4 minute read
Waisanding Sandbar
Dongshi Township, Chiayi County, Taiwan
Mitigating sandbar scouring with natural infrastructure materials. The Waisanding sandbar, located on the western coastal waters of Chiayi County, is the largest detached sandbar in Taiwan. Functioning as a natural barrier, the southern shallow water of the Waisanding sandbar provides an excellent aquaculture environment for oysters and acts as an important resource for oyster farming in Taiwan. Because of storm surge overwash, strong monsoon-wave longshore currents, and land reclamation for coastal structures, the sandbar area had decreased from 2,000 hectares to 1,000 hectares over the past 50 years. In 2022, to mitigate sandbar scouring and reduce wind-wave impact to the shoreline, groins and sand-trapping structures were constructed by the Water Resources Agency, Ministry of Economic Affairs (MOEA), Taiwan. These structures, made with locally sourced bamboo and bagged oyster shells recycled from oyster farming, were designed to be permeable to simultaneously maintain water flow and reduce sediment transport rates. Further, the porous structures would provide habitat for fish, shrimp, and benthic organisms. Additional sand-trapping structures were constructed collaboratively with assistance from the local community and fishing industry in consideration of future coastal protection of the sandbar. Following the Waisanding Sandbar Protection Project completion, local residents and fishers have learned how to effectively and proactively maintain their oyster farms, encouraging community buy-in while protecting and maintaining the sandbar.
Article Cover: The sand-trapping structure, constructed from bamboo stakes and oyster strings, in August 2022. (Photo by Water Resources Agency, Ministry of Economic Affairs [MOEA], Taiwan)
Producing Efficiencies
Longshore current sediment transport and wave overwashing are the primary impact factors to the Waisanding sandbar. After assessment, using coastal sediment transport model CCHE2D-Coast, a 300-meter-long groin and two 120-meter-long groins were constructed at the southern shoreline of Waisanding. These structures were expected to increase sand deposition on the northern side of the groins. Bamboo dikes were also installed at the eroded, waveimpacted area of the sandbar to reduce wave energy and current magnitude. Additionally, three sand-trapping structures were constructed behind the sandbar to intercept wash load carried by overtopping waves.
Using Natural Processes
Bamboo oyster racks were continually damaged during typhoon and winter storm events from strong wind and wave energy. The damaged bamboo was being carried by tide currents and moved to the shoreline, creating a coastal environmental problem. To address this issue, the project repurposed the damaged bamboo and discarded oyster shells to make the groins, dikes, and sand-trapping structures. Although both the bamboo and oysters shells were not sufficiently hard enough to withstand strong winds and waves, they met sustainable use requirements and were easily obtainable. Consequently, the project will reduce bamboo and oyster shell placement volumes and increase biological habitats through this reuse.
Broadening Benefits
The Waisanding Sandbar Protection Project was developed using National Oceanic Atmospheric Administration’s Coastal Zone Management Act requirements for biological conservation and coastal environment maintenance. As a result of the project, additional conservation projects were implemented around the sandbar, including a wetland, an artificial reef, no-fishing areas, and a habitat area for the Chinese white dolphin (Sousa chinensis). To comply with the conservation plans around Waisanding, natural materials rather than conventional were used to construct engineering structures, thereby reducing the volume of damaged bamboo and unused oyster shells, promoting local tourism, and contributing to an economical and environmentally sustainable model.
Promoting Collaboration
This innovative project successfully united government, coastal residents, and local industry stakeholders to plan and construct the sand-trapping structures for sandbar protection. Early in the project, some residents and stakeholders opposed this effort, but resistance turned into assistance after frequent communication explaining the sandbar protection concept, leading to construction in 2022. The local community collected damaged bamboo and unused oyster shells, and local industry assisted with transporting the materials to the Waisanding beach area. After, participants installed the materials into planned locations. Local residents helped to construct the sandbar, unprompted, lowering project costs.
