Sandbars are a landform like a small island formed as a result of seabed sediment slowly raising atop the sea level. They are formed mainly in places that are closer to the shore within the surf zone. Waves in the surf zone are less able to move forwards and thus have to leave the mud and sand in the surf zone. Sandbars block the high winds and long waves of the open sea, making the inland lagoon waters safe and calm, allowing for aquatic animals such as fish, shrimps, and shellfish to live and spawn there.
Wangzaliaoshan in Taijian National Park is a coastal sandbar on the west side of Qigu Lagoon. The coast along Tainan has a flat continental shelf, and windbreak forests of cassowary trees in the middle. The construction of Tseng-Wen Reservoir significantly decreased the sediment amount that Tseng-Wen River carried. Long waves and the peripheral circulation of typhoons have also exerted their influence over the past years. As a result, the sandbars surrounding Qigu Lagoon were eroded at an alarming speed. Between 1975 and 2005, Wangzaliaoshan had retreated up to 885 meters, roughly 29.5 meters per year on average (data credit: “National Parks Quarterly”; September 2013 issue), threatening existing facilities and windbreak forests, and impacting Wangzaliaoshan, the ecological system and the oyster farming industry in Qigu Lagoon.
Since the sand accumulation pattern of sandbars is prone to a number of complex factors such as hydraulic power and wind power, Taijian National Park Administration allocates necessary funds every year for consulting professionals and scholars and commissioning them to conduct field surveys. To deal with retreating sandbars, measures have been taken since 2018. For instance, the priority was given to setting up a belt of timber piles in severely eroded areas by using the piling method, adopting green construction materials, fusing local landscape, and by taking into account safety and ecological engineering. The timber pile belt will be pushed outward year after year after the sand-accumulated beach is restored, in the hope to ease the retreat of the beach on the west side of Wangzaliaoshan.