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

通过四年的科研资助研究，取得了以下成果。(1)对于人机界面友好的非定常流动模型，可以建立基于隐式有限差分法的模型。将非恒定流模型应用于越南红河三角洲的排水分析，验证了该模型的有效性。通过几种内边界条件的组合，该模型可以作为径流分析的Tank模型。(2)关于大面积低平地区的排水分析，我们选择了泰国湄南河三角洲的一个水稻区作为研究区域。通过水量收支分析，考察了漂浮稻区的滞留能力。在此基础上，提出了在堤防周围修建滞洪区和修建调度性水库的方案，并在一定程度上解决了汛期洪水和干旱两大难题…。更多的是环旱季。(3)在感潮河段修建潮流堰引起的潮汐异常波动，考虑运动方程中摩擦项的非线性，可以从理论上解决这一现象。由此，我们可以给出一个公式，可以计算出异常波动相对于距河口的距离的近似幅度。(4)利用非恒定流模型和最优化方法，建立了基于水位观测的渠道流量估算方法。我们将该程序应用于村中灌渠的田间试验，并通过建造一条小型模型渠进行了室内试验。结果表明，该方法是一种非常有效的流量估算方法。然而，我们发现了一个新的问题，即在非常小规模的简化模型试验情况下处理摩擦项。这个问题在本研究中没有得到解决，但应该在下一步进行分析。(5)对灌溉渠道系统在控制水力条件下从一种稳态过渡到另一种稳态的过渡过程进行分析，可以从理论上解决某些特定条件下的现象。根据该解，通过无量纲分析得到的代表性长度，可将渠道分为短渠和长渠。结果表明，短渠和长渠的瞬变过程机理有很大不同。也就是说，在短运河的情况下，不稳定度因来回的波浪而减弱，而在长运河的情况下，不稳定度因扩散而减弱。较少

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