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The Zhuoshui River is a major river in west-central Taiwan. Starting in the Central Mountain Range in Nantou County, the river flows west toward the Changhua Plain, where it forms the border between Yunlin County and Changhua County, and empties into the Taiwan Strait. With a total length of 186.6 km, it is the longest river in Taiwan. It is known for its frequent flooding and has the highest sediment load of Taiwan's rivers, which earned it the name "Zhuoshui", muddy water. The river serves as an unofficial boundary between the north and south of Taiwan.

The Zhuoshui River basin has been inhabited by various indigenous peoples for at least 4,000 years. Although many indigenous groups were assimilated or driven out by Han Chinese settlement starting in the 1600s, the Atayal, Seediq, Bunun and Thao retain some of their traditional lands in the Nantou part of the basin. Han immigrants built Taiwan's first irrigation scheme on the Zhuoshui River, enabling the economic growth of the region. During Japanese occupation in the early 1900s, the upper Zhuoshui River was exploited for its natural resources, and resistance from indigenous groups led to numerous military confrontations including the Musha Incident.

The river has considerable economic importance. It is the site of one of Taiwan's largest hydropower schemes, an interconnected system of reservoirs, tunnels and power plants which include the Sun Moon Lake reservoir, one of Taiwan's most popular tourist attractions. The river is a key source of water for irrigation and industry in central Taiwan. In recent decades, sand and gravel mining and the construction of the Jiji Weir have significantly degraded the channel of the river.

Geography
The Zhuoshui River drains an area of 3157 km2, the second largest in Taiwan, after the Gaoping River. The western part of the basin is plains, while the eastern part is mountainous. The river's headwaters and easternmost tributaries begin along the crest of the Central Mountain Range. The middle section of the Zhuoshui River is considered part of the Puli Basins, bisecting the Xueshan Range (to the north) and the Yushan Range, and also forming the northern boundary of the Alishan Range. This area also includes Sun Moon Lake, one of the largest lakes in Taiwan. The mountainous areas are primarily forest, while the coastal plain, the middle Zhoushui valley, and the Chenyoulan and Qingshui tributary valleys are used for agriculture. Annual precipitation ranges from 1000 to 1100 mm in the west, to 2200 mm in the east.

The basin includes 21 townships in four counties, but there are no major urbanized areas.
 * Changhua County: Dacheng, Zhutang, Xizhou, Ershui, Tianzhong
 * Yunlin: Mailiao, Lunbei, Erlun, Xiluo, Putong, Linnei
 * Chiayi: Alishan, Meishan
 * Nantou: Zhushan, Lugu, Jiji, Mingjian, Shuili, Yuchi, Ren'ai, Xinyi

The upper Zhuoshui River begins as the Wushe River in Nantou County. It originates at Hehuanshan in Taroko National Park, about 3220 m above sea level, and flows southwest to the Wushe Dam. Below Wushe Dam, it merges with the Wanda River, below which it is known as the Zhuoshui River proper. It flows west then south, forming a tortuous winding course through deep canyons. The river then joins with Kashe River and Danda River, the latter of which originates at Mount Xiuguluan. It then turns due west, flowing towards Shuili. The confluence with the Chenyoulan River (which drains from the north slope of Yushan) is considered the boundary of the upper and middle Zhoushui River. The Middle Zhoushui River has a much wider valley and is characterized by a braided channel. At Shuili Village it is joined by the Shuili River, the natural outflow of Sun Moon Lake. Further west it flows past Jiji town, where the Jiji Weir is located. At Zhushan town it is joined by its last major tributary, the Qingshui River.

The Zhuoshui River emerges from the mountains at the "Bitou Pass" north of Douliu City, flowing across the Changhua Plain towards the Taiwan Strait and forming the boundary between Changhua County (on the north) and Yunlin County. The section below Bitou Pass is known as the Lower Zhuoshui River. Although the riverbed is extremely wide – ranging from 3 to 5 km – it is mostly sand and gravel, except for occasional floods. The river's 1339 km2 alluvial fan is the largest in Taiwan, extending west from Ershui/Linnei Townships to the sea, and from Lukang in the north to Beigang in the south. It flows into the Taiwan Strait between Dacheng, Changhua and Mailiao, Yunlin. Historically the Zhuoshui River formed multiple channels fanning out across the coastal plain, including the Dongluo, Xiluo, Xinhuwei and Beigang Rivers. Presently the main stem is confined by levees to the Xiluo channel, and the other channels have become independent creeks.

Geology and morphology
The Zhuoshui River has the highest sediment content of any river in Taiwan. Annual sediment volumes average 40 million tonnes (Mt), with a low of 7.6 Mt in 1978 and a high of 120 Mt in 1996. Annual water volume averages 3.6 km3 and has ranged from a low of 1.1 km3 in 1980, to a high of 6.6 km3 in 1974. About two-thirds of the annual flow, and the vast majority of sediment transport, occurs from June to September during the typhoon season.

The upper reaches of the river are formed in weak, highly erosive sedimentary rock, principally shale and phyllite. Due to the abundant rainfall and steep terrain, the area sees frequent landslides, contributing to high sediment loads in the river and its tributaries. Parts of the upper river and its tributaries feature incised meanders, which create a landscape of twisting, zig-zagging canyons. The Chelungpu fault runs from north to south through the Zhuoshui basin, forming the path of the Qingshui River tributary. The 1999 Jiji earthquake ("921 earthquake") occurred along this fault and caused substantial landsliding that affected 3.5 percent of the Zhuoshui River basin.

Large boulders and gravel are deposited in the middle Zhuoshui River between Chenyoulan River and Bitou pass, giving the riverbed a rocky, rugged appearance. Tectonic uplift has raised old sediment beds, creating fluvial terraces along the middle Zhuoshui River. In the lower Zhuoshui River, the riverbed consists mostly of fine gravel and sand. The Zhuoshui River alluvial fan contains some of the deepest sediment deposits in Taiwan, with Quaternary alluvial deposits estimated at 1000 m in places. Due to the porous gravel and sand layers, this area supports one of Taiwan's most productive aquifers.

Ecology
Most of the upper Zhuoshui River basin is forested, with native tree species including the Taiwan beech, various Pistacia, Shorea and Quercus species, Taiwan red pine, Taiwan cypress, Taiwan hemlock, camphor, and Taiwan incense-cedar. Large areas are artificially planted with betel nut tree, tea tree, tung tree, bamboo and various fruit trees. Due to the river's frequent floods, most riparian plant species are herbaceous, especially in the lower section of the river. The flowering Taiwan hibiscus is commonly found along the river. The National Taiwan University Experimental Forest, established in 1901, extends from the south bank of the Zhuoshui River to the summit of Yushan, and includes 32770 ha used for forestry and biological sciences research. It also includes several nature reserves, including the Duigaoyue, Fenghuangshan and Yashanping reserves. The Fenghuangshan reserve is home to some 50 rare or endangered plants, particulary Machilus and Castanopsis species.

The river system also supports a diverse fauna, including 58 bird species, 23 fish species, 6 shrimp species, and 3 crab species. A variety of mammals are present in the upper Zhuoshui River, including the Formosan black bear, Sika deer, Taiwan field mouse, red-bellied tree squirrel, wild goats and boars, crab-eating mongoose, and Formosan rock macaque. There are also several amphibian and reptile species; the Wushe Reservoir area is known for its diversity of frogs.

In recent years the Zhuoshui River has seen lower dry season flows due to changes in rainfall patterns. Large areas of riverbed have dried out, causing a loss of vegetative cover that has in turn led to severe blowing dust issues. The most heavily affected areas are in Changhua County, south of the river. The Taiwanese government has conducted dust mitigation projects along 15.7 km of the river, including dust suppression ponds, riparian vegetation planting, and afforestation.

Indigenous peoples
The upper Zhuoshui basin has been inhabited by humans for thousands of years. Archeological evidence on the upper and middle Zhuoshui River suggests humans have been present since 2000–3000 BCE. Sites at Jiji and at Qubing (in Ren'ai township) have yielded stone axes, grinding stones, pottery shards and fishing nets. The Atayal have traditionally lived northeast of the Zhuoshui River and today they principally inhabit Ren'ai Township in Nantou County. The Seediq, recognized as a separate indigenous group in 2008, were formerly classified as Atayal by the Taiwanese government. The Seediq called the river Mtudu. Bunun communities are located along the middle Zhuoshui River and southern tributaries such as Chenyoulan River and Danda River. A third and much smaller ethnic group, the Thao people, mainly inhabits the area around Sun Moon Lake.

Hundreds of communities were located along the upper Zhuoshui and tributaries but due to the rugged terrain and difficulty of travel, each village had distinct customs and a unique language. The expansion of trails and roads into the highlands starting with Qing Dynasty rule had the effect of linking many remote settlements. The valley at Wujie (Fazhicun), located along the Zhuoshui River in southwest Ren'ai Township, was historically a hunting ground and contested area between the Atayal and Bunun. The tribes eventually negotiated a ceasefire and a fortified village was constructed at the boundary. Within their individual territories, tribal units practiced slash-and-burn agriculture and traveled seasonally to different hunting areas. Since the beginning of the 20th century, forced resettlement of once semi-nomadic groups, coupled with restrictions on hunting, changed them to more sedentary, agrarian communities.

The lower Zhuoshui River was home to the Favorlang and Hoanya, both Pingpu (Plains) ethnic groups.

Qing Dynasty (1640–1895)
Han Chinese immigrants from Fujian began to settle the area of the lower Zhuoshui River around 1640, and gradually expanded east as Qing China asserted control over Taiwan. Since then, indigenous territories have shrunk due to Chinese and later Japanese incursion. The Bunun once had a large population in what is now Puli but migrated south to the Zhuoshui River and to higher elevations as the number of Chinese settlers increased. Trails were gradually opened into the central mountains to enable trade with coastal areas. The Batongguan Trail was built in 1875 to connect east and west Taiwan, crossing the Central Mountain Range between Xinyi (the upper reaches of Danda River tributary) and Hualien County.

The Zhuoshui River was once known for its numerous floods and course changes, which forced residents along the lower river to move frequently, and prevented large towns from developing on the banks of the river. Some early Chinese settlers called it "Taiwan's Yellow River". The first written record of a flood in the Zhuoshui river was made around 1685. Some of the earliest important settlements were in Changhua County, on the Dongluo River, which at the time was the main branch of the Zhuoshui River. In the early 1700s Lukang, located at the Dongluo River mouth, grew into a major seaport receiving ships from mainland China. For many decades the center of regional commerce was Beidou, located upstream on the Dongluo River. Boats traveled on the Zhuoshui River as far upstream as Zhushan, Nantou. In the 1860s, flooding diverted the Zhuoshui River away from the Dongluo channel, which began to silt up. Lukang was no longer usable as a port and fell into decline.

From 1709–1719 the Babaozhen irrigation project, the first water conservation scheme in Taiwan, was constructed on the Zhuoshui River. Designed by engineer and farmer Shi Shibang, the project drew water from the river at Bizaitou (now Ershui). A barrier made of rattan and bamboo was created to divert water into Zhuoshui Canal. Ultimately, it would irrigate an estimated 19000 ha of land in 103 villages. The name Babao, "eight forts", refers to the eight forts of the Changhua Plain whose land received water from the project. Agricultural production rose greatly in this area and it became the most densely populated part of Taiwan until the 20th century. The main canal was 89 km long, with more than 230 km of branches. Parts of the canal system are still in use today.

Japanese rule (1895–1945)
In 1898, only a few years after the start of Japanese occupation, the Zhuoshui River experienced one of its largest floods in recorded history. The flood switched the river's course from the Xiluo back to the Dongluo channel and caused serious damage in Changhua and Yunlun Counties. Large tracts of farmland were either swept away or buried by sand, and many people moved out. In response to this flood and another in 1911, flood barriers were constructed along the river starting in 1912, blocking off the Xinhuwei channel. In 1916 the colonial government began planning flood control projects along Taiwan's major rivers. From 1918–1920, 76 km of dikes were constructed to fix the course of the lower river along the Xiluo channel, which today is simply called the lower part of the Zhuoshui. This opened vast areas of the Changhua plain to development, which were previously subject to annual flooding. In the 1920s, the Zhuoshui River was also connected to the Chianan Irrigation project, a system of canals stretching as far as Tainan, to support agriculture on the Chianan Plain south of the river. From 1932 to 1945, agriculture was greatly expanded in many townships including Beidou, Xizhou, Pitou, Erlin, and Fangyuan. Six villages were also established for immigrant farmers from Japan, and further irrigation and soil conservation projects were carried out to reclaim lands damaged by the 1898 flood.

Starting in 1902, the Japanese moved to secure natural resources in the upper Zhuoshui basin, particularly timber and hydropower. Indigenous peoples fought a guerrilla war against the Japanese advance for the next thirty years. The Japanese found it difficult to control the semi-nomadic indigenous tribes and forced many to settle in permanent housing. One of the major resettlements was the remote valley of the Zhuoshui River at Wujie. In 1930, Seediq warriors killed 130 Japanese in the Musha Incident (Wushe Incident), near what is now Wushe Dam. The Japanese were unable to effectively fight the Seediq in the rugged terrain and resorted to dropping mustard gas bombs. About 600 Seediq were killed, and the survivors were forced to move to Huzhu village in Ren'ai Township. The Japanese government was criticized heavily for these actions, and this led to changes in their policy towards indigenous peoples.

In 1922 the Jiji Line railway was built along the Zhuoshui River, linking Shuili and Jiji to the Western Trunk line. The primary purpose of the line was to enable the construction of Taiwan's first hydroelectric scheme at Sun Moon Lake. From 1934–1937, engineers constructed the Wujie Dam to divert water from the Zhuoshui River and built dams to raise the level of Sun Moon Lake approximately 20 m. Water flowed through hydroelectric plants before returning to the Zhuoshui River via the Shuili River. This system fulfilled all of Taiwan's electricity needs during the Japanese colonial period. The Japanese also began constructing the Wushe Dam in Ren'ai Township, but this project was stalled at the beginning of World War II. During the war, the hydroelectric system was bombed by the U.S. air force and heavily damaged. After Japan relinquished control of Taiwan, the Taiwan Power Company (Taipower) repaired and upgraded the system and also completed construction of the Wushe Dam in 1959.

1945 to present
After the end of the war, the Taiwan Water Conservancy Bureau was established in 1949 to manage development of the Zhuoshui River basin. The construction of dikes in the Japanese colonial period had caused severe aggradation in the lower Zhuoshui River, such that the riverbed was higher than the surrounding land. To alleviate the flooding risk, a system of spur dikes was developed to constrict the channel and speed up the water flow, allowing it to carry sediment more quickly to the ocean. In 1951 a landslide dam collapsed in the upper Zhuoshui River basin, causing a flood that killed 137 people, damaged 3000 ha of land and destroyed around 10,000 properties. This event highlighted the need for better flood control along the river. Starting in the 1970s, the increasing demand for sand and gravel in the concrete industry led to large illegal mining operations in the Zhuoshui River channel. Incidentally, this solved the problem of sediment accumulation, but mining led to separate issues, such as erosion that threatened to collapse bridge foundations. In 1985 the Taiwan Water Resources Agency, local police departments and city governments began to crack down on mining operations on the Zhuoshui and five other rivers in Taiwan. Over a six month period, 118 dredging ships were seized by authorities.

Starting in the 1960s, the lower Zhuoshui River basin experienced widespread subsidence, due to groundwater overuse resulting from increased agricultural production. This led to an increased risk of coastal flooding and saline intrusion. In response, the Jiji Weir was constructed by the Taiwan Water Resources Agency as part of a larger project to improve irrigation in the Zhuoshui River basin. The weir was planned in 1990 and completed in 2001. However, the Jiji weir has since trapped a large volume of sediment, reducing its capacity to supply water, and the overall effectiveness of the project. The weir has also had significant environmental impacts. By blocking sediment it has resulted in coastal erosion as far south as the Waisanding Island in Chiayi. Due to its design, the weir caused massive erosion in the Zhuoshui River channel downstream, forming what is known as "Jiji Canyon". The sedimentary strata beneath the river bed was exposed to create a landscape of ridges, gullies and cascades, as well as numerous fossil beds.

In 1999 the Jiji earthquake, or 921 earthquake, occurred with its epicenter in the Zhuoshui River basin. The earthquake killed more than 2,400 people and destroyed about 80,000 buildings in Nantou County. Several bridges across the Zhuoshui River were destroyed, the dams at Sun Moon Lake were damaged, and landslides and debris flows occurred widely across the river basin. Many of these collapses left permanent scars on the landscape, which continue to contribute elevated sediment volumes to the river, particularly during typhoons. One large landslide blocked the Qingshui River tributary, creating New Caoling Lake. The lake breached in 2004 during Typhoon Mindulle, causing flash floods in the Qingshui and Zhuoshui rivers.

In 2005 the Kuokuang Petrochemical Technology Co. proposed to build a refinery near the mouth of the Zhuoshui River. It would be constructed on 2773 acre of coastal wetlands. Residents in Changhua County adamantly opposed the refinery due to its environmental and health impacts, and potential effects on local agriculture. The Green Party and a number of nonprofits also became involved in the opposition. In 2011 President Ma Ying-jeou asked the Ministry of Economic Affairs to find an alternative site. The project was canceled the same year.

Hydroelectricity
The hydroelectric plants along the upper Zhuoshui River are operated by Taiwan Power Company (Taipower). The uppermost dam in the Zhuoshui basin is the 114 m high Wushe Dam, which stores water in Wanda Reservoir (also called Bihu, or "emerald lake") to feed the Wanda Power Plant. Although started in 1925 by the Japanese, the dam was not completed until 1959. The Wushe dam was originally designed to store 146000000 m3 of water, but has suffered from heavy siltation. In 2020, its capacity was estimated at no more than 37530000 m3. The Wanda Power Plant is supplied by water from Wushe Dam as well as a diversion of Wanda River. The outflow from this plant is then directed into the Songlin Power Plant. Together, the two plants can generate 76.6 megawatts (MW).

The Wujie Dam, located about 10 km downstream from Wushe Dam, diverts water from the Zhuoshui River through the 15 km long Wujie Tunnel into Sun Moon Lake. Sun Moon Lake, originally two natural lakes, was expanded by the construction of the Toushe and Shuishe dams in order to store Zhuoshui River water. The enlarged Sun Moon Lake can store 124000000 m3 of water. These works were initially completed by the Japanese in 1934. In 2006, the New Wujie Tunnel was excavated parallel to the original tunnel in order to increase the amount of water flowing from the Zhuoshui to Sun Moon Lake. West of Sun Moon Lake, water flows through penstocks into the canyon of the Shuili River, more than 320 m lower in elevation. The water first passes through the 100 MW Daguan Power Plant (Sun Moon Lake No. 1 Power Plant), first completed in 1934. Downstream, a tunnel leads to the 43.5 MW Jugong Power Plant (Sun Moon Lake No. 2 Power Plant) at Shuili village, completed in 1937. The water then empties into the Shuili River and returns to the Zhuoshui River.

In the 1980s, two pumped-storage hydroelectric plants were developed in this area using Sun Moon Lake as the upper reservoir, and new dams on the Shuili River as lower reservoirs. The Minghu Dam, completed in 1985, is located next to the Daguan Power Plant and can produce up to 1,000 MW. Mingtan Dam was completed in 1995, just downstream of Minghu Dam. It can generate up to 1,602 MW, making it the largest hydroelectric power plant in Taiwan. The power stations were constructed primarily to balance demands on the electric grid as Taiwan experienced rapid population growth. During the night, surplus power is used to pump water uphill into Sun Moon Lake, from which it is released back downhill during peak demand in the afternoon.

Irrigation
The Jiji Weir, completed in 2001 downstream of Jiji town, is a 352 m long barrage with eighteen flood gates. The weir is the primary location at which water is collected and distributed in the Zhuoshui River basin. It was designed with two intakes that link directly into the water supply systems of Changhua and Yunlin counties. The north intake has a capacity of 40 m3/s and supplies about 40000 ha of farmland in Changhua County. The south intake has a capacity of 90 m3/s, and provides water to 60000 ha of farmland in Yunlin and Nantou, as well as the Yunlin Islands Industrial Zone along the coast. Because the Jiji Weir only stores a small volume of water, its operations are coordinated with water releases from Wanda Reservoir and Sun Moon Lake, which provide additional river flow in the dry season.

The south intake is connected to the Chianan Irrigation system, which was designed to provide water to the Chianan Plain, enabling large scale rice cultivation in this relatively dry region of Taiwan's west coast. The Chianan Irrigation covers a total of 150000 ha and actually consists of two independent irrigation systems – one fed from the north by the Zhuoshui River and the other from the south by the Zengwen River. Water flows southwest through a system of canals, ultimately reaching the Beigang River. The length of the main canal from the intake to the Beigang River is 38 km, and the distribution network includes hundreds more kilometres of canals.

Despite the large network of canals delivering surface water, agriculture in the Zhuoshui River basin still depends in large part on groundwater. Overuse of groundwater has caused extensive subsidence in the alluvial plain, especially in Yunlin County. This has increased the risk of coastal flooding and threatened infrastructure including the Taiwan High-Speed Rail corridor. The Hushan Dam was built in 2016 in an effort to alleviate the water shortage. The dam stores water diverted from the Qingshui River tributary before it flows into the Zhuoshui, and is tied into the water distribution network of Yunlin. However, the dam has not provided enough water to overcome the groundwater deficit. Other efforts to reduce subsidence include shutting down certain wells and reducing losses from the irrigation system, which loses an estimated 36–40 percent of surface water to leakage and evaporation.

List of tributaries
Tributaries of the Zhuoshui River are listed from downstream to upstream. Reservoirs and lakes are indicated in italics.


 * Qingshui River (清水溪)
 * Jiazhouliau Creek (加走寮溪)
 * Shengmaoshu Creek (生毛樹溪)
 * Alishan Creek (阿里山溪)
 * Dongburui River (東埔蚋溪)
 * Beishi Creek (北勢溪)
 * Jiji Weir (集集攔河堰)
 * Qingshuigou Creek (清水溝溪)
 * Shipan Creek (石盤溪)
 * Shuili River (水里溪)
 * Mingtan Dam (明潭壩)/Mingtan Reservoir (明潭水庫)
 * Minghu Dam (明湖壩)/Minghu Reservoir (明湖水庫)
 * Sun Moon Lake (日月潭)
 * Chenyoulan River (陳有蘭溪)
 * Junkeng Creek (郡坑溪)
 * Shibachong Creek (十八重溪)
 * Heshe Creek (和社溪)
 * Songshan Creek (松山溪)
 * Chushui Creek (出水溪)
 * Haomajiaban Creek (郝馬戛班溪)
 * Shalixian Creek (沙里仙溪)
 * Zhuogun River (卓棍溪)
 * Danda River (丹大溪)
 * Junda Creek (郡大溪)
 * Luanda Creek (巒大溪)
 * Hayilaluo Creek (哈伊拉羅溪)
 * Majiaying Creek (馬戛英溪)
 * West Danda River (丹大西溪)
 * East Danda River (丹大東溪)
 * Kashe River (卡社溪)
 * Liqi River (栗栖溪)
 * Wanda River (萬大溪)
 * Shili Creek (十粒溪)
 * North Wanda River (萬大北溪)
 * South Wanda River (萬大南溪)
 * Wushe River (霧社溪)
 * Wushe Dam (霧社壩)/Wanda Reservoir (萬大水庫)
 * Taluowan River (塔羅灣溪)
 * Mahaipu Creek (馬海濮溪)