Jōganji River

A river that flows through the eastern central part of Toyama Prefecture and empties into Toyama Bay. It is a first-class river. It is 56 km long and has a drainage area of ​​368 square km. It splits into two rivers, the Magawa and Shomyogawa, in the upper reaches. The main Magawa originates on the western slope of Mount Yakushi in the Tateyama mountain range, and merges with the Yukawa River flowing from the Tateyama caldera along the way. The Shomyo River is called Jodozawa just below Mount Oyama in Tateyama, and falls as Shomyo Falls. It merges with the Magawa River at Senjugahara in Tateyama Town to become the Joganji River. Downstream, it joins the Wada River and Oguchi River to form terraces on both banks, and forms a typical alluvial fan at Kamitaki in Toyama City. A major earthquake in 1858 (Ansei 5) caused a major collapse of the caldera walls of Mt. Otonbi, and the valley walls upstream also collapsed, turning the downstream area into a sea of ​​muddy water during the snowmelt season. Heavy rains cause heavy sand and gravel to flow out, so erosion control work inside the caldera has been ongoing since 1906 (Meiji 39). Nearly one million tons of soil and sand flow out of the lower reaches of the Joganji River every year, raising the riverbed, and near Dainichi Bridge, which connects Toyama City and Tateyama Town, the river has a ceiling about eight meters higher than the rice paddy surface. There are eight dams in the Joganji River system, including Arimine Dam, and 27 power plants, with a maximum output of about 800,000 kilowatts (2005).

[Saburo Fukai]

"Joganji River History" (1962, Ministry of Construction, Hokuriku Regional Construction Bureau, Toyama Construction Office)

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

富山県中央東寄りを流れて富山湾に注ぐ川。一級河川。延長56キロメートル、流域面積368平方キロメートル。上流は真川(まがわ)と称名川(しょうみょうがわ)の二つに分かれる。本流の真川は立山(たてやま)連峰の薬師岳(やくしだけ)西斜面に発し、途中立山カルデラから流れ出る湯川と合流する。称名川は立山の雄山(おやま)直下では浄土沢とよばれ、称名滝となって落下し、立山町千寿ヶ原(せんじゅがはら)で真川と合流して常願寺川となる。下流で和田川と小口(おぐち)川をあわせて両岸に段丘を形成し、富山市上滝(かみたき)で典型的な扇状地を形成する。1858年（安政5）の大地震で大鳶(おおとんび)山のカルデラ壁が大崩壊し、上流の谷壁の崩壊もあり、融雪期には下流一帯は泥水の海と化した。大雨ごとに砂礫(されき)の流出が激しく、1906年（明治39）以来カルデラ内部の砂防工事が続けられている。常願寺川下流では毎年100万トン近い土砂の流出があり、河床が高くなり、富山市と立山町を結ぶ大日(だいにち)橋付近では水田面より約8メートルも高い天井(てんじょう)川となっている。常願寺川水系のダムは有峰(ありみね)ダムなど8か所、発電所は27か所、最大出力は、約80万キロワット（2005）に達する。

［深井三郎］

『『常願寺川沿革誌』（1962・建設省北陸地方建設局富山工事事務所）』

出典　小学館　日本大百科全書(ニッポニカ)日本大百科全書(ニッポニカ)について　情報 | 凡例