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Moonlight Harbor's stacked-stone revetment returns to nature, zero-cement challenge wins Golden Apple Award

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Moonlight Harbor has become more beautiful! Stacked-stone revetment returns to nature, zero-cement challenge wins the "Golden Apple Award"

Mention Moonlight Harbor and people think of the dazzling lantern festival. The lantern festival, now in its tenth year, draws hundreds of thousands of visitors annually. Yet in the past, Moonlight Harbor's stream water was foul and dirty, and its revetment kept collapsing. For more than a decade, construction projects lacked integration, and environmental problems went unimproved for a long time. In recent years, the engineering authorities switched to ecological engineering methods, and the remediation succeeded, earning selection by the river citizen group "Taiwan Rivers and Streams Network" as a second-term "Golden Apple" water environment project.

Two years ago, Wen Jian-an, manager of Chongjun Engineering Consultants, took on the plan to improve Moonlight Harbor. He brought private environmental groups into the advisory team, used no cement throughout, and instead adopted manual diamond-pattern stone placement to remediate the Moonlight Harbor waterfront, and selected native tree species as street trees along the embankment-top trail, letting Moonlight Harbor shine with natural splendor once again.

Moonlight Harbor, adjacent to farmland and residences, after waterfront remediation (Image source / Tainan City Government)

The lantern festival is hugely popular every year, yet the water quality is foul and dirty; Moonlight Harbor urgently needs to regain its former glory

Moonlight Harbor is located in Yanshui District, Tainan. Yanshui District was once adjacent to the Daofeng Inner Sea. The triangular zone carved out by the Bazhang River to the north and the Jishui River to the south resembles a crescent moon, which is why Yanshui is also called "Moonlight Harbor" and "Moon Harbor." During the Ming and Qing dynasties, Yanshui District was an essential stop for people and goods traveling between Zhuluo and the prefectural city. Because of frequent trade and transit traffic, its bustling prosperity ranked alongside the prefectural city, Lukang and Monga, earning the reputation of "first the prefectural city, second Lukang, third Monga, fourth Moonlight Harbor."

Later, the Daofeng Inner Sea lost its transport advantage as large amounts of river sand and gravel sedimented, clogging the port, and it gradually declined. Over the past decade, the curation of the Moonlight Harbor Lantern Festival has attracted hundreds of thousands of visitors each year. To let Yanshui District regain its former glory, the Tainan City Government sought to improve Moonlight Harbor through the "National Water Environment Improvement Plan" and the "Heart of Town Plan."

Is Moonlight Harbor's water environment problem very serious? Wen Jian-an, manager of Chongjun Engineering Consultants, which is in charge of the renovation plan, says that visitors who come for the lantern festival do not stay long, while local residents believe Moonlight Harbor is dirty and smelly, the waterside revetment keeps collapsing, and water-based activities have no future. "The lantern festival can attract outsiders, but to make people love Moonlight Harbor, you still have to start by improving the environment."

The Moonlight Harbor Lantern Festival is an annual highlight of Yanshui, Tainan (Image source / Tainan City Government)

In the past, water environment projects treated the symptoms but not the root cause, and the unstable revetment often collapsed

Walking along the riverbank, Wen Jian-an explained one by one the ingenuity behind every construction detail. The first is the revetment built of stone. The purpose of the revetments on both sides of the river is to prevent slope collapse and provide a buffer for users. In the past, waterfront projects at Moonlight Harbor usually altered the original waterfront structure, causing the water area and revetment to lose their connection and become unstable. "The old construction methods had low budgets and treated the symptoms but not the root cause."

Wen Jian-an explained that Moonlight Harbor was severely silted. In the past, when waterfront projects broke ground, as soon as the silt on both sides was dug open, slope collapse would occur due to insufficient stability. Then, in order to dredge again and build the revetment, construction would adopt a "slope-toe cut-off" approach, meaning the slope toe was cut off all at once and then a new revetment was built with new building materials. "The material usually used is cement."

What problems does this kind of construction cause? Wen Jian-an says this approach seems to save money, but maintenance funds must be allocated every year afterward. Also, the soil layers on both sides of the waterfront differ from the revetment's building materials, "which amounts to a fault line between the waterfront and the water area," making the revetment prone to instability and collapse. The waterfront trails and ramps also sink because they lose the support of the revetment's base. "It is built but then requires constant repair, and local governments do not necessarily have that much maintenance capacity." In addition, the completed trails often have poor circulation routes.

Before remediation of Moonlight Harbor, the water was eutrophic, dirty and foul-smelling (Provided by Wen Jian-an)

Manually placed stones are more stable, and creating a cross-section slows the spread of aquatic plants

"If ecological needs are to be met, cement is clearly not a good choice." Wen Jian-an says that in nature, the revetments beside rivers and streams have two major features: a stable base footing at the bottom and a gently descending slope. A stable footing must withstand water flow scouring, while a gently descending slope can prevent soil and rock loss on the slope.

The water flow at Moonlight Harbor is relatively slow, with less scouring. Wen Jian-an used manually stacked stones as the base footing. These stones were selected for both size and shape, then stacked one by one. Actually stepping on the stacked stones along both sides of the waterfront, there is no shaking or instability.

Wen Jian-an specifically notes that stone masonry is an ancient craftsman's skill. Craftsmen select stones according to need and stack them according to the shape of each stone, so the stacked stones can interlock and hold firm. This stability cannot be achieved by machine dumping.

In addition, Wen Jian-an was very particular even about the stacking height. "We deliberately left a cross-section." He explained that the bottom layer of stacked stones does not coincide with the water surface. The two layers of stones below the water surface and exposed above the water surface each maintain a distance of 5 to 10 cm from the water surface. "The stone surfaces do not exactly coincide with the water surface, but are like steps." This arrangement is meant to slow the spread of aquatic plants and facilitate subsequent maintenance and management.

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