Water Management and Operation of Irrigation System in Wide Paddy Area

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ObjectiveAn irrigation system in a wide and flat area has characteristics such as adjusting functions of water demand, time delays of response in system operation and restrictions of drainage operation afected by tidal actions. The purposes of this research are to clarify actual operations of the system and to get fundamental knowledges for optimizing system operations.Procedure and Result1. A water balance method was applied for analyzing actual water management in low lying paddy area with creek network. The ilntake operation of irrigation water in low lying delta area was evidently affected by the drainability of the area due to tidal actions.2. The dynamic programming method was applied as a technique of simulation and optimization for water management. The water demand in irrigation system is consisted of two components, one is the net duty of water in fields and another is the operation loss in conveyance. The ratio of the operation loss to the water supply is a very useful index of the free use or the limited use of water in fields.3. Operations of discharge and delay of responses in an open-channel irrigation system were discussed with mathematical analysis and experimental evaluations. The phenomena of response in system operation were transferred to downstream as dynamic, dynamic-kine matic and kinematic waves. A simple and useful equation was derived as a result of solving the linearized diffusion analog model in an effective range.4. In paddy fields, dissolved oxygen in overlying flooding water is transferred into submerged soil by miscible displacement and diffusion. Mathematical models of miscible displacement and diffusion are used to explain the mechanism of dissolved oxygen in submerged soils.