Classification of rivers in Japan

Rivers in Japan are classified according to criteria set by the River Law (河川法, Kasen Hō), which was introduced in 1967.[1][2] Rivers are designated as Class A or Class B river systems by the Ministry of Land, Infrastructure, Transport and Tourism (MLIT).

Class A rivers

Class A river system (一級水系, Ikkyū suikei) is a designation applied to rivers and waterways 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 rivers with this designation.[3]

List of Class A river systems

The number of dams only includes existing and unestablished dams that meet the criteria (15 metres (49 ft) 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 metres (49 ft) high are not considered dams.

The acronym BOD refers to biochemical oxygen demand.

Hokkaidō Development Bureau
Name Main stream length (km) Basin area (km2) Basin management Basin area population Tributaries Average annual flow rate (m3/s) BOD (ppm) Dams Hydroelectric plants
Teshio 256 5,590 Hokkaidō 94,000 160 134.52 0.7 14 (2) 3
Shokotsu 84 1,240 28,000 25 29.33 1.0 0 2
Yūbetsu 87 1,480 36,000 17 32.45 1.7 1 (0) 3
Tokoro 120 1,930 142,000 57 22.64 2.6 2 (1) 0
Abashiri 115 1,380 94,000 25 14.02 2.5 1 (0) 2
Rumoi 44 270 28,000 13 11.84 1.5 3 (0) 0
Ishikari 268 14,330 2,500,000 464 133.18 1.1 83 (1) 34
Shiribetsu 126 1,640 38,000 40 68.41 0.4 3 (0) 7
Shiribeshi-Toshibetsu 80 720 16,000 29 23.69 0.5 2 (1) 8
Mu 135 1,270 13,000 20 38.54 0.6 2 (0) 1
Saru 104 1,350 13,000 28 48.24 0.6 4 (2) 4
Kushiro 154 2,510 177,000 38 26.32 1.7 0 0
Tokachi 156 9,010 340,000 209 85.36 1.7 14 (3) 16

Tōhoku Development Bureau
Name Main stream length (km) Basin area (km2) Basin management Basin area population Tributaries Average annual flow rate (m3/s) BOD (ppm) Dams Hydroelectric plants
Iwaki 102 2,540 Aomori 482,400 97 76.07 1.6 21 (2) 5
Takase 64 867 80,372 23 50.10 0.9 3 (1) 0
Mabechi 142 2,050 Iwate, Aomori 188,000 30 47.62 1.1 6 (0) 5
Kitakami 249 10,150 Iwate, Miyagi 1,389,000 302 318.42 1.1 53 (1) 33
Naruse 89 1,130 Miyagi 190,000 61 26.49 1.3 13 (1) 3
Natori 55 939 1,125,589 30 17.32 1.1 9 (0) 7
Abukuma 239 5,400 Miyagi, Fukushima 1,380,000 197 52.22 1.9 19 (2) 25
Yoneshiro 136 4,100 Akita, Iwate 280,000 89 100.91 1.3 21 (0) 22
Omono 133 4,710 Akita 346,481 168 259.02 1.4 34 (0) 17
Koyoshi 61 1,190 80,000 44 60.60 1.1 12 (1) 7
Mogami 229 7,040 Yamagata 999,300 429 369.26 1.0 41 (1) 26
Aka 70 857 109,294 44 65.68 1.0 5 (1) 10

Kantō Development Bureau
Name Main stream length (km) Basin area (km2) Basin management Basin area population Tributaries Average annual flow rate (m3/s) BOD (ppm) Dams Hydroelectric plants
Kuji 124 1,490 Fukushima, Ibaraki 201,981 53 23.58 0.8 1 (0) 7
Naka 150 3,270 Tochigi, Ibaraki 912,217 197 74.43 0.9 22 (2) 12
Tone 322 16,840 Gunma, Nagano, Tochigi, Saitama,

Tokyo, Chiba, Ibaraki

 12,140,000 819 237.10 2.5 70 (4) 98
Ara 173 2,940 Saitama, Tokyo 9,300,000 127 27.77 4.4 13 (2) 11
Tama 138 1,240 Yamanashi, Tokyo, Kanagawa 4,250,000 52 40.28 1.7 2 (2) 5
Tsurumi 43 235 Tokyo, Kanagawa 1,840,000 11 7.83 8.0 0 0
Sagami 113 1,680 Yamanashi, Kanagawa 1,200,000 104 － 2.0 10 (3) 20
Fuji 128 3,990 Nagano, Yamanashi, Shizuoka 1,600,000 555 58.91 2.3 19 (0) 71

Hokuriku Development Bureau
Name Main stream length (km) Basin area (km2) Basin management Basin area population Tributaries Average annual flow rate (m3/s) BOD (ppm) Dams Hydroelectric plants
Ara 73 1,150 Yamagata, Niigata 40,000 61 115.00 0.6 5 (3) 6
Agano 210 7,710 Fukushima, Gunma, Niigata 590,000 243 401.55 0.6 62 (8) 60
Shinano 367 11,900 Nagano, Gunma, Niigata 2,950,000 880 503.15 1.0 90 (1) 122
Seki 64 1,140 Nagano, Niigata 210,000 78 50.32 1.5 5 (1) 16
Hime 60 722 20,000 47 44.07 0.5 0 19
Kurobe 85 682 Toyama 71,000 25 37.00 0.8 6 (5) 18
Jōganji 56 368 30,000 49 16.23 0.6 8 (1) 27
Jintsū 120 2,720 Gifu, Toyama 380,000 105 183.65 1.4 25 (7) 60
Shō 115 1,180 28,032 48 47.72 1.0 18 (9) 27
Oyabe 68 667 Ishikawa, Toyama 300,000 64 27.99 1.5 14 (2) 5
Tedori 72 809 Ishikawa 40,000 35 77.21 0.5 7 (2) 24
Kakehashi 42 271 110,000 13 18.02 1.0 1 (1) 0

Chūbu Development Bureau
Name Main stream length (km) Basin area (km2) Basin management Basin area population Tributaries Average annual flow rate (m3/s) BOD (ppm) Dams Hydroelectric plants
Kano 46 852 Shizuoka 640,000 76 21.40 1.5 0 7
Abe 51 567 170,000 36 41.44 0.8 0 2
Ōi 168 1,280 90,000 39 76.40 0.5 14 (7) 15
Kiku 28 158 70,000 25 2.21 1.8 2 (0) 0
Tenryū 213 5,090 Nagano, Aichi, Shizuoka 720,000 332 239.67 0.5 17 (5) 51
Toyo 77 724 Aichi 210,000 27 28.23 0.6 9 (1) 3
Yahagi 118 1,830 Nagano, Gifu, Aichi 690,000 94 43.99 1.0 25 (3) 25
Shōnai 96 1,010 Gifu, Aichi 2,500,000 76 26.21 4.7 18 (0) 2
Kiso 229 9,100 Nagano, Gifu, Shiga,

Aichi, Mie

 1,700,000 391 291.05 0.7 64 (9) 77
Suzuka 38 323 Mie 110,000 46 11.23 1.4 0 0
Kumozu 55 550 90,000 40 14.36 1.6 6 (0) 1
Kushida 85 461 40,000 68 20.55 0.7 4 (0) 5
Miya 91 920 140,000 55 45.70 0.5 5 (2) 6

Kinki Development Bureau
Name Main stream length (km) Basin area (km2) Basin management Basin area population Tributaries Average annual flow rate (m3/s) BOD (ppm) Dams Hydroelectric plants
Kuzuryū 116 2,930 Gifu, Fukui 666,225 147 108.26 0.8 20 (3) 25
Kita 30 211 Shiga, Fukui 21,389 12 11.68 0.6 1 (0) 1
Yura 146 1,880 Hyōgo, Kyōto 300,000 138 52.09 0.8 22 (3) 6
Yodo 75 8,240 Shiga, Kyōto, Ōsaka,

Mie, Nara, Hyōgo

 11,650,000 965 267.51 1.9 66 (1) 34
Yamato 68 1,070 Nara, Ōsaka 2,150,000 178 23.94 3.3 11 (1) 0
Maruyama 68 1,300 Hyōgo 150,557 97 37.40 0.9 7 (0) 5
Kako 96 1,730 820,000 130 45.89 2.6 19 (0) 0
Ibo 70 810 200,000 47 29.04 0.8 4 (0) 6
Kino 136 1,750 Nara, Wakayama 689,000 181 58.77 2.1 9 (2) 6
Kumano 183 2,360 Nara, Mie, Wakayama 84,000 103 163.54 1.3 11 (5) 30

Chūgoku Development Bureau
Name Main stream length (km) Basin area (km2) Basin management Basin area population Tributaries Average annual flow rate (m3/s) BOD (ppm) Dams Hydroelectric plants
Sendai 52 1,190 Tottori 200,000 87 61.68 0.8 6 (0) 17
Tenjin 32 490 65,500 32 24.03 1.2 8 (0) 8
Hino 77 870 60,800 56 33.55 1.1 12 (0) 14
Hii 153 2,070 Shimane, Tottori 435,000 227 40.26 1.4 24 (2) 13
Gōno 194 3,900 Hiroshima, Shimane 202,000 293 75.17 0.8 20 (2) 24
Takatsu 81 1,090 Shimane 38,600 92 51.88 0.7 4 (0) 5
Yoshii 133 2,110 Okayama 294,000 215 61.16 2.0 30 (1) 18
Asahi 142 1,810 335,000 147 57.01 1.8 25 (3) 9
Takahashi 111 2,670 Okayama, Hiroshima 273,000 121 61.81 2.5 29 (1) 19
Ashida 86 860 269,000 82 12.73 4.0 18 (2) 3
Ōta 103 1,710 Hiroshima 980,000 73 78.81 0.9 11 (2) 24
Oze 59 340 Hiroshima, Yamaguchi 26,500 23 12.05 2.6 4 (2) 6
Saba 56 460 Yamaguchi 31,100 32 18.69 0.7 4 (1) 1

Shikoku Development Bureau
Name Main stream length (km) Basin area (km2) Basin management Basin area population Tributaries Average annual flow rate (m3/s) BOD (ppm) Dams Hydroelectric plants
Yoshino 194 3,750 Kōchi, Ehime, Tokushima, Kagawa 641,000 356 107.67 0.8 23 (4) 32
Naka 125 874 Tokushima 59,000 75 62.88 0.7 4 (3) 5
Doki 33 140 Kagawa 35,000 11 1.83 3.9 2 (0) 0
Shigenobu 36 445 Ehime 233,000 75 2.24 5.0 8 (0) 1
Hiji 103 1,210 112,000 475 37.61 1.0 8 (2) 4
Monobe 71 508 Kōchi 40,000 35 30.78 0.7 4 (3) 6
Niyodo 124 1,560 Ehime, Kōchi 105,000 166 100.07 0.7 5 (3) 18
Shimanto 196 2,270 100,000 319 121.02 0.6 5 (0) 6

Kyūshū Development Bureau
Name Main stream length (km) Basin area (km2) Basin management Basin area population Tributaries Average annual flow rate (m3/s) BOD (ppm) Dams Hydroelectric plants
Yabe 61 647 Fukuoka 182,889 23 21.54 1.1 17 (2) 4
Onga 61 1,026 666,406 74 31.47 2.6 23 (0) 1
Yamakuni 56 540 Ōita, Fukuoka 36,801 39 20.81 0.9 1 (0) 1
Chikugo 143 2,863 Kumamoto, Ōita, Fukuoka, Saga 1,090,777 235 95.09 1.6 29 (2) 22
Matsūra 47 446 Saga 97,818 80 12.46 2.4 22 (0) 3
Rokkaku 47 341 122,827 79 4.36 2.1 9 (1) 0
Kase 57 368 133,412 51 14.10 1.0 3 (2) 8
Honmei 21 87 Nagasaki 54,583 18 2.11 1.8 2 (1) 0
Kikuchi 71 996 Kumamoto 208,694 68 39.56 1.1 1 (0) 4
Shira 74 480 131,375 16 25.39 2.5 3 (1) 4
Midori 76 1,100 517,189 59 36.17 2.4 4 (2) 11
Kuma 115 1,880 137,375 82 119.92 1.4 11 (4) 20
Ōita 55 650 Ōita 252,808 48 22.33 1.4 7 (1) 14
Banjō 38 464 56,527 52 12.17 1.1 5 (0) 0
Ōno 107 1,465 Kumamoto, Miyazaki, Ōita 206,818 138 61.36 0.6 14 (0) 10
Gokase 106 1,820 127,638 102 60.94 1.1 8 (2) 22
Omaru 75 474 Miyazaki 32,616 16 32.76 0.5 8 (4) 5
Ōyodo 107 2,230 Kagoshima, Miyazaki 601,321 134 107.61 1.3 16 (2) 12
Kawauchi 137 1,600 Kumamoto, Miyazaki, Kagoshima 195,944 129 91.09 0.7 4 (3) 5
Kimotsuki 34 485 Kagoshima 115,578 36 31.69 4.5 2 (0) 3

Class B rivers

The smaller, but important rivers are designated as Class B river systems (二級水系, Nikyū Seikei), nominated and managed by the local governments at the prefecture level, but reported to and concurred by the central government.

References
  1. "River Administration in Japan". Ministry of Land, Infrastructure, Transport and Tourism. Retrieved December 31, 2017.
  2. "河川法" [River Law] (in Japanese). Ministry of Land, Infrastructure, Transport and Tourism. Archived from the original on June 23, 2016. Retrieved July 6, 2016.
  3. "河川法第四条第一項の水系を指定する政令" [River Law Clause 4 Paragraph 1: River System Designation Ordinance] (in Japanese). e-Gov.go.jp. Archived from the original on March 5, 2016. Retrieved July 6, 2016.
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