On the Catchment-area of Water Reservoirs in Sanuki District, Sikoku

Abstract

In the Mitoyo plain of Sanuki, irrigation of rice depends chiefly on reservoirs, which can be classified into three types according to their properties. Type A has a natural catchment-area, type has both natural and artificial catchments, and type C has artificial catchment only, of which the percentages are A 51%, B 37%, C 12%. Types B and C, which depend on artificial catchment, amount to 4911%. The numerous reservoirs with enlarged catchment area of artificial construction form one of the characteristic features of the Mitoyo plain and the Sanuki district. Owing to the large number of these reservoirs and artificial catchments, following increase in the acreage of rice fields, 48% of the total rainfall can be stored in reservoirs.
The landscape of catchment-area is greatly affected by the velocity of the water gathered, quantity of water stored, sandy spaces and spaces filled with vegetation. The reservoirs into which sand flows, are equipped with devices to stop the sand current, and help to form a special landscape. Sincs ce such land tends to be reclaimed, more and more, so that wooded land is turned into fields. Thus facilitating sand flow.