Tidal Inlet Restoration of Sandbar, Tainan, Taiwan

This project is located on the sandbar of Wangye Harbor, Beimen District, Tainan City. A tidal inlet progressively developed due to wind and waves had caused the resisting function of natural sandbar for spring tides to disappear, which posed a severe threat to the fishery industry of inland lagoon fishermen. Therefore, it is in urgent need of remediation.

In the early years, the authority used bamboo piles and cubical sandbags to fix sand. Although they had specific positive effects in some areas, they did not effectively repair the tidal inlet area because of adverse oceanographic phenomena. According to satellite image analysis, the most severely eroded sandbar of Qingshan Harbor in Cigu District has retreated an average of 50m per year over the past two decades.

The restoration of tidal inlet must first overcome the challenges of turbulent ocean currents. Secondly, the impact of project feasibility, overall economy, eco-environment, and sustainable carbon reduction of the overall project also should be considered. After multi-scheme evaluations, the project adopted the ACETube^® as the repair solution. ACETube^® can be custom-made by selecting the appropriate dimensions according to the site conditions. It can be quickly constructed and achieve short-term restoration for the damaged tidal inlet. The total length of the ACETube^® was about 420 m. The in-situ sea sand was pumped into the ACETube^® to construct a three-layer stacked structure. Bamboo piles were driven on both sides of the ACETube^® to provide protection and fixation.

Over the past years, the constructed ACETube^® has experienced the attacks of waves and swells as large as 10 meters brought by strong typhoons after the completion of this project, yet the overall structure was stable, and the effect of sand trapping also was remarkable. As shown in Figure 2.2, from 2003 to 2012, the rate of shoreline retreat had significantly reduced to 6 m per year. By comparing the changes from 2012 to 2020, the shoreline has shown a stable trend, proving that the sandbar restoration has achieved the initial target for the goal of sandbar restoration and sustainable development of the lagoon.

The overall engineering planning of this project was conducted based on the principle of using local materials, which conform to the standard of natural-like engineering method and achieve carbon reduction. The construction of using natural bamboo piles combined with ACETube^® not only served as temporary fixings to protect both sides of the ACETube^® but also increased the effect of sand trapping and stabilizing for the overall project. In addition, this project used many in-situ natural materials for construction, avoiding using rigid reinforced concrete structures. Such considerations have achieved the maximum possibility of reducing the effect and impact of engineering facilities on the overall eco-environment.