Water Management and Operation of Irrigation System in Wide Paddy Area

（3）平原区灌溉系统具有需水量调节功能、系统运行响应时滞和受潮汐作用影响的排水运行限制等特点。本研究的目的是弄清系统的实际运行情况，并获得优化系统运行的基本知识。应用水量平衡法分析了河网型低洼稻田的实际用水管理情况。低洼三角洲地区由于潮汐作用导致的区域排水能力明显影响灌溉水的取水运行.应用动态规划方法作为水资源管理的模拟和优化技术。灌溉系统需水量由田间净需水量和输水运行损失两部分组成。运行损失与供水量之比是衡量农田自由用水或限制用水的一个非常有用的指标.通过数学分析和试验研究，探讨了明渠灌溉系统的流量运行和响应延迟问题。系统运行中的响应现象以动力波、动力-运动波和运动波的形式传递到下游。在有效范围内对线性扩散模拟模型进行求解，得到了一个简单实用的方程.在稻田中，上覆淹水中的溶解氧通过混溶置换和扩散作用进入淹水土壤。本文用混溶驱替和扩散的数学模型来解释溶解氧在淹水土壤中的作用机理。

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.