ABSTRACT
The accuracy of quantitative information on water cycle in how well the operation of irrigation system performs water allocation and drainage control is a crucial one. If return flow exists, performance of the water operation has to be evaluated by considering reused water factor.
A case study on such kind of analysis was conducted using data collected in a low-lying paddy area with creek networks irrigation system, located in the Oide district, Saga plain, Kyushu, Japan. A Complex Tank Model was applied for simulating the daily water cyclic in the system. Results show that the system yields remarkable irrigation water conservation characterized by the high value of ratio of water use (RPA) and ratio between the return flow and irrigation water (RWS). But there is severe impact on water quality that needs to be clarified. To overcome this problem, application of the model can be developed using Load Discharge concept
