Behind The Scenes

August 30, 2026

hyrdology, water management, water supply, West Lake

The Chinese city of Hangzhou is on the Qiantang River that empties into Hangzhou Bay which is a large, funnel-shaped indentation on mainland China’s east coast. Pacific Ocean tides are funneled by the bay to create a tidal wave (a.k.a. tidal bore) that can be as high as nine meters and travel up to 40km/hour as far as 100km upriver. The bed of the Qiantang River is a 40m layer of shifting sediment mostly carried down the coast from the Yangtze River and then deposited along the Qiantang River bed by the tide. “Like trying to build a bridge over the Qiantang” used to be a way of saying something was impossible. Not only is the river flow violent, but shifting sandbanks made it treacherous to navigate. Below right is an old image with some menacing-looking waves.

Two thousand years ago, the area that was to become modern Hangzhou was still underwater and part of an inlet off the Qiangtang River. This inlet was fed with freshwater from the Wulin River upstream and trapped in a lagoon by sandbanks of silt deposited by the river downstream. It was an unstable equilibrium easily upset by tides and floods.

Around 200CE in the Eastern Han Dynasty (东汉; 25–220CE), a local official called Hùa Xìn decided to solve the problem once and for all by having a mud seawall constructed in the position shown in the image at left. One story goes that he offered the local people one thousand coins per cart of rubble they brought to the mouth of the inlet and, when he said he wasn’t going to pay them, they emptied their carts and went home. I have my doubts about this story because, in 200CE, one thousand of anything seems implausibly huge. 　

Four hundred years on, the governor of Hangzhou was an official called Bai Juyi (772–846). The Hùa Xìn seawall had now failed and there were shortages of fresh water once again. Bai had a dike constructed on the north side of the lake to hold freshwater, and also built a new eastern seawall in much the same place as Hùa Xìn’s seawall had been. This fixed the size and shape of the lake to approximately the size and shape it is today. Once this new seawall was in place, the former dike had a bridge called Broken Bridge (断桥) inserted, and trees added to become what is known today as Bai Causeway (白堤). Bai wrote the following poem that is the only poem, Tang Dynasty or otherwise, commemorating this new eastern seawall. The White Sand Dike referred to is Bai Causeway seen across the lake. Bai’s poem encouraged people to look at and the lake and its causeway and see not a public works reservoir but a thing of beauty. And ever since, people have.

Bai Juyi, On Qiantang Lake Spring Walk (钱塘湖春行), 823 C

孤山寺北贾亭西，
水面初平云脚低。
几处早莺争暖树，
谁家新燕啄春泥。

乱花渐欲迷人眼，
浅草才能没马蹄。
最爱湖东行不足，
绿杨阴里白沙堤。

North of Gushan Temple, west of Jia Pavilion,
The lake’s restored water level rests beneath low-hanging cloud.
Early orioles jostle on sun-warmed branches,
Young swallows carry fresh mud to build their spring nests.

Wild blooming flowers dazzle wandering eyes,
Short spring grass barely covers the hooves of horses.
Nothing delights me more than wandering the lake’s eastern shore,
The White Sand Dike shaded beneath rows of green poplars.

Two hundred years later, Su Dongpo (1037–1101) arrived as governor of Hangzhou to find the city’s water supply was again threatened because the lake was clogged with weeds and silt. He ordered a full dredging and had the spoil used to make what is now known as Su Causeway. The causeway is on the western side of the lake and close to the mountains that were the source of the silt. It therefore creates a holding pond to slow the silt spreading across the entire lake. Six bridges along the causeway prevent the water in this partitioned lake from stagnating.

During Su Dongpo’s tenure, the eastern seawall had the lake on one side and on the other was the Qiantang River that continued to deposit silt. The city of Hangzhou didn’t begin to expand from the lake’s eastern wall but had a stage when it was a walled city built on the tidal flats. At times, it appeared as a fortified island. The map on the right below is a 16th century European imagining of how the city looked according to stories attributed to Marco Polo. Nevertheless, in 1100CE there were the beginnings of a city to the east of the lake and poets and assorted literati began to refer to Qiantang Lake as West Lake, conceptually separating it forever from the river from which it came. Even today, many people believe West Lake is a naturally formed lake.

This next poem is perhaps the most memorable and memorized of the many poems Su Dongpo wrote about West Lake. I accept I will never be able to fully appreciate the economy, richness and musicality of these poems.

SU Dongpo, Drinking at the Lake, First in the Sun, and then in Rain (饮湖上初睛后雨), undated Su Dongpo scenic verse

水光潋滟晴方好，山色空蒙雨亦奇。欲把西湖比西子，淡妆浓抹总相宜。	The brimming waves delight the eye on sunny days; The dimming hills present rare view in rainy haze. West Lake may be compared to Lady Xi Shi, Whether plainly dressed or richly adorned.

This and other poems encouraged the public to give their labour more readily because it was now in the service of Beauty or, at the very least, for something greater than themselves and for the enduring benefit of others. It became noble. Municipal records for silt dredging were never going to motivate people. Su Dongpo was a good administrator and his other confirmed intervention was three stone towers marking where the lake was deepest. Su allowed people to use the edges of the lake to cultivate either water chestnuts or water caltrop in exchange for keeping those edges free of silt but they weren’t allowed to cultivate the triangular area bounded by these three stone markers because it would somehow lead to the degradation of the lake. I wasn’t sure about this story either because the area bounded by the stone markers isn’t that large compared to the area of the lake but documents confirm this as the ostensible reason. The markers were rebuilt as pagodas in the Southern Song or Ming Dynasty. These two hydrological interventions are included in a list of Ten Scenes for visitors to West Lake to enjoy. Below is the full list. Su Causeway always comes first but the order of the other nine isn’t fixed.

Spring Dawn over Su Causeway (苏堤春晓, Sudi Chunxiao）
An embankment formed from dredge silt and whose purpose was to slow sediment drift across the entire lake. Its segmented arched bridges maintain water exchange across the lake to prevent stagnation. The causeway is fitted with stone gauges to monitor silt accumulation.

Three Ponds Mirroring the Moon (三潭印月, Santan Yinyue)
The legal and hydrological purpose of the three stone towers was intended to demarcate an inner zone where people were forbidden to plant water‑chestnut or water‑caltrop because their cultivation would accelerate the silting of the lake basin.

Wind Ripples at the Lotus Courtyard (曲院风荷, Quyuan Fenghe)
The Lotus Courtyard is a natural filtration zone that uses lotus plants to reduce eutrophication and suspended sediment load.

Autumn Moon over Peaceful Lake (平湖秋月, Pinghu Qiuyue)
Peaceful Lake is a deep central basin storage zone captures mountain runoff silt to prevent it from reaching the shallow and sensitive shores.

Lingering Snow on Broken Bridge (断桥残雪, Duanqiao Canxue)
An inlet on the northern lake regulates the volume of mountain streams to prevent sudden surges of silt after storms.

Orioles Singing in the Willows (柳浪聞鶯, Hua Gang Guan Yu)
Silt from eastern mountain streams flowing close to shore is trapped by bankside buffer plantings.

Viewing Fish at Flower Pond (花港觀魚, Liulang Wenying)
Flower Harbour is a secondary mountain stream sediment trap that intercepts silt before it enters the main body of the lake.

Evening Bell at South Screen Hill (南屏晚钟, Nanping Wanzhong)
South Screen Hill indicates the ridgeline of the southern watershed that is artificially graded to slow hillside runoff and silt transport into the lake.

Twin Peaks Piercing Clouds (双峰插云, Liangfeng Chayun)
The twin north and south peaks define the ridgeline that forms the lake’s primary western watershed, the eastern side of which is the source of all silt from the mountains. This side is densely planted with forests to mitigate catastrophic flash floods that would dump sediment into the lake basin.

Sunset Glow over Leifeng Pagoda(雷峰夕照, Leifeng Xizhao)
Leifeng Pagoda is sited on a ridge separating the unpredictable waters of the Qiangtang River to the south, and the placid waters of West Lake to the north.

Su Causeway and the three stone markers both have hydrological functions intended by Su Dongpo but there’s no certainty about the others. Seven can be understood in terms of hydrology but we can’t say if this is post-rationalization by Southern Song Dynasty poets or even their tribute to Su Dongpo’s linking hydrological purpose to scenic beauty. The scene Sunset Glow over Leifeng Pagoda has no hydrological backstory but it it is a profoundly poetic reminder that the boisterous and unpredictable Qiantang River is on the south side of the ridge and the calm and placid West Lake to the north. This, after all, is what West Lake was all about. Sunset Glow over Leifeng Pagoda therefore deserves place in the canon even if it may have been included only to complete a set of ten scenes. There was already the Northern Song Dynasty (960–1126) precedent of Eight Views of Xiaoxiang (潇湘八景) with individual scroll paintings and lyrical four-character titles for eight scenic spots in the Xiangjiang River basin in Hunan Province. There was also the local precedent of Hangzhou poet Pan Lang (潘閬, 962–1009) and his Jiuquanzi ten-part landscape verses, the most famous of which feature the Qiantang River and its tides.

Nobody knows what the selection criteria were for the original Ten Scenes but in 1984, Hangzhou Daily, the West Lake Parks and Gardens Bureau, and a number of local companies, called for nominations for a new set of Ten Scenes. Results were announced in 1986 but the public weren’t impressed. After five years of nominations and consultations, a second new Ten Scenes was announced in 2007 but people still preferred the original ten.¹ I don’t understand why anyone would have thought a New Ten Scenes was a good idea. Lists such as Twelve Modern Wonders of the World are always underwhelming.

Chinese landscape design and poetry was introduced to Japan and Korea by traveling monks in the Tang Dynasty but the advent of the Ten Scenes meant that circular paths around lakes with islands and causeways began to feature prominently in temple gardens and private pleasure gardens unburdened by problems of water supply and maintenance funding. In Japan, the features of the West Lake landscape were often miniaturized as shukkei compressed scenery with, say, the silhouette of a distant canopy of trees standing in for mountains. Below are two versions of Su Causeway in Japan. The first is at Koshikaswa Korakuen Garden of 1628 and which was the first miniaturized Su Causeway in a Japanese garden. The second is at Kyu-Shiba Detached Palace Gardens from about 1678.

Su Causeway at Koshigawa Korakuen Garden

This isn’t a matter of copying or imitation because Su Dongpo’s causeway hydrological device also happened to be a pleasurable landscape device to go from one place to another, with water on each side. Japanese variations include bridges (left, below) and causeways (middle) with a change of direction so there’s water on both sides as well as behind and in front. Some people interpret the bridge at the Daisen-in garden at Daitokuji temple (right) as a causeway with a waterless body of water on each side. Zen. Traversing the emptiness, crossing the void.

Two droughts in the middle of the Ming Dynasty, in 1442 and 1456 CE, meant that West Lake and tourism revenue from it both dried up, pressing home to officials the obvious truth that lake maintenance and municipal revenue were inextricably linked. Municipal ledgers for the period 1580–1790 confirm a stable reciprocal fiscal loop in which tourist income driven by Ten Scenes-related tourism funded dredging and embankment repair. Apart from during those two periods of drought, the aesthetic identity of West Lake has been detached from its role as a supply of fresh water since Southern Song Dynasty ( 南宋; 1127–1279). Even today, all dredging and other maintenance work continues to take place out of sight so as not to detract from visual enjoyment.

In the past, collection of floating debris was performed by people using nets. The two arms of this electrically-driven vessel extend and contract to bring debris into the vessel for collection and processing. This operation takes place mostly unnoticed in broad daylight as the entrapments are at water level and the vessel resembles an antique pleasure boat. When not in operation, the vessel returns to a semi‑concealed, traditional-style building on Yanggong‑di, next to Liu Manor (刘庄).²

Since 1986, the Fuchun River (富春川) Inter‑basin Water Diversion Project has supplied the city of Hangzhou with fresh water. (Fuchun River is the part of the Qiantang River on the south side of that large island in the bottom left of the image below.) This all happens invisibly. The quality of the water in West Lake is closely monitored by sensors and regulated by a linked network of six inlets and eight outlets, as well as by selected species of fish and lake-bed plantings. The average depth of West Lake is 2 meters and its deepest part is 2.5 meters. The water is transparent for the first meter. For aesthetic reasons, mostly.