ON-SITE EXPERIMENTS AND HYDRAULIC EVALUATION ON RUNOFF CONTROL BY RAINWATER STORAGE IN PADDY FIELDS

近年来，由于流域城市化导致径流特性发生变化，洪涝灾害频繁发生。为了应对暴雨带来的严重灾害，除了河流治理工程外，日本许多城市化盆地都计划建设雨水储存设施。然而，由于此类设施的建设成本较高，合适的建筑地点有限，筹备计划尚未进行。因此，城市郊区剩余稻田的利用作为流域内雨水储存的替代措施受到了关注。但在一个雨季的夏天，稻田里充满了水稻耕作所需的水。为了利用水田控制洪水径流，本研究提出了改善水田雨水蓄水功能的新方法。一般情况下，水田里有一个灌溉渠道的进水口和一个…更多的出水口通向排水沟。新提出的用稻田代替雨水储存设施的方法包括以下两个步骤1。在进水口设置带水位传感器的自动闸门。这种设备可以通过检测降雨期间水位的上升来关闭灌溉渠道的流入水。将出水口的宽堰改成窄堰，以减少向排水渠道流出的水。这种方法比孔板更好，因为它可以在过度暴雨时保护作物不被淹没。自2004年以来，我在日本爱知县新川盆地的一些实际水田进行了现场试验。从水田与常规堰和窄堰水田的水位对比可以看出，该方法提高了雨水的蓄水功能。其次，对一个由30个水田组成的流域，通过径流模拟分析，评价了各水田治理的防洪效果。径流模型以运动波动理论为基础，模型参数由试验区现场观测资料确定。根据概率设计降雨对水稻区径流过程的模拟结果表明，缩小出水口堰宽，可大幅度降低出水高峰流量，并可将高峰时间推迟数小时。因此，通过本研究提出的改进方法，我可以认识到水田作为防洪设施的替代方案是有用的。较少

In recent years, flood disasters have become to occur frequently by change of runoff characteristics due to urbanization of a river basin. In order to deal with serious disasters by heavy rainfall, in addition to the river improvement works, construction of the rainwater storage facilities has been planed in many urbanized basins of Japan. However, the preparing plan has not been in progress because construction of such facilities costs high and the suitable building sites are limited. Thereupon, a utilization of paddy fields remained in the suburbs of a city gains attention as an alternative measure for the rainwater storage within a basin. But during a summer as a rainy season, paddy fields are filled with water for the rice fanning. In order to control a flood runoff by utilizing paddy fields, I suggested new methods to improve the rainwater storage function of the paddy fields in this retherch.Generally in a paddy field, there is an inlet aperture from an irrigation channel and an … More outlet aperture to a drainage channel. New suggested methods to substitute paddy fields for rainwater storage facility consist following two procedures.1. To set up the automatic sluice gate with wath-level sensor at the inlet aperture. This equipment can shut inflow water from an irrigation channel by detecting rise of wathrlevel during a rainfall2. To replace a wide weir of the outlet aperture by a narrow weir in order to reduce outflow water to a drainage channel. This method is better than the orifice because it can protect the crops from submergence during an excess heavy rainfall.I have carried out the on-site experiments for some actual paddy fields in the Shinkawa basin, Aichi prefecture, Japan, since 2004. From comparison of wate-levels in paddy field with conventional weir and paddy field with a narrow weir it is clear that the rainwater storage function is improved by the suggested method. Next, for a drainage district that consists of 30 paddy fields, a flood control effect by the improvement in each paddy field is evaluated through the runoff simulation analyses. The runoff model is based on the kinematic wave theory, and the model parameters are identified by observed data in the on-site experiment district. According to the simulation results on the runoff processes from the paddy fields district for a probabilistic design rainfall, it is possible to reduce the peak discharge of outflow largely and to delay the peak time for several hours by contracting the weir width at the outlet aperture. Therefore, I can recognize that the paddy fields become useful as alternative of the flood control facilities by the improvement methods suggested in this research. Less