Classification of rivers in Japan

Rivers in Japan are classified according to criteria set by the River Act (河川法), which was introduced in 1967. Rivers are classified by the Ministry of Land, Infrastructure, Transport and Tourism (MLIT).

Pre-1967 river administration
At the beginning of the Meiji era, river construction mainly consisted of low water construction such as securing water for boat transportation and irrigation, but after the middle of the Meiji era, boat transportation declined with the spread of railways, and on the other hand, development of river coasts exacerbated damage from floods. As the number of floods increased, a shift was made to high water construction to prevent flooding by building levees.

The old system was enacted in 1891 following the proclamation of the Meiji Constitution. As Japan's first modern public property management system, a systematic legal system for river management was established. However, due to the background of its enactment, the old River Law had strong overtones of control by state power, and, reflecting the social situation at the time, placed more emphasis on flood control than water utilization.

New River Act
Over the following 70 years, due to post-war social and economic development, the use of river water for hydroelectric power generation and industrial water increased rapidly and because of inconsistencies that had arisen in the system implemented by the old River Act, the new River Act was enacted in 1962, with the following changes:


 * All rivers and river systems are classified into four classes
 * Entities in charge of rivers are required to formulate a plan for integrated water management
 * Establishment of regulations related to water use
 * Establishment of regulations to prevent disasters caused by dams

1997 amendment
The River Act was amended in 1997, changing its text to have a greater emphasis on conservation of natural environments, and the consultation and participation of local residents in forming water management plans.

Impact
The 1967 River Act simplified the management of waterways in Japan by merging previously separate systems into one unified water management system. Before this, the river management system in Japan was seen as heavy-handed and overly bureaucratic. Especially post-1997 amendment, there is now greater community involvement when formulating plans regarding rivers and water management.

Class A rivers
Class A river system (一級水系) is a designation applied to rivers systems deemed to be important to the economy of the nation as a whole, as well as those deemed important to the conservation of nature within Japan. There are currently 109 river systems with this designation. If a river system is designated Class A, all the constituent rivers are also designated as such. Therefore, Class B rivers cannot coexist with Class A rivers in the same river system. This designation is also called First Class.

Class A river (一級河川) is a designation which applies to important individual rivers. There are 13,994 rivers with this designation.

Generally speaking, areas surrounding Class A rivers will suffer greater damage in the event of a flood.

List of Class A river systems
The number of dams only includes existing and unestablished dams that meet the criteria (15 m or more in bank height) of the River Law. The management entity is irrelevant. The number in parentheses is the number of dams on the main river, excluding tributaries. The number of dams does not always exceed the number of hydroelectric plants because plants with intake weirs less than 15 m high are not considered dams. The acronym BOD refers to biochemical oxygen demand.

Note: Okinawa has no Class A rivers.

Class B rivers
Smaller or less important rivers are designated as Class B river systems (二級水系). They are nominated and managed by the local governments at the prefecture level, but reported to and concurred with by the central government. There are 7,090 rivers with this designation. Because all of their river systems are designated Class A, there are no Class B rivers in Saitama and Shiga prefectures.

This designation is also called Second Class.

Mutatis mutandis rivers
14,314 rivers in Japan are designated as mutatis mutandis rivers (準用河川), meaning that they are not assigned Class A or B designation, and are under the control of the mayor of the encompassing municipality. An example of this is the Kuno River, managed by the mayor of Odawara.

Ordinary rivers
Rivers that are not designated Class A, Class B, or mutatis mutandis, are called ordinary rivers (普通河川), and the 1967 River Act does not apply to them. These do not include public sewers or agricultural canals. Management of these rivers is carried out by the local municipality.