Sanmonkyo Gorge

A gorge in the middle reaches of the Yellow River in central China. It is located on the border between Sanmenxia City in western Henan Province and Pinglu County in Yuncheng City in southern Shanxi Province. Two rock islands made of hard syenite protrude from the bottom of the valley, and the waterway that flows between them is called Renmen, Shenmen, and Kimen from the north, hence the name Sanmenxia. Since ancient times, it has been considered the most difficult place to navigate the Yellow River. A reef described as Taichu in the "Yu Gong," which is said to have been compiled during the Warring States period, is located just downstream from the rock islands, and the entire Sanmenxia was sometimes called Taichu. In 1957, as part of the Yellow River flood control project, construction began on the Sanmenxia Dam, which has a storage capacity of approximately 40 billion tons, using this rock island, and basic construction was completed in 1960. However, since the rate at which the dam lake was filled with silt from the Yellow River exceeded the design speed, modifications were made to increase the silt flushing capacity, and hydroelectric power output has been limited to 250,000 kilowatts.

Sanmenxia City (prefecture-level city) is an industrial city that uses this electricity. It governs two city districts and two counties, including Mianchi, and acts as the governing agent for two county-level cities (as of 2017). Population: 2,240,700 (2017). It is rich in underground resources such as gold, bauxite, and coal. It is served by the Longhai Line and the Zhengxi High-Speed ​​Railway (Zhengzhou-Xi'an). It has been a key transportation hub connecting the Central Plains and Guanzhong since ancient times, and the Heiguan Ancient Road, which connects Mianchi County under its jurisdiction to Tongguan County, was registered as a World Heritage Site in 2014 as a component asset of the "Silk Road: Trade Route Network of the Chang'an-Tianshan Corridor" (World Cultural Heritage).

[Editor, Michihiro Kono, December 12, 2017]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

中国中部、黄河(こうが)中流部にある峡谷。河南(かなん)省西部の三門峡市と山西(さんせい)省南部の運城(うんじょう)市平陸(へいりく)県の境界に位置する。谷底に堅い閃長玢岩(せんちょうひんがん)からなる岩島が二つ突出しており、この間を流れる水路を北から人門、神門、鬼門とよぶことから三門峡という名称が生まれた。古来、黄河水運最大の難所とされた。戦国時代に編纂(へんさん)されたといわれる『禹貢(うこう)』に底柱(ていちゅう)の名で記載されている岩礁は岩島のすぐ下流にあり、三門峡全体を底柱（砥柱(しちゅう)）とよぶこともあった。1957年、黄河治水の一環として、この岩島を利用して貯水能力約400億トンの三門峡ダムが着工され、1960年基本工事が完成した。その後、黄河の泥によるダム湖の埋積速度が設計を上回ったため、排砂能力を高める改造工事が行われ、水力発電も出力25万キロワットに抑えている。

　三門峡市（地級市）はこの電力を利用する工業都市である。2市轄区、澠池(めんち)など2県を管轄し、2県級市の管轄代行を行う（2017年時点）。人口224万0700（2017）。金、ボーキサイト、石炭など地下資源が豊富。隴海(ろうかい)線、鄭西高速鉄道（鄭州(ていしゅう)―西安(せいあん)）が通じる。古くから中原(ちゅうげん)と関中(かんちゅう)とを結ぶ交通の要衝であり、管轄下の澠池県から潼関(とうかん)県へとつながる崤函古道(こうかんこどう)は2014年、「シルク・ロード：長安‐天山(てんざん)回廊の交易路網」の構成資産として、世界遺産の文化遺産に登録された（世界文化遺産）。

［河野通博・編集部　2017年12月12日］

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