Effective water management and control for a large scale irrigation/drainage system

通过科学研究补助金的四年研究，取得了以下成果。 (1)对于用户友好的非定常流模型，我们可以开发基于隐式有限差分法的模型。我们将非定常流模型应用于越南红河三角洲的排水分析，可以证明该模型的有效性。我们还表明，通过结合多个内部边界条件，该模型可以用作径流分析的 Tank 模型。 (2)关于大片低洼地区的排水分析，我们选择了泰国湄南河三角洲的一个浮稻区作为研究田。通过水收支分析，考察了浮稻区的缓滞能力。于是，我们提出了围堤修建缓洪区和修建调节水库的工程，并证明该工程可以在一定程度上解决雨季洪水和旱季干旱两个难题。 (3)对于潮汐河流中修建潮汐堰引起的潮汐异常波动，考虑运动方程中摩擦项的非线性，可以从理论上解决该现象。结果，我们可以给出一个公式，可以计算相对于距河口距离的异常波动的大致幅度。 (4)关于通过观察水位来估计灌溉渠中的流量，我们开发了一个使用非定常流模型和优化方法的程序。我们将该程序应用于使用 Murataka 灌溉渠的现场实验，以及通过构建小型模型运河进行的实验室实验。结果，我们验证了该程序对于估计流量非常有效。然而，我们在非常小规模的简化模型实验中发现了处理摩擦项的新问题。本研究并未解决该问题，但应在下一步进行分析。 (5)关于水利设施控制时灌渠系统从一种稳态到另一种稳态瞬态过程的分析，可以从理论上解决某些特定条件下的一些现象。根据该方案，可以通过无量纲分析获得的代表长度将根管分为短根管和长根管。结果表明，短运河和长运河的瞬态过程机制有很大不同。即，在短运河的情况下，不稳定性通过波的往返而减弱，而在长运河的情况下，不稳定性通过扩散而减弱。较少的

Through four years study by the grant-in-Aid for Scientific Research following results are obtained. (1) About the user-friendly unsteady flow model, we can develop a model based on the implicit finite difference method. We applied the unsteady flow model to the drainage analysis for the Red river Delta in Vietnam, and we can show the effectiveness of the model. We also show that the model can be used as the Tank model for the runoff analysis by combining several interior boundary conditions. (2) About the drainage analysis in a large low-flat area, we selected a floating rice area in the Chao Phraya River Delta in Thailand as the study field. Through the water budget analysis, we examined the retarding capacity of the floating rice area. As the result, we proposed a project to build retarding area by surrounding dykes and to construct regulating reservoirs, and we also showed that the project could solve to some extent two difficult problems of flood during rainy season and drought du … More ring dry season. (3) About the abnormal tidal fluctuation by a construction of a tidal weir in a tidal river, we can solve the phenomena theoretically considering non-linearity of the friction term in the movement equation. As the result, we could show an formula that can calculate approximate amplitude of abnormal fluctuation with regard to the distance from the river mouth. (4) About the flow rate estimation in an irrigation canal by observing water levels, we develop a procedure by use of an unsteady flow model and optimization method. We applied that procedure to the field experiment using Murataka irrigation canal and also to the laboratory experiment by constructing a small-sized model canal. As the result, we verified that the procedure is very effective to estimate flow rate. However, we identified a new problem of treating friction term in case of the very small-scale reduced model experiment. This problem was not solved in this study but should be analyzed in the next step. (5) About the analysis of transient process from one steady state to the other one in an irrigation canal system when hydraulic facilities are controlled, we could solve some phenomena theoretically in some specific conditions. According to the solution, canals can be classified to short and long canals by a representative length obtained through non-dimensional analysis. As the results, we could show that the mechanisms of transient processes are quite different between short and long canals. Namely, in the case of the short canals, the unsteadiness is weakened by waves that go and return, and in the case of the long canals the unsteadiness is weakened by diffusion. Less