Kako River (Japan)

This article is about the river in Japan. For the river in Guyana, see Kako River.

Kako River 加古川
The Kako River, taken from a bridge in Ono.
Native name	加古川 (Japanese) Kako-gawa (Japanese)
Location
Country	Japan
Prefecture	Hyōgo
Physical characteristics
Source	Mount Awaga
• location	Hyōgo Prefecture
• coordinates	35°15′43″N 134°54′58″E
• elevation	962 m (3,156 ft)
Mouth	Harima Sea
• location	Hyōgo Prefecture
• coordinates	34°43′57″N 134°48′27″E
• elevation	0 m (0 ft)
Length	96 km (60 mi)
Basin size	1,730 km2 (670 sq mi)
Discharge
• location	Kakogawa
• average	51.82 m3 (1,830 cu ft)
Basin features
Population	2,440,000

The Kako River (加古川, Kako-gawa) is a river that flows through Hyōgo Prefecture, Japan. It is the largest river in Hyōgo Prefecture, both in terms of total length and basin area, encompassing 21% of the prefecture's land area. It rises at Mount Awaga, and flows 96 kilometres (60 mi) south, reaching the Harima Sea and forming part of the border between Kakogawa and Takasago cities. The Ministry of Land, Infrastructure, Transport and Tourism (MLIT) has designated the Kako River system as Class A.

The Kako River has historically played a major role in the economy of the region. Since the Yayoi period, the river has been used for water, irrigation, leisure, and trade. The Toryu-nada rocks near Kamitakino are a popular tourist spot. The river hosts a diverse ecosystem, and is known for its ayu sweetfish, for which there is an annual festival.

Geography

The Kako River originates from Mount Awaga, 962 metres (3,156 ft) above sea level. Flowing through Tamba and Nishiwaki, it joins the Sugihara and Noma rivers, before continuing south through Ono and Miki, where it is combined with the Tojo, Manganji, and Mishuku rivers. It reaches the Harima Sea at Onoe-chō, where it forms part of the border between Kakogawa and Takasago.

The river has a length of 96 kilometres (60 mi) and a basin area of 1,730 square kilometres (670 sq mi). Among the river systems in Hyōgo Prefecture, it is the largest in terms of both the length of the main channel, and the area of the basin. The basin encompasses 21% of Hyōgo Prefecture's land area. The Kako River system contains 129 tributary rivers. Within the basin, 59% of the land is considered mountainous, 26% is agricultural land, 11% is residential land, and 4% is used for other purposes.

Municipalities

The Kako River basin encompasses eleven cities and three towns. These include:

• Tamba
• Tamba-Sasayama
• Nishiwaki
• Taka
• Katō
• Ono
• Sanda
• Miki
• Kasai
• Kakogawa
• Inami
• Takasago
• Himeji
• Toyono (in Osaka Prefecture)

Six national parks have been designated in the river's vicinity, including the Setonaikai National Park. As of 2017, the population of the basin area was estimated to be 640,000.

Etymology

Panorama of the Kako River, taken from Tamba.

The name "Kako River" was already established by the middle of the Kamakura period. The name was also sometimes written as Kagogawa (賀古川). Theories as to the name's origin include:

• Emperor Keikō named the river Kako because the mouth of the river resembled the back of a deer (鹿, Ka) when viewed from Mount Hioka.
• According to the Harima Fudoki, a description of Harima Province written in 715 CE, there is a legend stating that the region surrounding Mount Hioka was named Kako-no-kōri (鹿児の郡, lit. Deer child country).
• As the Kako River was an important transportation route to the inland areas of Harima Province, the river became known for the many sailors (水夫, Kako) that lived at the river's mouth.
• An old port near present day Ōtsu had a view of the river mouth from which the bay resembled a lake, so the Kako River got its name from the bay that surrounds it (囲む, Kakomu) like a lake.
• The region was named after the many deer that lived there at the time.

History

Pre-Asuka period

Humans have inhabited the area surrounding the Kako River for at least 1,500 years, due to the fertile soil in its basin. Many Yayoi period ruins are found in the wetlands surrounding the river. At that time, waterway technology was undeveloped, so rice paddies and villages were formed by planting rice in wetlands or selecting areas in alluvial fans where water could easily drain. It is apparent that there were many battles during this period, and many of the area's villages were defended by moats.

Asuka and Kamakura periods

In the year 607, a weir was constructed on the lower reaches of the river by Prince Shōtoku. In 1225, a village called "Kunikane" was washed away during a heavy flood. There is also evidence that another weir was constructed towards the middle of the river during this period. Boat transport using the Kako River seems to have been active since the year 701, with records stating that there was a ferry dock built in Noguchi Village (present day Kakogawa City).

Late Sengoku to early Edo period

After Toyotomi Hideyoshi subdued the area towards the end of the Sengoku period, boat transport using the Kako River became much more prevalent. The political and economic centre of Japan moved from Kyoto to Osaka, and the route for transporting rice tributes changed accordingly. Almost all of Hyōgo Prefecture became the territory of the Hideyoshi Clan after the unification of the country, but during the Edo period, Terumasa Ikeda was given 520,000 koku of land in the area. Himeji Castle was built on this land in 1607.

The river was dredged in two phases during this time; in 1594, the route from Takasago to Daimon was completed, and from 1606, the route from Daimon to Takino was completed. This made the river much easier to navigate by boat. Taking advantage of the increased boat traffic, the Ikeda Clan set up ships in Takino and Takada to collect customs duties, with a price of 51 momme.

Docks and distribution facilities began to spring up in various places along the Kako River by this point. In particular, the towns of Takino, Shinmachi, Daimon, and Ichiba began to flourish due to increased trade. In the latter half of the Edo period, there were 37 docks in the basin area, with 300 boats in operation. Mass production of salt in the area began when the Irihama salt fields were built downstream of the Kako River. In 1646, the Himeji Domain granted fishing rights from Takasago to Inokuchi to Matsuo Gorobei in exchange for 200 momme per year. Villagers had to pay 10 momme for a fishing license.

The Kako River continued to play an important role in ensuring the passage of people and goods until the Banshu Railway (now the Kakogawa Line) was constructed in 1913.

Flood control

The Kako River flowing past Nishiwaki. A bridge on the Kakogawa Line can be seen in the background.

The flow of the Kako River has often changed due to large floods. The first known flood control measures were put in place by Sakakibara Tadatsugu, then lord of Himeji Castle, who ordered the construction of an embankment on the right bank of the river. This was done in order to make crossings easier, prevent flooding of downstream villages, and increasing available land for agriculture. Construction of the embankment lasted from 1658 to 1660, and is the foundation of the embankment that exists on the river today. Construction of the initial embankment required 600,000 people, and was completed in just one month. However, it was not successful in controlling flood damage, and repairing the embankments and providing relief to flood victims became an annual ritual for the local clan.

Modern history

Since the Meiji era, floods along the Kako River have been well-documented. The largest flood in the river's history was caused by the Akune Typhoon in 1945; over the two days the typhoon was active, the total rainfall was measured at 240.1 millimetres (9.45 in). Damage estimates counted 50 houses destroyed, 400 houses flooded, and 31 individuals killed or injured.

Full-scale renovation of the lower section of the Kako River began in 1919 and was completed in 1932. In 1920, an iron bridge was constructed across the river, made necessary as the previous bridges were repeatedly washed away by floods. The Kakogawa dam began construction on March 1, 1939, and was completed on May 1, 1945.

In order to develop post-war farmland and secure irrigation water for the purpose of increasing food production, construction of additional dams began in 1945. Industrial water supply projects began in 1952, with construction of the Heisho Dam beginning in the same year, and the Gongen Dam beginning in 1962. The rapid population increase in Kakogawa area led to increased difficulty in securing domestic water. Construction of the Kakogawa Weir began in 1981 in order to secure water for domestic purposes and to improve the safety of water use in the lower reaches of the Kako River.

With the implementation of the 1967 River Act, the Kako River was designated a Class A river system, deeming it important to the conservation of nature in Japan. Another flood occurred on September 28, 1983, caused by Typhoon Forrest. Total rainfall during the typhoon was 225.1 millimetres (8.86 in). In 1994 and 2000, the Kako River experienced droughts. During the drought in 1994, water intake was restricted by up to 40% for tap water and industrial water for around one and a half months. Further droughts also occurred in 2005, 2009, and 2013. Following the Great Hanshin earthquake in 1995, roads on the riverside were improved as to ensure the passage of relief and recovery vehicles in the event of a disaster.

Typhoon Tokage

On October 20, 2004, Typhoon Tokage made landfall, bringing an average rainfall of 225 millimetres (8.9 in) for the two days the typhoon was active. An estimated 537 hectares (1,330 acres) of land was flooded, and 516 houses were damaged. After this, the Kako River was improved to prevent similar damage from occurring in the future. In May 2000, the Kako River Disaster Prevention Station was established to protect lives and property from floods and earthquakes.

Tourism and leisure

Toryu-nada viewed from the south.

Toryu-nada (闘竜灘) is a tourist spot in the Kako River. It is a collection of rocks sitting in the middle of the river; it is said that the appearance of the stream running over the rocks resembles a dragon. The area surrounding Toryu-nada also famous for its ayu sweetfish. There is an Ayu Festival held on May 3 each year. The Kakogawa Marathon is held along the banks of the river. There are a great number of parks along the riverside, including Takasago Seaside Park located at the river mouth.

Ecology

Every year since 1991, a survey on the Kako River's ecosystem has been conducted by the Ministry of Land, Infrastructure, Transport and Tourism. Much of the river basin is surrounded by laurel forest, but small beech forests can be found in areas like the northern ridge of Mount Rokkō. According to a 2003 survey, 620 aquatic plant species in 112 families were present in the river. There are 90 species of fish, and 32 species of shrimp, crab, and shellfish present in the Kako River. It has the highest number of species of any river flowing into the Seto Inland Sea in Hyōgo Prefecture. Because the stream gradient is small, fish that prefer gentle flow (bitterlings, killifish, catfish, etc.) are distributed all the way to the upper reaches.