Geotextile tubes as submerged breakwaters. Improvements in wave transmission reduction for beach restoration: Fid-Bau Portal

Geotextile tubes as submerged breakwaters. Improvements in wave transmission reduction for beach restoration

Solis Pomentel, Alfonso / Leija Mariana, Gonzalez / Escalante Sergio, Aguilar

The north coast of the Yucatan Peninsula in Mexico has been in a regression process for decades. After Hurricane Gilbert (1988) and Isidore (2002), beach erosion increased dramatically. Human actions around the development of harbors and the unregulated construction of groins have accelerated this process and a consequence of this has been that beaches, infrastructure, and private properties are in permanent risk of destruction. Since 2004, Axis Ingenieria has developed several engineering solutions based on the use of geosynthetic materials. The construction of submerged breakwaters (SBW) built with geotextile tubes (GTT), engineered to mitigate incident wave energy over the beach, have had a successful performance for coastline stabilization and restoration of lost beaches. The key factor is controlling littoral drift along 60 km of the coastline and protecting critical eroded segments with SBW without affecting down-drift beaches. The basic parameter to identify when designing a SBW is the wave transmission coefficient Kt as the ratio between the transmitted wave height reduced due to presence of the structure and the incident wave height (Kt=Ht/H). This article summarizes the efforts to evaluate this parameter specifically for the local conditions in Yucatan, based on physical modeling testing, that may be replicated for different beaches governed by similar geomorphological characteristics and wave climate conditions. The response of wave transmission to GTT working as a SBW is similar to impermeable concrete structures that have been permanently used for coastal protection. The dimensionless parameter Kt is sensible to relative submergence. Based on empirical experience on-site, by controlling Kt ≥ 0.6, the alongshore sediment transport reduction does not compromise stability on adjacent beaches. This applies exclusively to the beaches on the northern coast of Yucatan. However, in general terms, model results using local wave climate conditions, are a fundamental element to control Kt, when designing the cross section of a SBW. Empirical formulation for Kt shows an increment of the incident wave for higher values of the relative freeboard due to the presence of the SBW. This has to be taken into consideration when defining submergence to ensure that is always Kt < 1. More tests are required to fully identify adequate submergence frontiers. Further research must also include evaluation of the relative width of the crest for wave dissipation in combination with relative submergences to improve the approach to wave transmission coefficient Kt for designing GTT as SBW.