Ishikari Plain

Japanese: 石狩平野 - いしかりへいや

A plain in central-western Hokkaido, extending from the middle to lower reaches of the Ishikari River. Its area is about 4,000 ^km2 . It is the largest plain in Hokkaido, spanning the jurisdictions of the Ishikari Subprefectural Bureau and the Sorachi Subprefectural Bureau. It is made up of the alluvial plains of the Ishikari River and its tributaries, the Yubari River, the Chitose River, and the Toyohira River, and the alluvial fans in their upper reaches. The east side is bordered by the Yubari Mountains, which run north to south, the south side is connected to the Yufutsu Plain by a watershed of about 24m, and the southwest is separated by the foothills of the volcanic belt from Mt. Teine to Mt. Tarumae. The old coastline of the Ishikari Plain once connected Zenibako, Sapporo, Ebetsu, and Tobetsu, but it is believed that the plain expanded as the sediment carried by the Ishikari River was deposited only on the coast by the coastal current of Ishikari Bay. Several rows of beach ridges (→ Beach ridges) in the northern part of Sapporo record the formation of the Ishikari Plain. The meandering Ishikari River often floods, leading to the development of natural levees, oxbow lakes, and back marshes called yachi. In the low marshes, the remains of marsh plants and soil containing volcanic eruptions from Mt. Tarumae, Mt. Eniwa, and Mt. Usu form peat bogs, known as poor soil that is difficult to drain. Since the first Tondenhei villages were established in the Kotoni and Yamahana districts on the outskirts of Sapporo in 1875, pioneers have worked to develop the peat bogs, cultivating rice, onions, lily bulbs, and other crops. From around 1920, comprehensive development projects were carried out, including flood control works for the Ishikari River, drainage, irrigation, and land improvement works such as soil addition. As a result, the large plains of Chichibu, Bibai, Shinozu, Horomui, and Oyafuru were transformed into rice paddy areas. Development continued even after World War II, and today the peat bogs account for about half of Hokkaido's rice paddy area. In addition to the city of Sapporo with a population of 1 million, there are over 10 small and medium-sized cities such as Ebetsu, Iwamizawa, Bibai, and Sunagawa. It is the political, economic, and cultural center of Hokkaido.

Source: Encyclopaedia Britannica Concise Encyclopedia About Encyclopaedia Britannica Concise Encyclopedia Information

Japanese:

北海道中西部，石狩川の中流から下流に広がる平野。面積約 4000km²。石狩振興局，空知総合振興局の所管区域にまたがる北海道第1の広い平野で，石狩川とその支流の夕張川，千歳川，豊平川などの沖積平野とそれらの上流域の扇状地からなる。東側は南北に通る夕張山地に接し，南側は 24mほどの分水嶺で勇払平野に続き，南西部は手稲山から樽前山にいたる火山帯の山麓部で区切られる。古い石狩平野の海岸線はかつて銭函，札幌，江別，当別を結ぶ線であったが，石狩川の運搬した土砂が石狩湾の沿岸流によって海岸部にかぎって堆積したため平野が拡大したものとみられる。札幌市北部の数条の浜堤列（→浜堤）は石狩平野の生成の記録。蛇行の激しい石狩川はしばしば氾濫して，自然堤防や三日月湖，谷地と呼ばれる後背湿地などが発達。低湿地では湿原植物の遺骸や樽前山，恵庭山，有珠山など諸火山の噴出物を含んだ土壌が泥炭地を形成し，排水困難な悪土として知られる。1875年最初の屯田兵村が札幌郊外の琴似地区，山鼻地区に設置されて以来，開拓民はこの泥炭地開発に取り組み，イネ，タマネギ，ゆり根などを栽培した。1920年頃から石狩川の治水事業とともに排水，灌漑，客土など土地改良を含む総合開発事業が行なわれた。その結果秩父（ちっぷ），美唄，篠津，幌向（ほろむい），生振（おやふる）などの大原野が水田地帯に生まれ変わった。第2次世界大戦後も開発事業は継続され，今日では北海道の水田面積の約半分を占める。100万都市札幌市のほか，江別市，岩見沢市，美唄市，砂川市など中小都市も十余を数える。北海道の政治，経済，文化の中心地域をなす。

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