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

Basic information

• Case ID: INT-043-1
• Intervention type: Restoration
• Intervention description:

  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.

• Landscape/sea scape ecosystem management: No

• 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.

• Approach implemented in the field: No
• Specific location:

  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).

• Country: Mexico
• Habitat/Biome type: Coastal |
• Issue specific term: Nature-based (general)
  

Evidence

• Notes on intervention effectivness: Effect of vegetation depends on physical parameter measured, initial dune morphology/profile, and simulated wave conditions. In summary - the experimental results help us understand the role of coastal dune vegetation along the beach profile during storms; it can be seen that by reducing/retarding the dune erosion, limiting the breaking wave height and run-up and generating lower undertow compared to the unvegetated tests and thus sediment transport, dune vegetation enhances the resilience of a beach. The presence of dune vegetation does not really modify the beach profile dynamics nor the dune erosion regime; its role can be described as only retarding the erosion, by slightly attenuating hydrodynamics. It can be stated that the vegetation increases the resistance and the resilience of the beach profile; as observed in our tests the vegetation lets the dune provide sediment to the beach in the reflective profile and strengthens the dune in the dissipative profile. under profile A the vegetation prevented overwash, but authors don’t explicitly conclude so for profile B. No explicit conclusion in relation to how vegetated dunes reduce risk of coastal flooding, results focused on how vegetation impacts erosion regime.
• Is the assessment original?: Yes
• Broadtype of intervention considered: Not applicable
• Compare effectivness?: No
• Compared to the non-NBS approach: Not applicable
• Report greenhouse gas mitigation?: No
• Impacts on GHG: Not applicable
• Assess outcomes of the intervention on natural ecosystems: No
• Impacts for the ecosystem: Not reported
• Ecosystem measures:
• Assess outcomes of the intervention on people: No
• Impacts for people: Not reported
• People measures:
• Considers economic costs: No
• Economic appraisal conducted: No
• Economic appraisal described:
• Economic costs of alternative considered: No
• Compared to an alternative: Not reported

Evaluation methodology

• Type of data: Quantitative
• Is it experimental: Yes
• Experimental evalution done: Ex-situ/lab
• Non-experimental evalution done: Not applicable
• Study is systematic: