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An irrigation tank or tank is an artificial reservoir of any size, mainly in India. (The word ''sagar'' refers to a large lake, usually man-made).〔(【引用サイトリンク】title=Architecture on the Indian Subcontinent - glossary )〕 It can also have a natural or man-made spring included as part of a structure. Tanks are part of an ancient tradition of harvesting and preserving the local rainfall and water from streams and rivers for later use, primarily for agriculture and drinking water, but also for sacred bathing and ritual. Often a tank was constructed across a slope so to collect and store water by taking advantage of local mounds and depressions.〔(【引用サイトリンク】title=Tank management )〕 Tank use is especially critical in parts of South India without perennial rainfall where water supply replenishment is dependent on a cycle of dry seasons alternating with monsoon seasons. == Reasons for why Tank irrigation more common in South India== 1. The undulating relief and hard rock’s make it difficult to dig canals and wells. 2. There is little percolation of rain water due to hard rock structure and ground water is not available in large quantity. 3. Most of the rivers of this region are seasonal and dry up in summer season. Therefore, they cannot supply water to canals throughout the year. 4. There are several streams which become torrential during rainy season. The only way to make best use of this water is to impound it by constructing bunds and building tanks. Otherwise this water would go waste to the sea. 5. The scattered nature of population and agricultural fields also favours tank irrigation. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「irrigation tank」の詳細全文を読む スポンサード リンク
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