２

180

30

53

２

児島湖

総社駅

一級河川高梁川

児島湾

瀬戸内海

30

干拓地（明治以後）

埋 立 造 成 地

干 拓 前

干拓地（明治以前）

N

鏡野町

津山市

奈義町

西粟倉村

勝央町 美作市

真庭市

新庄村

新見市

高梁市

吉備中央町

美咲町

久米南町

赤磐市

和気町

備前市

瀬戸内市岡山市

早島町

倉敷市

玉野市

総社市

矢掛町井原市

笠岡市

浅口市里庄町

早島ＩＣ

水島ＩＣ

和気ＩＣ

賀陽ＩＣ

有漢ＩＣ

北房ＩＣ

落合ＩＣ新見ＩＣ

久世ＩＣ

湯原ＩＣ

蒜山ＩＣ

院庄ＩＣ津山ＩＣ

美作ＩＣ 作東ＩＣ

鴨方ＩＣ笠岡ＩＣ

玉島ＩＣ

倉敷ＩＣ

岡山ＩＣ総社ＩＣ

山陽ＩＣ

児島ＩＣ

備前ＩＣ

About 20,000 ha of the total area of farmland in the Okayama Plain

(about 25,000 ha) was created by reclamation.

In ancient times, there was a shallow sea called Kibi no Anaumi (lit. perforated sea in Kibi Province) between Kojima Island in the Seto Inland Sea and the mainland, where more than 20 islands were scattered.

The three major rivers in Okayama—the Yoshii River, the Asahi River, and the Takahashi River—were flowing into the shallow sea at this time. What is more, iron sand required for Tatara iron making by swordsmiths such as those of the Bizen Osafune school had been collected in the Chugoku Mountains in the upper reaches of the rivers for a long time. Therefore, a large amount of sediment had flowed into and piled up in the sea to form mudflats. That is why reclamation had been promoted in the area over the centuries.

Marine chart in the Sengoku period

（１）Sengoku period (The 15th century)～Meiji period (The 19th century)

The Okayama Plaintoday

The Kojima Peninsula today

Kojima Bay in 1897

◎As a result of the reclamation project led by the Ukita family in the Sengoku period and theproject led by the Mizunoya family of the Bitchu Matsuyama Domain in the early Edo period,Kojima Island was connected to the left bank of the Takahashi River, and thus Kojima Bay wascreated.

Furthermore, the Ikeda family of the Bizen Okayama Domain implemented a large-scalereclamation project to develop new fields including Koujima Shinden and Oki Shinden. About7,000 ha of new fields were developed in the Edo period(1603-1868) alone.

Kojima Bay

②Kojima Bay in 1925

（２）Meiji period(1868)～Taisyo period(1926)

Kojima Bay

◎In the Meiji era, the Japanese government requested a Dutch engineer, Anthonie RouwenhorstMulder, to formulate a reclamation plan. According to his plan, the reclamation of Kojima Bay wascarried out by dividing about 5,500 ha of the 7,000-ha area of the bay into eight sections.

◎Later, the Kojima Bay reclamation project was turned over to Denzaburo Fujita, a business tycoonin Osaka. The reclamation work was started in 1899. Though it faced many problems, thereclamation of the first and second sections was completed in 1913.

③Kojima Bay in 1950（３）Ｔａｉｓｙｏi period～Ｓｙｏｗａ period

◎The reclamation of the third and fifth sections was started in the early Showa era and completed in 1950. Meanwhile, the reclamation of the sixth and seventh sections was turned over to the

Ministry of Agriculture and Forestry, and work on the sixth section was completed in 1955.◎In 1950, to deal with a shortage of agricultural water caused by the reclamation, the construction

of a closing dike with a length of 1,558 meters was commenced in Kojima Bay. Since its completion,agricultural water has been secured by the freshwater lake created by the dike, Lake Kojima.Moreover, by regulating the water level, the dike has protected the reclaimed land behind it from

salt damage and tidal waves.

④The Kojima Bay reclaimed land today（４）Current

Lake Kojima, with an area of about 1,088 ha, was thus created in 1959. Four years later, in 1963, the reclamation of the seventh section was completed, marking the completion of the entire Kojima Bay reclamation project.

【干拓のしくみ】

陸地海

干潟

堤防の築造

干満の差を利用した自然排水

及びポンプによる強制排水

・道路、用水路、排水路の整備

・除塩用の溝や暗渠排水による

塩分の排出を促進

干潟が発達した敵地を選び、

堤防線を計画陸地海

干潟

干拓地

①堤防線の計画

②堤防の築造・完成

③潮止め

④地区内工事

海

海

海埋立地

【干拓と埋立の違い】

陸地

【干拓と埋立の違い】

Mechanism of reclamation

Construction work of a flood-control dike

Since there was no concrete at the time, the dike was constructed with brushwood, riprap and plaster, adopting a traditional method from the Edo period.

Kojima Bay was a muddy sea, in which the dike could have easily sunk under its own weight as soon as it was constructed just as in a bottomless swamp. Therefore, its construction was really tough work.

締切堤防工事の様子 完成式（渡り初め）S34.2.1

締切堤防改修状況(S55～H13)

旧樋門(御幸樋門）

旧樋門(弁天樋門）

新樋門

御幸樋門

弁天樋門

児島湾締切堤防竣工記念切手

Outline of the Kojima Bay closing dike

The Kojima Bay closing dike today

L=26.00mL=44.00m L=33.50m

▽平均潮位 TP+0.11m(AP+1.44m)TP-0.53m(AP+0.80m)

▽かんがい期管理水位

▽堤防高 TP+4.17m(AP+5.50m)

止水矢板

児島湾締切堤防標準断面図

○児島湾締切堤防堤防：延長Ｌ＝ 1,558ｍ（石積囲い土堰堤）樋門：６門

幅 24.0ｍ 高さ 7.5ｍ閘門：１箇所

幅 8.0ｍ 高さ6.1ｍ(湖側) 7.0ｍ(湾側)築堤：農林省（昭和25年～昭和36年）

国営児島湾沿岸農業水利事業改修：農林水産省（昭和55年～平成13年）

直轄海岸保全事業 岡山地区

○児島湖湖面積：1,088ha貯水量：2,607万㎥流域面積：543.66㎢流域人口：67.2万人（H25年度末）

○管理状況管理者：岡山県(昭和50年1月1日 国から管理受託)操作者：児島湾土地改良区（県より操作委託）内 容：締切堤防樋門の操作（約３００回／年）

用排水機場の運転操作（用水2機場、排水19機場）

児島湾

児島湖

Management of the Kojima Bay closing dike

妹尾川排水機場

七区排水機場七区用排水機場

丙川排水機場

藤田用排水機場

Altitude and drainage pumping stations around Kojima Bay

水稲とレンコン

ビール麦

パイプラインによる給水状況

千両なすのハウス栽培