Application of Complex Tank Model for Evaluating Performance of Water Operation in a Reused Water Irrigation System

A case study on the performance of irrigation water operation was conducted using data collected at a reused water irrigation system of low-lying paddy area with creek networks, located in the Oide district, Saga plain, Kyushu, Japan. The complex Tank model was applied for simulating the daily cyclic water in the system. Results showed that the system performed the remarkable irrigation water conservation. This phenomenon was marked by the great values of ratio of water use (Rwu), in which the calculated values for all of blocks were over 100% for paddy season of 1997. It was found that the total return flow in usual fine day and heavy rain day of paddy season were 10 and 80 mm/day, respectively. It was also proven that the effective return flow contributed significantly as reusable irrigation water. This interesting point was shown by the high values of the ratio index of the effective return flow to the amount of usable water in creek network (Riu) that ranged of 0.5-0.86. The study clarified that the recycle use of irrigation water accumulatively occurred at the lower block of creek networks.