Mendoza, E.; Odأ©riz, I.; Martأnez, 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.
Wave flume experiment, to test effect of planting vegetation on coastal dunes. The laboratory beach profile model was constructed with live Ipomoea pes-caprae, which are creeping, dune-forming plants that are found in tropical and subtropical areas all over the world (Ridley, 1930; Thorne, 1954). Two sandy beach profiles, A and B, were modelled simultaneously Profile A was set on one side of the flume, composed of a horizontal berm and a narrow dune. This profile is similar to the profile tested by Kobayashi et al. (2009). Profile B was placed on the other side of the acrylic sheet, parallel to profile A. Profile B, featuring only a wide dune, is a small scale reproduction of a typical beach profile from the Mexican coast of the Gulf of Mexico. The dune plant selected for these experiments was Ipomoea pes-caprae, given its pantropical distribution and effective dune building performance. This species is tolerant to both salinity (its seeds and branches are dispersed by ocean currents) and burial by sand (Devall, 1992; Martínez et al., 2002). The plants were reproduced vegetatively from individuals that were growing on the beach at the field station of CICOLMA, Veracruz, on the Gulf of Mexico (19° 30' N, 96° 22'W). The plants were taken to Mexico City once they were strong enough to survive the move. The plant densities used in the experiments were similar to those observed in their natural environment (i.e. 5, 12, and 18 branches per square meter corresponding to low, medium and high densities, respectively); the small scale vegetation cover was defined in Silva et al. (2016). The plants were transplanted into the dunes of the beach profiles, verifying that the sand was not compacted during this process, then the plants were covered with dry sand until only the leaves were exposed on the surface, as in natural conditions.
|Climate change impacts||Effect of Nbs on CCI||Effect measures|
|Coastal erosion||Positive||Morphodynamic response of a dune-beach system with vegetation to storms was assessed. erosion regimes observed - free surface elevation and velocity profiles were recorded during the tests and the profile evolution was measured at the end of each experiment. Free water surface elevation was recorded with 11 wave gauges (WG), which were placed at the same coordinates for both profiles, and are shown in Figure 1. Velocity profiles were recorded with Ultrasonic Velocity Profilers (UVP) along each beach profile. The profile morphology was measured with a laser total station. the deformed beach profile was measured at the end of the test.|
The plants were reproduced vegetatively from individuals that were growing on the beach at the field station of CICOLMA, Veracruz, on the Gulf of Mexico (19° 30' N, 96° 22'W).