A is a

hydraulic engineering Hydraulic engineering as a sub-discipline of civil engineering is concerned with the flow and conveyance of fluids, principally water and sewage. One feature of these systems is the extensive use of gravity as the motive force to cause the move ...

and

flood control Flood management or flood control are methods used to reduce or prevent the detrimental effects of flood waters. Flooding can be caused by a mix of both natural processes, such as extreme weather upstream, and human changes to waterbodies and ru ...

structure unique to the

alluvial Alluvium (, ) is loose clay, silt, sand, or gravel that has been deposited by running water in a stream bed, on a floodplain, in an alluvial fan or beach, or in similar settings. Alluvium is also sometimes called alluvial deposit. Alluvium is ...

floodplain A floodplain or flood plain or bottomlands is an area of land adjacent to a river. Floodplains stretch from the banks of a river channel to the base of the enclosing valley, and experience flooding during periods of high Discharge (hydrolog ...

of the

Kiso Three Rivers The are the three major rivers that make up the alluvial plain area of the Nōbi Plain of Japan. The three rivers are the Kiso River, the Ibi River and the Nagara River. Given their location, they are sometimes referred to as the Nōbi Three R ...

in central Japan. It is comparable to the European

polder A polder () is a low-lying tract of land that forms an artificial hydrology, hydrological entity, enclosed by embankments known as levee, dikes. The three types of polder are: # Land reclamation, Land reclaimed from a body of water, such as a ...

, although a ''wajū'' is usually not

reclaimed Land reclamation, often known as reclamation, and also known as land fill (not to be confused with a waste landfill), is the process of creating new land from oceans, seas, riverbeds or lake beds. The land reclaimed is known as reclamation ...

. The hardships endured for centuries by farmers whose lives revolved around the ''wajū'' has given rise to the term .

History

Since prehistoric times sudden

freshet The term ''freshet'' is most commonly used to describe a snowmelt, an annual high water event on rivers resulting from snow and river ice melting. Description A spring freshet can sometimes last several weeks on large river systems, resulting ...

s along the course of the major rivers of Owari and

Mino Mino may refer to: Places in Japan * Mino, Gifu, a city in Gifu Prefecture * Mino, Kagawa, a former town in Kagawa Prefecture * Mino, Tokushima, a town in Tokushima Prefecture * Mino, an alternate spelling of Minoh, a city in Osaka Prefecture * Mi ...

in late spring caused by snowmelt in the

snow country is a novel by the Japanese author Yasunari Kawabata. The novel is considered a classic work of Japanese literature and was among the three novels the Nobel Committee cited in 1968, when Kawabata was awarded the Nobel Prize in Literature. Writ ...

, especially in the

Japanese Alps The is a series of mountain ranges in Japan which bisect the main island of Honshu. The peaks that tower over central Honshu have long been the object of veneration and pilgrimage. These mountains had long been exploited by local people for raw m ...

and Koshi, created great suffering for agricultural communities. The ''wajū'' was developed to protect fertile riparian farmland from becoming submerged by rising water levels during these freshets. ''Wajū'' are known to have been in use since at least the 16th century, but some ''wajū'' are reputed to be much older, such as which was allegedly completed in 1319. To develop a ''wajū'', an area of land, usually a

river island River Island (stylised as RiverIsland and abbreviated as RI) is a London-based, multi-channel fashion brand, founded in 1948 by Bernard Lewis (entrepreneur), Bernard Lewis. The retailer has a presence in over 125 of worldwide markets, in stores ...

, was enclosed by a

levee A levee ( or ), dike (American English), dyke (British English; see American and British English spelling differences#Miscellaneous spelling differences, spelling differences), embankment, floodbank, or stop bank is an elevated ridge, natural ...

ring. In the event of a levee failure, most ''wajū'' incorporated structures allowing for vertical evacuation. One evacuation system used by those who could afford to build it, such as the well-to-do

gōnō ''Gōnō'' (豪農) were the upper-class Peasant, peasantry in the late Edo period and early Meiji (era), Meiji era Japan. They held considerable wealth and power in local communities, and aside from being major landowners, some owned small rural ...

, was the , a sort of

tower house A tower house is a particular type of stone structure, built for defensive purposes as well as habitation. Tower houses began to appear in the Middle Ages, especially in mountainous or limited access areas, to command and defend strategic points ...

above the high water line built on a foundation in ''ishigaki'' style. For lower class people, including peasants and rural samurai (gōshi), who couldn't afford to build ''mizuya'', there was the an artificial earthen high ground similar to the

terp A ''terp'', also known as a ''wierde, woerd, warf, warft, werf, werve, wurt'' or ''værft'', is an artificial dwelling mound found on the North European Plain that has been created to provide safe ground during storm surges, high tides and ...

s of Northern Europe or the

cattle mound Cattle (''Bos taurus'') are large, domesticated, bovid ungulates widely kept as livestock. They are prominent modern members of the subfamily Bovinae and the most widespread species of the genus ''Bos''. Mature female cattle are called cow ...

s built on American ranches. Over the centuries, the ''wajū'' suffered numerous failures due to engineering deficiencies. In the 18th century, was among the first to suggest redirecting the rivers to relieve water pressure on the ''wajū'' and compensate for the inadequacies of the existing system of pressure-regulating aqueducts, known as . In the late 19th century, the ''wajū'' were improved and reinforced using technology imported from Europe.

History

See also

References

Further reading