Hakone Irrigation Canal

Also known as the Fukara Canal, this canal was built by digging a tunnel under the Kojiri Pass on the outer rim of the Hakone crater to funnel the waters of Lake Ashinoko in Sagami Province (Kanagawa Prefecture) into the Fukara River in Fukara Village, Sunto County, Suruga Province (Susono City, Shizuoka Prefecture), and then changing the course of the canal and digging a new river to connect it to the Kise River. This canal provided irrigation water to 29 villages in the former Igumi (part of Gotemba City, Susono City, Nagaizumi Town, Shimizu Town, etc.) covering an area of ​​over 500 hectares. This canal is characterized by the fact that it crosses the Sagami-Suruga border and the river system, and that it has a huge tunnel under Kojiri Pass, 1,341.8 meters long, with an average gradient of 1 in 250, and an elevation difference of 9.8 meters between the intake and outlet. The area south of Fukara Village opens out into the foothills of Mount Hakone and Mount Ashitaka, with the Kise River flowing from north to south, but the water volume is small and a deep eroded valley has formed, making it insufficient for irrigation purposes and impossible to develop.

Around 1663 (Kanbun 3), Oba Gennojo, headman of Fukara village, conspired with Tomono Yoemon, said to be a merchant in Asakusa, Edo, and others, and with the understanding of Hakone Gongen's betto Kaicho, who had traditional authority over the waters of Lake Ashi, Oba, Tomono, and others applied to the shogunate to excavate the tunnel. Construction began in 1666 and was completed in 1670. It is said that more than 330,000 laborers were mobilized, and the construction cost was 6,000 or 9,700 ryo, and the tunnel was dug using only iron without using gunpowder. As the tunnel construction progressed, it was often obstructed by the shogunate and others due to the presence of the Hakone checkpoint, and there were tragedies such as the disappearance of Tomono and others shortly after completion, which led to the subject of Teru Takakura's novel "Hakone Irrigation Canal."

Some speculate that the prototype of this construction method can be traced back to Gorobei Weir (Saku City, Nagano Prefecture, completed in 1631) at the northern foot of Mt. Tateshina. As this was an irrigation canal that crossed the Sohoku and Suruga provinces, there were disputes over water rights with people from the Hayakawa River system in Kanagawa Prefecture, such as the Sakakawaguchi Destruction Incident in 1896 (Meiji 29).

[Atsuyuki Wakabayashi]

"Shizuoka Prefecture Sunto County Journal" (1917, Sunto County Office)" ▽ "Takakura Teru's "Hakone Irrigation Canal" Revised Edition (1971, Toho Publishing)"

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

深良(ふから)用水ともいう。箱根外輪山湖尻(こじり)峠の下に隧道(ずいどう)を掘り、相模(さがみ)国（神奈川県）芦ノ湖(あしのこ)の水を駿河(するが)国駿東(すんとう)郡深良村（静岡県裾野(すその)市）の深良川に注ぎ、さらに流路変更や新川掘削工事などを施して黄瀬(きせ)川に結び、かつての井組29か村（御殿場(ごてんば)市の一部および裾野市、長泉(ながいずみ)町、清水町など）、面積500ヘクタール余に灌漑(かんがい)用水を供した用水。この用水の特色は、相駿国境および水系を越えた用水路であること、また湖尻峠の下に長さ1341.8メートル、平均勾配(こうばい)250分の1、取入口と取出口の標高差9.8メートルという巨大な隧道をもつことである。深良村以南の地は箱根山および愛鷹(あしたか)山の裾に開け、北から南に黄瀬川が流れているが、水量も少なく、また深い侵食谷を形成しており、灌漑用には不十分で開発も不可能であった。

　1663年（寛文3）ごろ深良村名主大庭源之丞(おおばげんのじょう)は、江戸浅草の商人と伝えられる友野与右衛門(よえもん)らと図り、芦ノ湖の水につき伝統的に権限をもつ箱根権現(ごんげん)の別当快長(かいちょう)の理解も得て、大庭、友野らが元締(もとじめ)となって幕府に開削願いを出し66年に着工、70年に完成させた。動員された人夫33万余人、工事費も6000両とか、9700両などといわれ、工法も火薬など用いず鉄のみだけで掘り開けたという。隧道工事の進展につれ、箱根関所の存在にかかわり、幕府などの妨害をしばしば受け、また完成後まもなく友野らが消息不明になるなどの悲劇を伴っていたため、タカクラ・テルの小説『箱根用水』の題材にもなった。

　なお、この工法の原型を蓼科(たてしな)山北麓(ろく)の五郎兵衛堰(ごろべえぜき)（長野県佐久市。1631完成）に求める推測もある。相駿二国にかかる用水路であったため、1896年（明治29）の逆川口破壊事件など神奈川県早川水系の人々との水利権をめぐる争いもみられた。

［若林淳之］

『『静岡県駿東郡誌』（1917・駿東郡役所）』▽『タカクラ・テル著『箱根用水』改訂版（1971・東邦出版）』

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