Water Management and Operation of Irrigation System in Wide Paddy Area

目的宽阔平坦地区的灌溉系统具有需水调节功能、系统运行响应时滞、受潮汐作用限制排水运行等特点。这项研究的目的是澄清系统的实际操作，并获得优化系统操作的基础知识。采用水量平衡法对河网低洼稻区的水分管理现状进行了分析。低洼三角洲地区灌溉水的利用明显受潮汐作用下该地区的排水能力影响。将动态规划方法应用于水资源管理的模拟与优化。灌溉系统的需水量由两部分组成，一是农田净需水量，二是输水运行损失。运行损失与供水量之比是衡量田间用水免费或有限的一个非常有用的指标。采用数学分析和试验评价相结合的方法，对明渠灌溉系统的泄流和延时运行进行了探讨。系统运行中的响应现象以动态波、动态波和运动学波的形式传递到下游。在有效范围内对线性化的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，上覆水中的溶解氧通过混相置换和扩散转移到淹没土壤中。利用混相置换和扩散的数学模型解释了沉水土壤中溶解氧的形成机理。

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.