Abstract
In the Tedori river alluvial fan area, which has gravely sand beds and very steep gradient, return flow analysis of irrigation water in paddy area for dual-purpose of irrigation and drainage main canal systems was carried out. Research was conducted at test paddy area having 179 ha useing new procedure for return flow of irrigation water. The main result was as followers: 1)The methods of the return flow of irrigation water for very complicated irrigation and drainage systems was proposed. The accuracy of this method was verified by comparison with the calculated and observed discharge. 2)Using this results, shortage of irrigation water was analyzed before reservoir construction and land consolidation, which was remarkably decrease percolation because of soil compaction. 3)Reasons of many intake weir being in this paddy area would be traditional customs before reservoir construction and land consolidation, in spite of the study area has lot of irrigation water. 4)At present, the reuse of irrigation water systems was very well functioning for enlarging paddy management area because of change from private farmer to company or village management.
