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Bali, a small and active volcanic island in the humid tropics, is close to the east of Java, Republic of Indonesia, with an area of about 5,600km2 and a total population of about 2.8 millions. Subak system, a traditional irrigation system of Bali island, is considered to be an example of skillful and developed irrigation system at the foot of volcanic mountains.
Osamu SHIMMI (Fri,) studied this question.