was constructed 120 m off the shore. The structure, made of prefabricated concrete elements, has been effective as a coastal defense barrier and has also provided a habitat for several reef species. Five years after the placement of the structure the beach front, which had previously registered erosion problems, had returned to its natural cycle of summer growth and winter retreat and a large number of fish and coral species were using the habitat provided by the structure. However, the coral reef growing on this prefabricated structure was not long-lasting. The massive and persistent occurrence of Sargassum in 2015 brought oxygen depletion, reduced pH, an excess in nutrients and less water transparency on the Caribbean coast, leading to the decline of the reef habitat. Further studies are necessary to test whether reef species recolonize the prefabricated substrate.

Beach Erosion in San Benito Chiapas, Mexico: Assessment and Possible Solution

ABSTRACT Delgadillo-Calzadilla, M.A.; Mendoza, E.; Silva, R.; González-Vázquez, J.A., and Infante-Mata, D., 2014. Beach erosion in San Benito Chiapas, Mexico: Assessment and possible solution. The study area is on the Gulf of Tehuantepec, where a harbour was built at San Benito, near Tapachula, Chiapas, in 1972. Two breakwaters, of 630 m and 800 m, respectively, were constructed to provide protection to the harbour channel. Erosion problems were detected near the harbour even before it was opened to trade. The original design had many flaws as no wave climate analysis had been done and littoral drift had not been taken into account. In 1975, 17 groins were built with the aim of reducing the erosion on the adjacent beach. These were unsuccessful and, in 1980, a rock armour apron was built at the most seriously eroded section in a further attempt to minimize the problem and to protect the population. However, the erosion continues at a rate of around 25 m per year in some sections. Commercial and navigation activities at the harbour are important for the population of San Benito and its surroundings, so coastal management policies must facilitate harmonic coexistence between human activities and the coastal system. This study analyses the problem and offers alternative solutions for minimizing the beach erosion using hard and/or soft solutions.

Measurements and Modelling of Small Scale Processes of Vegetation Preventing Dune Erosion

ABSTRACT Mendoza, E.; Odériz, I.; Martínez, M.L., and Silva, R., 2017. Measurements and modelling of small scale processes of vegetation preventing dune erosion. In: Martinez, M.L.; Taramelli, A., and Silva, R. (eds.), Coastal Resilience: Exploring the Many Challenges from Different Viewpoints. Journal of Coastal Research, Special Issue No. 77, pp. 19–27. Coconut Creek (Florida), ISSN 0749-0208. Traditionally, actions taken to reduce vulnerability to beach erosion have been based on protecting economic resources, recreational activities and human lives. Hard infrastructure for coastal protection has proven effective, but the side effects have been called into question, given that making the coastal system more rigid alters the natural dynamics, degrades environmental services and damages the landscape. Ecosystem based coastal defence strategies are now seen as a more environmentally friendly alternative which can maintain and even increase the resilience and resistance of coastal zones. This work aims to improve the understanding of the behaviour of nature-based coastal defences by analysing the morphodynamic response of a dune-beach system with vegetation to storms. Small scale tests were performed in which beach profiles with natural dune vegetation were exposed to high energy waves. Free surface elevation and velocity profiles were recorded during the tests and the profile evolution was measured at the end of each experiment. Erosion regimes of collision and overwash were observed in the dune profiles with a berm, whereas swash and overwash regimes were observed when no berm was present. Retarding erosion time seems to be the most relevant morphological effect of the dune vegetation, which gives a slight, but relevant, contribution to the resilience and resistance of the beach profile. In turn, the wave breaking point is displaced seawards and bed velocities close to the shoreline are lower when vegetation is present, both of which explain the protective role of vegetation on the beach profile. To develop a numerical tool capable of reproducing the morphological evolution of the beach profiles tested, the CSHORE model was calibrated and validated for the laboratory data finding good correlation.

Towards Coastal Management of a Degraded System: Barra de Navidad, Jalisco, Mexico

ABSTRACT González-Vázquez, J.A.; Silva, R.; Mendoza, E., and Delgadillo-Calzadilla, M.A., 2014. Towards coastal management of a degraded system: Barra de Navidad, Jalisco, Mexico. The area known as Barra de Navidad is a barrier lagoon system on the Mexican Pacific. Over the last 40 years the system has undergone serious negative changes in its dynamic processes, mainly due to the anthropogenic activities that have taken place there. The main elements that have damaged the equilibrium of the system are the removal of the distal tip of a sandspit, the dredging of a navigation channel, the construction of a breakwater, the cutting down of large areas of mangrove and the construction of tourist infrastructure on the coastal dunes. These changes have decreased the resilience of the system, thereby increasing its vulnerability. In addition, the lagoon has developed a severe problem of silting and alterations to the hydrodynamic patterns in the system have caused a dramatic retreat of the coastline. The degradation of the system has affected the population and their economic activities to such a degree that a series of hydrodynamic analyses have been carried out to propose a short-term, urgent solution which will be part of a long-term plan that will bring self-sustainable balance to the system.

Human Impact on Coastal Resilience along the Coast of Veracruz, Mexico

ABSTRACT Martínez, M.L.; Silva, R.; Lithgow, D.; Mendoza, E; Flores, P.; Martínez, R., and Cruz, C., 2017. Human impact on coastal resilience along the coast of Veracruz, Mexico. In: Martinez, M.L.; Taramelli, A., and Silva, R. (eds.), Coastal Resilience: Exploring the Many Challenges from Different Viewpoints. Journal of Coastal Research, Special Issue No. 77, pp. 143–153. Coconut Creek (Florida), ISSN 0749-0208. Coastal ecosystems are naturally exposed to recurrent disturbances, which act as drivers of ecosystem dynamics, but in recent years, human impact has exerted intense pressures, resulting in altered dynamics and thus, reduced resilience. In this work the state of Veracruz, on the Gulf of Mexico, was used as a case study to assess the impact of human activities and explore how these have affected coastal resilience. A regional diagnosis was performed, considering coastal morphology, sediment characteristics, shoreline dynamics, natural, and transformed ecosystems, conservation areas, and built infrastructure. The various causes of the chronic erosion taking place in the area are: subduction, rising sea levels, a fall in the amount of available terrigenous sediments and the inadequate design of coastal protection structures, all of them have dramatically reduced the resilience of coastal ecosystems. Considering that population growth, and the increasing needs for goods and services add pressure to coasts, several actions are suggested to reinforce the resilience of the coast of Veracruz: (a) It is vital to recover the sources of terrestrial sediments, move or remove infrastructure or implement sand bypass when possible; (b) it is urgent to consider ecosystem-based coastal zone management; (c) without a proper diagnosis of the status of the coast, coastal management may result in increased environmental problems and risk. These points can be applied elsewhere, as the problems are often very similar. Coastal managers, ecologists, engineers, decision makers and society in general are jointly responsible of the future of the fragile and dynamic coasts.

Innovative Engineering Solutions and Best Practices to Mitigate Coastal Risk

Engineering solutions are widely used for the mitigation of flood and erosion risks and have new challenges because of the expected effects induced by climate change in particular sea level rise and increase of storminess. This chapter describes both active methods of mitigation based on the reduction of the incident wave energy, such as the use of wave energy converters, floating breakwaters and artificial reefs, and passive methods, consisting of increase in overtopping resistance of dikes, improvement of resilience of breakwaters against failures, and the use of beach nourishment as well as tailored dredging operations.Existing coastal management and defense approaches are not well suited to meet the challenges of climate change and related uncertanities. Professionals in this field need a more dynamic, systematic and multidisciplinary approach. Written by an international group of experts, Coastal Risk Management in a Changing Climate provides innovative, multidisciplinary best practices for mitigating the effects of climate change on coastal structures. Based on the Theseus program, the book includes eight study sites across Europe, with specific attention to the most vulnerable coastal environments such as deltas, estuaries and wetlands, where many large cities and industrial areas are located. * Integrated risk assessment tools for considering the effects of climate change and related uncertainties* Presents latest insights on coastal engineering defenses* Provides integrated guidelines for setting up optimal mitigation measures* Provides directly applicable tools for the design of mitigation measures* Highlights socio-economic perspectives in coastal mitigation

Chapter 3 – Innovative Engineering Solutions and Best Practices to Mitigate Coastal Risk

Engineering solutions are widely used for the mitigation of flood and erosion risks and have new challenges because of the expected effects induced by climate change in particular sea level rise and increase of storminess. This chapter describes both active methods of mitigation based on the reduction of the incident wave energy, such as the use of wave energy converters, floating breakwaters and artificial reefs, and passive methods, consisting of increase in overtopping resistance of dikes, improvement of resilience of breakwaters against failures, and the use of beach nourishment as well as tailored dredging operations.Existing coastal management and defense approaches are not well suited to meet the challenges of climate change and related uncertanities. Professionals in this field need a more dynamic, systematic and multidisciplinary approach. Written by an international group of experts, Coastal Risk Management in a Changing Climate provides innovative, multidisciplinary best practices for mitigating the effects of climate change on coastal structures. Based on the Theseus program, the book includes eight study sites across Europe, with specific attention to the most vulnerable coastal environments such as deltas, estuaries and wetlands, where many large cities and industrial areas are located. * Integrated risk assessment tools for considering the effects of climate change and related uncertainties* Presents latest insights on coastal engineering defenses* Provides integrated guidelines for setting up optimal mitigation measures* Provides directly applicable tools for the design of mitigation measures* Highlights socio-economic perspectives in coastal mitigation