Ukishimagahara

This is a coastal wetland stretching from Fuji City to Numazu City in Shizuoka Prefecture. It was once a marshland, but the lagoon-like Fuji Numa, Ukishima Numa, Kashiwabara Numa, and Sudo Numa between the foot of Mt. Ashitaka and the sand dunes at the back of Suruga Bay were filled in with sediment carried by the Numa River and small rivers from the mountains, and the marshes disappeared. However, due to poor drainage and the risk of flooding and the floating island phenomenon occurring during floods, the First Showa Floodway was completed in 1943 (Showa 18), and the Second Floodway was completed in 1963, and rice paddy cultivation was promoted. The area has thick, soft mud and peat layers, but land use has changed due to the addition of earth, and National Route 1 (formerly the Fuji Bypass) crosses Ukishimagahara. Previously, the Negata Kaido road that ran along the foothills of Mt. Aitaka was the east-west transportation route, while the Tokaido road passed over the sand dunes to the south to avoid the low-lying marshes.

[Kitagawa Mitsuo]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

静岡県富士市から沼津市にかけての沿岸低湿地。かつては沼地であったが、愛鷹(あしたか)山の裾野(すその)と駿河(するが)湾奥部の砂丘との間の潟湖(せきこ)状の富士沼、浮島沼、柏原(かしわばら)沼、須津(すど)沼などが、沼川や山地からの小河川の運搬する土砂によって埋め立てられ、沼は消滅した。しかし、排水不良地で湛水(たんすい)の害や、浮島現象が洪水時に生じるため1943年（昭和18）第一昭和放水路を完成、1963年第二放水路を完成して水田化を進めた。泥層や泥炭層などの厚い軟弱地盤の地帯であるが、盛り土による土地利用の変化もみられ、国道1号（旧、富士バイパス）が浮島ヶ原を横断する。以前は愛鷹山麓(さんろく)に沿う根方(ねがた)街道が東西の交通路であり、東海道は南の砂丘上を通り低湿地を避けていた。

［北川光雄］

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